J-D 544 E Alternator/charging puzzle

[Tony Wells]

OK, this ought to be an easy one, but the coffee hasn't soaked in very deep. I have a loader that is charging up a storm, (err, I mean normally, about 13.9 VDC). Problem is the charge indicator light is on. This has a Delco reman pn TY6775 alternator. There is proper voltage at the alternator B+ and at the battery, but the light stays on. I don't have the schematic so I can't see which of the other three terminals either supplies the light, or grounds it.

Oh, and this is the 4 wire alternator. Connections appear shaky, but wiggle test has no effect on light.

Anyone have a quick simple answer? I don't, at the moment anyway.

 

[Delmer]

TRADITIONALLY, the excite voltage came from the ignition switch, through the alternator warning light, and to the excite terminal on the alternator. If the wire broke, the light burned out, etc. then the light would not light obviously, but the alternator would not charge either. Hence, you check the light to see if it comes on when you turn the key, before starting. Obviously your light is functioning if it lights up while running. Unless it's shorted somewhere in addition to the supplying the excite voltage.

Simple answer, the alternator is weak and not fully exciting itself so the current keeps flowing and the light does not go out. What happens if you turn all the accessories on at half engine speed?

 

[Tony Wells]

Delmer, thanks for the reply. I’ll have to get back to you on that. Got pulled onto another machine. I’ll post back ASAP on that test.

 

[JL Sargent]

This may be a problem with a bad relay. On my JD backhoe, if the auxiliary relay doesn't close the charge light is on and the hour meter doesn't change.

 

[Tony Wells]

JL, I’ll check that too as soon as I get back on it. Trying to outthink a 6 speed Allison in a F750 first.

Thank you!

 

[hookedondiesel]

My opinion, I think 13.9 or less is not enough to turn out the light. You should have a good 14.5 volt's. The voltage regulator in the alt is probably going, or a bad connection somewhere. Most likely the regulator inside the alt.

 

[Coaldust]

This might help. The JD TY6775 is a Delco 10si 76 amp unit. The indicator circuit with warning light, may simply have a bad connection. You could easily bypass (to test) the indicator circuit with your test light. Go from terminal 1 to battery and your test light should stay off.

Or, like Hookedondiesel suggested, your vr may be faulty. There is a test tab on the back of the unit that allows you to full field the alternator and bypass the VR. The voltage should jump to about 14.7v when you do that.

If your circuit for 1 and 2 is correct, (no bad connections) and you have a load on the system, 13.9v is a bit low. You could have 1 bad diode in the rectifier.

 

[Tony Wells]

I took a little time to go back to this machine, but just a little. The output of the alternator is pretty steady, even when turning on the limited accessories. This machine doesn't have many. As usual, the voltage drops for a second or two when switching on the accessories, but comes back, so that tells me the VR is probably doing its job. 13.9 is maybe a little low, but part of that is determined by the state of charge of the battery, which in this case is brand new. If no charge is needed, the VR should trim the alternator input down to avoid overcharging or drying out the battery. My suspicions are that the light should be on only if one side of it is more negative than the other, showing that there is actual current flow in a certain direction. Usually a diode controls which way the current flowing make the light come on. As long as the battery is charging, the current balance causes the light to go out since the current is flowing into the battery rather than from it. If the engine and systems are running from the battery, as in the case of an low current from the alternator, the flow is reversed and the diode allow the light to come on.
But if there are relays involved, then it's possible they are faulty or poorly connected, and there could be a leaky diode somewhere. I can and will check all of that. I also have a good starter/alternator shop I can take the alternator to for load testing. I'll put a scope on the output, which will show a bad diode in the rectifier bridge. I can also ground the test tab and see if the voltage comes up. Kind of have my doubts there, but since it's such an easy test, why not...

I've run this machine under accessory load for several hours without depleting the battery, and the alternator output remains a steady 13.9. I don't really see a problem with that. I feel the problem is in the wiring surrounding the indicator light.

Coaldust, thank you for that diagram. It will help me pick my test points.

 

[JL Sargent]

Does the light come on every time? Or does it come on only sometimes?

 

[Tony Wells]

It's constantly on when running. Engine speed nor load affect it.

 

[Coaldust]

Keep us posted.

 

[Tony Wells]

By all means! We have poor weather for the next few days, so I don't expect to spend any time on it for a bit, but I will post my findings.

 

[Delmer]

You're overthinking things in post #8. The light turns on and off based on current flow like you say. A diode is used instead of a warning light on some wiring diagrams for gas engines, in order to keep the excite circuit from "backfeeding" the ignition circuit and keeping the engine running even with the key off.

I'm thinking the issue is going to be close to the warning light wiring, but not that circuit itself. That is it will be an alternator problem, or alternator to battery problem, or else it will be an issue with something else on that ignition circuit like a poor connection at the ignition switch and the alternator backfeeding to "help out" that circuit. Maybe a ground somewhere, but I can't think of where.

 

[Coaldust]

Delmer,

Yes. There is much overthinking going on.
Especially, talking about a 50 year old Delco 10si. The simplest and purest alternator and charging circuit ever designed. One of the first transistorized circuits ever used on a car, except for the AM/FM radio. But, when this alternator hit the market, FM was still an option. Paid extra for that.

But, why not? It’s fun anyways. Pulling the scope out, looking at some wave forms. We are going all in on this one. Whatever it takes to turn that red indicator lamp off. We’ll get er’ figured out

 

[mg2361]

Serial number?

Check your alternator relay. That controls the light in your instrument panel.

 

[Midnightmoon]

Try jumping alt power to excite lug on alt and see if charging output goes up. I think I remember a 544 not charging until you revved the engine up but that may have had a week alternator we had to replace a few months later. I have a deere alt in shop now probably same vintage on a gen set. It will slowly go up to 14.5 but hangs at 13.7 for a bit.

 

[hookedondiesel]

Tony, you asked for a quick simple answer, here it is....swap the alt.

 

[Tinkerer]

Tony, you asked for a quick simple answer, here it is....swap the alt.

BBBut that may end the discussion !
mg2361's info about the relay is one thing in the circuit that a not many people are aware of.
I don't know how he remembers all of the technical info he posts.

 

[mg2361]

13.9 is maybe a little low

As long as it stays above 13.5 with all the loads on (lights, blower, etc) I wouldn't worry about the charging voltage. 13.9V is just fine.

 

[Tony Wells]

Tony, you asked for a quick simple answer, here it is....swap the alt.

Yabbut that takes all the fun out of it. Especially if the problem is a silly bad connection. Feel like I ought to at least check that stuff first.

And mg, I said a little low, not condemnably low....I would like to see it higher, but I'll take the 13.9. And I believe that should be enough to extinguish the light, so I'm not itching to replace the alternator just yet.


And for the record, overthinking is one of my most outstanding failings when it comes to some things. Maybe that paints me a fatalist, or maybe a victim of "paralysis by analysis", but I freely admit this. Of course, most of the (over)thinking is when I'm away from the machine at home on the sofa or something. At the machine, I poke, probe, prod and test everything I can get to, looking for the problem.

And I do appreciate all the comments, recommendations and suggestions from you guys. I recognize that most all of you have more time in trade than I do when it comes to heavy equipment, but as a general wrench, I'm not exactly new. Made by first official greasy dollar rebuilding 4 straight six Chev's in a friend's work fleet when I was just 10.