Simplest route - High power variable supply

[eeka chu]

This isn't strictly audio related, which is why I'm positing it under 'Everything Else'.

I require a somewhat high power variable supply for some research I am now involved in.

I need to be able to alter the current output and voltage of the supply. As a rough estimate of the domain, I will require an output current at a maximum of 10 to 100 amps and a maximum open circuit voltage of between 100 and 400 volts. High currents and high voltages essentially.

For a noiseless audio quality supply, that would certainly be a challenge, but I don't require any real degree extreme filtering. Standard rectification with a simple inductor or capacitor filter would most likely be fine.

I would like to ask how I should go about regulating such ratings however.

One thought was perhaps a stack of car batteries, but that'd get expensive quickly.

Another was to use a parallel stack of three pin high voltage regulators. Or a gigantic Variac - but that's probably going to be one of the most expensive options.

I'm not really after finalised designs, I'd just like to hear your opinions on the topologies that would be suitable for such a supply and how you'd go about it.

Again, there's no real need for dead on precision or noiseless power, I just need to be able to connect my scope to it, set a rough current or voltage and observe an effect.

The work, as you probably guessed, involves sweeping the voltage and current of the system to test for an optimum or pattern in the result.

If the topology didn't involve a monster sized, hundred kilo heat generating element it'd be useful - but I'm willing to accept that at the moment.

So... what kind of topology might you use?

[Enzo]

Wow, there is a challenge. You need a variable supply putting out from 1000 to 40,000 watts of power. If your mains are 240VAC, then you need 167 amps for the 40kW. HAve you that available? WIll you need the full current at the full voltage? Or is it more like we will need 100 amps at 100v and the 10 amps at 400v? Intermittent or pulsed duty or continuous? Car battery can put out 100 amps, but not for a long time.

Do you need to limit current, or will the load handle that? DO you require isolation from the mains or not? Does it have to be DC? I don't know about over there, but over here the basic mains are 240VAC center tapped. Industry uses a lot of three phase AC at those and higher voltages. The local power company can install a power tap at many other voltages. The tall lamps over street intersections and highway ramps run on 440VAC. Perhaps you could get the electric supplier to put up a tap for you. Then rectify it.

Does the voltage have to be clean? That is, could you vary the voltage with a triac? SOme large industrial triacs could control the power into some rectifiers. Does the voltage have to be smoothly variable or is it OK to use steps?

Do they make Variacs that large? Rectifiers are no problem.

How important is money? College project or government budget? Doesn't sound like basement work. Can you discuss the project or is it classified or waiting patents?

Arc welders can provide tons of amps, but the voltage is not so high. High voltage is easy except not st such currents.

A generator driven by a variable speed motor even comes to mind. Military used to use motor driven generators. I forget the term for them now - I'm getting senile.

I worry about stacking car batteries or other lower voltage things. The voltages and currents might add, but you can easily exceed the voltage breakdown ratings of the items. You don't want catastrophic failure of a car battery.

[dangus]

If this is serious, I'd suggest renting an appropriate power supply from a place that hires instruments. Or, renting time at a lab that is equipped for stuff like this.

I designed and built a power supply with a current-regulated output up to 75 amps, but the voltage was pretty low (10V?). I got a transformer custom-wound, then used a big triac on the primary, big rectifiers on a heat sink on the output, and a couple of humongous surplus electrolytics to fiilter it Regulation used an integral controller, and it worked great. I would have liked to have used an inductor in the output, but it would have needed something ridiculously large, and made the unit even less portable than it was already.

I guess if you could score a surplus transformer and other components, this might be feasible. Maybe rewind the secondary of an arc welder...

The motor-generator idea could maybe be done using automobile alternators. There's models with over 100A capacity; you could run a few in series to get higher voltages.

Or, use a big string of car batteries to get a few hundred volts. Then, "just" use a switching regulator to drop the voltage.

It wouldn't hurt to study the techniques used for big DC motor speed controls. Maybe you could pick up something like that surplus.

[Brian Donaldson]

You'll need to use a switching regulator or a variac or you'll have to buy thousands of dollard worth of heat sink for whatever semi you use to burn the excess. Plus hundereds of dollars woth of semis.