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[evtricity]

Was interested to know what cell balance figures people have when they check the Zero App (Battery 2 tab).

My 2014 SR 11.4kWh battery started out quite low (<10mV) but since I exclusively use 2 x 2kW fast chargers (to take the voltage to 116V) I've found that the cell balance now hovers between 100-137mV which seems too high. I'm tempted to change the chargers to temporarily stop at a lower voltage e.g. 114V, and set a lower current to give the BMS more time to self-balance and get the figure down at least under 50mV again.

Thanks

[Electric Terry]

Left on the charger, the cells should top balance to 2 mV

So check your balance when the bike has fully charged overnight.  If it's not at 2 mV, leave it plugged in to the charger for longer and check to see if it gets less and less.   The balance resistors are quite small and burning off even a little excess energy from the highest cells can take a long time.  and in the 11.4 monolith, one BMS has to burn off the energy of 4 cell bricks, so it can take many many days if it hasn't regularly been left plugged in over night each night.

The cells are very well matched from birth by internal resistance to maintain a very close balance even without a BMS.  Trust me, after 40,000 miles without balancing my cells on my 2012, they were still within 15 mV.  But this is at the top of the charge.  at 4.15v per cell.  But when the cell is at the low end, near 3.2v per cell, they could be two hundred or more mV out of balance.  But when charging they quickly got closer and closer. 

Just saying make sure you are checking the balance after it's finished charging, not when the battery is close to empty.

[Burton]

I am with Terry here, leave it plugged in a while to balance.

My nominal overnight charge is like 10.4 ... if I let the cells balance over a weekend and check the nominal voltage again they come up to around 10.64

As Terry stated the chargers don't balance the pack. They need to be 116vdc to be able to bring the bike up to near the same voltage. At 114vdc you are only looking at 90-95% SOC ...

[evtricity]

Thanks for the feedback.

I'll plug in an onboard charger to do the top balancing as the TC chargers aren't suited to that as they reduce current to 0.5A and shut off when they reach the specified maximum voltage - currently 116v.

[Burton]

It is worth noting those of us using external chargers to "speed charge" up to say 90-95% occasionally use stock chargers to balance the pack out say once a month depending on how often you ride.

If you have a reaper dongle you can also see the current voltage of each cell by running the BMS command at prompt. While more advanced it will also give you more detail about what your BMS currently sees.