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1486 Alternator problems


TB5288

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Got something I can't quite wrap my head around. Alternator quit charging. Volt gauge dropped and baler monitor voltage reading showed the same as tractor volt gauge. Took the alternator off and had it tested. Alternator tested fine. Did not take it apart, but tested good on stand. So I got to looking and found the resistor for the exciting wire was bad, had no voltage getting to the alternator on that wire. I replaced the resistor and everything worked fine. Go back to baling and the voltage dropped again. Didn't have testing equipment with me but I know the back of the alternator was not magnetized. Anytime I've found the alternator not magnetized, it was not charging. So I headed back to the shop and while driving back the alternator started charging again. Everything seemed fine. I started testing voltages and this is what got me confused. With the engine shot off, I have 12.5 volts going in the resistor and about 7 volts coming out. The seems normal. At the alternator I have 12.5 and the battery terminal, 12.5 at the battery terminal on the regulator plug and 7 on the exciting wire. That all seems fine. With the engine running(and charging) I have about 13.5 at battery terminal and the regulator plug, but at the exciting wire I have 19 volts. I have 19 at the alternator plug and also coming out of the resistor in the cab. Why would I have that? I've never checked that voltage before but I sure can't believe that's correct. I talked to the test shop and this guys been doing this for 40 years, I've never had a problem with his work or knowledge. I thought the regulator was maybe stuck. He said if the regular was stuck the voltage would be that high on both regulator terminals. Any ideas?

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Well at least your voltmeter reads accurate. On my 1586 the alternator reads 14.1V and the battery reads 14.1V but the meter in the cab reads <12V. Don't know what's wrong and can't get the instrument panel out far enough to see in behind to do anything with the wiring. 

Does sound like your alternator is flakey though. Just grab a 10SI from the auto parts store and swap it in to see what happens.

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@Matt Kirsch pull the panel out enough to loose the 2 clips on the sides, and remove the face -- pull the volt gauge out and check the terminals on the back side -- sometimes tarnish and sometimes the terminals ate just loose
there is a plastic part on the rear with a resistor that cracks and loses connection

@TB5288 Those voltages are normal
Check for loose connection or broken wire on the excite wire
Would have been a good time to open that alternator and look at the brushes -- may be worn to the point of intermittent contact

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1 hour ago, HydroTek said:

@Matt Kirsch pull the panel out enough to loose the 2 clips on the sides, and remove the face -- pull the volt gauge out and check the terminals on the back side -- sometimes tarnish and sometimes the terminals ate just loose
there is a plastic part on the rear with a resistor that cracks and loses connection

@TB5288 Those voltages are normal
Check for loose connection or broken wire on the excite wire
Would have been a good time to open that alternator and look at the brushes -- may be worn to the point of intermittent contact

19 volts normal on exciting wire?? I did the same test on my 5288, has the same alternator, it had 13.5 volts on both regular terminals. I put that alternator on 1486. Both terminals had 13.8. There must've something wrong with the alternator that was on the 1486 that doesn't show up on bench tester.

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I had an excite wire get high voltage and burn out once. It burnt the wire in two before I found out. Lucky it didn't start a fire. I replaced the alternator and wire then.everything was fine.

try a different (known good) and see what you get.

I don't remember what the alternator shop said was wrong with my alternator but it was bad. It's been 10 years or more...

Thx-Ace

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On 10/19/2023 at 12:37 PM, Matt Kirsch said:

Well at least your voltmeter reads accurate. On my 1586 the alternator reads 14.1V and the battery reads 14.1V but the meter in the cab reads <12V. Don't know what's wrong and can't get the instrument panel out far enough to see in behind to do anything with the wiring. 

Does sound like your alternator is flakey though. Just grab a 10SI from the auto parts store and swap it in to see what happens.

Im gonna need one for my 1566 for next spring 10si the one to get? Whats everyone running for amps? Bigger the better? 90 or so amp suffice?

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2 hours ago, 1566IH said:

Im gonna need one for my 1566 for next spring 10si the one to get? Whats everyone running for amps? Bigger the better? 90 or so amp suffice?

Take a look at what you have. If the two small terminals are like this, =, it's a 10DN. If they are like this, --, it's a 10SI.

If I'm not mistaken they switched from the 10DN to the 10SI during 66 series production. Early 66's had the 10DN and an external regulator.

The one I bought was around 65 Amps. Not a huge electrical demand on my 1586, really. Once the batteries are topped off about the only load is the digital dash and its valiant efforts to produce RPM readings.

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5 hours ago, 1566IH said:

Im gonna need one for my 1566 for next spring 10si the one to get? Whats everyone running for amps? Bigger the better? 90 or so amp suffice?

Depends what you do with tractor and what's on it. I normally start a tractor and use it for hours so plenty of time to charge the battery. Also I rarely work at night, and everything has LED lights, so electrical load is minimal. If you have a bunch of start stop type work, or 17 monitors in the cab, you'll want lots of amps. If electrical load is low, amps required is low.

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They are available from auto parts suppliers like Napa, O'Reilly's, rock auto, ect.

I find it looking up a 1984 GMC suburban 350 etc. Check out the pics to be sure it's a 12si. The fan on front is the key.

From rock auto an ACDelco (made in China) 78 amp 12si is currently $70 plus shipping and tax. They tend to run a bit more locally.

If you get one from your local Napa, O'Reilly's, etc it should have a lifetime warranty. It's much money convenient to return one locally than to ship it back. 

You will have to change the pulley and may have to clock it 

Here's a good write up about them.

http://www.madelectrical.com/electricaltech/delcoremy.shtml

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I can overhaul one of these in my sleep?

If I can now get parts.

At the dealership, I tore down the cores and put together good ones from the pieces.

The parts department furnished bearings and brushes.

There was new, rebuilt, and the shop rebuilds.

My shop rebuilds were run on the test stand and verified good.

I was warranty so if one came back bad, I just handed the farmer another. No paper work. Just another service.

When the cores went back to the rebuilder, the rotor was bad, stater was bad, diode trio was bad, regulator was bad. They were junk!

The combine ones had a third terminal which was for the tachometer and swing arm brushes which stood up better in the dust.

My GMC pickup soon had that option on a 6.2 diesel. I never did get the tach working.

 

 

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