Category Archives: BMS

Airwheel – BMS Shunt

Airwheel Q3

The Airwheel Q3 260wh has two paralleled 130Wh battery packs, each with its own  BMS (battery management system). Even this setup, if not shunted, is still dangerous, tatane33 has had a fractured jaw because of a sudden power cut on his Q3. Peppuzzo has shunted both BMS for added security. He wants a fail safe wheel, which is understandable even if shunting just one BMS is probably enough. Continue reading

BMS, how to make your wheel safer

Most unicycles use bicycles’ BMS (Battery Management System) which has a overdischarge cut-off circuit (T1) to prevent the battery from discharging under the LiIon recommanded voltage. It’s a feature usefull for off-the-shelf bicycles’ batteries but for monocycles, it’s
1) unecessary since the mainboard deals quite well with voltage warning
2) utterly, incredibly stupid since a cutoff by the BMS results in a faceplant for the rider. In other words, the wheel’s designer prefers to protect the battery by hurting the user!!! Many many users have been harmed, especially when the wheel is cold (under 10°C), since the batteries’ internal resistance increases and triggers the cut-off more easily. Continue reading

A2 Generic – BMS shunt

The A2 wheel is a generic X3 clone. The wheeler had a power cut because of a defective cell. After the shunt, no more power shutdown, even if the defective cell has not yet been replaced. All that happens then is a much less powerfull wheel because the defective cell (to be replaced) behaves like a short, leaving a battery pack with lower voltage, though a much more preferable and manageable situation than a sudden cutoff. More evidence of the criminally stupid idea of integrating a cutoff circuitry in an electric unicycle.

P.S. The wheel electronics is accessed from outside, which is a good point ! Mainboard is a X3 generic, with the same ridiculous heat sink which doesn’t sink anything and needs to be added a big aluminium plate.

Shunt by connecting B- to P- :

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