alternator

[Ellis Kinney]

Farmall M tractor. 12 volt, negative ground, electronic ignition, with an alternator, one wire. I'm not sure of the brand. Anyway it has quit alternating. Always before I have been able to let the tractor warm up for a bit and then rev the engine and it would start charging. Not this time. Is there a simple test for an alternator or just buy a new one? I don't think it was very expensive. Thanks, Ellis

 

[timcasbolt]

Might be worth your time to install a new regulator before you replace the alternator. Others on here have expressed a differing opinion, but I've found the self-exciting type to be less reliable.

 

[grandpa Love]

Farmall M tractor. 12 volt, negative ground, electronic ignition, with an alternator, one wire. I'm not sure of the brand. Anyway it has quit alternating. Always before I have been able to let the tractor warm up for a bit and then rev the engine and it would start charging. Not this time. Is there a simple test for an alternator or just buy a new one? I don't think it was very expensive. Thanks, Ellis

Easy, quick,and simple,pull the old one off,go to AutoZone,buy this one. We use them a good bit. Even on a cub it starts charging immediately,no revving needed.

 

[BarnyardEngineering]

Short answer, no. There is nothing you can do to test the alternator. You can check for broken wires in your wiring harness, but that's about it.

All the tester does at the parts store does is hook up the alternator like it is in your car/truck/tractor, and spin it up to see if it charges. If it doesn't it's bad.

 

[matthies]

If it's an old style Delco there is a D shaped hole on the back side to bypass the regulator to see if it will charge. Just stick a small screwdriver in to hit a tab and the alt case at the same time. Newer Nippendenso's could do the same thing. I am sure you can do it with most of the alternators just need to find out how.

 

[used red MN]

Is the crank to fan/water pump belt tight?

 

[Fritz Maurer]

Yes. Get a test light. If you have power at the post of a one-wire unit, that would point to an alternator issue. Starter shop would tell you exactly what's wrong, as opposed to vague information from a a-p store.

 

[caterpillar guy]

bWe quit reuilding them as the parts got so bad and hard to get around here that it was easier to just repalce3 the alternator. 2 ways you can check if it is the alternator . 1 pull the battery cable off if it stops it is the alternator 2 check for voltage at 2/3to wot. Should give about 12.8-13.8 volts if not most likely the alternator. higher it is over charging and less is not keeping it up.

 

[wore out]

bWe quit reuilding them as the parts got so bad and hard to get around here that it was easier to just repalce3 the alternator. 2 ways you can check if it is the alternator . 1 pull the battery cable off if it stops it is the alternator 2 check for voltage at 2/3to wot. Should give about 12.8-13.8 volts if not most likely the alternator. higher it is over charging and less is not keeping it up.

Many of us think it's really bad juju to intentionally disconnect a battery cable with the engine running. IF the alternator WOULD happen to be charging that can cause a voltage surge if as much as a hundred Volts, potentially damaging the alternator an possibly even giving you the shock of your life if you happen to touch the cable end and ground. Sure, you may have have done it dozens of times with no issue, but the possibility of undesirable results DOES exist!

Do it, if you must, but maybe don't suggest it to guys unaware of this?

 

[caterpillar guy]

Lets see if it is not charging that voltage spike you speak of will not happen and will show when the battery stops subsidizing the alternator. IF it is charging I suppose it could though I've never had a problem over the last 40 years. I will also admit with all the diesels we have that test is pretty mute since it would not make much difference with a manual shut off through the throttle.

 

[used red MN]

IF it is charging I suppose it could though I've never had a problem over the last 40 years.

“As predicted” last words spoken before he settles in to his coffin. Do yourself a favor if this “has to be the test you use” first check to see if metal is magnetically attracted to the rear alternator bearing.

 

[Bob M]

Many of us think it's really bad juju to intentionally disconnect a battery cable with the engine running. IF the alternator WOULD happen to be charging that can cause a voltage surge if as much as a hundred Volts, potentially damaging the alternator an possibly even giving you the shock of your life if you happen to touch the cable end and ground. Sure, you may have have done it dozens of times with no issue, but the possibility of undesirable results DOES exist!

Do it, if you must, but maybe don't suggest it to guys unaware of this?

Years ago I was fooling with my mom's Dodge station wagon. I disconnected the battery ground cable with the engine running and the headlights on to see if it would still run.

There was a brief bright flash and the engine quit. Every lamp that had been lit (head/tail lights, dash lights and dome light) had burned out. And when the ground was reconnected the alternator was DOA.

A very expensive lesson for a 16 year old(!)

 

[wore out]

Years ago I was fooling with my mom's Dodge station wagon. I disconnected the battery ground cable with the engine running and the headlights on to see if it would still run.

There was a brief bright flash and the engine quit. Every lamp that had been lit (head/tail lights, dash lights and dome light) had burned out. And when the ground was reconnected the alternator was DOA.

A very expensive lesson for a 16 year old(!)

I know the feeling, Bob!

I have a gas-powered John Deere 4020 with a 12 Volt internally-regulated Delco alternator with a battery disconnect switch to disconnect the battery during long periods of non-use. (It's a dedicated snow blowing tractor.)

Several years ago, at night, I accidentally kicked the battery disconnect switch with a snow boot.

The lights flashed BRIGHT, then all was dark.

Burned out 2 LED headlights, 2 incandescent headlights, an incandescent rear worklight, and the alternator!

So, YES, such a voltage surge is a real thing!