How to check Alternator true Amperage

[GNONYX]

Hi All,
How can you tell if the Alternator is 120 amp, beside having it check by your auto store?
Please keep in mind I know about the factory coded 120A stamp on the housing. Thanks

 

[wiseman]

Hi All,
How can you tell if the Alternator is 120 amp, beside having it check by your auto store?
Please keep in mind I know about the factory coded 120A stamp on the housing. Thanks

I am not a too much of an electrical guy, but if you put a voltmeter on your alternator and change the settings to amps, that should tell you how may amps it is pulling or putting out. Connect the black lead to a good ground (neg. Post on battery) and the red lead of voltmeter on the positive terminal on the back of the alternator. Switch the voltmeter to 12v D.C. to read volts and Change it to ampere from there to read amps.

 

[mikestertwo]

You really can't check the current rating unless you have the equipment to put the alternator under a heavy load and check the output.

 

[precizion818]

I am not a too much of an electrical guy, but if you put a voltmeter on your alternator and change the settings to amps, that should tell you how may amps it is pulling or putting out. Connect the black lead to a good ground (neg. Post on battery) and the red lead of voltmeter on the positive terminal on the back of the alternator. Switch the voltmeter to 12v D.C. to read volts and Change it to ampere from there to read amps.

You can read voltage this way, but to read current this procedure will not work unless you are in series with the load from the car. You will damage or blow a fuse internally to the meter doing it this way. Also the alternator would have to be under a load while checking this

 

[turbo nasty]

There are some clamp on ammeters that read dc but as mentioned hard to test the load with out the proper bench test equipment.

 

[A2000RICH]

Hi All,
How can you tell if the Alternator is 120 amp, beside having it check by your auto store?
Please keep in mind I know about the factory coded 120A stamp on the housing. Thanks

the current (amperes) output by an alternator is actually a demand thing---------the amps output from an alternator vary depending on the need of the related accesories and is constantly changing----------testing alternators for proper functioning is rather easy-------testing them for maximum performance is not so easy without special equipment--------here are some fundamentals---------with a simple voltmeter measure the voltage at your battery terminals with a simple voltmeter-------the highest voltage that a fully charged six cell lead acid battery will ever produce is 12.8 volts--------if it reads higher than that with the engine running you know for sure that your alternator is at least working to some degree------any voltage above 12.8 can only come from the alternator--------try turning on as many accesories as you can and see if it stays above 12.8-------if it does your alternator is at least working reasonably well-------- if it reads in the 13 or 14 volt range it is working rather good----------without having a load cell of some sort you cannot fully test a alternator to a full 120 amp rating on the turbo regal because there aren't enough accesories to fully load it to that degree-----------testers in atuo parts stores usually cannot fully load or drive a alternator but usually indicate a pass or fail condition --------testers of that sort tend to be rather large and costly--------I have two such behemoths------a Electric Power Equipment Company 1148A with a 32 HP motor and a Crumbliss 2115 with the 20 horsepower option that can fully load test alternators to 800 and 500 amps respectively but you are not going to find such critters in an autoparts store nor do you really need one---------the only thing that really matters is does your alternator keep the voltage above 13 volts or so-------14 is even better--------if so it is fine and it is providing all the amps that you can possibly need-----------if you really want to test it bring it to my shop sometime and we will put it to the test.............Richard

 

[Red C5]

I just had mine checked but took it to auto parts store. Took them a few seconds to get all data.

 

[GNONYX]

the current (amperes) output by an alternator is actually a demand thing---------the amps output from an alternator vary depending on the need of the related accessories and is constantly changing----------testing alternators for proper functioning is rather easy-------testing them for maximum performance is not so easy without special equipment--------here are some fundamentals---------with a simple voltmeter measure the voltage at your battery terminals with a simple voltmeter-------the highest voltage that a fully charged six cell lead acid battery will ever produce is 12.8 volts--------if it reads higher than that with the engine running you know for sure that your alternator is at least working to some degree------any voltage above 12.8 can only come from the alternator--------try turning on as many accessories as you can and see if it stays above 12.8-------if it does your alternator is at least working reasonably well-------- if it reads in the 13 or 14 volt range it is working rather good----------without having a load cell of some sort you cannot fully test a alternator to a full 120 amp rating on the turbo regal because there aren't enough accessories to fully load it to that degree-----------testers in auto parts stores usually cannot fully load or drive a alternator but usually indicate a pass or fail condition --------testers of that sort tend to be rather large and costly--------I have two such behemoths------a Electric Power Equipment Company 1148A with a 32 HP motor and a Crumbliss 2115 with the 20 horsepower option that can fully load test alternators to 800 and 500 amps respectively but you are not going to find such critters in an autoparts store nor do you really need one---------the only thing that really matters is does your alternator keep the voltage above 13 volts or so-------14 is even better--------if so it is fine and it is providing all the amps that you can possibly need-----------if you really want to test it bring it to my shop sometime and we will put it to the test.............Richard

Richard, you are a true Mentor, Thank you for the advice and favor.
The reason why I was asking since the factory is coded 120A stamp on the housing, and on my is coded 100 amp would that make a differences? My engine is mostly stock with the exception of, hot-wire kit, 60# injectors, adj. FP, ScanMaster, A/F gauge set up, and other small accessories. Thanks again

 

[A2000RICH]

Richard, you are a true Mentor, Thank you for the advice and favor.
The reason why I was asking since the factory is coded 120A stamp on the housing, and on my is coded 100 amp would that make a differences? My engine is mostly stock with the exception of, hot-wire kit, 60# injectors, adj. FP, ScanMaster, A/F gauge set up, and other small accessories. Thanks again

100 amps could be borderline------------if you send it to me i can check it and upgrade it if needed-----------usually costs less than $80 for parts to get in the 140/160 range...............RC

 

[GNONYX]

100 amps could be borderline------------if you send it to me i can check it and upgrade it if needed-----------usually costs less than $80 for parts to get in the 140/160 range...............RC

Rich, I'll pm you

 

[L8TRH8R]

Does anyone sell a direct fit 250-300 amp alternator for our cars? Looking at a Stinger, but, they want $485.00 DEALER COST!! I'm ordering one tomorrow however would like to find a less expensive option if possible... Thanks

 

[earlbrown]

good god! Are you welding out of the trunk of your GN?!!!

 

[L8TRH8R]

good god! Are you welding out of the trunk of your GN?!!!

No, but, I'm running dual nozzle alcohol, hot wire kit, every gauge known to man, and 2500 watts of stereo with a 20k motor. Grounds are all updated to 4 gauge but it isn't enough. The post was in hope of useable information, not posts from the peanut gallery....

 

[salvageV6]

I'd add a second battery and isolator for the stereo before I went with an expensive alternator.

Nothing on the car performance parts list posted dictates any amperage over stock.

Some of the expensive high output alternators don't work so well at lower rpms so make sure they give you an output curve graph before you buy it.

I can see operating the stereo cranked at idle and low rpm, more than when the car is in performance mode say at the track etc. That's the only item on the list that warrants any extra amperage.

If you don't see any useable information consider it a peanut gallery post.

 

[earlbrown]

The post was in hope of useable information, not posts from the peanut gallery....

Actually it looks like the peanut gallery threadjacked GNONYX's tech post with a WTB ad.



useable information for WTB dilemma's...
http://turbobuick.com/forums/forums/parts-wanted.35/

 

[L8TRH8R]

I'd add a second battery and isolator for the stereo before I went with an expensive alternator.

Nothing on the car performance parts list posted dictates any amperage over stock.

Some of the expensive high output alternators don't work so well at lower rpms so make sure they give you an output curve graph before you buy it.

I can see operating the stereo cranked at idle and low rpm, more than when the car is in performance mode say at the track etc. That's the only item on the list that warrants any extra amperage.

If you don't see any useable information consider it a peanut gallery post.

Thanks. At the track I won't have the box in the car. Just hoping to have the best of all worlds, Montana is a big state, I might wanna pass someone on the Interstate at 20 psi blasting Earth Wind & Fire

 

[L8TRH8R]

Actually it looks like the peanut gallery threadjacked GNONYX's tech post with a WTB ad.

useable information for WTB dilemma's...
http://turbobuick.com/forums/forums/parts-wanted.35/

Yes I poached a nearly year old thread. Before I posted on this one I saw you had the exact same response for some else who inquired about hi output alternators... That was the reason for my response. Maybe ops will make a wanna be comedian section.