Re: Cheap, high amp dc power supply?

On Fri, 03 Mar 2006 15:06:32 -0600,
twags6@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx (twags6) wrote:

Is there any way to make a dc power supply capable of 50+ amps at
12-13.8 vdc? Basically, I'm looking for something to simulate the
power from a car without the whole battery and charger setup. Parts
express sells a nice rackmount one, but I'd rather not part with $190.

TIA

Consider designing what you want. A linear supply for 50 amps is
usually too inefficient to be practical. (or you live in Antarctica
and the waste heat will go to heating a room)

I have a couple of SCR controlled supplies that I like for high
current and low heat. One (0-48 volts 5 amps) uses a two diode FWB
and phase controlled SCR pass element, the other (0-24 volts 10 amps)
uses a pair of SCR's that provide both rectification and control
(downside is it takes a separate transformer winding to power the
trigger circuit)

Neither of mine are "regulated" but as long as the line and load stay
reasonably constant . . . I use them to control DC motors. Place I
worked at awhile back used a similar scheme to control an
electromagnet for a welding deflector - It has feedback and a
differential amp to provide regulation.

With SCR's you just need to increase the size of the SCR for more
current - the rest of the circuit pretty much stays the same. Easy to
control 50 amps or more and make it continuously variable from
0-whatever with high efficiency.

For sensitive loads you need good filtering - but if you're talking
about 50 amps at 12 Volts you're probably not dealing with a sensitive
load, at few amps 20,000 ufd would be plenty.

A lot of good, free, power supply design info is at:

www.ieeta.pt/~alex/docs/ApplicationNotes/DC%20Power%20Supply%20Handbook.pdf

I picked up a surplus 1,200 VA toroidal isolation transformer - it
would make a nice power supply, The beauty of a toroid (in that size
range especially) is it only takes two turns of wire (2.4T/V on mine)
for every volt of output - right now it is working as a spot welder.
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