Starters & batteries

[Pressureangle]

On 12/3/2021 at 2:07 AM, Kiwi_Roy said:

A starter motor is almost a short circuit so if it locks up its probably pulling 250 Amps or More, I measured the starter on my VII once and found it drawing in the 150 - 170 Amp range.

Any DC motor with brushes is also a generator, as it spins its producing a Voltage in the opposite direction to the battery, this is known as Back Electromotive Force (Back EMF for short), the faster it spins the less current it draws. Of course if its not spinning the only thing the limits the current is the load resistance and the batteries internal resistance.

Its quite easy to measure the starter current all you need is a shunt made of regular wire and a cheap multimeter with a millivolt range. I'm sure there's a copy of my home made shunt sketch on here somewhere.

We call BEF 'Flyback' in the U.S.