power Supplys DIY

[wantsout]

I got two Transformers and wired them in series, (they are 24 volts ac each). I want at least 48 volt DC for my Geckos, got me a 25 amp bridge rectifer and wired that up. and checked the output voltage it was around 71 volts. (I thought that was OK under a no load condition. ) put 5 each 6800MDF 50 volt capacitors on it and plugged it up. But what do you think happened I smoked some of the caps. they werent rated for enough voltage.( some I had on a junk board). My Question is this. What do you guys use for smoothing out the ripple from you homemade power supplies. Or what size are your capacitors...

[Al_The_Man]

What did you expect running 50v caps on 70v?
You want at least 100v~125v rating minimum.
Al.

[klmjr]

48 volts AC will give you about 68 vdc output under no load. most transformers have slightly higher output voltage than their rating when not under load. At full rated load they should put out 24vac. Thats why you measured 71 volts. If you have a heavy load that can return power to the supply during deceleration, you may need to install a energy dump circuit. There is a schematic for one on the Gecko site. As long as the current rating on the transformers is sufficient the supply sounds like it should work fine. Just make sure you use a capacitor of at least 100v rating. The size of the cap depends on voltage and current required, at the voltage you are using about 1000 uf per amp of current should be fine. There is a more precise calculation in the FAQ at the gecko site. Be careful, these kinds of voltages and currents can be fatal even if it is DC.
klmjr

[wantsout]

Thanks for that information, On the caps I was thinking they were too small and the smoke proved me right. will have to look around for some bigger caps at 125 volt rating.and will have to look at that schematic for that ckt. Had the two transformers and thought I would hook them up in series because I wanted more than 24 volt on the geckos I am planning on using. there a little cheaper then a 60 volt transformer at 20 amps around 155.00 dollars. a little more than i wanted to spend at the moment..

[wantsout]

Found out I can wire my 50 volt capacitors in series and it will double the voltage rating but half the MFD rating,But I have enough 50 volt 6800MDF capacitors that i can get the 1000microfarad per amp motor rating. (just wire the capacitors off your bridge rectifer postive to neg to postive to neg to ground of your supply..