My PCBs for my BMS arrived today. Now I just need to assemble, program and test them.
Each time I drive my car, I learn a little more. Here’s a run down of what I’ve learned…
1. The current shunt should be installed on the bottom of your battery pack, between the negative terminal of the pack and the negative side of the motor controller. I originally installed it on the positive battery lead, but realized the voltage reading on my meter wouldn’t work.
2. With the meter, I can read pack voltage, current draw and amp hours. It is interesting to see the effects of shifting and how much hills can suck your pack dry (I guess my car is heavy, I should probably get it weighed).
3. My batteries are not very well balanced. After sitting in storage for 2 years, 3 of the cells are just a bit higher than the rest. Once I get my BMS installed I will do a full balancing on the pack to hopefully correct this. Until then, I don’t feel comfortable doing a full charge (up to 4V per cell) or a full discharge (thinking I go down to 2.8V per cell). I’ve only been driving my car on short trips so far ( less than 20 miles).
4. Cold weather = voltage sag. It hasn’t been much more than 40deg F the last couple weeks. Taking short trips doesn’t give the pack a chance to warm up. With a relatively full pack I can easily get the cells to drop below 2.5v (avg) if a gun the throttle. It bounces back pretty quick after the acceleration. This was why I wasn’t getting the acceleration I expected out of the motor controller until I tweaked the voltage limits.
5. The Mes-Dea vacuum pump is a bit loud. I mounted it on a thick piece of neoprene and wrapped it in foam to quite it down. It kind of ruins that hole “turn the key and hear nothing” thing, but it’s not too bad.
6. Power steering will be nice.
My dad brought his trailer over and we hauled the Boxster down to the DMV. 45 minutes later, I picked up my new plates and drove the car home (Dad following me just in case something went wrong). Fortunately the trip back was uneventful. The car felt great on the road. Acceleration feels similar to the stock vehicle (maybe a little less). I’m going to play with the Zilla settings to try for a little more oomph. Shifts very smoothly even without pressing the clutch (note to future builders, you probably don’t need a clutch).