AC-DC Power Supply

[BobWarfield]

You can find transformers and such to handle that many watts, but you may find it easier to build a couple of supplies and split which motors get which supply.

Industrial Hobbies also has a 65V 20A supply that you might consider. You'd have to contact them and see if they'll sell you one. They're revamping their online store and it isn't listed separately at this stage.

My notes on building a supply are here:

http://www.thewarfields.com/cnccookb...CNCDrivers.htm

There are better notes available, especially on the GeckDrive Yahoo Group, I think there is a whole document, and Campbell Designs also has some power supply info.

Toroidal (and regular) transformers are often available on eBay as are the capacitors. I recently bought a toroid to build a supply for my mill which will be about 1000 watts, but haven't started it yet. I liked the handy little Ajax CNC board for the rectifier and inrush protection, they're cheap and compact:



Looks like I hit the Gecko recommended voltage limit pretty close, eh? LOL

Be careful with these power supplies, they crank out some juice!

Best,

BW

[Al_The_Man]

Just as a Comparison, I have two Excello Knee mills which I used the original motors and power supply when I retro-fitted them, they are actually larger motors than the ones TimDC mentioned, mine are SEM at 40"-lb each, his are 30"-lbs Baldor.
I would estimate the Power supply on mine to be at least 2kva.
Al.

[walter]

Al,
what's the difference between the big blue caps and the ones in the pic?

[Al_The_Man]

I have found the black ones in your pic come mostly in printed cicuit mount, The Blue ones shown in Bob's are generally come with terminal top and are designated 'Computer Grade', I have never looked into wether they are superior, but I tend to use the Blue ones in my supplies, I have never had one fail, and they are easier to use generally because of the terminal feature.
Al.

[walter]

They're massive in size.. Does it affect the ability to store the energy?
Bob's device has smaller toroid and a massive cap, the other device has similar output, but bigger toroid and small caps.

I would appreciate any explanation of this..

[TimDC]

Originally Posted by Bubba "Mariss Freimanis" is the gentleman behind the gecko series of drives. He is very active on this and other on line activities and is/has been very helpful to the community providing a wealth of information in addition to producing great products. If you do a search, I think you will find more information than you really care to know on the subject. Bubba

Thanks, I'm reading through some of his posts now, helpful stuff.

[Al_The_Man]

Originally Posted by walter They're massive in size.. Does it affect the ability to store the energy? Bob's device has smaller toroid and a massive cap, the other device has similar output, but bigger toroid and small caps. I would appreciate any explanation of this..

The Physical size of the Toroid is usually relative to the VA rating.
For Electrolytic chemestry this may help.
http://electrochem.cwru.edu/ed/encyc...r-cap.htm#app1
Electrolytics are best kept with a small charge on them, if left in storage too long they may fail if too high a voltage is applied at once, If you have had one on the shelf for a long time it pays to apply a small voltage to them over a period to restore them.
Al.

[walter]

Thanks!

[BobWarfield]

The two little black caps are probably lower capacity than the big blue one. BTW, to increase capacity, wire capacitors in parallel.

The formula I got off the Gecko board said to size capacitors as:

80,000 * amps/volts

In my case, I am running 4.5 amps / 72 volts * 80,000 = 5,000 micro Farads.

The cap I bought are 4000 mF, which I deemed close enough. Bigger caps are going to give you a little less ripple in the voltage, which may help slightly, but most of these motors won't care too much. The other thing bigger caps will do better is deal with inrush current, but my Ajax rectifier board does that for me, so I didn't sweat it.

These big caps are also 400V rated, which is way more than needed for this application.

For my mill's power supply I'll probably hook two of these big caps in parallel. I got a whole box of 'em off eBay for $30.

Best,

BW

[walter]

Good info. Thanks.

[Kipper]

I came across this handy online resource for selecting transformers and capacitors...Hope it's of use to others. http://www.k7mem.150m.com/Electronic...fmr_Spec_Input