Alternator keeps cooking itself

[Sebculb]

Hola everyone,

Would anyone know anything about things that can cause an alternator to repeatedly cook itself? '97 JD 310D backhoe. The alternator is relatively new, perhaps six months. I bought it from the expensive commercial electromechanic shop because they have the parts on hand and are pretty knowledgeable, if very expensive. A couple weeks ago my machine wouldn't start, batteries were dead. Checked the alternator, wasnt charging. Took it to the shop, $50 later they gave it back with new brushes and bearings, and it was charging again. Batteries wouldn't stay charged, so I got a new battery. (down to one big battery from two smaller batteries).

Charged the new battery for a bit before installing just to make sure, 12.7 volts. Checked for a drain on the system at the negative terminal just out of curiosity, and it was registering a 12.7 v drain with the machine turned off, tracked it to the alternator. Not enough amperage in the drain to turn on a bulb-style circuit tester though. Took the alternator back to the shop, they replaced a $20 diode or plate or something and gave it back to me. Still had the same drain. They said it's always gonna be there, something about a condenser or something and that the amperage is negligible on a battery. Vocabulary is translated from spanish, we're in Costa Rica.

Machine started great, strong turnover, charging at 14+ volts. Dug a small ditch at my house, couple days later went to do another job nearby. That day smelled the hot electrical smell while working, touched the alternator and it was hot enough to give me a blister burn on my hand. Let the machine cool down a bit, disconnected the alternator and drove home on battery power. Alternator was always charging but clearly not right.

Now they "fixed" it again and charged me $200. This is starting to be a pain in the ***. This time they replaced the regulator, diodes, plate and one phase of the bobbin. remember, spanish translation if it doesn't make sense. The people at the electromechanic shop say that only battery related things can do it, that if were caused by a short circuit it would register a significant battery drain while the machine is turned off. They're saying my old batteries that wouldn't accept a charge cooked it the first time and that my new battery has a defect or something and is low on charge or something and that's what cooked it this time. They got a "specialist" from a local battery shop to come and check the acid levels and he said they're low, I left it at his shop so he could do more extensive testing overnight. I'm sure they're all in cahoots.

The battery is a big 950 amp Mack battery from the local CAT dealer, can't imagine that's the problem but exhausting all their explanations before raising ****. However, if they were trying to give me a runaround, I'd expect them to tell me that my hoe's hodgepodge electrical sytem is short circuiting and that's to blame. That would be a definite possibility because previous owners have done who knows what with it, most fuses aren't connected to anything. However, the alternator shop says that's not really a possible cause.

Anyone have any insight? sorry for the long winded explanation but figured it's better to know the whole story.

Thanks!

 

[nybirdman]

I would think you have a dead short and no fuse.

 

[ruffdog]

Does the alternator have an internal regulator/rectifier or is it separate? It sounds like the regulator was working at some point but is the rectifier? The rectifier's job is to turn ac current to dc and it does this through diodes. Diodes are like little one way valves that only allow currant to go one way. If you have a 3 legged alternator and one diode is bad, it would be working against its self. If all of that is ok, maybe you have a major short to ground?

 

[Sebculb]

Thanks! ...uhh... whazzat mean? I'm sorta learning this stuff as I go. Dead short? No fuse? Does that mean there's a short going directly back to ground and no fuse to burn out before it gets out of control? How does that hit the alternator?

Thanks!

 

[Sebculb]

Does the alternator have an internal regulator/rectifier or is it separate? It sounds like the regulator was working at some point but is the rectifier? The rectifier's job is to turn ac current to dc and it does this through diodes. Diodes are like little one way valves that only allow currant to go one way. If you have a 3 legged alternator and one diode is bad, it would be working against its self. If all of that is ok, maybe you have a major short to ground?

I very well may have a short to ground, but the dude at the alternator shop says that wouldn't be an issue unless it's losing charge while it's turned off. Would he be wrong? Again, I dunno that much about this stuff. Thanks!

 

[Billrog]

Shop guy is right. A bad or running the machine with no battery will burn it up. I think the gauge would show a discharge if there was a short. I'm just a trial and error guy so only repeating my experiences.

 

[Industrial Toys]

I don't see why no battery would fry the alternator. No reason at all. And if they persist, ask them to explain that. I bet they can't

My first question is where is the voltage regulator? Internal to the Alternator? An alternator will produce varying DC level depending on RPM, so you need a Voltage regulator.

It is usually the Diodes that will cause slight leakage, or some call it a rectifier.

 

[Sebculb]

It has an internal regulator. Thanks for the responses! The more I learn about it the better I can understand if the dude's a charlatan or not. Or maybe fix it myself.

 

[WranglerX]

Got access to different shop?... I would look for some place else and get different opinion...

For what you have invested in that alternator you probably could have purchases a new 1 wire "generic" alternator and all you may have had to do is adapt mount and or fan belt.... Not sure about Costa Rica but in US you can get a 40 amp 1 wire alternator new for around $60 USD... Import fees and shipping may be a killer for you though...

Dale

 

[Roadworthy]

Your electric shop may be taking your money because you have it and they don't. They may know little more than you about the electrical system and be shining you on experimenting as they go. Either way you lose. From your tale it sounds as though they have not seen the tractor - this is all hit or miss as you bring them parts. Your description of the way the system is wired sounds as though the alternator is always connected to the battery. If that's the case it is probably trying to work with the battery and maintain current as you have the starter engaged. I think in a normal system when the starter is engaged everything else electrical is disconnected, though I could be mistaken. If the alternator is trying to "help" the battery, it is looking effectively at a short circuit for a brief period of time. This could cook the alternator in short order. You will probably continue to experience electrical problems until you get the wiring sorted out. It will probably be a lot less expensive than continuing to buy parts as you destroy them. Or you could disconnect the alternator and put the battery on a charger when not using the tractor.

 

[Agvg]

The alternator is always connected, when starting the rpm are so low that there are no charge, and almost all alternators are self regulating when it comes to current so that's not a problem anyway.

 

[Agvg]

I don't see why no battery would fry the alternator. No reason at all. And if they persist, ask them to explain that. I bet they can't

My first question is where is the voltage regulator? Internal to the Alternator? An alternator will produce varying DC level depending on RPM, so you need a Voltage regulator.

It is usually the Diodes that will cause slight leakage, or some call it a rectifier.

The battery works as a buffer/load and helps the regulator to keep voltage with in specifications, without battery you can get very high voltage spikes and that can fry diodes in the rectifier.

 

[Industrial Toys]

Sorry, "BUFFER" is not an electronic term. Neither is SURGE, a term that is always thrown around. I have worked with, designed and build many voltage regulator circuits. Never got spikes on the output. A small cheap capacitor is usually added to the output and input and often several at different values, to stabilize voltage fluctuations and remove transients and noise. Can't see that anyone would build a voltage regulator that relies solely on the capacitance of the battery. Which still would not address the transients. An automotive or tractor electrical environment is very hostile for electronics and any such circuits must be built with this in mind.

 

[jwstewar]

I just went through this last year with my New Holland. I burnt the OEM up, a cheap Chinese replacement, and almost another local replacement before I figured out the caused. In my case it was the charge wire going from the alternator to the battery. It had a quick connect up under the dash area. This quick connect had gotten hot and melted and making intermittent contact. It would make contact, alternator would start charging and then it would lose contact. It would burn the diodes out of the alternator. I had to cut the quick connect out of the wires and just wired the two parts together and soldered. No issues since. Took some digging to find that one. Incidentally, to guarantee I never have another alternator problem, I had the shop rebuild my OEM alternator and I have it sitting on the shelf

 

[Agvg]

Sorry, "BUFFER" is not an electronic term. Neither is SURGE, a term that is always thrown around. I have worked with, designed and build many voltage regulator circuits. Never got spikes on the output. A small cheap capacitor is usually added to the output and input and often several at different values, to stabilize voltage fluctuations and remove transients and noise. Can't see that anyone would build a voltage regulator that relies solely on the capacitance of the battery. Which still would not address the transients. An automotive or tractor electrical environment is very hostile for electronics and any such circuits must be built with this in mind.

But you are talking about voltage regulators with input and output in a traditional way I suppose? Not a voltage regulator that control's a 3 phase generators output by regulating the field in the rotor?

 

[WranglerX]

Your electric shop may be taking your money because you have it and they don't. They may know little more than you about the electrical system and be shining you on experimenting as they go. Either way you lose. From your tale it sounds as though they have not seen the tractor - this is all hit or miss as you bring them parts. Your description of the way the system is wired sounds as though the alternator is always connected to the battery. If that's the case it is probably trying to work with the battery and maintain current as you have the starter engaged. I think in a normal system when the starter is engaged everything else electrical is disconnected, though I could be mistaken. If the alternator is trying to "help" the battery, it is looking effectively at a short circuit for a brief period of time. This could cook the alternator in short order. You will probably continue to experience electrical problems until you get the wiring sorted out. It will probably be a lot less expensive than continuing to buy parts as you destroy them. Or you could disconnect the alternator and put the battery on a charger when not using the tractor.

Typically a 1 wire alternator is direct connect to battery and has internal isolation (diodes) from battery ....... If there is regulator between alternator (multi wires) and battery, regulator should protect alternator (isolate) from battery. ..

Alternator generally do not producer any voltage until they get a short charge of 12 volts through "ALT" lamp in instrument panel to initiate the charge sequence...Seriously double the theory the alternator is trying to produce voltage to help battery to start tractor, as at this point alternator is not energizes or spinning fast enough to produce any voltage/amperage...

Generally the diodes in alternator protect alternator from drawing excessive voltage/current from battery, only way a alternator can "drain" a battery is to have defective diodes or bad regulation circuit...

If "shop" has not correctly repaired alternator after several trips to shop, go some where else, they are no qualified to to fix the alternator....

Also some system have a fuse in alternator out put. if a fuse is there and blown, it may be cause of all your problems....

Not sure if below statement it absolute, but various reads on different web pages tend to support this theory...

Don't Disconnect the Battery with the Engine Running

Dale

 

[Industrial Toys]

Firstly, I realized my "Bad" suddenly when making lunch. Obviously there are all kinds of "BUFFER" circuits in electronic logic.

No, not talking about generator VRs. Electronic VRs in general. MOST suggestions regarding electrical stuff on here are at least somewhat false it seems. Sometimes, the real fault or reason is never realized but it's just an assumption.

One reason not to disconnect a battery when running is because the leads could short! Again, such articles are so vague, without specifics, to be a joke.

 

[Agvg]

But there no point to do anything before the wiring between B+ on the generator and battery is 100% in working order, do also check B- so you are sure it's grounded properly.

 

[Industrial Toys]

If it was me. I would put a cheap appropriately rated fuse on the alternator output. HATE mechanics, electrical fixes or anything not OEM. 9/10s of the time, there was no reason to abandon the OEM wires and run new clothes lines around the engine compartment. Just because YOU couldn't figure out what was going on.