On Monday, November 21, 2016 at 2:17:10 PM UTC-5, AlfySande wrote:

Hi...i am a new user here. As per my knowledge the bad batteries caused
the electronic controller to draw too much current in an attempt to
maintain speed.That's just a guess, though. It is hard disagnose
something with no information.


I think you left out a step:

a) The batteries ran low.
b) The user kept 'upping' control to maintain speed.
c) As long as the motor is turning, things are (mostly) OK.
d) The motor (brush-type) stops dead, but the speed control is still on MAX.
e) Now the full - remaining - battery capacity is going through the fuse.
f) *POOF*

But, the batteries are sulphated, the speed controller has been overheated, the motor overheated - or at least those commutator contacts arced. Altogether a mess.

Any properly designed system would have a condition meter and a low-battery cut-off to prevent this. And a thermal breaker in addition to the fuse.

Peter Wieck
Melrose Park, PA