Wrecked i-MiEV Battery Pack Discussion

[PV1]

Don, no reason both packs can't be charged together with the on-board charger. It'll take longer, but should work just fine as the aux. pack's BMS is present for the most part.

[DonDakin]

Hey PV1,

I wonder how it would work. If you have both packs connected during charge. Doesnt the bms taper the charge current as the battery get to full ? how would that work with two packs if the charge state of each one is different ? Maybe the fuller pack would charge the less full one and things would equalize out but i would monitor that closely during charge.

I would worry that if the external pack hit the high voltage limit on the cells and could not control the charger to tell it to taper the charge then the charge current might push the cells over 4.1 volts. Perhaps this would not happen because the packs would equalize but If not it would be a bad situation.

What do you think ?

Don.....

[PV1]

The only way that cells in the external pack would go over 4.1 volts is if the external pack is mis-balanced, which would be fixed by the BMU over the longer term. The external pack sees the same voltage as the main pack, so one pack wouldn't be overcharged when they're connected to the same charger. It looks like both packs are balanced, and since both still have functioning BMUs, they should stay balanced. Even still, the cells have headroom and can go to 4.2 volts.

With the relatively tiny size of the on-board charger especially across two packs, the two packs won't become mis-balanced, but if they should, they will auto-equalize. This project isn't much different than how Tesla and Nissan battery packs are constructed with multiple cells in parallel (except they are paralleled at the cell level and this is paralleled at the pack level). Since they are the same size, voltage, and chemistry, the two packs' median voltage will result in the SoC of each pack being very close to each other if not the same. Being that the external pack is connected automatically when the main pack is connected, there shouldn't be an instance when the two packs become severely out of balance with each other unless the external contactor fails to engage or the fuse blows. At this point, the main pack must be brought back to the voltage of the external pack before they are re-connected.

Dani, it may be possible to connect an OBDLink to the external pack's CAN lines and have two instances of CaniOn running at the same time. One monitors the car and the original pack and the other watches the external pack.

[DonDakin]

Hey Dani,

So I had another look at the online wiring diagrams.

In the section:MAIN BATTERY MANAGEMENT SYSTEM

The first diagram shows the current sensors in the battery wired to the BMU.

There are 4 wires RED GREEN WHITE and BLue on pins 31,32,33,42 of one of the yellow BMU connectors. I guess these were not connected in your battery external battery. I believe there are 2 current sensors.

In any case you can also measure the voltage on these pins in the operational car and then play with it to figure it out if you have not already.

CHeers

DOn......

[Zelenec]

I wonder what happened almost 2 years ago. Any progress on the project?