Up to ~1000 A constant current supply 10-40 VDC

Question

So a little background to explain the need. Occasionally we need to test starter motors (for engines) and provide enough power when the load (engine) causes the starter to pull in excess of sometimes 1000 A. Granted, this is for quite large starters. The test would need to last a minute or so, but foregoing the need to alter designs, we'd like to just go ahead with a continuous demand rating.

So I've got a fair understanding of linear power supplies and some common designs of higher currents, such as multiple transformers/taps, bridges, parallel transistors (2N3055, etc.), but in my own experience I have only "engineered", mathematically, relatively simple sub-circuits, RLC, and other simple circuits (555 timers, opamp 747, etc.) using Kirchoff voltage/current, Thevenin, systems of ODE/PDEs, phasors, etc. But really I rely on the community for a suggestion on what to look for. (And ideally a schematic!)

Some of the design requirements are

1. 10-40 VDC (some are 24 VDC starters and a few are 36 VDC)
2. Maximum of about 1000 A at 24 VDC ~ 25000 watts/VAC
3. Be a current supply more than a voltage supply, similar to the idea of having the load in series with a much larger resistor.
4. Lastly (I think), is to be able to use single-phase, two-phase, or 3-phase input.

For larger loads, 110 VAC at the main is not going to work. For some idea of portability (we are a start-up business and have plans to grow and move) it would be nice to be able to run off "single" phase or three phase. This way each leg could supply a good amount of the load. (Can these be joined after the rectifier bridge or smoothing cap?)

By the way, companies such as DynaPower, though awesome, are just way too far out of our budget for right now. Besides, it's much more fun to build it yourself!

For what it's worth, we had thought of purchasing a used portable welder but were worried about the voltage adjusting itself to give the required current, and therefore power, to the load. I wouldn't know how to limit voltages at these currents...

Answer 1

I don't think that you will be happy with a regular power supply aproach, e.g. adjustable from 10V to 40V. For 40V and a regulation you need about 42V before the regulation. When you put it to 24V and draw 1000A you will have (42V - 24V) * 1000A = 18KW waste power.

You could mitigate this situation using a transformer with different output voltages for 12V, 24V and 36V. Already taken this step i would also consider if your starter motors realy need a regulated power supply, this would reduce your circuit to a transformer, rectifier and some capacitors. As a last step i would build a separate power supply for each voltage, then you could do some tests in parallel.

If you realy need a regulated power supply i would think about a switching one and considering the impression that i have from your experience in relation to the requirements i would perhaps buy one.

Answer 2

So, use exactly what the big trucks use - big batteries - these can be charged (I think "trickle charging" might be a little of an understatement of course). Don't waste time and effort designing something that might take a year to properly engineer - use what the trucks use (or the buses, lorries, trains, planes or whatever).

You say that replacing the batteries is expensive - I bet it's cheaper than the effort to design a 40kW DC power supply.

Answer 3

Batteries sound like a simple relatively inexpensive approach as well.
I would suggest using the the battery pack from a forklift as the basis for your project.
they should last for quite a few cycles.