High power DC-DC

Hi,
I'm looking to do 1-120VDC to 115VDC high power conversion. I have a generator that I want to hook up to some lithium batteries in order to charge them. Power will be up to 250A. I'm looking for either a prebuilt solution that I can buy/customize, or how to design one myself.

Anyone know where to start?

Sorry, no answer, just questions. What are you doing with these lithium batteries? 115VDC at up to 250A? You need a peak of around 30kW of power? That just seems a bit extreme to me...

Charging them. They're in a car.

Are you really sure you need 1 to 120 volts input range? Large dynamic range makes switching power supplies harder to design. A factor of 120:1 input voltage range is huge.

You say "power" will be up to 250 amps, but that's actually a current spec. Do you mean output current by that? If so, that implies nearly 30kW as Joshua pointed out. Surely you don't expect to get that when the input voltage is only 1V. That would require 30kA!

You need to go back and figure out what the specs really are. If you don't know how to go about that, describe the problem so that we can come up with a realistic set of specs.

30-120VDC would probably work on the input. Yes, I meant current. This is for application in an electric car. 30kW is not a lot compared to regular car engines. It takes 200A @ 115VDC to get the car moving at 35-40mph.

If it's not really feasible, that's an answer too.

30V at 30kW requires 1000 amps, and that's not considering losses.

200A at 115V is 23kW. It might take that to accellerate up to 40 miles/hour, but that's huge for just maintaining speed on a straight and level road. Something still doesn't add up. In any case peak battery output isn't the same as desirable charge current.

Again, explain what you are really trying to do. I don't think your current specs reflect what you really need.

Just because the battery pack may need to put out 250A at 115V, that doesn't mean it needs to be or even should be charged at that rate. What are the bare battery pack specs?

At the input end, where is this 30-120V coming from? Why is the variation so large? You said it was a generator, but what is it rated at and what is driving the generator? How much overall power is available to run the generator? Can this generator even put out 30kW when it's only producing 30V? Why can't the battery current be in part decided by the amount of available power?

There is a lot you're not telling us. You really need to provide more details of the bigger picture.

I don't think you understand. I never said it would be a constant 30kW. I said 1-120VDC at currents up to 250A. 200A is probably more realistic in terms of what will actually happen. Yes, my numbers are correct, the EV I am working on does in fact require 23kW to maintain 35-40mph. It's heavy and non-aerodynamic.

The battery pack we are using is this: http://elitepowersolutions.com/products/product_info.php?cPath=27_38&products_id=138 100AH @ approx 102VDC. It requires 115VDC to charge it. It is able to charge as fast as it can discharge: 300A continuous, 400A for a short time.

I have a small gasoline engine hooked up to an electrical motor in order to generate a DC current. The DC-DC generator I want to build/buy will take the output of the motor, convert it to 115VDC, and use it to charge the batteries. Because varying the gasoline engine RPM changes the voltage output of the electrical motor, the DC-DC converter needs to be able to handle whatever the generator outputs.

Litium Ion batteries are not as simple to charge as lead acid or NiCads. The battery company you list also sells chargers.

How about just a simple high power diode(rectifier)?