Messages

1221

General Mach Discussion / Re: Can two 36v power supplies be used in series to get 72v?

« 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?"

1222

General Mach Discussion / Re: Can two 36v power supplies be used in series to get 72v?

« on: April 24, 2009, 02:52:02 PM »

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?

1223

General Mach Discussion / Re: Can two 36v power supplies be used in series to get 72v?

« 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.

1224

General Mach Discussion / Re: Can two 36v power supplies be used in series to get 72v?

« 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.

1225

General Mach Discussion / Re: Can two 36v power supplies be used in series to get 72v?

« 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?

1226

General Mach Discussion / Re: Can two 36v power supplies be used in series to get 72v?

« 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.
 

1227

General Mach Discussion / Re: Can two 36v power supplies be used in series to get 72v?

« 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.

1228

General Mach Discussion / Parallel port for PCI bus that works with Mach3 - just passing along info

« on: April 23, 2009, 07:33:55 PM »

After much research I bought this dual parallel port to run a second BOB off Mach3. This is, incidentally, my favorite place to buy my geek stuff.

http://www.newegg.com/Product/Product.aspx?Item=N82E16815166007

It works in a really old computer runing Win2000 (the one that actually tuns the mill), a relatively new computer running XP and even a 'middle aged' computer runing Windows 7 beta. I did not test it with Vista. It took quite a bit of tinkering to sort out, so I though I'd pass this info along and save people some time if they go with this card (apparently lots of cards don't work with Mach at all.)

Caveats are:

1) Go to www.MOSchip.com to get the drivers for the chipset on the card. The ones that come with the card didn't work for me . . YMMV.

2) The card has two ports.  You need to give Mach3 the address of what the device manger lists as LPT3 as that's the port address for the connector on the card itself. There is a second connector on a bracket that connects to the card with a ribon cable. So that one must be LPT2.

Hope this is helps someone.

1229

General Mach Discussion / Re: Can two 36v power supplies be used in series to get 72v?

« 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.

1230

General Mach Discussion / Re: 0-10 volt output for vfd

« on: April 23, 2009, 05:57:51 PM »

My first controller fluctuated all over the place. I gave up on it and got a board from Homann and it was better, but still fluctuated too mych to be usefull. I tried every suggestion to resolve it including setting up the breakout and speed controlers on a new computer in my office and just runing it with a voltmeter attached. The wires were literally only inches long and there were no machine tools anywhere around. Still fluctuated.

Peter was kind enough to send me one of his new design controllers and breakout boards to try.

These things are awesome! The controller is PWM and it the control voltage it puts out is dead steady . . at leaste in my nice quiet office on a new computer. Honestly I was afraid when I got it down on the old battle axe computer next to the mill, it would be fluctuating again.

I was just waiting for a second parallel port for the computer to arrive and and I just got it hooked up today on the machine tool. Still dead steady on the volt meter AND The spindle motor finally runs nice and steady! 

Happy camper here. Highly recommend Homanns new stuff . .  and I rarely endorse anything.