Alternator problem possibly?

Kinda beating a dead horse. I posted a few comments on the technical side about alternator testing. Long story short....I bought the stage 3 upgrade kit from bamatoy97 a few years ago. I upgraded to the 130 amp alternator. Since day one of the install my voltage would drop from about 13.9 to 12.8 when i turn on the headlights and the car is in drive with my foot on the brake...(such as at a redlight) When I take off it goes back up. The other morning I started the truck and my battery light came on and the alternator was putting out 12.1 volts. I checked it with a volt meter at the alternator itslelf. I left it and rode my damn bicycle to work. Came back home and it cranked up fine and back up to 14.1 volts. I did hours of testing from videos off of youtube about voltage drop. Everything/grounds and such look good. I even replaced the battery cable ends for the hell of it. I have a 3 month old AGM battery and it load tests fine. In even put it on the battery tender for the night. Tonight when i get off of work I am going to take the alternator off and put the stock on back on. I found a company local that can rebuild it if needed. I havent had a problem since the other day however with my headlights on my voltage still goes to 12.8-13.1 when in park sitting still. Just wondering if there is some sort of short related to headlights and being in drive and low RPMS? I dunno what the hell else to test. I just have to make a 4 hour trip Saturday and don't wanna get stranded. I even sent a few messages to Timmah! and he gave me some suggestions. Just wondered if anyone else has any ideas....

 

making an assumption here... stock headlights - sealed beam... about 7 amps per bulb. I do not know the specs on that alternator meaning how many amps and at what rpm.

 

A common problem is for some of the diodes in the rectifier to fail, then you will only get partial power, especially at idle. That's if the diodes fail open. If a diode fails closed the voltage will drop more. This just happened on my other car.

You can put your multimeter on AC voltage and get some indication of if some diodes are bad. Bad diodes will cause a fluctuating voltage which the multimeter will pick up as AC voltage. Or you can get it tested at an autoparts store.

The best way to test is to actually disassemble the alternator, take the rectifier out and test each diode with the diode test on the multimeter.

On the other hand, depending on the configuration of the alternator, it may be designed to put out high current at higher RPMs only. I mean there's a trade off depending on how the stator winding is configured. Some will maintain higher voltage and current at low RPM at the expense of less current at higher RPM (compared to other alternators).

 

Fwiw a lot of alt upgrades are actually downgrades at idle or low rpm, especially if they are rewinds. You have to spin them up to make them work. A factpry swap will usually do better at low rpm.

 

Hey Mike, since you started this thread, I figured I'd supply a link to the video you already know exists but maybe others on this forum don't yet. It really does sound like you might have a diode problem as @DrZ said above since you have an inconsistent voltage output.

Here's a good write-up for alternator repair on T4R.org: In my video, we show how to pull the alternator and replace the brushes. Worn down brushes are a common cause for an alternator to put out low voltage. It takes a while for these brushes to wear down. If you're near the 200,000 miles range and you're alternator isn't putting out somewhere around 13.8 -14.2 volts, a new set of brushes might be all you need.

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I see the part number for the brush. How do I find it for the rectifier ir diode?. I saw some message that it was 130 dollars....hell I will buy a new one for that off of eBay with a 1 year warranty.

 

The part number for the rectifier or diode weren't listed in our video or the write-up I provided a link to. You can either contact an online Toyota parts seller like Camelback Toyota or your local dealer for the part numbers.

Sure, you can find a rebuilt aftermarket alternator online for pretty cheap but they are probably not going to be the same quality as the OEM Denso alternator on your rig. If it was cost effective, I'd rather fix my OEM Denso alternator than roll the dice on a rebuilt aftermarket one. How many times have you heard auto parts stores starters, alternators and other replacement parts die an early death? Sure, it might have a lifetime warranty but they don't compensate you for your time and inconvenience to replace the part again. Something to think about.

 

Slight hijack! What is the best way to tell if the belt is chirping at startup, or the if the noise is coming from the pulley shaft bearing? The noise goes away in a few seconds...

 

I put an aftermarket rectifier (labeled Transpo, ~$50) in my other car and 3 diodes were blown after 30,000 miles. Now, I would only trust a Denso rebuild, and I'd go with that over replacing just the rectifier if the rectifier is that expensive.

If the voltage was low from day one on the upgraded alternator, then it's probably by design (at low rpm).

What ever you do, I would suggest getting one of those USB chargers with voltage reading that fit in the cigarette lighter. This way you can keep an eye on your voltage.

 

I have a scanguage and always keep a fluke meter in the truck. I wonder if I can put my stock alternator diodes and rectifier in the 130 another one or not?