How to test an alternator.

[1989accordaz]

I have a volt/amp meter. How do you test the alternator at the alt?

Is it Red probe to post going to battery and black probe to alt housing? I just don't want to short anything out.

Thanks

[smufguy]

let the car idle at the normal operating temperature and use the red on the positive terminal and black on the negative terminal. whatever reading u get, its the alternator reading.

[Hondaisok]

Output should be between 13.9 and 15..1 volts dc with lights, heater fan, etc. on. If not, you may be reading your battery output only. Switch meter to a/c, and if there is a reading, you probably have a bad diode in your regulator.

[AZmike]

To fully test the alternator you need to measure how much current it can put out. Most autopart store will do this test for free.

[Deadhead]

Output should be between 13.9 and 15..1 volts dc with lights, heater fan, etc. on. If not, you may be reading your battery output only. Switch meter to a/c, and if there is a reading, you probably have a bad diode in your regulator.

we just did this in my auto tech class. It's 13.5-14.5 optimal voltage when the engine is at 2500 rpm.

To check the amps the alternator is putting out, you need a machine such as the vat-40.

as stated above, go to autozone or wherever and they will test it for free.

[Hondaisok]

Your class is a little at odds with the Honda Service Manual, but close enough. You can put your ammeter between the white lead and post B to determine amperage only. In my ignorance, I thought the dude just wanted to check the voltage. I forgot all the experts on here.

[Deadhead]

well, they teach a general number of what to look for in all vehicles. Obviously things can and will change between different companies.

with that amperage test, you might need to have a friend help you. I forgot about that test lol. You want to rev the motor to 2500 rpm to get the alternator to full output.

[Hondaisok]

Hey Deadhead, I wasn't flaming you. I know alternators vary in their output. Good luck in your class!

[Deadhead]

haha, i wasn't taking it as a flame. I figured you knew that, but i had to say it anyway :P

[MessyHonda]

well i did it the ghetto way...start the car...let it warm up and then disconect the positive side on the batt...if the car still runs then your alternator is good and if it dies it does not work..easy as that...also the bat should have 12.5v already so if your car is on and it drops more than that you might have a bad alternator

[Hondaisok]

Hey, that's cool, Messy. I hope you are putting some kind of load on the system while testing it. You may find yourself on Lover's Lane with no lights some night.(or is that the object?)

[Deadhead]

well i did it the ghetto way...start the car...let it warm up and then disconect the positive side on the batt...if the car still runs then your alternator is good and if it dies it does not work..easy as that...also the bat should have 12.5v already so if your car is on and it drops more than that you might have a bad alternator

With a lot of vehicles, that will cause some major problems. RacerX's alt got fried when a guy at autozone did that to his car. He got a free alternator, but still.

oh, and it's 12.6v :P each cell in a battery should have 2.1v and I can't remember the specific gravity of the cells where it should be...

[1989accordaz]

OK, I had enough juice in my battery to run it to Autozone, and it tested @ 4 V. So I was practically runnnig with my battery, which is now dead. This alternator lasted 4 weeks. But both the battery and the alternator were under warranty. Put the new batt and alt in, tested 14.5 V.

BY the way the the alt failed the rectifier test.

Thank you all for your input!

[MessyHonda]

With a lot of vehicles, that will cause some major problems. RacerX's alt got fried when a guy at autozone did that to his car. He got a free alternator, but still.
oh, and it's 12.6v :P each cell in a battery should have 2.1v and I can't remember the specific gravity of the cells where it should be...

well i have done it all the time (same old alt that came with the car 157k miles)...and most of the time is bad contact on the batt or the batt is dead...i just looked and my batt was installed on oct 02 and it still works good. talk about load...phhs i had my headlights, stereo, amp running and you can just see my headlight dim to the beat of the music...talk about Ghetto..my amp takes up to 80 amp(kicker 1400watts) and our alt can only put out 65 amps...thats why i wanted to do the convertion to the legend alternator like CKE did. but they only have like 87,88 and 89 legends at the junk yard plus im going to take out my stereo for something less powerfull