2nd Gen Non-Engine/Transmission What's the best way to test the alternator output

[TGriffith]

I've had recent charging problems, the batteries test good, the alternator is new, the battery temp gauge is new at this point I'm guessing it's the PCM but would like to verify, what's the best way to test the voltage coming out of the alternator? my thought was to remove the wire off the the back and connect one connector from the multimeter to the alternator and the other to the wire I just removed, is there a better/safer way?



thanks for the help

 

[Gary - K7GLD]

Sticking my neck out a bit - I usually use a quick-and-dirty check of using a good digital multi-meter to measure voltage right at the battery. It should be somewhere over 14 volts with the engine at a fast idle.



Problem with this simple method, is the possibility of other issues other than the alternator or PCM preventing proper charging voltage at the battery - but it's a start...



Don't overlook the possibility that ONE of the batteries might be bad (even if it SEEMS good), causing the PCM/alternator to not function properly - best way to test batteries for condition and balance is with a breakdown meter.

 

[Fishin Guide]

You could wire in an ammeter to check the amps. And voltage is easy to chek on a running engine with the pos/ neg terminals as Gary noted.



You can have volts and not enough amps. I believe the PCM contols the regulation of the alternator as well.



Dave

 

[WDixon27]

that would pop the fuse on the meter or out right fry it, too much load, without access to a inductive amp clamp or other current measuring device i would look at the voltage with, the engine off and one battery at a time by unhooking one, engine running at various rpms with all accessorys off, and finally with everything on that you can turn on checking it at various rpms, the voltage may drop a little at idle with a full load but should remain above battery voltage at all times and should rise quickly when idled up

my thought was to remove the wire off the the back and connect one connector from the multimeter to the alternator and the other to the wire I just removed

 

[WestTN]

The output is DC, so an inductive probe will not work. You would need a shunt and they are scarce and expensive in the necessary 200 amp capacity range. In this very hot weather the output should be in the 13. 7 volt range. In very cold weather it will be in the 14. 4v range. If the voltage is in range, there is no problem with the alternator. If it had a bad diode the voltage would be low. Voltage is the pressure and amperage is the current flow.

 

[Bob4x4]

The output is DC, so an inductive probe will not work. You would need a shunt and they are scarce and expensive in the necessary 200 amp capacity range. In this very hot weather the output should be in the 13. 7 volt range. In very cold weather it will be in the 14. 4v range. If the voltage is in range, there is no problem with the alternator. If it had a bad diode the voltage would be low. Voltage is the pressure and amperage is the current flow.

Voltage by itself is not the best test... ... ... ... Alternators are rated in amps not volts. Load test it and you will see what it can do. If it matches the rating you are good to go,otherwise start troubleshooting. The majority of the testors out there(old school) will have an inductive pick-up the measure the amps while under full load. Some of the newer stuff relies on electronics and will just say normal. (such as the midtronics).



Bob

 

[WDixon27]

dc amp clamps are not that expensive, i think my 400A snap on was around $125, you plug it into a decent multi meter and set the meter to mv and what you read is what you got. i would of gone further into measuring the amps but the average joe has no real use for a amp clamp, that and generally i've found over the years if you have good voltage with the charging system loaded down the amps are there, if you don't have good voltage then it's time to go further and look at the output and diagnose what's up

The output is DC, so an inductive probe will not work. You would need a shunt and they are scarce and expensive in the necessary 200 amp capacity range.

 

[FDziurda]

Alternator Quick Test

It's not an accurate test, but this will let you know if your alternator is working properly. It only takes a few minutes.



Start your truck and turn on everything you can ( headlights, AC w/fan on high, etc). Rev engine to about 1500 rpm. Take a digital multimeter, and measure the voltage accross the battery. You should see at least 13. 8 volts, and as high as 14. 5 volts, showing that the alternator is able to keep up with the load.



You can also insert a DC ammeter in series with the output of the alternator, if you wish to see how much current it is producing. Use caution and DO NOT short anything if you use this method. It can damage the alternator.



Good Luck,



Frank Dz