Can a bad alternator wipe out a voltage regulator? (1 Viewer)

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I got a BJ44 recently and I absolutely love it! The batteries stopped charging after a while though.

I read some very helpful posts from @bj40green and I'm pretty sure my voltage regulator is bad. It's very discolored, and only putting out half a volt on the white/green wire described in this post: BJ42 - Electrical system woes (24v) - https://forum.ih8mud.com/threads/bj42-electrical-system-woes-24v.825227/#post-9470166

Anyways, the reason I have this question: the alternator was rebuilt near the end of 2019. It still looks very clean and new. If they did the rebuild wrong, could that take out the voltage regulator? I believe in checking what was recently changed when problems come up so... I'd hate to spend the money on a replacement all to blow it up again.

There are 3 wires on a plug going into the alternator, measuring from the alternator side of the plug to ground had one connection at 0 ohms (which looks fine according to the wiring diagram), another at a lowish ~3.5 ohms, and another at a much higher ohm reading that I probably don't need to worry about. It was really hard to see what color the wires are. If the voltage regulator was feeding 24 volts to that 3.5 ohm connection, there would be over 6 amps drawn, which seems high to me, but I don't really know what I'm talking about at this point.
 
What do you have between the two brushes, field and ground on alternator?
24v ext volt reg
Should have about 20 ohm
 
Hi iliketrucks,

You can bypass the regulator by putting wires into the block conector and straight to the alternator for a few seconds to test the alternator.

The 3 pin regulators are hard to find for a 24v.

I had the exact same problem and it was the rotor in the alternator, a shop rebulit It, and it still didn't work.

Also check your 30 / 30 amp meter on your instrument cluster ( pre 1980 ), the power runs through this, so if the guage is damaged you wont have charge, just a long shot. You can put a nut and bolt through each conector to join them together to test. ( Disconnect your batteries before you remove the instrument cluster! )

If yours is post '80 disregard this.

Keep looking on mud, most of this information I learned from members here at the time.


ToyotaDyna

-----

Looking for a LHD, Diesel Landcruiser?
Canarian Land Cruiser Exports • DIESEL • LHD
 
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I haven't had time to get back to it yet, but I appreciate the responses and I'll check in again hopefully this weekend
 
What do you have between the two brushes, field and ground on alternator?
24v ext volt reg
Should have about 20 ohm
Capture.JPG

Well I couldn't stop thinking about it so I made some time... This is the test for the field windings right? (taken from the 2B manual). I measured about 5.5 ohms, and this is a 24 volt rig... Am I on to something?

Besides the simple fact that my voltage regulator is only putting out half a volt on the white/green wire, I noticed that it looks like it got pretty hot inside at one point, which made me think hey maybe something it's feeding (the alternator) is drawing too much power. It's worth looking into things when a voltage regulator made it 40 years but then fails maybe a few thousand kilometers after a rebuilt alternator.
 
Hi iliketrucks,

You can bypass the regulator by putting wires into the block conector and straight to the alternator for a few seconds to test the alternator.

The 3 pin regulators are hard to find for a 24v.

I had the exact same problem and it was the rotor in the alternator, a shop rebulit It, and it still didn't work.

Also check your 30 / 30 amp meter on your instrument cluster ( pre 1980 ), the power runs through this, so if the guage is damaged you wont have charge, just a long shot. You can put a nut and bolt through each conector to join them together to test. ( Disconnect your batteries before you remove the instrument cluster! )

If yours is post '80 disregard this.

Keep looking on mud, most of this information I learned from members here at the time.


ToyotaDyna

-----

Looking for a LHD, Diesel Landcruiser?
Canarian LandCruiser Exports • LHD • Diesel
That sounds like a good test! I didn't think of that idea, and I might have to give it a try soon depending on what else I find out. And it's an '81.
 
View attachment 2679885
Well I couldn't stop thinking about it so I made some time... This is the test for the field windings right? (taken from the 2B manual). I measured about 5.5 ohms, and this is a 24 volt rig... Am I on to something?

Besides the simple fact that my voltage regulator is only putting out half a volt on the white/green wire, I noticed that it looks like it got pretty hot inside at one point, which made me think hey maybe something it's feeding (the alternator) is drawing too much power. It's worth looking into things when a voltage regulator made it 40 years but then fails maybe a few thousand kilometers after a rebuilt alternator.
5.5 ohm does not sound right.
Yes it is the rotor winding and 19 ohm is the 24v impedance spec.
My old one (open wire now) had and my new from Yourex are 19 ohm.
Field and earth wire are for the rotor (brush), the third one is the N neutral for the light.

Can you remove the brush holder and measure the rotor impedance on the slip rings. 5.5 ohm sound like a bad contact?

Edit: you have an old manual when there was no 24v internal voltage reg. Those rotor have a different impedance (I think 10 ohm) I did try one in my ext volt reg alt and worked. I since bought an aftermarket one (Youex) installed it but the 3b is all in part...
 
Can you remove the brush holder and measure the rotor impedance on the slip rings. 5.5 ohm sound like a bad contact?

Edit: you have an old manual when there was no 24v internal voltage reg. Those rotor have a different impedance (I think 10 ohm) I did try one in my ext volt reg alt and worked. I since bought an aftermarket one (Youex) installed it but the 3b is all in part...
Are you saying to pull the brushes and measure directly from slip ring to ground? I haven't pulled brushes on one before, I'm assuming it's pretty straight forward?

Also it has the voltage regulator on the firewall if that matters
 
Similar to my bj75, if you can remove the brush holder it would tell you the direct impedance between the two slip rings. Brush come out with the holder, no need to take them apart.
Also it will give you a chance to see the condition of brush ( lenght and weld) and rings, dust.
identify each isolator washer in order to reinstall these the way it was (check FSM in case they were in wrong order...)
My alternator was working fine with a 20 ohm rotor and a 10 ohm rotor (from 24v int volt reg).
There is some test you can do on the regulator. Sometime test fails just because contacts are corroded...Before doing adjustment, clean contact a bit with crocus kind paper.
You can connect ground to ground and feed positive to field, with 24v you will have full charge. Can't run like that forever (batteries).
I imagine you can install thick paper between contact (reg relay) so it will stay in trickle charge through the regulator resistor (should provide half ishh voltage to field).

As long as rotor is fine (19 ohm), brush are fine. Regulator pass test, fuse holder clean and not corroded...
 
2.9 ohms from one slip ring to the other, no good?
Slip rings to ground were fine though (open lead/infinite)
I can try testing the regulator and also feeding positive directly to field soon
I really appreciate your help so far, I'm learning a lot, and I want to get driving this thing more!
 
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Hi,
Well not sure, if there is 2.9 ohm between slip rings, I wouldn't feed field directly with 24v.

The winding on rotor create a magnetic field which cross the stator windings. Looks like your rotor lost some isolation and winding contact??

I imagine there is around 1.2 amp going to the rotor when impedance is 19 ohm.
With 2.9 ohm at 24v it could be 8 amp
I'm afraid it will create more heat than field?

Does it have overheat history or jammed because of a front bearing failure?
 
I imagine there is around 1.2 amp going to the rotor when impedance is 19 ohm.
With 2.9 ohm at 24v it could be 8 amp
That's kinda what I was thinking caused the voltage regulator to fry, low field winding resistance pulling too much current from it, though I'm not an expert.

I don't have too many details on the alternators history, I know it was rebuilt by a shop in 2019 based on a receipt the previous owner included. On that invoice it just said the batteries were dead and the alternator wasn't producing voltage so the shop sent it to another shop for a rebuild.

My friends dad owns a local rebuild shop, maybe I'll talk to him and see of the rotor can be rewound to the right specs. From looking around online it doesn't seem like a super common practice but possible.
 
If there is no visual damage on the rotor's coil winding, no sign of overheat.
Could it be a 12v rotor? I know sounds weird but I have this B series manual 1980 and resistance between both slip rings 12v type 2.8 - 3.0 ohm. Coincidence?
Seem to have fine spline at vac pump.
 
I started thinking that was the case, especially since it was pretty much right at the 12 V alternator specs, but then I went out the other day and it measured 18 ohms! Just checked it again tonight since we're talking about it and reading low again at 4.0 ohms. So I'm speculating there's something going on with the insulation on the windings maybe and it's changing with vibration/temperature?

I've had no luck finding a used alternator, there is a shop locally that says if there's a rotor winding issue they send it to a place in Washington and it takes a long time to come back. It seems like I can buy a new one from Japan for about a grand... (any experience with amayama or nengun? Edit: heavily considering japan4x4) None of the options stand out to me, it all kinda sucks haha. Luckily it doesn't suck much power and it's a weekender, so currently I just drive it a little bit and then charge the batteries at home, but it's sure inconvenient.
 
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I did find an alternator, and though I've only used it for the day, it works so far. This one measured 18 ohms for the rotor, that's more like it! Time will tell if it's as good as OEM. Perhaps we have an option out there for the older 24 volt B engines now? My alternator was part number 27030-56120, this one is Eurostarter.de part 1240607AM


I did have to grind down the circled feature in the attached photo. The original alternator has the same thing, but it's mirrored on the opposite side, so it wasn't in the way. Also worth noting is the smaller oil banjo bolt is mirrored on the opposite side, but that was not an issue for me. It's a pretty direct replacement. Just cover all the holes when you grind the aluminum!

I'm going to send the old OEM alternator out to a place that can rewind the rotor, but the turn around time will be long. I bought this alternator because I didn't want to have the cruiser down for weeks if not months. After all, it's summer time and I haven't even been able to drive it much yet! When I get the original back from repairs I'll keep it as a spare.

temp.jpg


temp2.jpg
 

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