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Dad Mechanic
Dad Mechanic, Mechanic
Category: Car
Satisfied Customers: 202
Experience:  I have worked on everyting from Model Ts to 2012 Autos,
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basic test for an alternater with an ohm meteringram alternator

Customer Question

what are the basic test for an alternater with an ohm meter
ingram alternator
Submitted: 2 years ago.
Category: Car
Expert:  ddamato1986 replied 2 years ago.

ddamato1986 :

Hello I would be willing to assist you if you like?

Customer :

could you tell me how to test a basic 12v alternator with an ohm meter , i have established that it is not working by replacing it

Customer :

need to know how to decide if v reg is faulty or brush/windings are the problem

ddamato1986 :

Sure thing set your meter to Ohms

ddamato1986 :

Test a fuse to make sure the meter is reading properly, should be 1-3 ohms

Customer :

ok

ddamato1986 :

Is there a AC setting on your meter?

Customer :

yes

ddamato1986 :

DC?

Customer :

yes

ddamato1986 :

Okay set the meter to DC 20V if you can and place one probe on the positive terminal of the car's batter and one probe on the car's negative terminal of the battery while running.

ddamato1986 :

battery

ddamato1986 :

A normal charging reading would be between 12.6-14.1Volts

ddamato1986 :

anything below that and you may have a bad battery or there is high impedence ( resistance) in the battery cables, possibly due to corrossion.

Customer :

ok i have no v at the alternator

ddamato1986 :

Is the car runnig?

Customer :

the battery is 12.8

Customer :

the battery is 12.8v

ddamato1986 :

okay that seems about right.

Customer :

i changed the alternater the other day the new one is working

ddamato1986 :

If you rev the engine up you should see a change in the volatage reading. typically if you dont see the reading get abouve 13V the alternator is bad or weak.

Customer :

the alternater had no output trying to work out if it is the v reg or brushs / wireing

ddamato1986 :

That is the best and easiest way to test for an alternator. Have I answered your question?

Customer :

the alternater had no output trying to work out if it is the v reg or brushs / wireing

ddamato1986 :

Test the cables going to and from the alternator to the battery and the battery to ground on the Ohm setting, if the resistance is above 3 the cable is bad or corrodded

Customer :

no the cables are 1.67 ohm , the alternator is the problem, what is the ohm reading from + output to the case of the alternator

ddamato1986 :

Give me one second

Customer :

ok

ddamato1986 :

Between 3-6 ohms should be standard

Customer :

its showing open curkit

ddamato1986 :

Where did you purchase the alternator?

Customer :

it has a bosch ee14v3 9 190 067 005 v reg with brushs , brushs are ok with on grouving on the stator

Customer :

at a local outlet

ddamato1986 :

Well I dont think I can help you any further. It seems like you may have a defective alternator many of the ones purchased at local stores are refurbished.

Customer :

what is the ohm reading for the stator

ddamato1986 :

I cannot help with that Im not sure I will seek advice from another expert.

Customer :

ok

Expert:  Dad Mechanic replied 2 years ago.
I'm sorry you are experiencing difficulty. Let me ask you some questions first. Where do you live? Did you buy the alternator at a reputable store, if yes they should be able to test both alternators. Are you able to dis assembly the alternator? How many wires or on the alternator beside the large red one. Jim
Customer: replied 2 years ago.

hi jim , there is an exciter wire D+

from B+ to alternator is open curcit

 

Customer: replied 2 years ago.

 

from B+ to alternator case is open curcit

 

Expert:  Dad Mechanic replied 2 years ago.
Well you haven't answered my questions soo I will do my best to see if i can help you. From what I have Read in some of your answers to the other expert you have a multi meter. Without dis assmbling the alternator there are no real tests to be preformened with your ohm meter. You can eleminate other problems. First of all set your meter to dc volts you will usually have a 20 or 50 volt setting. Now black terminal to case of the alternator and the red terminal to the large wire terminal of the alternator. Try this with the key off & with the key on you will have 12 volts nessary to have 12 volts key on or both. Now if you don't have 12 volts move the black wire to the negitive terminal of the battery. If now you have 12 volts there is a ground problem at the alternator. If you still don't have 12 volts you have a suppy from the battery to the alternator. I'm not sure about the D+ wire but i would disconect it from the alternator. Once again black of the meter to the al;ternator case red wire of the meter to the D+ (wire) you should have voltage with the key on. once again move the black to the neitive batter terminal you should have voltage key on. I think the other expert covered how to check about charging rate quite well. once again i'm sure if you return to the store where you purchased the unit they will check it for you. I asked where you were located to direct you to a plce tht would check your alternator for free. Jim

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