Power Supply Question

[BobLWeiss]

Hello, I'm sort of new here and have been building my own machine for awhile. I am at the point of finishing making my first controller board (using picstep as a basis for my design) and I need to get a power supply together. From what I've read most people seem to go with linear type supplies and not switching. Well no one said this hobby is cheap and I am in it for the long haul but I do want to save money where I can. My machine isn't that big, its 24" x 16" x 6" and the steppers are 80oz/in 8 wire type. I noticed that you can get a 24-36v/12 amp or larger powersupply fairly easily from Ebay etc but they are all switching type. Does it really hurt to go with a switching type or would you rather buy a transformer and rectify it yourself? The cost of a transformer that puts out that many amps is over $100 itself. Does anyone know where you can get transformers cheap? Ebay has way to many to even comprehend. There are so many types out there. The drivers can handle 55v/3amp per phase but my motors aren't that big (yet). I have a 24v/6amp switching ps I got off ebay but I don't think its enough power. What did most of you do for your power needs?

Sorry for the long post, just trying to learn and figure what's best the first time around...

[ViperTX]

You can use either.....also "whispering".....most have switched to Toroids for unregulated bulk DC supplies.....

[Bubba]

Bob,
When I need a new power supply, I took an old Microwave transformer and cut out the HV (2000V) winding and wound my own with new magnet wire. I found (by testing) on one particular transformer that 1 turn = .9 volt so I just divided my required output by .9 and wound that many turns. Wire size is based on amps required and it works for me!

Just another option.

Bubba

[OCNC]

Believe it or not as I was driving around this morning doing an errand I came across a discarded Sanyo microwave. I took it home, removed the transformer, cut off the high voltage winding and wound on 25 turns of #12 wire that I stripped out of a 15' scrap of Romex that was laying around. At 1V per winding, sure enough I got 25V on the secondary. It was almost too simple and I started wondering how much current I would be able to draw from the secondary without melting something. After seaching the net for a while I found two articles that might be of interest to others regarding power supply design. One is on transformers and the other on linear power supplies. (Both are from the same audio site.)

Chris

Transformers
Linear power supplies

[Bubba]

Chris,
I have found two surplus houses that carry magnet wire:
www.mjpa.com They carry .5 lb spools in sizes up to #14
www.surplussales.com They have a much better selection

Bubba

[Sanghera]

How much amperage do you get out of these microwave power supplies?
Thanks.

[Bubba]

To be honest, beats me. I just know that I can crank up my servos (3 of them) and haven't lost steps (cutting air) at 120IPM and I have done some 2 and 3 axis milling and haven't stalled them yet!
The only problem I have had (my fault) was the other day when I was in MDI mode and told it to rapid with an edgefinder in the chuck. I hit the e-stop about 1/2 second after the edgefinder hit a clamp and I had one axis fault out (I now have a 90 degree edgefinder
Also, I have not finished tuning the geckos after a recent power supply change so I know they are not optimum yet.

[OCNC]

Originally Posted by Sanghera How much amperage do you get out of these microwave power supplies? Thanks.

Using a graph in the 'ARRL Handbook' that relates power handling cabability to core cross sectional area I determined that the transformer I have should handle about 7 to 8 amps continous (approx. 150-180 watts). The handbook suggests that intermittent duty can tolerate an increase of as much as 50%.

Chris

[Sanghera]

Hmmmm. This sounds good, just the right voltage and amperage. Where can you get the right wire to use when building this?
Thanks.

[Al_The_Man]

Try one of your local motor rewind shops they may sell you the part end of a reel of enameled wire.
Al

[Bloy2004]

..Just curious about insulated wire for winding....
I have an 8" toroid 1.5KVA with 10awg and unwound(clipped off) the enameled wire to bring down the secondary voltage. heh...unfortunately I overzealously took way too much off and in dismay looked at the pile of bits of short enameled wire from the assault. So I had some ordinary 3wire10awg house wire(white,black, bare ground) and rewound the the toroid with the white insulated wire to get back to the desired voltage. It works fine and so far doesn't get warm as am not overburdening with max draw but am wondering....
The question is...
Will this type of "coated" wire impair the function of the transformer in any way I should be worried about?
I used solder and heavy shrinktube to connect the "enameled" end and new wire before rewrapping....and had to go completely around the toroid one and a quarter times....about 50 to 75 ft of wire.

[Al_The_Man]

If you are not talking alot of turns then it probabally wont matter, the reason is for enameled wire is that not only do you get high density of winding, but the turns remain as close to the core as posible, i.e. closest coupling of the magnetic flux.
Al