Messages

231

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

« 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.

232

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

« 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.
 

233

General Mach Discussion / Re: What size motors?

« on: April 26, 2009, 10:20:09 AM »

It is not very difficult (famous last words) to make ball screws for any machine tool.

'If any machine tool' you mean manual machines as well, It has been my understanding that the main problem is back-feeding when the much lower friction B.S.'s are fitted?

234

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

« 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.

235

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

« 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.
 

236

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

« 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.

237

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

« 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.

238

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

« 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.

239

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

« 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.

240

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

« 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.