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Mach Discussion => General Mach Discussion => Topic started by: simpson36 on April 14, 2009, 10:16:32 AM

Title: Can two 36v power supplies be used in series to get 72v?
Post by: simpson36 on April 14, 2009, 10:16:32 AM
I'm using a 36v power supply which is  fine for the axis steppers, but I'm contemplating getting a 72v servo motor as well.

Q: can a pair of unregulated CNC power supplies (mine is from Keling) have thier outputs wired in series to get 72v or would that cause a problem?

Alternately, could a step up transformer be used to create the 72v for a single motor while the rest of the setup continued to run on 36v?

These are probably very rudimentary questions, but I'm not good with electrons so I appreciate the opinions and advice from those who are.

Thanks.
Title: Re: Can two 36v power supplies be used in series to get 72v?
Post by: HimyKabibble on April 14, 2009, 10:44:15 AM
Connecting two supplies in series should work fine.

Regards,
Ray L.
Title: Re: Can two 36v power supplies be used in series to get 72v?
Post by: ostie01 on April 14, 2009, 12:43:12 PM
Some will work and some will not, you'll have to verify the spec of your power supply. Look for a PDF file from keling.

You can't use a step up transformer to crank up voltage from a DC source, you're looking for disaster, transformer only work for AC voltage
Title: Re: Can two 36v power supplies be used in series to get 72v?
Post by: HimyKabibble on April 14, 2009, 03:41:24 PM
Some will work and some will not, you'll have to verify the spec of your power supply. Look for a PDF file from keling.

You can't use a step up transformer to crank up voltage from a DC source, you're looking for disaster, transformer only work for AC voltage

These are unregulated supplies - transformer, rectifier, filter caps.  There's no way it won't work....

Regards,
Ray L.
Title: Re: Can two 36v power supplies be used in series to get 72v?
Post by: simpson36 on April 15, 2009, 09:06:39 AM
Thanks for the replies.

The power supply: (KL-320-36 36V/8.8 or 9.6A) http://www.kelinginc.net/SwitchingPowerSupply.html

 . . have 3 sets of terminals, but internally they are all connected together, so it is actually only one output from one rectifier/transformer. There are three caps, but again they are in parrallel and connected to the same trace on the output.

So, refining the question a bit; using two of these powere supplies, can I use a 36v terminal from each power supply to drive steppers @ 36v  and then also series wire a set of terminals to get the 72v for the servo motor?
Title: Re: Can two 36v power supplies be used in series to get 72v?
Post by: HimyKabibble on April 15, 2009, 11:06:31 AM
Thanks for the replies.

The power supply: (KL-320-36 36V/8.8 or 9.6A) http://www.kelinginc.net/SwitchingPowerSupply.html

 . . have 3 sets of terminals, but internally they are all connected together, so it is actually only one output from one rectifier/transformer. There are three caps, but again they are in parrallel and connected to the same trace on the output.

So, refining the question a bit; using two of these powere supplies, can I use a 36v terminal from each power supply to drive steppers @ 36v  and then also series wire a set of terminals to get the 72v for the servo motor?

Yes.  Wire the - side of one to the + side of the other.  For a 36V device, you can use the two terminals from either supply, and for a 72V device use the unconnected + and - terminals.  It would be best if you used the "low" side 36V supply for the 36V devices (the one whose + terminal is connected to the - terminal of the other supply), so both 36V and 72V devices have the same "ground" reference.  Otherwise, you'll need to be VERY aware of which devices are using which "ground" reference, to avoid shorts.  And make sure the - side of the "high" side supply is NOT tied through its case to your system ground.

Regards,
Ray L.
Title: Re: Can two 36v power supplies be used in series to get 72v?
Post by: Jeff_Birt on April 15, 2009, 12:25:46 PM
Be VERY VERY careful. Unless the power supply is designed for series operation you will have problems. Many switch type power supplies tie the DC common to earth ground through a small resistor. Chaining two in series would be a bad idea. If a power supply can be put in series it will be stated so on the data sheet.
Title: Re: Can two 36v power supplies be used in series to get 72v?
Post by: simpson36 on April 15, 2009, 12:37:23 PM
THANKS guys!

This is exactly the sort of caveats I was looking for.

A wise man once said it is more important to know what you don't know than what you do know. I'm not good with electrons, so I appreciate the help.

I am capable of checking the items cautioned about. I am using a separate power supply for the electronics side of things and the Keling 36v goes only to the Gecko 203V drives, which are 'unkillable' per Gecko, so hopefully I can't do too much damage if I go ahead with this scheme.

However, I'm thinking it might be wise for me to buy the Gecko 320 and a little NEMA23 36v servo motor to play with first. I have the stepper thing pretty well figured out, but this will be my first taste of servos. Objective is to get some experience under my belt doing a usefull project (repowering my stepper driven indexer) before I do my next mill conversion . .  which will be 100% servo powered.

Thanks for the advice, much appreciated.
Title: Re: Can two 36v power supplies be used in series to get 72v?
Post by: ostie01 on April 15, 2009, 12:54:06 PM
Some will work and some will not, you'll have to verify the spec of your power supply. Look for a PDF file from keling.


That's what I said.

Connecting two switching power supply in series or parallel if they are not designed for that purpose can be a bad thing and you're looking for trouble

Look at the Doc file attached



Title: Re: Can two 36v power supplies be used in series to get 72v?
Post by: HimyKabibble on April 15, 2009, 02:30:07 PM
Be VERY VERY careful. Unless the power supply is designed for series operation you will have problems. Many switch type power supplies tie the DC common to earth ground through a small resistor. Chaining two in series would be a bad idea. If a power supply can be put in series it will be stated so on the data sheet.

It's ***NOT*** a switching power supply! It's a plain, unregulated linear supply!  There is absolutely no risk of damage.

Regards,
Ray L.
Title: Re: Can two 36v power supplies be used in series to get 72v?
Post by: Jeff_Birt on April 15, 2009, 03:07:51 PM
The link to the power supplies he provided are indeed switch mode (even though he did say 'unregulated'). The same warning goes for linear power supplies as well. The common terminal can be bonded to the earth ground. The other problem you can run into is having parts (like filter caps) in the poser supply that are only rated for the voltage of one supply. Spikes and surges could cause a single supply to see a greater voltage across it than it was designed for.
Title: Re: Can two 36v power supplies be used in series to get 72v?
Post by: ostie01 on April 15, 2009, 03:22:00 PM
You're right Mr.Birt

KL320-36 is a trademark for Keling. It is the same model as the 350 series from Meanwell.


http://www.meanwell.com/search/s-350/default.htm
Title: Re: Can two 36v power supplies be used in series to get 72v?
Post by: simpson36 on April 15, 2009, 03:30:07 PM
My apologies to all if I misdescribed the power supply. Not intentional . . . as I said, I'm not well versed in this stuff which is why I thought I should link to what I have.

Unfotunately I can only make an uneducated observation of things like a PC power supply which has several voltages supplied and assume there must be some simple way it does this.

I'm an engineer, but when it comes to electronic design, I'm at 'Electrons for Dummies' level, but I'm not afraid to risk asking stupid questions . . . . like . .

What is the difference between unregulated and switching? Are these mutually exclusive? Why would one be better over another.

Title: Re: Can two 36v power supplies be used in series to get 72v?
Post by: ostie01 on April 15, 2009, 03:42:56 PM
Unregulated power supply will have a drop of voltage when it has to deliver some current, this is proportional, more current = less voltage

This is not true for a regulated power supply, the voltage will remain constant even with a rush of current

Switching power supply use high frequency square wave instead of the ordinary 60Hz sine wave to produce more current is a smaller enclosure. With high frequency, this put less stress on the component, an produce less heat.

At the output of the switching supply, the current is switch back to ordinary 60Hz sine wave but this often mean more noise for component that are affected by this.


Jeff
Title: Re: Can two 36v power supplies be used in series to get 72v?
Post by: Jeff_Birt on April 15, 2009, 04:00:34 PM
Quote
KL320-36 is a trademark for Keling. It is the same model as the 350 series from Meanwell.

Does it say MeanWell on it or is it just similar to a MeanWell? I ask as I tired to get a datasheet on their power supplies months ago and was told none were available. I am somewhat dubious that they are MeanWell as if they were they should state such as MW supplies are well known for being top quality.

As to PS types. Yes an unregulated supply and a switch type supply are two different critters; kind of like a gasoline and diesel engine are different. An unregulated supply is type of linear power supply and is basically a big transformer and bridge rectifier with a few filter capacitors. It's actual output voltage depends entirely on load, the bigger the load the lower the voltage. They are simple but not real efficient. You can also have regulated linear supplies which will keep the voltage more constant but they are still inefficient.

Switch type power supplies basically work by rectifying the AC (making it DC) and then chopping up the DC (into pulsating DC) in a controlled manner. A transformer is used to convert the pulsating DC into another voltage where it is again rectified and filtered some. It is more complicated but more efficient, smaller and does not produce as much waste heat.
Title: Re: Can two 36v power supplies be used in series to get 72v?
Post by: ostie01 on April 15, 2009, 05:50:55 PM
Jeff,  You are probably right.


I'm pretty sure too that they are all build at the same place, probably China and are distributed all over the world but each seller with put their own model number on it.

Here at home, I have several switching power supply and some can be connected parallel and some not, all depend on their basic design.

Just look at stepper driver you can buy from China, They are the same as those we can buy in North America but with different model number.

Some are cheaper, but often, they are identical.

Mr Birt, By the way, nice website
Title: Re: Can two 36v power supplies be used in series to get 72v?
Post by: Jeff_Birt on April 15, 2009, 06:43:51 PM
MeanWell builds their supplies in Thailand and somewhere else I can't think of (but not China.) Nothing against Chinese made products in general but if I can't track down the OEM or find good documentation from the seller I tend to shy away (no matter where it is made.) BTW, the S-350 series from MeanWell is a very good choice for small systems. It uses a hiccup/constant current style overload protection which is ideal for this application. It is what I sell/use on smaller machines. My main point was the same as yours, you just have to be careful when trying to tie power supplies together.

Thanks for the kind words on the website.  :)

Title: Re: Can two 36v power supplies be used in series to get 72v?
Post by: ostie01 on April 15, 2009, 09:24:09 PM
Hi Jeff.

Just took a picture of one of my switching power supply, it's made by Mean Well and we clearly see the Made in China Logo

Maybe even Thailand is now too expensive for Mean Well
Title: Re: Can two 36v power supplies be used in series to get 72v?
Post by: simpson36 on April 16, 2009, 05:01:43 AM
MeanWell is based in Taiwan (China).

My Keling PS does not say MeanWell anywhere on the ourside, but the Keling par numbers exactly shdow those of MenWell. THe physical appearance as well as every spec also matches exactly. All good evidence that Meanwell may manuf the PS for Keling.

The Keling mdel 320-36 that I have is working fine so far. I like the automatic thermostatically controlled fan.

Anybody have good or bad things to say about Kelings's servo motors?
Title: Re: Can two 36v power supplies be used in series to get 72v?
Post by: Jeff_Birt on April 16, 2009, 08:40:36 AM
I guess I had my head up my butt concerning where MW was manufactured. I sent Keling an email to again ask about their power supplies. I may have to buy one to compare to see if it is a genuine MW or a knock-off.
Title: Re: Can two 36v power supplies be used in series to get 72v?
Post by: simpson36 on April 16, 2009, 10:44:26 AM
Thanks to all for the info and advice!

Here is what I have decided to do:

For now I am going to buy a 36v NEMA 23 servo motor, matching 300 line encoder and a Gecko 320

I'll use the power supply that I have which one of you graciously calculated for me that I still have some 'room' on.
 
Hopefully I will be able to get everthing proved out and working good and then I can think about getting a bigger motor and probably a separate power supply for it.

Title: Re: Can two 36v power supplies be used in series to get 72v?
Post by: simpson36 on April 23, 2009, 06:18:16 PM
Here is an update on this project:

I got my servo motor, encoder and Gecko 320 drive. Got everything running and adapted the servo motor onto the 4th axis.

Everything works great!. I can turn (within reason) and threading is perfect. Holding power is not as good as it was with the big stepper, but that's a compromise with the smaller servo motor and only a 300 line encoder. Both can be remedied if the need arises.

Here's the problem. I fried the power supply. This was totally my fault and I knew full well I was overloading it badly with the servo added in there. The power supply is advertised as having overload and short circuit protection (theoretically Simpson proof), and the fuse did blow, but not untill after the power transistors were toast. At least that what I think is wrong with it.

So, I ordered new transistors for it and that may or may not fix it. I was planning anyway to get a larger power supply, and the one that I cooked is not expensive, so no biggie.

Eventually I will be replacing the little 36v NEMA23 servo with a larger 90v NEMA34, but in the mean time, I'll need to power the 36v servo, hopefully with the larger 72v power supply I am planning to get.

Here is the question: can I power the 36V 4A servo with the 72V power supply if I put a 9ohm 140 watt resistor ahead of it? That's what I come up with, but I don't have confidence that these are the correct numbers or if I'm heading for frying something else.

I have my limit switch issue resolved, so the power supply is the last upgrade and I'll be done with the CNC mods for a while.



Title: Re: Can two 36v power supplies be used in series to get 72v?
Post by: Jeff_Birt on April 23, 2009, 10:20:40 PM
That would be a really bad idea. The voltage drop across a resistor is directly proportional to the current through it. So when your servo driver is drawing less current it will have more voltage across it. Not a good thing.
Title: Re: Can two 36v power supplies be used in series to get 72v?
Post by: NosmoKing on April 24, 2009, 12:01:55 AM
If looking to get a larger supply, I would seriously  consider getting or putting together a linear supply with a Toroidal transformer, If fused right they are pretty much bullet proof, switching supplies for steppers or servo's is not really necessary.
There is a Guy on ebay that makes them to order, if necessary,  AnTek.
And if you need a low current auxiliary supply, you put an over-wind on to suit.
Title: Re: Can two 36v power supplies be used in series to get 72v?
Post by: Dan13 on April 24, 2009, 12:43:15 AM
Hi,

Another option to get higher DC voltage is to use a "voltage multiplier circuit". It's a very simple, commonly known, circuit, utilizing  two diodes and two capacitors. I used it on my lathe since I didn't have a suitable outlet from the transformer to get 80VDC. So I got them from 28VAC using this circuit.

Daniel
Title: Re: Can two 36v power supplies be used in series to get 72v?
Post by: HimyKabibble on April 24, 2009, 01:02:29 AM
Hi,

Another option to get higher DC voltage is to use a "voltage multiplier circuit". It's a very simple, commonly known, circuit, utilizing  two diodes and two capacitors. I used it on my lathe since I didn't have a suitable outlet from the transformer to get 80VDC. So I got them from 28VAC using this circuit.

Daniel

Yes, but compare to a proper full-wave rectified supply it will have only half the current capacity, and will require double the filter capacitance to maintain the same ripple voltage.  Overall, not a good solution for a high-current device like a motor.

Regards,
Ray L.
Title: Re: Can two 36v power supplies be used in series to get 72v?
Post by: simpson36 on April 24, 2009, 05:59:59 AM
http://www.kelinginc.net/SwitchingPowerSupply.html   Model KL-7220

This is what I bought.

I ride the short bus when it comes to electronics, I'm afraid . . and while I can sort of reason out what an 'over wind' is (a tap basically?), the term  'toroidal transformer' is alien speak.  ???

Yes, I know now that switching power suppies are not only unnessesary, but not recommended by Gecko. I suspect they may also cause a lot of noise, but that's just speculation.

If the new transistors fix the 36v supply that I have now, I could use that to power the little servo for the time being.

Eventually, I will probably replace the little servo with a larger NEMA34 90v ort 72v servo, but meanwhile, there must ne some way to get 36V from a 72V transformer easily. I have ordered a pair of 9.1ohm 100watt resistors. I read that a 'voltage reduction' circuit uses a resistor on both the positive and negative wires and I have also read that the resistor goes only on the + wire, I have no idea which is better or why. Seems to me a DC motor  swithces polarity depending on the direction, so there is no '+' wire in reality. Is that correct?

I would like some more explaination as to why  the voltage drop across a resistor based on current draw is going to pose a problem. I have a little better  understanding of the difference between 'switching' and 'unregulated' now, and my understanding is that 'unregulated' supplies do not compensate and the voltage drops when the draw goes up. Gecko recommends 'unregulated' supplies, so I presume they must be designed to handle the voltage drop.

So I don't understand why a votage drop on a  . .  36v  'tap' would be a problem for the servo motor if I put the resistor upstream of the Gecko. What am I missing?

http://www.kelinginc.net/K23-120-36.pdf

This is the little servo motor. Quite the little brute actally. If a resistor was sized to give 36V @ 4A and the voltage was geater at less draw and fell off over 4A, what would the result be in performance and would it damage the motor? I'm fairly certain it would not bother the Gecko drive. The drive is rated for 80V and and it has an adjustent to limit output current anywhere between 0 and 20A.






Title: Re: Can two 36v power supplies be used in series to get 72v?
Post by: Dan13 on April 24, 2009, 07:00:56 AM
Ray,

What determines the current capacity is the capacitors. And as you know, a capacitor can deliver enormous currents. As to the capacitance, you're right - you need the same capacitance twice - one for each half of the rectified signal.

Daniel
Title: Re: Can two 36v power supplies be used in series to get 72v?
Post by: Dan13 on April 24, 2009, 07:09:28 AM
Simpson,

You got me confused... are you seeking to get 72VDC from 36VAC or vice versa?

In any case, voltage reduction by using resistors is not good for the purpose of powering motor drives, since the current the drives draw is not constant and there is no way to calculate the resistors required.

Daniel
Title: Re: Can two 36v power supplies be used in series to get 72v?
Post by: HimyKabibble on April 24, 2009, 07:52:04 AM
Ray,

What determines the current capacity is the capacitors. And as you know, a capacitor can deliver enormous currents. As to the capacitance, you're right - you need the same capacitance twice - one for each half of the rectified signal.

Daniel

Daniel,

Sorry, but that's not correct.  Take a 24V/5A, or 170W, transformer, connect  it to a full wave rectifier and filter, and you'll have a 34V/5A, or 170W,  power supply.  Connect that same transformer to a voltage doubler and filter, and the power the transformer can deliver remains 170W, but you've douibled the voltage, so the current must be halved.  There's no free lunch here.

Regards,
Ray L.
Title: Re: Can two 36v power supplies be used in series to get 72v?
Post by: NosmoKing on April 24, 2009, 09:53:06 AM


 I would like some more explaination as to why  the voltage drop across a resistor based on current draw is going to pose a problem. I have a little better  understanding of the difference between 'switching' and 'unregulated' now, and my understanding is that 'unregulated' supplies do not compensate and the voltage drops when the draw goes up. Gecko recommends 'unregulated' supplies, so I presume they must be designed to handle the voltage drop.


A couple of problems  with using a resistor to drop voltage is that not only is it wastefull (heat producer) it is of no practical use unless the current remains a constant value, any variation in current with affect the output voltage.
Switching supplies are regulated, linear supplies may be regulated or un-regulated, Linear unregulated are sufficient.
Although unregulated, if designed for the maximum current, there should be minimum volt drop when highest current is drawn.
The aim is for the reservoir capacitance to maintain the peak DC.
Incidentally, a little known fact is when building your own linear supply, if you over design the sizing of the smoothing capacitor, you will increase the VA rating required for the transformer.


Title: Re: Can two 36v power supplies be used in series to get 72v?
Post by: simpson36 on April 24, 2009, 09:57:53 AM

AC is not part of the question. The thread started with me wanting to power a 72v DC motor with TWO 36V EC supplies.

I decided to use a 36V motor instead of the 72V, so the question became acedemic. I  threw things off by saying my PD was unregulated when it is actually switching and is regulated. I did not know the difference at first. So I learned something very useful about PS, but I don't think there was agreement on an answer.

The situation has changed now and I have kiled the 36v PS and replaced it with a 72V unregulated PS and now seek to run a 36V motor off the new 72V power.

I know it is possible, I just don't know exatly how to go about it and I also know it would not be 'regulated', I just don't know if that will be a problem, or why. I am mostly interested in the why.

At least one of the power supplies listed at Keling have an unregulated 83V output and also a 5V regulated output, so obviously it is doable.

If indeed 'unregulated' means the voltage fluctuates with load, and these are the type of power supplies recommended for my CNC setup, why then would a simlar fluctuating voltage downstream of a resistor be unacceptable?

This seems on the surface to be contradictory, and I would like to understand the issue better. If anyone can shed some light on these question, it would be much appreciated.
 
Title: Re: Can two 36v power supplies be used in series to get 72v?
Post by: simpson36 on April 24, 2009, 10:19:08 AM
" . . . any variation in current with affect the output voltage."

This is what I don't get. Isn't this exactly what an 'unregulated' power supply does anyway? If so, why then is this an argument against knocking down the voltage with a resistor?

I'm not concerned with efficienecy or the resistor getting hot. The ones I bought are contained in finned alumuninum cases. I only spent 9 buck on the pair of them, so it's no biggie if I don't use them, but I would like to come away with a better understanding of this issue.

"Although unregulated, if designed for the maximum current, there should be minimum volt drop when highest current is drawn."

The little servo motor runs at 4A and draws a max of 20A at 36V. An onbvious solution is to buy another 36V 9A power supply and set the output current limit on the Gecko drive to 9A. But that doesn't make for a very interesting discussion.

How would one design an unregulated supply for this if they had availble 72V DC to start with instead of 110V AC? Is a transformer the answer?
Title: Re: Can two 36v power supplies be used in series to get 72v?
Post by: HimyKabibble on April 24, 2009, 10:40:26 AM
" . . . any variation in current with affect the output voltage."

This is what I don't get. Isn't this exactly what an 'unregulated' power supply does anyway? If so, why then is this an argument against knocking down the voltage with a resistor?

I'm not concerned with efficienecy or the resistor getting hot. The ones I bought are contained in finned alumuninum cases. I only spent 9 buck on the pair of them, so it's no biggie if I don't use them, but I would like to come away with a better understanding of this issue.

"Although unregulated, if designed for the maximum current, there should be minimum volt drop when highest current is drawn."

The little servo motor runs at 4A and draws a max of 20A at 36V. An onbvious solution is to buy another 36V 9A power supply and set the output current limit on the Gecko drive to 9A. But that doesn't make for a very interesting discussion.

How would one design an unregulated supply for this if they had availble 72V DC to start with instead of 110V AC? Is a transformer the answer?

The problem is the resistor will only give you the desired motor voltage at one current setting.  If the current is higher, the power wasted in the resistor increases, and the voltage at the motor decreases.  If the current is lower, the power wasted in the resistor decreases, and the motor voltage increases.  If you use a 9 ohm resistor you will get 36V on the motor *only* when it's drawing 4A, and it'll work fine under those conditions.  Under and conditions where the motor is drawing less than 4A, the motor will get higher voltage, because the voltage drop across the resistor will be proportionately less.  At 1A, the motor will see 63V.  The motor does *not* always draw 4A.  It draws 4A only at maximum load.

It's difficult to explain to someone without an electrical background why this is a bad idea, but it is.  The high voltage the motor *will* see at times will greatly increase the eddy currents in the iron of the motor.  Eddy currents cause heating, and the amount of heating is proportional to the square of the applied voltage, so doubling the voltage will quadruple the amount of heat generated.  This is why when choosing stepper power supplies you select the voltage based on the rated voltage and inductance of the motor, and don't simply go for the highest violtage you can put your hands on.

Designing an unregulated supply to deliver a specific voltage and current requires having a transformer with the proper voltage and current rating.  The output voltage will be the transformer rated voltage multiplied by the sqaure root of two.  So, a 24V transformer would be used to build a ~34V power supply.

Regards,
Ray L.
Title: Re: Can two 36v power supplies be used in series to get 72v?
Post by: NosmoKing on April 24, 2009, 10:58:46 AM

This is what I don't get. Isn't this exactly what an 'unregulated' power supply does anyway? If so, why then is this an argument against knocking down the voltage with a resistor?


The little servo motor runs at 4A and draws a max of 20A at 36V. An onbvious solution is to buy another 36V 9A power supply and set the output current limit on the Gecko drive to 9A. But that doesn't make for a very interesting discussion.

How would one design an unregulated supply for this if they had availble 72V DC to start with instead of 110V AC? Is a transformer the answer?
I decided to use a 36V motor instead of the 72V, so the question became acedemic. I  threw things off by saying my PD was unregulated when it is actually switching and is regulated. I did not know the difference at first. So I learned something very useful about PS, but I don't think there was agreement on an answer.

The situation has changed now and I have kiled the 36v PS and replaced it with a 72V unregulated PS and now seek to run a 36V motor off the new 72V power.


If indeed 'unregulated' means the voltage fluctuates with load, and these are the type of power supplies recommended for my CNC setup, why then would a simlar fluctuating voltage downstream of a resistor be unacceptable?

This seems on the surface to be contradictory, and I would like to understand the issue better. If anyone can shed some light on these question, it would be much appreciated.

OK, If I understand correctly, now you have a 72VDC supply and you really need 36V?
Is this unregulated supply you have a linear supply or switching type? Does it have either a large Laminated or Toroidal transformer or does it appear to contain a fair amount of electronics?
This will pretty much decide as to whether you have viable options.
The difference between a dropping resistor and an unregulated DC supply is the resistor is going to drop voltage in a linear fashion directly related to current.
The direct output of a properly rated DC supply, whether unregulated or not will tend to maintain the voltage either due to Capacitive storage as in linear or by electronic means as in switching supply.
The slight change in voltage due to change in current will be no where as drastic as it will be by use of a dropping resistor.



Title: Re: Can two 36v power supplies be used in series to get 72v?
Post by: simpson36 on April 24, 2009, 12:24:07 PM
Thanks very much for the info. I know it takes patience to explain things to persons uneducated in your field. I have simlar problems on the mechanical end.

I think I understand why the resistor is perhaps not a good choice. If I understand it correctly, the higher voltage available to the motor when it is not drawing 4A might cause it to overheat. I can get my brain around that idea. The motor actually draws 20A max, presumably when stalled . . .  which is how I cooked the little 9A PS . . I had the lock on the indexer and started the program running. I was wondering for a few seconds why the indxer was not spinning until after the flash of light on the shelf over my head . . . and everything went dead   ::)


The power supply I just bought is listed as unregulated.     http://www.kelinginc.net/SwitchingPowerSupply.html   It is Model KL7220

Can't say if it is 'linear' because I do not know what that means relative to a power supply. What is 'toroidal' by the way? I know what the word means, but as with 'linear' I can't relate that to a power supply in any way that seems logical.   :-[

So there is still the option of a step down transformer. If I found a transformer that halves voltage and is rated to carry 20A @ 36V on the output, (or 10A 72V input, I suppose), would that be suitable for running the little servo off the big 72V supply?

OR . . .  venturing farthur into the swamp . .  to tap the transfomer where the voltage is 36V? I have no idea if this is  a reasonable idea, but it makes sense to pose the question as long as you guys remain willing to tollerate me pestering you.




Title: Re: Can two 36v power supplies be used in series to get 72v?
Post by: Dan13 on April 24, 2009, 12:48:11 PM
Ray,

What determines the current capacity is the capacitors. And as you know, a capacitor can deliver enormous currents. As to the capacitance, you're right - you need the same capacitance twice - one for each half of the rectified signal.

Daniel

Daniel,

Sorry, but that's not correct.  Take a 24V/5A, or 170W, transformer, connect  it to a full wave rectifier and filter, and you'll have a 34V/5A, or 170W,  power supply.  Connect that same transformer to a voltage doubler and filter, and the power the transformer can deliver remains 170W, but you've douibled the voltage, so the current must be halved.  There's no free lunch here.

Regards,
Ray L.


Ray,

Got your point, you were meaning the bulk current capacity the transformer can deliver. But you never walk on the edge of the transformer's current capacity, and what is more important for a motor drive is the peak current - and this one can be quite large with any circuit using that big a capacitance.

With steppers for example, the drive would hardly draw 1/3 the motor's rated current. I have mounted an ammeter on the lathe where I used the voltage doubler circuit and the current never goes above 0.5~0.7A. The steppers are rated 2.1A.

However, as you pointed, a voltage multiplier circuit might not be good in systems that use servos, due to their tendency to draw large currents under load.

Daniel
Title: Re: Can two 36v power supplies be used in series to get 72v?
Post by: NosmoKing on April 24, 2009, 01:13:01 PM
A transformer, static type that is, can only process AC, and you cannot drop the AC input to your switching  supply as the supply will put out (or attempt to) the rated voltage as the voltage drops.
The reason I was asking is if you had a linear supply that had a Toroidal transformer, this looks like a Large donut BTW, you can quite easily take off windings to tailor it to the voltage you need.
If I were you I would look into building your own Linear P.S. There are only basically three components, not counting fusing etc.
If you a fairly capable with a soldering Iron, it should be no sweat.
Between previous postings and forums, together with web articles , there must be hundreds  of how-to's out there.
If you do find a transformer closer to your required voltage/current, you are half-way there.
The formula for the transformer AC  output is DC output required x .7      DC x.7 = AC output.
Title: Re: Can two 36v power supplies be used in series to get 72v?
Post by: HimyKabibble on April 24, 2009, 02:16:15 PM
Ray,

What determines the current capacity is the capacitors. And as you know, a capacitor can deliver enormous currents. As to the capacitance, you're right - you need the same capacitance twice - one for each half of the rectified signal.

Daniel

Daniel,

Sorry, but that's not correct.  Take a 24V/5A, or 170W, transformer, connect  it to a full wave rectifier and filter, and you'll have a 34V/5A, or 170W,  power supply.  Connect that same transformer to a voltage doubler and filter, and the power the transformer can deliver remains 170W, but you've douibled the voltage, so the current must be halved.  There's no free lunch here.

Regards,
Ray L.


Ray,

Got your point, you were meaning the bulk current capacity the transformer can deliver. But you never walk on the edge of the transformer's current capacity, and what is more important for a motor drive is the peak current - and this one can be quite large with any circuit using that big a capacitance.

With steppers for example, the drive would hardly draw 1/3 the motor's rated current. I have mounted an ammeter on the lathe where I used the voltage doubler circuit and the current never goes above 0.5~0.7A. The steppers are rated 2.1A.

However, as you pointed, a voltage multiplier circuit might not be good in systems that use servos, due to their tendency to draw large currents under load.

Daniel

You still size the power supply to the maximum continuous load it needs to support.  If the 36V supply is rated to handle the maximum load, and you then put a voltage doubler on it, you can no longer support the maximum load.  If your 36V supply has lots of "extra" capacity, then a doubler will probably work, but that would not normally be the case.  And a stepper motor *will* draw its maximum rated current when it is under maximum load.  That may not occur often, but when it does, if your supply drops out, the stepper *will* lose steps, if not stall.  In any case, the supply must be sized to support the maximum load, always.  My point still holds - whatever the continuous rated current of the 36V supply (and that is the way power supplies are spec'd and rated - not by instantaneous peak current), adding a voltage doubler *will* reduce it by half.

Regards,
Ray L.
Title: Re: Can two 36v power supplies be used in series to get 72v?
Post by: simpson36 on April 24, 2009, 02:35:18 PM

http://www.mouser.com/Search/ProductDetail.aspx?qs=sGAEpiMZZMtwaiKVUtQsNVph2yGGEGyO0kpwY0%2fK3NA%3d

This looks like it would do the trick, but the cost is more than a new 36v power supply, so it would not be a practical solution.

Title: Re: Can two 36v power supplies be used in series to get 72v?
Post by: simpson36 on April 24, 2009, 02:52:02 PM
(http://www.thecubestudio.com/pictures/KL7220-135x81.jpg)

This is my new power supply. So far, I know is is unregulated, I think it is toroidal, and I still have no idea what linear means.

"The reason I was asking is if you had a linear supply that had a Toroidal transformer, this looks like a Large donut BTW, you can quite easily take off windings to tailor it to the voltage you need."

How does one go about finding and taking off the 36V?
Title: Re: Can two 36v power supplies be used in series to get 72v?
Post by: NosmoKing on April 24, 2009, 03:18:07 PM
That looks like the AnTek version, I buy my Toroidal transformers from him, like the one in the rear of the picture.
Linear has come to be the description for any  transformer-bridge-capacitor supply, but technically it would normally have a series pass transistor or? for linearly (non-digital/switching) control of the DC output.
The tailoring of Toroidal transformers is fairly easy, you have to know the turns/volt to know how many turns to take off, say you wanted to reduce a winding by 10v output and the transformer had 2turns/volt, then removing 20 turns would do it, turns can also be added to increase the output also. Or you can add a completely separate winding, as long as you do not exceed the total VA of the transformer.
If you want to find out exactly before hand, then wind on a small conductor of 10 turns and measure the AC, the math can then be done.
Title: Re: Can two 36v power supplies be used in series to get 72v?
Post by: RHOLLIDAY on April 24, 2009, 11:04:07 PM
You can use a voltage doubler circuit if your transformer has extra current capacity.  Get some 40V 22000 mf capacitors , remove the +wire from the Bridge rectifier and connect it to one side of the AC transformer lead this will be your 36v positive lead  . Connect the  minus side of the new capacitors to the +side of the old capacitor connect the + terminal of the Bridge Rectifier to the + side of the new capacitors this will be your 72v line. 
Title: Re: Can two 36v power supplies be used in series to get 72v?
Post by: simpson36 on April 25, 2009, 01:08:41 PM
Thanks for the info.

Situation has changed and now I need to run a 36V motor off the 72V power supply. Can that be done in a similar way with a 'votage halver?"

Title: Re: Can two 36v power supplies be used in series to get 72v?
Post by: RHOLLIDAY on April 25, 2009, 01:19:59 PM
If you use the voltage doubler you will have both 72v and 36v outputs. 

Robert
Title: Re: Can two 36v power supplies be used in series to get 72v?
Post by: HimyKabibble on April 25, 2009, 03:19:34 PM
If you use the voltage doubler you will have both 72v and 36v outputs. 

Robert

He has a 72V power supply, not a 36V supply.  He doesn't need a 144V supply....

Regards,
Ray L.
Title: Re: Can two 36v power supplies be used in series to get 72v?
Post by: Dan13 on April 25, 2009, 03:28:01 PM
I think if he can find a zener diode that can handle this voltage at the current he needs, then it would be the best solution...

Daniel
Title: Re: Can two 36v power supplies be used in series to get 72v?
Post by: HimyKabibble on April 25, 2009, 03:36:54 PM
I think if he can find a zener diode that can handle this voltage at the current he needs, then it would be the best solution...

Daniel

That would be one bloody HUGE Zener diode, and it would be *constantly* dissipating as much heat as the motor running full load.  There is no easy way to get 72V down to 36V at the kind of currents required by a motor.  It requires a regulator.  The only viable solution is to buy a suitable 36V power supply.

Regards,
Ray L.
Title: Re: Can two 36v power supplies be used in series to get 72v?
Post by: Hood on April 25, 2009, 05:24:02 PM
If it has a toroidal transformer then there is a chance it has two 25v outputs in series.
 Now I know very little about this kind of stuff but would taking a tapping from one of these secondaries and then rectifying and smoothing not do the job? Of course it may have two 50v secondaries wired in parallel or indeed just have a single secondary but most toroidals I have seen have the two.
 Then again its probably just as easy to build a second power supply and not have to worry about exceeding any limits..
Hood
Title: Re: Can two 36v power supplies be used in series to get 72v?
Post by: NosmoKing on April 25, 2009, 05:34:49 PM
It does appear to have dual outputs, so it may be worth investigating the AC secondary voltage values, it would not be hard to modify.
 
Title: Re: Can two 36v power supplies be used in series to get 72v?
Post by: HimyKabibble on April 25, 2009, 09:37:10 PM
It does appear to have dual outputs, so it may be worth investigating the AC secondary voltage values, it would not be hard to modify.
 

We have a guy who is obviousl not terribly adept with electrinics.  Do you *really* want to have him modifying a fairly high-power piece of electronics by remote control?  Sounds like a recipe for disaster (and possibly a trip to the emergency room) to me....

Regards,
Ray L.
Title: Re: Can two 36v power supplies be used in series to get 72v?
Post by: simpson36 on April 26, 2009, 02:54:43 AM
Thanks to everyone for the education. Here is what I learned primarily:

It is a lot more complicated that I imagined. There is no agreement at all on how to go about this.

I'm an engineer who spent many years building prototypes of all kinds and doing fault analysis on machines and packaging lines and I had a machine shop with my own heat treating furnace. I cut all kinds of exotic high strength materials including H7 H11, Inconel, Ampco Bronze, etc. I'm a newbee at building my own CNC, but I'm not inexperienced at machining or mechanical design.

While I am definately not up to speed on electronics, I've done work at a Chlorine plant where the cell rows run at hundreds of KV. When you walk the 'tunnel' which has fiberglass grating, your skin tingles and your hair stands up. Needless to say, I know enough to not blow myself up. I think "don't touch the wires that are making that crackly sound" is a good rule . .LOL!


Anyway, this issue is now moot as my solution was to buy a NEMA 34 72V servo motor from www.homeshopcnc.com   

I also have on order replacment power transistors that *might* fix my existing 36V supply (yes, I'm handy with a soldering iron, as well as a desoldering iron). If so, then maybe I'll get another Gecko and use the little 36V servo on my troublesome Y axis, otherwise, I'll just pitch the PS and sell off the little servo and move forward. 

Title: Re: Can two 36v power supplies be used in series to get 72v?
Post by: NosmoKing on April 26, 2009, 10:12:19 AM
Good luck with the repair.
Personally if I happen to post a problem that were out of my field, I would like to see all options and self evaluate whether I have the capability to carry them out.
I figured that being an Engineer, albeit mechanical, you would have the ability to assess your own comfort zone in using any of the suggestions.

Title: Re: Can two 36v power supplies be used in series to get 72v?
Post by: simpson36 on April 26, 2009, 10:34:45 AM
NOsmoking,

I very much appreciated every suggestion and exactly as you point out, I realistically assesed my ability to devine a doable solution from all those cards laying on the table in front of me. While I can solder very well, if my life depended on my designing a circuit more complicated than a light bulb with a switch, I would be long gone . .LOL!!

As with my question about wiring limit switches at 24v and interfacing back to the 5v BOB, what I needed and could not get was someone to make me a schematic with part numbers. Given that, I can build things electronic. But I assess my ability to design electronic circuits as near zero and my abiltity to fry expensive components at near 100% . . ;D

The last thing I want is to put off people who are sincerely trying to help, but when there is conflicting information, I really have no way to determine which is correct. I was able to repair a variable speed drive by replacing the MOSfets, so I'm simply parrotting that proceedure with the power supply.  I take zero credit for fixing the controller. It was a FAQ on www.littlemachineshop.com that led me to try replacing the MOSfets. I can desolder an huge transitor and solder in an identcally numbered replacment, but I'm not foolish enough to believe I had ANY idea if it would work or why . . .  ::)

Anyway, my ability to run a 72V motor on a 72V power supply is relatively high, so that was the safe route to take, methinks, but I value every response, even if in the end there is no clear solution.
Title: Re: Can two 36v power supplies be used in series to get 72v?
Post by: NosmoKing on April 26, 2009, 10:40:46 AM
NOsmoking,

As with my question about wiring limit switches at 24v and interfacing back to the 5v BOB, what I needed and could not get was someone to make me a schematic with part numbers. Given that, I can build things electronic.


I could draw a 24-5v  interface up if you still need it, let me know the BOB.
 
Title: Re: Can two 36v power supplies be used in series to get 72v?
Post by: simpson36 on April 26, 2009, 07:34:20 PM
Nosmoking,

My particular problem was resolved in this way:

1) I found the interface schematic published on the Gecko website.

2) I decided to sidestep the whole 24V issue and go with photointerruptors instead of switches. I asked again on the forum for a wiring diagram for that  . .  I got good intentions and promises, but no schematic. I was, however, critisized for even wanting to use photointerruptors on the limits because mechanical switches are 'just as good'.  ::)

3) Peter Homann of Homann Designs was kind enought to review the interface schematic and catalog cut on the interruptor that I sent him and he provided a lot of information on how the schematic could be modified/simplified for use with the photointerruptors.

4) the entire issue became moot as when I totalled the cost of components at retail, it nearly equalled buying a prebuild indexer from CNC4PC, so I bough another of his excellent indexers (I use on on the spindle) which includes both the photointerruptor and the interface. When I get a chance I will install it as the X axis limit and just plug it into the BOB the same as the spindle indexer.

However, the limit switch wiring potentially causeing false e-stops seems to be a fairly common problem, so someone like yourself publishing a schematic on how to bump the voltage to 24V and interface that back to the BOB would be a great service to the CNC commumity here, methinks. If you do come up with something, I will be happy to host it and provide you a link to use for access. I'll even add a copyright notice on the image for you if you choose. That's not much, but it is at least something I can contribute.
 
To answer your question, I have two BOBs, the Gecko specific BOB fropm CNC4PC (C6G, or something like that I think) and the newest BOB from Homann Designs (for which I believe there is no documentation yet). They are just TTL 5v so far as I know. Let me know if there is any information I can procide you that would help with the design of the circuit . . within the limits of 'Electronics for Dummies' level where I am mired.







Title: Re: Can two 36v power supplies be used in series to get 72v?
Post by: NosmoKing on April 26, 2009, 08:55:37 PM
I think I know what you have in mind, but are you looking at something that can be constructed using discrete components, or using off the shelf industrial components where possible, obviously the former will be alot cheaper but require some electronic dexterity with a soldering iron.
I could also include for reference a costlier mostly pre-built solution which can be made somewhat cheaper by buying surplus etc.
A handy feature would be led indicator for input status?
N.


Title: Re: Can two 36v power supplies be used in series to get 72v?
Post by: simpson36 on May 02, 2009, 11:31:24 AM
Couple updates:

New transistors did fix the 36v switching supply. People considering these supplies from Keling should know that although they are listed as 'overload protected' the fuse blows only after the transitors have fried and shorted out.

My new 72V unregulated supply is in and working. Like getting new motors!  Amazing difference.  The little mill now shakes the whole friggin table it is sitting on!


As to the schematic to interface photointerruptors for use as limit switches, it turns out that CNC4PC makes a pre-wired optical interruptor setup with 6 sensors and a little contoller board all set up and ready to hook into the breakout. This is the hot setup. No muss no fuss, already figured out and built. Just needing to be installed on the mill. Here is the scoop:



Steve,

No, there is no simple way of connecting the sensors in series or parallel.  Maybe you might want to consider the C16: http://www.cnc4pc.com/Store/osc/product_info.php?cPath=29&products_id=183, which does what you are trying to do.

Arturo Duncan

http://cnc4pc.com

http://cnc4pc.com/live_help.htm


From: Steve Simpson [mailto:steve@thecubestudio.com]
Sent: Friday, May 01, 2009 4:01 AM
To: Arturo Duncan
Subject: Enquiry from CNC4PC

I have one of your indexers on my spindle as a tach. I just bougth another to use as a limit switch.

Mach3 can use one pin and a daisy chain of limit switches.

Quesiton: is it possible to daisy chain 3 NTE3100 interruptors to your indexer board for use as limit switches?
Title: Re: Can two 36v power supplies be used in series to get 72v?
Post by: Jeff_Birt on May 02, 2009, 11:48:48 AM
Quote
People considering these supplies from Keling should know that although they are listed as 'overload protected' the fuse blows only after the transitors have fried and shorted out.

That should just NOT happen. I have tried a few times to get a better data sheet for their supplies but have not succeeded.
Title: Re: Can two 36v power supplies be used in series to get 72v?
Post by: NosmoKing on May 02, 2009, 02:25:28 PM

Quesiton: is it possible to daisy chain 3 NTE3100 interruptors to your indexer board for use as limit switches?[/i][/color]
I have built and test a three-in-series arrangement for somebody on another forum using similar devices H22A1's.
Title: Re: Can two 36v power supplies be used in series to get 72v?
Post by: simpson36 on May 04, 2009, 06:31:10 AM
Jeff:

I'll pass along what info I have collected on this issue that may be helpfull to you.

The 36V 8.8A PS sells for $60 on Keling. The equivalent Mean Well is $140 from electronics suppliers.

The transitors that cooked are FUJI  2SC3320  sell for under $5 each - cannot find specs

Replacement per NTE cross ref is  NTE2311      sell for over $16 each from the same supplier.

The significant spec on the NTE2311 is 15 amp. (data sheet avail from NTE if you need more specs)

With a $22 delta in just that one component of a $60 product, it is easy to speculate how Keling keeps the cost down.

These are the pair of high speed switching transistors on the back edge of the board, heat sinked to the case.

Question: Which transistors are in the Mean Well?


I am replacing the rectifier, voltage regulator and silicon diode with equivalent parts . .  just 'cause.

Hope this info is useful.


NoSmoking:

Schematic?









Title: Re: Can two 36v power supplies be used in series to get 72v?
Post by: simpson36 on May 04, 2009, 06:40:14 AM
While I have the guru's attention, here is another power supply question:

My new 72V unregulated dual rectifier 20A toriodal tranformer power supply is claimed to have significant overload capability, but it does not seem to perform that way.

I have 3 steppers limited by their Gecko drives at @3A each and a servo at 7A continuous that can pull as much as 40A, but the Gecko drive limits it to 20A max.

If the servo starts too quickly the stepper will stall and vice versa, so I'm not getting the overload capacity I thought I would have.

Which component do I upgrade to increase the overload capacity?


Title: Re: Can two 36v power supplies be used in series to get 72v?
Post by: Jeff_Birt on May 04, 2009, 12:31:15 PM
Speaking frankly, and not to knock anyone, I think the Keling power supplies are MeanWell knock offs. I have tried and tried to get data sheets for the power supplies from them to no avail. I don't think you would have fried a true MeanWell supply that way.

Unregulated supplies are just that, unregulated. The more current they supply the lower the output voltage is. When your servo starts and hogs a bunch of current the voltage is going to drop way down. To prevent sags all you can do is use a bigger supply, add more filter capacitors or not drive the servo as hard.
Title: Re: Can two 36v power supplies be used in series to get 72v?
Post by: simpson36 on May 05, 2009, 04:21:20 AM
Well. my replacements for the rest of the chips in the 36v supply will arrive today. If that fixes it, fine , otherwise, it goes in the trash.

The annoying thin about the Keling is that they make this claim:

A:  Stepper Motor Driver Power Supply Specifications:

1: High Efficiency, Low Temperature, Small Size.
2: Over Load and Short Circuit Protection.
3: Over Voltage Protection.
4: Input: 120VAC or 220V


I was abusing it, no doubt about that, but I expected the worst to happen would be a trip or blown fuse.

If one was to buy the $60 Keling unit and immediately install a pair of transistors @ $32 and the other chips at about $9, you now have a $101 power supply and you are out the time to swap chips and have obviously voided any warranty. I think I would sooner shop around for the best price on a Mean Well or equiv.




I understand that unregulated means the voltage drops, but it seems incredible to me that a 20A power supply (that claims huge overload capacity) can start with 72V and drop so far with a max draw of 29A that it cannot keep a 4V stepper going.

The PS has dual rectifiers. Does that mean 10A per rectifier, or will either supply the total 20A? Can the rectifier limit current?
 

40A max draw on this NEMA34 servo seems like a formidable hit.  Imagining 3 or 4 of these pulling juice at the same time is kinda scary  :o
Title: Re: Can two 36v power supplies be used in series to get 72v?
Post by: NosmoKing on May 05, 2009, 10:26:26 AM
There is a couple of things you can check if you suspect voltage collapse, if the load is sustained long enough to obtain a reading, first check the AC in to the bridge to see how far it drops, if at all, if the voltage drops substantially, then the transformer characteristics cannot sustain the load and apart from changing the transformer there is not much you can do, if the AC remains fairly constant, then it would be the DC ripple is increasing due to the load.
An increase in capacitance may help, but as you increase the Capacitance the VA requirement of the Toroid goes up, so if you were to have sustained high load, you may see transformer heating.
I will forward the circuit via mail.
N. 
Title: Re: Can two 36v power supplies be used in series to get 72v?
Post by: Jeff_Birt on May 06, 2009, 01:11:17 PM
I have been using the MeanWell S-320-48 for smaller machine but I was testing a MeanWell SP-320-48 yesterday as it has a universal input, and power factor correction and is CE approved. It was solid as a rock. One hour at 80-85% load and the built in fan kept the case cool. I could not overload it with the types of steppers I would use on such a system so I directly shorted the output. The supply shut right off and started again when the short was removed (just like the data sheet says).

A good quality switching supply with proper overload protection is hard to kill.
Title: Re: Can two 36v power supplies be used in series to get 72v?
Post by: simpson36 on May 06, 2009, 01:40:56 PM
Just to finish up this story, I received the rest of the replacement chips yesterday and installed them in the fried 36V Keling Switching PS

No joy.

So, I sniffed around the area with an ohm meter where the power transisitors left their scorch marks and I found there was a resistor and a diode that got cooked along with the switching transistors. 
Replaced those and Viola! Up and running again.

Theoretically I have replaced the weak links with better quality componenets and now have a reliable PS.


I don't have the courage, frankly, to short the output as a final test  :-\


NoSmoking; got the schematic, thanks.
Title: Re: Can two 36v power supplies be used in series to get 72v?
Post by: simpson36 on May 09, 2009, 07:28:55 AM
Another update:

My repaired switching power supply put out two amps for a few minutes and the more fireworks. It is now in the trash and I just kept the nice aluminum case to put Geckos or a speed controller in someday perhaps.


Anyway, I found what will hopefully be a permanent solution to the delema. I found a fellow who will make up an unregulated power supply for me that can be switched back and forth from 38V to 76V. You have to contact him and ask for what you want as his listed PS do not automatically have this feature. He did not charge extra to custom build a PS the way I need it. Hopefully this will be the end of the drama.


http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=370197063676&ssPageName=ADME:X:AAQ:US:1123





Title: Re: Can two 36v power supplies be used in series to get 72v?
Post by: NosmoKing on June 09, 2009, 01:57:23 PM
I have been buying my Toroidal's from him for some time, apparently he builds these transformers also.
They are easy to tack on an auxiliary winding if you find you need it, 5v,12, 24v etc.
Nosmo