Overcharging/overvoltage

Overcharging/overvoltage

Postby Bannisterr on Sun, 23 May 2021 4:57 +0000

Hey lads and gals,

Was curious if anyone has dealt with a similar issue as the search function didn't give me much to go off.

My 2005 kun26r seems to be overcharging. It is causing my battery light to turn on intermittently and my subwoofer is unable to handle the amount of current with the engine running and automatically switches off.

Have replaced with a new alternator with no change.

Voltages:
Car off and 20 mins cool down battery voltage:12.9v
Car on battery voltage: 15.5-16.0v
Alternator- 16.0-16.6v

Any info would be great, cheers lads
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Re: Overcharging/overvoltage

Postby flyingdoctor on Sun, 23 May 2021 6:50 +0000

oops... 16.6V

Are you sure that the new alternator is working correctly?

I would not drive any further for I was concerned about all those electronic control units...

You have any error codes in the OBDII?

Tim
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Re: Overcharging/overvoltage

Postby Bannisterr on Sun, 23 May 2021 7:21 +0000

Hey Tim, thanks for the reply.

There's always the chance I got another dud alternator when I replaced it, I will continue testing it tomorrow to confirm or deny this.

I have been getting a battery light and airbag light intermittently which are definitely to do with the over charging. Sadly I'm lending my techstream to a friend at the moment so I'm unable to read the codes.

Could a faulty battery be causing such a spike in voltage or is it more likely to be another faulty alternator.

Cheers mate
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Re: Overcharging/overvoltage

Postby Rob_Wood on Mon, 24 May 2021 2:39 +0000

Moreover likely to be the regulator/ rectifier ... Usually mounted inside or on the back of the alternator.. If the replacement alternator is second hand, then maybe consider putting in an RE55 ONLY TO USE AS A TEST. Once the test is complete, then consider what step you might take for a more permanent solution.
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Re: Overcharging/overvoltage

Postby martynvella on Mon, 24 May 2021 6:44 +0000

You would need considerable knowledge, experience and tooling to substitute a RE55 or any other non genuine reg, not really a logical test step. RE55s are designed for positive regulation and denso alternators are negative regulated.
It would take a totally open cct battery to make any such difference so would not be capable of starting the engine.
Check the alt fuse under the bonnet is intact as this is the voltage sensing circuit the regulator references to, many have had a diode fitted there to lift the regulating voltage and fatigue and crack solder joins, replace the fuse completely and see how you go.
Hiluxs also have a problem of the wiring harness carrying this wire rubs through under the front of the engine, have seen this 3 times so worth a look.
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Re: Overcharging/overvoltage

Postby Bannisterr on Mon, 24 May 2021 8:05 +0000

Thanks lads,

I'll have a look today and report back with what I find :)
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Re: Overcharging/overvoltage

Postby Bannisterr on Mon, 24 May 2021 3:23 +0000

Afternoon everyone,

After having a look, my 100amp ALT fuse has blown. :(

Any ideas on where I can source a new one? I'm assuming only toyota make them :)
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Re: Overcharging/overvoltage

Postby Rob_Wood on Mon, 24 May 2021 6:13 +0000

SuperCheap Auto or Auto-One or other after market suppliers probably have them. Fuses can be a fairly generic item to access, but for crying out loud make sure you get the correctly rated replacement. Over-rating a fuse will almost certainly cost you some big bikkys. Especially if you haven't found out why the first fuse blew.
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Re: Overcharging/overvoltage

Postby Bannisterr on Mon, 24 May 2021 6:59 +0000

Totally agree with finding the correct fuse rating. I ended up running to my local Toyota dealership and bought a new fusible link.

Just installed the new one with no change, still reading 16v at the battery. I have tested it with 2 meters to rule out faulty equipment and also tested it with another battery. Same issue.

It's currently pissing down in Perth so it's a little hard to work on it, but tomorrow I'll be looking for any shorts like mentioned above.

Besides a faulty voltage regulator, are there any other things that could cause this? I'd like to rule out everything else before buying another expensive alternator :mrgreen:
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Re: Overcharging/overvoltage

Postby martynvella on Mon, 24 May 2021 7:12 +0000

Before you throw another expensive alternator at it take the car, or just the alternator to an auto elec and have it tested.
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Re: Overcharging/overvoltage

Postby martynvella on Mon, 24 May 2021 7:15 +0000

By the way, the alt fuse I was refering to earlier it only a 7.5 amp from memory not the main 100 amp fuse.
It is one of the small ones in tbe under bonet fuse box.
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Re: Overcharging/overvoltage

Postby Rob_Wood on Mon, 24 May 2021 7:22 +0000

Another quick question ... The new fuse, has it remained in tact? Don't just look at it, use the multimeter to properly test it OUT of the car.

What circuit is the smaller fuse for?
Is it blowing when you replace it?
Maybe consider waiting until the rain stops? Tracking water can cause more problems with the bonnet open while you're working.
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Re: Overcharging/overvoltage

Postby Bannisterr on Mon, 24 May 2021 7:46 +0000

I checked the 7.5 amp also but it was okay. I will double check that tomorrow though just incase. I think taking the alt to an auto sparky would be a good idea, ill add that to the list of things to do.

Prior to installing the new fuse linkage, I did a small solder job on the blown one just to make sure I wasn't about to waste a brand new 60 dollar fuse. Didn't blow so I chucked in the new one. It seemed fine visually but I will check it with a multimeter tomorrow.

Just to be clear, the only blown fuse I've found so far is the 100 amp alternator fuse.

Fingers crossed the rain calms down tomorrow so I can knuckle down on the issue. Cheers lads
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Re: Overcharging/overvoltage

Postby martynvella on Tue, 25 May 2021 6:14 +0000

Doesnt sound right to me. If the 100 amp fuse is blown many things stop working correctly and you would definatly not get 16 volts at the battery. My guess there would be it has been bypassed hopefully with another fuse.
My advice at this stage would be to disconnect the 4 pin plug from the rear of the alternator then drive the car directly to your auto sparky. Acting on advice from a forum in this case you run the risk of doing a lot more damage than you already have. I have been working as a qualified auto electrician since the 80ies and without the car in my posession I am not comfortable giving further advice, the balance of possible damage and your understanding of what I say and your lack of confidence in electrical diagnostics is far from a good ratio.
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Re: Overcharging/overvoltage

Postby 241steve on Tue, 25 May 2021 6:36 +0000

Rob_Wood wrote:Moreover likely to be the regulator/ rectifier ... Usually mounted inside or on the back of the alternator.. If the replacement alternator is second hand, then maybe consider putting in an RE55 ONLY TO USE AS A TEST. Once the test is complete, then consider what step you might take for a more permanent solution.


If its blowing the 100 amp fuse time for a new alternator would be the easyest fix, unless something happened like forgot to disconnect the battery and sorted the body but id assume that would near weld the lug to the body.

MOD note: edited to keep the discussion civil.
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Re: Overcharging/overvoltage

Postby Bannisterr on Tue, 25 May 2021 12:21 +0000

Hey Marty, I agree and chances are ill be taking it to an auto sparky tomorrow if I can't find any obvious causes today. Vehicle won't be driven until it is fixed.

There's a good chance the 100Amp fuse was blown a while back as the car wasnt on the road for a good 6 months due to medical issues and during that time alot of stuff was done to the car. From suspension to new injectors (professionally done). Wouldn't surprise me if at some point the battery shorted on the body.

After a bit of messing around today I found something interesting. Starting the car initially, it had a cool 13.5-14.0v at the battery. After about 1 minute of run time it spiked again up to 17v. I inspected the Alt-S fuse and found that when temporarily removed, it dropped the voltage back to normal. I definitely won't leave it out, but figured it might give some insight on the cause.

Note the 100amp fuse is still fine - tested visually and with a meter
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Re: Overcharging/overvoltage

Postby Bannisterr on Tue, 25 May 2021 12:59 +0000

Going to test the resistance on the sense wire, given that when removing the alt-s fuse it drops back down to normal. It may be possible that the alternator is compensating for that difference?
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Re: Overcharging/overvoltage

Postby Bannisterr on Tue, 25 May 2021 2:34 +0000

Hey guys just an update,

Sense wire only has a drop of about 0.5v so I guess that's not the issue.

Still a little confused as to why the issue disappears after removing the ALT-S fuse though. Chances are ill be taking it to an auto sparky tomorrow.

Any other ideas would be appreciated as I'm a broke ass student so taking it somewhere is the last resort :mrgreen:

Cheers lads
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Re: Overcharging/overvoltage

Postby martynvella on Tue, 25 May 2021 3:02 +0000

Is the alt s fuse live with ign on? It should be at B+ potential but could be through a relay, if it is grounded before the fuse it could cause such a fault.
Without looking at the car it is only guessing and that could cost you a whole lot more than you think.
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Re: Overcharging/overvoltage

Postby Bannisterr on Tue, 25 May 2021 3:43 +0000

Will check if alt s is live with ign on after work,

My auto sparky mate recommended I try temporarily bypass the wiring loom and connect the white sense wire behind the alternator straight to the positive battery terminal (added a 7.5amp fuse inline just as a precaution). This corrected the over charging issue and made the alternator output the correct amount.

Seems like im on the right track, will have my techstream back this week so that might help a bit.
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