I'm using a miniBMS system in my batteries, and the loop is connected to a Thunderstruck motors EVCC unit, which fires off a buzzer if the loop drops (indicating a low voltage event) while driving or turns off the charger if it's charging (indicating a high voltage event).

A few days ago I was driving around (short trip, pack no where near discharged, but not super close to fully charged either...) and the buzzer started to sound in a very regular pattern (about 1 second on, one second off).

I have never experienced this pattern of sounds before.

Sometimes at the end of a long trip I've gotten a low voltage event and the buzzer will sound briefly if I am drawing a lot of amps, but the buzzer would always stop as soon as I let up on the throttle.

This buzzing on/off/on/off continued while driving for another mile and when I was parked at home. I switched everything off and started it back up again (resetting power to the EVCC) and the pulsed buzzing continued.

I have a physical switch in my BMS loop for testing purposes, and when I opened it, the buzzer went from intermittent pulsing to solid on, so the EVCC was definitely still monitoring the loop.

I have a parallel pack trackr system that monitors the voltage of (every pair of) cells and everything looked normal on it, no pair of cells was low enough to be triggering a low voltage alarm.

I left the truck sitting for a few hours, and when I tried it again the intermittent buzzing had cleared and gone away. I've driven it a good 100 miles since then with multiple charge cycles and haven't heard it again.

The other option is that the EVCC was signaling the buzzer in it's own pattern for some other type of fault (and then honoring the dropped loop signal to turn it on continuously), but the support staff at TSM felt that the pulsed signal was coming from the BMS loop, and the EVCC manual doesn't mention the buzzer sounding for anything other than a BMS loop event.

I'm just wondering if anybody has experienced this type of on/off/on/off loop signal with the miniBMS boards before, and if so, what it indicates?


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