Step Up 10mV - 200mV to 5V @ 20A

[krsbuilt]

I am working on a project where i have a single power source that is rather unstable and small, but produces a lot of current. the power source varies between 10 and 200 millivolts at about 2000 amperes and i need it to be stepped up to a steady 5V voltage. I'm not going to post any of the other details such as what the power source is and what it will be used for, but 5V at 20 amperes is plenty of power for what I'm doing.

 

[Bob S]

Is this 50 or 60 Hz, or DC?

Bob S

 

[0xDEADBEEF]

The ways I see, are: a transformer with a forced modulation of the input signal, a buck boost converter, flywheels, and then there is this system where you charge capacitors in parallel and discharge them in series.

 

[0xDEADBEEF]

One more idea would be a motor coupled to a generator.

 

[krsbuilt]

This is DC current. But is there a such thing as a low voltage motor? I haven't seen such a thing before. Maybe I'm not looking hard enough. The capacitor idea sounds good, I'll try that next chance I get.. I may be thinking of something else, but isn't transformer modulation for AC?

 

[0xDEADBEEF]

Well the idea was that you could modulate the voltage artificially with something like an array of FETs (to get enough current through) then send the current into a transformer to step up the voltage, and rectify it afterwards. To drive the FET you could use the generated voltage, just for starting it you would need a battery.

As far as the motor goes you would probably have to build something yourself. I don't know any place in industry where you cannot choose to use voltage of at least 1V to run a motor.

 

[Ken Freeman]

I agree with the need for an auxiliary start-up power source.

An initial view of an overall power processing strategy for your system needs is as follows: Create an inverter of some sort to chop the source current and drive the primary of a specialized transformer, designed to carry such a current and to operate at the chopping frequency. Probably the chop freq should be chosen to allow a 1-turn primary to be used, since any array of conductors that will carry 2000 amps without disturbing levels of Joule heating is going to be rather thick and resistant to winding.

Once you have that transformer driven, there are many choices, but essentially you will need a rectifier, smoothing filter, and possibly a high-power DC/DC converter to control the quality of the desired 5 volt power.

You need about 100 watts at the load end. Considering the very low voltage of your source, I would not initially assume you'll have an overall efficiency greater than 50%. I expect there will be a lot of loss in the chopper, due to the very low voltage of the source. The source voltage is not large compared to ohmic voltage drop in the chopping MOSFETS. Switching losses might also be large. Assuming you need to get a continuous 200 watts from the source and you will get 2000 amps, you need the source voltage to not fall below 100 mv. However, you describe the source as 10 to 200 mv. Even with perfect power processing efficiency you will need a reliable 50 mv.

Is this source feasible, considering your load requirements?