2 alternators in one week

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Resident Herpetologist
Dec 4, 2004
I've had 2 alternators die on me within one week and I'm wondering what might be the cause.

Here's what has happened. A week ago Saturday I was on a cave trip leading a small caravan up an old logging road. The 60 went belly deep into a mud hole and I had to winch out (Warn 12k), then later in the trip had another short winching episode. Afterwards the voltage seemed a little low but nothing of concern. The next morning the voltage was flat at 12 v. Had about a 4 hr drive home and the voltage remained at a steady 12 v.

At the house I had a spare alternator so I swapped that in. BTW these are the stock alternators on a 2F. During this past week charging was normal, around 14 v (Autometer gauge). Then this Saturday I used the winch to pull down some large dead limbs from an large oak, only 3-4 winchings. After this the voltage was a little low but I thought that it was simply the battery being recharged. I did not drive the 60 until this morning when I noticed that this second alternator was dead.

Both alternators were rebuilt at the same time by a local shop a few years ago. So could it be that the VR's have given out on both alternators, and could it be from the demands of recharging the battery? Or coincidence that both failed following the winching? Or should I just avoid winching on Saturdays?
This is assuming the 60 alt is internally regulated. ( I'm still a newb at Toy stuff)
This is a real stretch, but since it seems to be connected to the winching, then could your winch motor be drawing an overcurrent? Excessively high resistance can cause excessively high draw, and if the planets have been aligned just right, could you have killed the alts that way? How about the winch sending current back down the alt, frying the diodes? Again, a variation on the overcurrent aka short, theme. Check the winch wiring for poor connections/ signs of shorting.
This all should affect the battery first, so that's one reason for the real stretch.
Also, are the alt mounting points very rusted, or freshly painted? Basing this on the idea that the alt grounds through it's mounts/bolts.
Lastly, check your fusible links.
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You need to figure out what the mode of failure is for both alternator before you can remedy the problem, otherwise you'll just start playing musical components.
Are you sure it's the alt? Did you check voltage both with the engine running and also off? Did you use a multi-meter to measure, not the dash guage? Seems wierd to have two alts fail, I'd suspect something else. Winching puts more strain on the battery, which is one component I'd look at. An alt shop can test the alternators too to see what's up.
If its for the 60 I have a brand new toyota VR and Alt for sale.... Not to pimp my junk but you could get it cheap and I could get it out of my way. Good luck on figuring it all out.
You need to figure out what the mode of failure is for both alternator before you can remedy the problem, otherwise you'll just start playing musical components.

Could it be a grounding issue? I had a new from Toyota alt. go bad--then added new grounding straps from block to frame and other redundant straps that seems to have solved the prob.
Had the time to take a look at the alternator still in the Cruiser following the FSM. Fusible links checked out ok. Disconnected the B terminal and cranked up the engine, the alternator was not putting out any voltage. Then checked the IG terminal and had 12 volts at the terminal. Checked the L terminal on the regulator and had a reading of 12 v. Lastly checked the continuity between the F and L terminals on the regulator and I think the results from this indicate a bad regulator. With the multimeter on and unconnected the reading on the display was 1, with the probes in contact with the F and L terminals the reading dropped to somewhere around 0.2 or 0.3.

If the regulator has gone bad I will know the answer to what component failed but not why.

I had both alternators checked out by a shop. The first one had a bad diode and one of the soldered leads had melted. Voltage regulator in the second alternator had gone out.

Could the demands of recharging the battery after the winching events stressed the alternators to the point of damage? The battery is a 3 month old Optima Blue Top if that info has any bearing on the question.
Check the connectors, alt to batt circuit and pos battery cable for damage or corrosion causing high resistance. Yep, even the pos battery clamp. Enough excessive resistance in that circuit can cause stupid high current draws, and being that each diode in a normal OEM alt is rated for 30-60 amps roughly, it will fry them. The inrush from your winch motor must be astronomical. I don't have as neat of an explaination for the 2nd alts bad VR, except heat or bad grounding.
I know you've probably done this, but also check the battery for internal shorts, as a bad battery is the most common way to kill an alt.
i think you need a bigger battery mate the winch is drawing the battery down to its lowest level to quick and the alt is rcognizing this and trying to com pinsate for it with charghing hence the diode failiare in one short bursts of off on off with the winch will blow a regulator if it is trying to do exactly as i mentioned before ,, just an idea ,run it past the guy that checked the alts for ya
I've reworked the system and the winch is no longer connected to the starting battery which is fed by the stock alternator. In the last couple of weeks I've swapped a 130 amp alternator in place of the smog pump and installed a second deep cycle battery. Winch is now connected to this second independent setup.

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