collink wrote:I've done it successfully. I added 12kwh worth of batteries in the "trunk" area of a 2012 Leaf. It has been driven around for months thereafter. I can't say that there are never any problems but they're rare and clear with a power cycle. The car used to get perhaps 55 miles per charge but now I can just barely squeeze out 85 miles if I really run it dead. However, my integration was a bit more involved than the average hobbyist project. The Leaf BMS is smart enough to do many checks before it'll enable anything and that makes it tough.
1. I'm connected in line with the big power wires coming out of the main pack.
2. I have my own contactor to trigger my pack in
3. I've tapped the power wires going to the main pack's contactors so I know when they're closed
4. I'm reading CANbus from both the Leaf BMS and a BMS on the add-on 12kw pack
5. You have to close your contactor only once the main system has precharged and closed for driving.
6. You must open your contactor immediately if the main pack opens
7. You can't close until the voltages measured on both sides are almost the same. Sometimes this delays linking the packs until driving for a while or charging for a while.
Basically, it is computer controlled and uses a contactor. If you don't cooperate that way then the BMS will scream at you and you go nowhere. I wouldn't say that such a project is super easy but I can vouch for it being possible. You absolutely cannot have voltage from your pack getting to the motor controller or other HV components until the Leaf is ready. Otherwise, the car will slap you and it'll be hard to clear the errors. My system is fully automatic now but it took a lot of work and experimentation to get there.
Thank you very much "Collink" for very important basic input because confirm my principle how to plan to do it.
Is observing status of main pack contractor + voltage primary and secondary battery pack enough for connect battery together or you on your case check additional conditions (form CAN bus....) ?
Which BMS are you use?
Is second battery requires the BMS configured in way that never reaches more than 4,1V per cell with strong balance current.