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[Richard230]

I hadn't ridden my 2018 Zero with Power Tank for the past month. When I turned it on yesterday the SOC indicated 72% (a month ago it was at 90%).  I was also greeted with warning lights. A repeating pattern of two and then five more. Pulling out my Zero manual I found that red triangle warning light pattern is noting that the bike's "Module Variance Too High". The owner's manual says to contact either Zero or my dealer to resolve the problem. Not wanting to do that, I thought about it a bit and decided that "module variance too high" likely meant that the individual battery packs were out of balance. I first checked the Zero battery app and it showed pack voltages being 1-3 mA differences. But I thought that the app might be missing something, like the Power Tank. So I plugged in the bike using the OBC and 40 minutes later the SOC was up to 80% and the warning lights were off and things are looking normal again. That saved me a trip to my Zero dealer. I assume that recharging the battery packs a bit brought them back into a better balance.

[MVetter]

Right so, you were on the cusp of understanding what happened but you over-thought it. The packs were definitely out of synch. If memory serves, if there's a difference of more than 1 volt then the PT will disconnect. The pack itself may still be totally balanced, but the Monolith could have been at 109vdc and the PT could have been at 111vdc and the bike went, "Nope! Too much."

If and when this happens again just charge the packs. The lower pack will charge first and when the two are close enough the other pack's contactor will close and they'll be 'mated' back up again. Just Power Tank Things.

[Specter]

Whenever you add additional capacity / packs etc to a battery bank, the voltages of them MUST be as close as possible.  This is the bikes way of saying you need to balance things.  Im sure it originally manu'd to read what came with the bike, add ons, not so much.  Charging balanced them so you are good, remember, when the voltage is unbalanced, even a volt or 2 of difference could make hundreds of amps of current flow between the packs when you plug them together as they try to equalize each other, this obviously could pose a huge problem if you were to happen to blow an internal fuse or something on them, essentially bricking your battery pack until you opened it up to change the fuse / fusable links etc etc.

Even in better circumstances, thats a lot of heat and wear on the battery, with absolutely nothing useful coming from it.

Aaron

[Richard230]

I thought the same thing. So this morning I fully charged the bike (at 1460 watts) to 100% SOC and then let it sit for a couple of hours at 4.2 watts. No doubt I should have done this before, but now I am sure that all of the modules are happy. 

[Curt]

So "balancing" has to do with millivolt differences between cells within a battery pack, while "variance" is voltage difference between two battery packs?

If you were experiencing the latter, it seems like Zero raised an error unnecessarily, and in a particularly bad way telling you to go to a dealer. All it had to do was operate normally, give a reasonable charge estimate (72%). At some point it would be plugged in and get "unvarianced".

[MVetter]

The Power Tank and the Monolith are two independent batteries with their own independent BMSes. During a balance cycle each BMS keeps its bank of cells balanced. They also *try* their best to keep the packs at the same voltage as each other, but any number of factors can cause them to deviate just a bit. If the variance is too great, aka 1 volt, the Power Tank disconnects until a charge session can happen and the packs can be brought back together aka under 1 volt difference.

[Richard230]

The Power Tank and the Monolith are two independent batteries with their own independent BMSes. During a balance cycle each BMS keeps its bank of cells balanced. They also *try* their best to keep the packs at the same voltage as each other, but any number of factors can cause them to deviate just a bit. If the variance is too great, aka 1 volt, the Power Tank disconnects until a charge session can happen and the packs can be brought back together aka under 1 volt difference.

That makes sense. The main reason that I started this thread is that if anyone else got the same fault code, they would charge up their battery pack first before contacting Zero or their dealer. Who know what might come out of their advice. Bring it in, perhaps?