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Ask Canuck Tech Your Own Question
Canuck Tech
Canuck Tech, Auto Service Technician
Category: Car
Satisfied Customers: 532
Experience:  Red Seal Journeyman Technician, 20 Years experience
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What is the amparage max to the field wire on a 100 amp alternator?

Customer Question

what is the amparage max to the field wire on a 100 amp alternator?
Submitted: 5 years ago.
Category: Car
Expert:  Canuck Tech replied 5 years ago.

Canuck Tech :

Hi there - Are you building and wiring this, or are you troubleshootong?

Canuck Tech :

The amperage would be a function of the resistance of the rotor

Canuck Tech :

I've never seen a spec for his, but I would think maybe 20 amps maximum. Depending upon the length of the wire for the field I would think 14 or 12 gauge wire would keep you out of trouble

Canuck Tech :

If you want to figure this out, Take 14 volts, and divide it by the resistance of the rotor coil. This will give you (roughly) an amperage number in the field circuit

Canuck Tech :

If this information is helpful, please "accept" Thanks. Todd

Customer:

We are trouble shooting a Superformance kit Cobra a friend baught. Since the former owner changed out the engine out the alt has not worked. e pulled it and had it checked and it was bad. installed a new one did not work. replaced regulator and it blew the reg. Pulled and had it checked by parts house and checks ok. Installed a new regulator and no output to field. Tried jumping to field and the amperage was high enoughto melt a 20ga jumper. the "factory wire" to regulator only look to be 18ga. hence the amperage question.

Canuck Tech :

Is the regulator installed on the power side, or ground side of the field circuit?

Canuck Tech :

with an external regulatro, there a 2 scenarios - Situation 1 is where switched ignition power is fed to the field circuit in the alternator, and the regulator controls the ground. Situation number two is where the regulator is before the alternator' sfield circuit, and one of the brushes is grounded

Canuck Tech :

You need to figure out which way the car is wired, and whether or not you have the correct regulator - one that controls power or gound

Canuck Tech :

If this info was helpful, please "accept" Cheers Todd

Canuck Tech :

Let me know how you made out, and shoot me a note if you need more information.

Customer:

Power. We have 4 terminals on regulator. Idiot light, 12v from ignition, stator and field.

Canuck Tech :

Then it would appear that the regulator got shorted to ground before the alternator. 20 gauge wire is pretty small.

Canuck Tech :

Gotta go. I'll be back online later tonight. Todd

Customer:

I will be unavailable until late this evening. wanted to let you know so you would not await a response

Canuck Tech :

OK. Let me know how it goes. Cheers Todd

Canuck Tech :

And the outcome is...?