DIY Electric Car Forums banner
1 - 6 of 6 Posts

·
Registered
Joined
·
2 Posts
Discussion Starter · #1 ·
Hello,
I'm looking at doing a bit different of an electrical conversion- I have a Jaguar that is on it's last leg engine wise. In looking at various options, I'm considering a conversion to electric drivetrain- However, I'd like to develop something similar to a diesel locomotive in function- I.e a constant speed diesel engine powering a generator to drive the wheels- with a battery pack to act as a shock absorber or buffer for short bursts of high demand.

I'm far from an expert in EV systems, however I understand the basics of electricity. Best I can tell, I could just wire the outputs from my diesel engine/generator unit to the charging circuit of the battery pack, with a protection circuit for overcharging and a start/stop control for the motor- For example going downhill and regen is on, there's no need for the generator to be on. Basically it would be a separate unit that would only charge- everything else would be handled by the battery pack.

My question is this- Am I able to charge the battery packs like that with no problems? Or do you have any experience with a hybrid system like that? Assuming I use a BMS. I'm thinking that (30) 180 Ah batteries and a 400 amp generator would be a good pair. Am I in the right ballpark? Because the current engine in the car is giant and heavy, it would only add around 150 lbs to the total weight of the car.

I'm liking the Curtis 1238 series of motors and controllers, (specifically the 1238-7601) and would be open to recommendations on batteries and other motors. I wasn't planning on running a differential on that has a ratio of 2.88:1 connected to the drive motor. That seems to work pretty well at a 29" tire, around 75 mph at 2500 RPM. Assuming no loss through the diff, (I know it would be some) it would also give me close to factory torque/hp figures.

I did some very rough calculations on fuel economy based on existing data, and it looks promising, even calculating in a fair bit of loss.

Please let me know if this is something you have any insight on, I understand it's a lot of information not specifically pertaining to the drive system itself. The big question is can I tie a charger into the batteries while they are in use with no ill effects- I'm open to doing something DIY, but don't want to re-invent the wheel if there's an existing kit.
Thanks!
 

·
Registered
Joined
·
6,273 Posts
What you are describing is a series hybrid.

Yes, that will work if you control it properly (which is more complex than you seem to think), but it is not very efficient because all of the energy needs to be converted from mechanical to electricity (in the generator) and back to mechanical (in the motor), and going through controllers as well, and every stage loses energy to inefficiency. That's why very few cars are built as series hybrids.
 

·
Registered
Joined
·
6,273 Posts
I'm liking the Curtis 1238 series of motors and controllers, (specifically the 1238-7601) and would be open to recommendations on batteries and other motors.
There are no Curtis motors. What you're seeing somewhere would be a Curtis controller (1238-7601) and some motor that the seller is packaging with it, probably an induction motor from HPEVS such as their AC-20.

That's not much power for what is likely a heavy car.
 

·
Registered
Joined
·
6,273 Posts
I'm thinking that (30) 180 Ah batteries and a 400 amp generator would be a good pair. Am I in the right ballpark?
I assume that you mean 30 cells, all connected in series. These would likely be LiFePO4 (LFP) cells, since that's what individual cells people were buying (and some still do) for conversions; that would mean 96 V nominal and 180 Ah battery capacity. Charging at just over 2C (twice the current required to fully charge or discharge in one hour) might be a bit fast for these cells, but some of the generator output would be going to the motor so not all would be charging the battery.

That's about 40 kW of generator output, which is comfortably more than the average sustained consumption of the vehicle in any driving situation, and there is more than enough energy storage (17 kWh) to meet short-term higher power demands. Either you're lucky :), or you understand the power requirements for this configuration.
 

·
Registered
Joined
·
2 Posts
Discussion Starter · #5 ·
What you are describing is a series hybrid.

Yes, that will work if you control it properly (which is more complex than you seem to think), but it is not very efficient because all of the energy needs to be converted from mechanical to electricity (in the generator) and back to mechanical (in the motor), and going through controllers as well, and every stage loses energy to inefficiency. That's why very few cars are built as series hybrids.
I appreciate the insight- And I might rethink my design a bit, because I agree the energy loss converting over is a substantial amount that I don't think is needed. Thank you for the assistance!
 

·
Registered
Joined
·
249 Posts
I’m wanting to build the same thing. Except I’m wanting to go 16S with lifepo4. It’s for a small VW dune buggy
 
1 - 6 of 6 Posts
Top