Testing Starter

[Safari bob]

How many amps should a 12V starter draw on a bench test? Same question for a 6V starter. How many amps should the 12V and 6V starters draw when installed? Thank you.

Bob

[Kurt in NJ]

I have good data for 6v
cranking- 145-165A @5.1volts
spinning free-2700 rpm ,50 amps @6v
locked -- 14 ft lbs,560 amps, 3.75 volts

[nkaminar]

Kurt, that is really good data.

For those who want to do their own test, there is something called a battery shunt. It is a resistor with low resistance that is placed in series with the starter. The voltage across the shunt is proportional to the current. So measuring the voltage at the shunt will tell you the current.

[rotorwrench]

A person can purchase a clamp on inductive meter that will read voltage and amperage. I haven't tried one of the low cost ones yet but they don't cost all that much.

[old31]

I have one of those clamp on multimeter but I don't understand it. Where would I hook that up to on a strater?

[Crankster]

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Another sort of clever method can be used if you have a carbon pile type load tester.

First, measure the battery cranking voltage for several seconds with ignition disabled. Then connect the load tester to the battery and apply increasing resistance to the battery until the identical voltage achieved previously is met on the scale. The starter current draw can be inferred by the figure indicated by the ammeter.

[Bruce of MN]

Originally Posted by old31

I have one of those clamp on multimeter but I don't understand it. Where would I hook that up to on a strater?

Clamp it around the power lead to the starter.

[Crankster]

I like vintage tools too, they did make analog dial type "clamp on" ammeters for this test back at least as far as 1930s. It gets its indication from stray magnetism or somesuch, how do it know? But they work.

[katy]

Originally Posted by rotorwrench

A person can purchase a clamp on inductive meter that will read voltage and amperage. I haven't tried one of the low cost ones yet but they don't cost all that much.

I have one of these: https://www.amazon.com/UNI-T-UT204-A...4231088&sr=8-1

Goes up to 400 amp DC, works good.

[Safari bob]

Thanks to all for your help!

[nkaminar]

Katy, thanks for the link. The last time I looked at clamp on induction ammeters they only worked on AC current. But that was probably 50 years ago.

The current in the wire causes a magnetic field around the wire which then causes a magnetic field in the iron part that clamps onto the wire. Inside the meter there is a coil around that clamp and the magnetic field in the clamp causes a current in that coil which is read by the meter and scaled to convert to current in the wire. DC is harder to read because there is only a step change in the magnetic field.