My magic Pie shut down when I increase the speed

[Smartyzer]

Hi, I bought a Magic Pie to my father in 2009 from Golden Motor and he's very happy with.  This summer he can't us it.  At lower speed is ok but as soon he increase the speed it shut down.  We have to unplug the battery and replug to restart the Magic Pie.  The battery seems OK.  have you any idea what might be causing the problem ?

Thank's for your help,
Martin

[Bikemad]

Hi Martin andto the forum.

It sounds to me like the battery is very weak and the voltage of one (or more) of the cells is dropping too low under load and forcing the BMS to cut the power to prevent it from being overdischarged.

I don't know what chemistry your battery is (LiMn or LiFePO₄), but if it's an 8 years old LiMn battery pack, it has achieved a very good lifespan.

With a weak battery, you should notice that the LEDs will start to go off one after another as more load is placed on the battery (or more throttle is applied) just before the battery power is cut off completely by the BMS.

If the battery is old and weak, it probably needs to be replaced (unless you can find someone with a suitable spot welder who would be prepared to replace all of the individual cells instead).

The screw terminal cells used in the more recent LiFePO₄ batteries are much easier to replace.

Alan