monotec battery rating

indianajo

Well-Known Member
Some new person rebuilding a mototec had some confusion about battery amp ratings, with a burnt motor & controller. His thread disappeared from introductions. If he moved his thread somewhere else, here is the answer.
First off some precision in names would help. Lead acid batteries rated in amps usually have a CCA or cold crank amps rating, usually 400 to 1000. The most usual rating on lead acid batteries is amphours, which is the number of amps the battery will put out for 20 hours times the hours. Thus a 12 AH battery will put out 0.6 A for 20 hours. A 16 AH battery will put out 0.8 amps for 20 hours.
The amps put out by the battery is usually limited by the load, not the battery itself except the internal resistance limites the CCA.
If you take your old controller apart, I suspect the fets will be shorted gate to drain or source. Overheating kills most cheap controllers because the heat sink is inadequate. Alternately the main capacitor can be shorted, although this is less usual. You can prevent this from melting the wiring in the future by putting a fuse between battery & contoller. I use a 30 a agc3 fuse since my 1000w controller is rated at 26 amps.
A 1600 ma charger will put out 1.6 amps into the usual dead 36 v battery (not shorted).
What will burn the wheel motor is too much voltage which leads to too many amps, or too much heat. As riding up steep long grades will cause. Having too many amphours on the new battery only increases the range, not the voltage or amps drawn by the motor.