Need a DC maker..

[RODL]

I am looking for a schematic for a AC to DC converter. I have a variable AC source that I would like to generate a variable DC output with.
I would like a 0-150 volt, 25-30 Amp output. The circuit would not be energized for more than 10-15 seconds at a time. I want to use this for accurate pickup tests of DC coils and electrical power system relays so I would like a fairly clean DC. Can any one help???

[Mike]

You'll need high-current, high voltage rectifier diodes and high voltage caps. ON semiconductor, [url=http://www.onsemi.com,]www.onsemi.com,[/url] makes many high-poower diodes.<p>You will also need at least 250V caps, totaling 10,000uf for that very clean power you need.

[haklesup]

A standard bridge rectifier followed by an RC filter sould be sufficient. The output will be unregulated meaning that when you connect a load, the voltage might drop a little but for your application that should be OK. I imagine you will connect a relay then gradually increase the voltage until the contact closes, since the load is always connected, the voltage should be easily measured and be predictable.<p>A regulated variable supply of that range and current would be expensive and complicated to build. <p>Use Shottkey Diode rectifiers. The smaller voltage drop across the diodes at high current translates into a lot less heating and more power transferred to the output. The caps should have a voltage rating higher than 150V but less obviously they should also have low ESR since the ripple current will be high you don't want to heat the caps that way. Filter caps often have ripple current ratings on the catalog page or spec sheet.<p>Those must be some "honkin-big" relays you got there. I can understand the voltage range but that seems like a lot of current to close a relay. High current translates to a strong magnetic field needed to pull in a heavy armature. <p>If you search on "Filter Calculator" or "power supply design" or similar you will turn up a few web pages to help you decide the values of the R and C in the filter. For that current and voltage expect caps almost the size of soda cans and expect prices around $30 each.

[toejam]

i would use a a 30 amp or better bridge rectifier hooked up to to a variac. with a 15 second duty cycle. a ten amp variac would do, you will have to re fuse it,if you forget to turn it off, it will fry, and set the voltage before you connect it (do not adjust it under load). Better yet get a 25 amp one if you can afford it.