160vdc diy power supply questions

[born2bewilder]

Hello. I recently picked up some surplus servo motors, intended for use a three-axis table, eventually. The factory recommended servo drives (and associated accessories) are thousands above my price range, so I've been looking to put together my own power supply.

I was thinking about acquiring a Granite Devices VSD-E or -XE, these run at a max 160vdc, and since the motors I have run at that or higher, I'd like to assemble a power supply capable of supplying that voltage.
Since I haven't any formal training in electronics, I'd like to run my ideas past everyone here, and see if I can clear up some of the uncertainties I have with the whole thing.
The plan, such as it is at this point, is to use a surplus control transformer (I recently picked up a 1000VA model), rectify this to ~165vdc, and use some smoothing capacitors to keep ripple to <5%.

Questions I have so far:
1. I tried using this design calculator, and it suggested that for 160vdc and 5.0a, I should be using smoothing capacitors rated to 290v. I had been eyeballing some 20,000uF, 200VDC, 250VDC surge rated caps. Can anyone explain why the suggested ratings might be so high? I assume there must be a reason, although I don't know what it is.

2. I was also curious whether one can have too many caps? If I had, say, 100,000uF of caps, would there be any issues with inrush capacitor charging currents? Or, does placing them after the isolation transformer negate any such problem.
Corollary: If I used a larger control transformer, such as a 3kVA or 10kVA model, might that become a problem that needs addressing? I read a site that discussed using series resistors and triacs and stuff to limit charging currents.

3. In my research so far, I haven't run across voltage regulation circuits suited for voltages over 30vdc or so. Does anyone know an inexpensive design that would allow this system to output a regulated 160vdc with continuous currents in the 10A+ range (I'm thinking ahead a bit).

4. I've read that control transformers are typically designed for surge currents up to 7x the rated load. This suggests that I needn't size my transformers based on maximal possible load, but rather that I keep my average load under the VA rating. Can anyone confirm or deny?

5. My control transformer is your typical rectangular laminated transformer type. I noticed that most DIY dc supplies use torroidal transformers. Is there a particular advantage to this type I should be aware of?

If anyone could give me any input concerning these Q's, I'd appreciate it.

b2b

[Al_The_Man]

Originally Posted by born2bewilder Questions I have so far: 1. I tried using this design calculator, and it suggested that for 160vdc and 5.0a, I should be using smoothing capacitors rated to 290v. I had been eyeballing some 20,000uF, 200VDC, 250VDC surge rated caps. Can anyone explain why the suggested ratings might be so high? I assume there must be a reason, although I don't know what it is.

Personally I have used ~+20% rule for cap sizing if you have a 120v transformer the peak DC is going to be around 165vdc, allowing for Back emf spikes etc 20% should be OK I would think 290v is rather on the high side.
The ones you selected should work based on my experience.

Originally Posted by born2bewilder 2. I was also curious whether one can have too many caps? If I had, say, 100,000uF of caps, would there be any issues with inrush capacitor charging currents? Or, does placing them after the isolation transformer negate any such problem.

Apart from the high inrush, sizing larger also creates a problem with transformer sizing when running at close to the rated current.
Increasing Capacitor size, requires an increase in VA.

Originally Posted by born2bewilder 3. In my research so far, I haven't run across voltage regulation circuits suited for voltages over 30vdc or so. Does anyone know an inexpensive design that would allow this system to output a regulated 160vdc with continuous currents in the 10A+ range (I'm thinking ahead a bit).

You do not need a regulated supply for steppers or servo's.

Originally Posted by born2bewilder 4. I've read that control transformers are typically designed for surge currents up to 7x the rated load. This suggests that I needn't size my transformers based on maximal possible load, but rather that I keep my average load under the VA rating. Can anyone confirm or deny?

You can size your transformer for total maximum load x60% as a rule, it is very seldom you are going to run everything flat out, for any extended period anyway.

Originally Posted by born2bewilder 5. My control transformer is your typical rectangular laminated transformer type. I noticed that most DIY dc supplies use torroidal transformers. Is there a particular advantage to this type I should be aware of?

Toroidal transformers are a slightly more efficient but you would not notice any appreciable difference, the advantage comes if you want to modify the secondary or add a small auxiliary winding or two.
It is usually very much easier to make additions/corrections due to the nature of construction.
Al.

[born2bewilder]

Thanks for the fast reply!
That should clear things up quite a bit... for a while anyway.

b2b