How Do You Test An Alternator?

[Ty Lee]

Can someone tell me how to test an alternator and can it be done on the tractor or do you have to remove it.

 

[omahagreg]

Does the engine run? Assuming it runs, check voltage at battery, WITHOUT it running. A good battery will read 12.6 volts. Start engine, turn on all electrical load you have (AC, Heater fan, lights, etc) read voltage at battery. A proper alternator will send 14.6 volts to battery. Hope this is a starting point. Greg

 

[Jeff in TX]

Start the tractor and let it run for as minute or so. Pull the POSITIVE cable off of the battery with the tractor running. If it dies the alternator is not charging. If it keeps running the alternator is charging. It may not be putting out enoygh amps, but enough to work. You would have to test the output with a meter for that.

 

[chess]

with engine running an lights an other things turned on just hold screw driver on rear of alternator an you should feel magnatism pull screw driver against rear of case.

 

[rvirgil_KS]

Assuming it's the common Delco with internal regulator.

Battery voltage, engine off should be about 12.6 volts. Should increase up to about 14 V. with engine running. If not:

1. With a "one wire" version, rev engine. It it does not begin to charge remove alternator and take in for a test.

2. With 3 Wire, switch off,engine not running it should have battery voltage at output and pin 2 on the outer plug, no voltage on pin 1.

With switch on, engine not running battery voltage at output and pin 2, some voltage on pin 1

With engine running, There should be approx 14 volts charging voltage at all 3 pins. If no voltage at pin 1 check back to switch source.

Do not disconnect battery cable with engine running. This presents safety hazzard and can smoke the alternator.

 

[Ty Lee]

So one person says don't disconnect battery, may smoke alternator and another on says disconnect battery cable. I'm a little confused. So I or shouldn't I disconnect cable for one of the tests. Looks like the easy test is to test battery with engine off at 12v then start it up and turn every thing on and see if it is at 14v. Yes the tractor does start and run. It is new but I'm having electrical problems.

 

[thurlow]

That's interesting; some of my tractors will run without an alternator, generator or batteries.

 

[Anonymous-0]

Never remove a Battery cable with the engine running . It creates a huge voltage spike that can fry the diode trio inside the Alt.

 

[camju]

you can take a dead battery and boost it then turn on the lights if they get brighter when you rev the engine the alt is working

 

[pete 23]

Don't take the cable off when running. Just for the record, Case used to ship some of their combines without batteries years ago, but they had a large resistor hooked to output terminal of alternator so I was told by mechanic who worked across the street at Case dealer before we were incorporated into CaseIH dealership. That way, they could jump start them and load them without a battery but you needed to remove resistor when installing a battery. And, like others have shown and said, several different ways to check to see if it is charging. The old screwdriver on back of alt is a good quick check. If you really want to give it a complete test you need to have an ammeter and voltmeter and carbon pile to apply sufficient load to test for rated out put of both amps and volts. I just love my clamp over wire meter I bought (AFTER I RETIRED) and have the old Allen carbon pile battery load tester I used for near 40 years that the new owners threw out so I can get a good test of an alternator without having a test bench anymore.

 

[Ty Lee]

So it there something wrong with checking it engine off at 12 volts and then checking it when running with lights on and seeing if it is at 14v? Do alternators on tractors usually have a fuse?

 

[omahagreg]

Volt meter should tell you most of what you need to know. Might bring up more questions, but should be a good starting point. Greg

 

[Ty Lee]

Volts read 13 when tractor off and 11.6 with tractor running with lights and radio turned on. No magnetic feeling at back of alternator. I guess it is bad. Tractor only has 400 hours. What causes them to go out. I did have some problems when wiring up the round baler that cause some shorts and some fuses blew. Does alternator have a fuse?

 

[Owen Aaland]

Unless you tell us what make/model tractor you are working with you are going to continue to get generic answers. It would also be helpful to know what brand of alternator you have since some tractor makers have used alternators from different manufacturers on the same model tractor.

Checking for magnetism when the alternator is running is a quick test but having it does not in any way mean that the alternator is working. The magnetism is created by the field coil in the rotor and is only indicative of the input side working. Unless the diodes and stator are also good you will still have not output even if you get magnetism.

 

[36 Coupe]

Jeff ,keep this Dufus advice to yourself.This can ruin diodes in the alternator and cook the regulator.An alternator runnuing with out a load can put out 110 volts under certain conditions.

 

[36 Coupe]

Do not disconnect the battery when the engine is running.

 

[anonomous]

It seems everyone is missing the obvious. You state that this tractor is new, so why not call the dealer about the warranty?

 

[Mike (WA)]

My OC4 diesel runs fine, but a couple months after I bought it, I tried to start it and the battery was dead. On further investigation I found that the alternator is not even hooked up. I have to recharge the battery a couple times a year. Yeah, I know- but I'll fix it when I get a roundtuit.

I think your test only works for gas tractors, and then only if you don't let the smoke out of the alternator in the process.

 

[Ty Lee]

The Tractor is a 2005 Kubota M105S. I pulled theh alternator and took it in for test they said it was fine. I can not find a fuse to it, they all seem fine. There in no magnetic feeling when running and the volts get lower when you start the tractor and turn lights, AC, stereo etc. on. I"m guessing it has no power to it or some fuse is bad but I at a loose right now and the hay is burning up.

 

[Ty Lee]

The Tractor is a 2005 Kubota M105S. I pulled theh alternator and took it in for test they said it was fine. I can not find a fuse to it, they all seem fine. There in no magnetic feeling when running and the volts get lower when you start the tractor and turn lights, AC, stereo etc. on. I"m guessing it has no power to it or some fuse is bad but I at a loose right now and the hay is burning up.

 

[Janicholson]

There is probably a fusable link in the charging system. it will look like a piece of wire,(usually in a fuse box or circuit box)
THis link will be connected with spade terminals or connectors. It will probably be internally broken (check continuity end to end. Replace with the same amp rating) it is a big fuse! Jim

 

[Brian Jasper co. Ia]

Sorry 36, Jeff is right. There are other loads with the key on. The battery is simply a load.

 

[36 Coupe]

Battery is the only thing that draws enough load.Gauges ,lights ,regulators will be wiped out.In an auto or truck the computer, fuel pump and injectors will die .any lights on will burn out.Just ask the guy in the alternator shop about disconnecting a battery when the engine running.My truck has 12 pages of electrical diagrams no place for Dufus to be playing.You two should get together with the guy that stands on the frame of his post hole auger to make it dig.

 

[36 Coupe]

If the battery is charging when you pull the cable the spark will light off the hydogen gas and explode the battery.

 

[Ty Lee]

Well I just got back to a computer. I did the simple test by testing battery with engine off, it had 12 volts with new batter. With engine started it also had 12 v, all lights etc. turned on. All dried the magnetic feeling on back of alternator and nothing. Took alternator to repair guy in town and he checked it and said it was fine. Put it back on tractor and still not charging battery. Using volt meter check that alternator was getting 12 v through red wire in back. Also using volt meter measure large wire that leaves alternator and it only reads 12 volts. Not sure what to do now. Any ideas, the guy with the repair shop, could not be checking every thing. Baled all weekend changing batteries every few hours.