Phil Hobbs wrote:



Sure, but if it ever had enough torque to start up against the load,
that amount of current wouldn't blow the fuse. Of course it might be a
super slow blow variety that eventually went, but saying that the
current went up because the voltage went down makes no sense unless it's
using a SMPS.


** Battery current goes up with diminishing voltage due the actions of the driver increasing the throttle setting and so the duty cycle of the PWM drive.

The fuse copes with normal start up since it has a long thermal time constant. But if the motor is unable to get the scooter moving for any reason and the driver increases the throttle to full, the time constant is soon exceeded.

Also, most SLA batteries incorporate an internal fuse as a last line of defence against a short or near short. This is also slow acting and just maybe was the culprit in the OP's example.

I have some experience with SLA and wet cell batteries used with a 12V starter motors for RC boats using high performance, glow plug engines. This involves putting a severe load on the battery for a few seconds at a time, sometimes pulling the terminal voltage down to near half if the engine is flooded with fuel.

SLA battery life was fairly short used in this way, so I eventually upgraded to a 40AH maintenance free car battery with a 20A in-line blade fuse for safety. The fuse kept popping so got replaced with a domestic AC supply circuit breaker, also rated at 20 amps. This was *perfect* as it protected the battery from a dead short ( 2kA breaking capacity ), rarely opened in normal use and when it did could be reset in 2 seconds.



..... Phil