Spare battery pack..... what to do ?

Hi everybody here


I have the opportunity to get a dammaged Citroen C-Zero for very low price (front is dammaged, airbags explosed).
The car has just 3800km , and has a 16kwh battery pack with 88 cells (so not the 14,5kwh with 80 cells like some have)

My willing is to :

1) increase the actual capacity of 16kwh to 20/21 kwh
2) keep the remaining cells as spare in case of dammage of our ones.


What do you think, is it possible ?
In case not possible, I will keep the complete pack as a complete spare !

I don't think the car will let you add 1/2 the cells to the existing pack. You'd have to keep the voltage the same, so you'd end up using all 88 cells of the second pack, paralleled to the first pack and get a capacity of 32 kWh, netting a rough 100 mile range. If Siai47 would chime in, he's run one i-MiEV with two packs before.

Take the second pack and put it on a small, lightweight trailer for an easy 40 mile boost.

I'd definitely try to get the car. A battery pack alone is $13,000 USD, more than what many of the used i-MiEV's are selling for, and then there's the price of replacement parts.

It's not to hard to parallel an additional pack and make it work. Sounds like the OP's car is a 80 cell pack, therefore he would need to remove one of the modules so the voltages matched. I only did it on a temporary basis to see if it would work (and it does) but the pack needs to be disassembled so the modules can be arranged to fit in the interior of the car. A bunch of jumpers needed to be fabricated to put the modules in series. In my car I had already removed the Chadmeo connector and replaced it with an Anderson style connector that was switched on or off from the dash. A couple of things to consider. From a driving standpoint the car doesn't like all the extra weight at the very rear of the car. That is the only place to stack the modules and still use the rear seats. Try putting 360 pounds of sandbags in the back and check how the car handles before you decide that's where you want them. For my test, I put the modules on a plywood base with some legs on the front to go down to the rear footwells, took out the rear seatbacks and slid them up as far as I could to the front of the car. Plugged in the Anderson connector and went for a ride. Initial range indication showed about the same as normal around 70 miles. The difference was that the segments on the "gas gauge" dropped very slowly and the 70 mile range kept falling very slowly. I drove it well over 100 miles and still had range left. So here are the real problems---. First, you need to move the mass of the pack toward the front if you want any handling. Doing this makes the car a two seater with storage above and behind the addition modules. Second, you need to really secure the modules and provide protection to the electrical connections as you have 360 volts with a lot of stored energy riding behind you. You wouldn't want to get into an accident with 33 pound concrete blocks flying around the passenger compartment with high voltage electrical wires connected to them. Finally, there is no way to monitor the temperature or balance the cells in the pack. This is a serious issue with Li-Ion batteries. The battery cells will stay in balance for a while, however you need to monitor the individual cell voltages and manually balance them if necessary. There are test points in the modules so you can monitor the individual cell voltages and you could balance each cell with a small hobby charger but you would be doing it 80 times. In my opinion, this final point is a game killer for long term use of the parallel pack. If I was really going to do this, I would never put the modules inside the car. I would build a very small trailer and tow it with the I-MiEV. The ultimate design would be one that had a two point connection to the car and a single spring mounted castoring wheel under the trailer. That way, other then the additional length (which is small with these designs) there would be no problem backing or parking the car.

An eLithion BMS could provide the protections necessary for the extra cells. It would need the ability to control the contactor connecting it to the car, so if something goes wrong, it will disconnect from the car, but with that some way to control pack voltages would be needed. That would be tough on the contactor to connect two packs that are several volts apart.

I agree on putting the second pack on a trailer. Securing that much weight inside the car may be a challenge, plus you get to keep the car a 4-seater and can leave the second pack at home when you don't need the extra range.

By all means- trailer that second pack. (Warning, slippery slope ahead.) The more you can keep of the donor systems, the better. Imagine if your range trailer included the i-MiEV drivetrain. I can testify that an i-MiEV with double the highway passing power is a lot of fun, thanks to my pusher trailer. An i-miev 'skateboard' that's not much more than the battery and drivetrain could become a trailer that turns any vehicle into a hybrid, and one with very strong regen!

Secondly, think of the benefit of keeping the charger attached to your second pack. Charge from two EVSE at once, or on a long round trip, drop your trailer at a charging point and continue onward, picking up the fully-charged trailer on your way home!
These things are already being done, mostly in quiet by hobbyists, but there are a few that publish their adventures.
My friend Stephen used his range trailer to go from Canada to Mexico and back in less than a week- over 2500 miles on batteries only, in 2011! :mrgreen:
http://www.facebook.com/pages/The-Range-Trailer/257589060955815