# Generator Capacity?

1. Apr 16, 2015

### GarbageGasMan

I am working on a project to convert my truck into a hybrid while not losing performance. The plan is to use the 350ci engine to run a generator to charge the batteries and to provide power to the two electric motors. I'm looking for a system similar to the Fisker Karma, where it can be run on just the batteries or just the generator power. The two motors I have picked out operate at 72-125 volts AC and 100-700 amps. my intention is to remove the transmission and transfer case from my truck and connect the generator to the engine in its place. The electric motors would then connect to the differentials via drive shafts. I'm assuming that the engine will be sufficient to run the generator since I'm not really increasing the horsepower of the vehicle.

2. Apr 16, 2015

### Staff: Mentor

Try analyzing everything in terms of power as the first step.

1. How much power does it take to propel the truck at top speed?
2. How much power does it take to accelerate the truck?
3. How much power can the electric motors provide?
4. How much power can the engine deliver to the generator?
5. How much energy (power times time) do the batteries need to store? How many batteries of what size/weight is that?
If everything sounds good at that level, then you can start thinking of efficiencies, voltages, frequency, cost and all the other factors.

3. Apr 16, 2015

### GarbageGasMan

I'm pretty well past that point. I can upload the dyno test sheet for the motors I have picked out if that's necessary but I can tell you they deliver 184 ft/lbs to 173 ft/lbs of torque from 0-2500 rpm. At that spec I could actually run one of them on my truck and still be pretty close to what I'm currently getting out of the 350ci TBI engine that has over 250,000 miles on it. The mechanical side of things is pretty easily inside my wheelhouse, but my limited understanding of how to do the electrical left me with an answer that my generator had to be in the 30,000 - 70,000 watt range which is way more than I think is feasible to put in the truck. I really only want a minimum amount of batteries on it, just as a power reserve. I intend the truck to run basically under the electrical power that is generated 99% of the time.

4. Apr 16, 2015

### Staff: Mentor

No you're not past that point. You should answer all 5 of those questions before deciding on feasibility. Don't forget to express all the answers in the same units: Watts and watt-seconds for the batteries.

If the answers turn out to show the idea I feasible, that answers your question, right?

5. Apr 16, 2015

### GarbageGasMan

The company that I am getting the electric motors through specializes in electric vehicle conversions and can supply appropriate batteries in sufficient quantities for me to do the conversion just to electric, but I want the vehicle to operate without the use of the batteries. For example: The original torque rating for my engine was 194 ft/lbs at 2500 rpm, the two electric motors I have can generate as close as is needed to that power rating. At 2500 RPM, which is right around 66 MPH after passing directly through my differential, the motors should be producing 173 ft/lb of torque and running at 650 AMPS and 108 Volts each. If I'm not to mistaken that would be roughly 70,200 watts of power, per motor. Maybe I'm looking at this from the wrong angle but that seems like an excessive number.

6. Apr 16, 2015

### Staff: Mentor

70 kw of electric power corresponds to 93 horsepower. Two motors. Does your engine make 200 hp? Those are the kind of questions you need to answer.

Excessive? How many horsepower do you need to go 66 mph before the conversion?

Batteries? Suppose you need 140 kw of power, for one hour. How many lead-acid batteries is that? (more than you can carry is the answer).

I'm trying to encourage you to answer your own questions. If you put everything in the same units (watts) you can do it.