Amp Controls

Constant Current sources are fairly easy to build but at 25A you need to be ready to dissipate some power. The Current source will require some voltage overhead to do its work as well. When you limit the current the load voltage will vary based on its equivalent resistance - V = I * R when ever the load resistance is below the min required to drop the full battery voltage minus the current limit circuit minimum voltage drop. If I read you application correctly that will be at about 0.480 ohms assuming the current limit circuit and battery are ideal. When the load resistance is >= 0.480 ohm the load current will drop off below the 25A setpoint following I = Vbat/Rload and when the load resistance is <= 0.480 ohm the current will limit at 25A and the load voltage will follow the equation Vload = 25 * Iload. The Current control circuit will drop the remaining voltage and also dissipate power equal to 25A * (12V - Vload). The 12V source will not be ideal and is likely to drop some voltage at 25A. If this is what you are looking for then please elaborate a bit...

Is this a constant current circuit that will remain in current limit at all times?

Is this just a protection circuit that will momentarily clamp surges?

What is the expected load voltage or voltage range at 25A?

There are some companies who are making such devices (Power supply) by which u can set your max. current limit. In India a co. called APLAB is making these kind of Power Supplies

Danfoss drives (vfd's or vsd's) will take care of your need if you set them up to look at amps.

A simple way to do that is to use a PWM generator driving a power MOSFET. It is very cheap and reliable.

25 A is not a high current and by varying the pulse width at constant voltage one can control the load current. It also depends on what load you have. I built a test bench for DC-hydraulic power packs and works fine.

Happen to see this today. Perhaps it will solve your problem.

http://www.mitedu.freeserve.co.uk/Circuits/Power/clps.htm