working on a 1974 taylor dunn personnel cart with no manual.

Dodgydave

Joined Jun 22, 2012
9,666
If it's the same circuit or similar, start by using an ohm meter on the rheostat terminals( with no power applied) and check the resistance from slow to fast,.
 

tcmtech

Joined Nov 4, 2013
2,867
That speed control circuit or variations on it has been around for over a century now. :eek:

I've seen it used on everything from golf carts to industrial machinery like forklifts and electric vehicles.

The most common cause of your problem is the brush or contact that sweeps across the huge variable resistor/rheostat gets worn out or stuck and stops making contact with the rheostat or resistor wire gets worn and corroded preventing the it from conducting power through the contact.

Given the rheostat always starts at maximum resistance that end wears the most and is where dead spots tend to develop first essentially cutting the low speed operation end out of the system leaving you with only having the upper speed/power end working on full on or off mode.

Also the mechanical parts that hold the movable brush/contact can wear out allowing the assembly to lift off the rheostat at the starting end of travel as well.
 
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