Puzzling alternator issue

[3p141592654]

This morning was cold for So Cal (4C) and the Supra had been sitting all weekend in the rain and wind.

I started the car normally except that I happened to have the datalogger hooked up because I had added some new code I wrote over the weekend that I wanted to test. After a normal start, I looked down and was surprised to see the logged battery voltage of 11.5V. I checked the dash but no idiot lights were on, everything seemed normal, except the wipers which were real sluggish.

Not really believing the datalog, I went inside and grabbed my DVM and plunked the probes on the battery posts, sure enough 11.5V! Then, as I stood there with the probes on the battery I heard the tone of the alternator change and the voltage jumped up to normal 14.2V. Weird, I drove to work and the battery voltage was normal the whole time.

In the evening I datalogged again, but after starting the battery voltage jumped up to 14 and stayed there for the whole drive.

The alternator is the original, so I'm not really too stunned its acting up, but the way it stopped and then started seemed very strange, and with no idiot lights either. I've got some new brushes so I'll put them in and see if the old ones are worn out.

Here's the two datalogs. The first is the morning with 3 minnutes of no charging (yellow trace on plot). The second is the drive home, nothing weird about it at all.

 

[IJ.]

Mine did that after running out of brushes...

 

[jetjock]

Does sound like brushes. Good thing they're easy to change. Better do it before the slip rings get torn up.

Brings back memories. My car left me with it's original alternator. I replaced the brushes and bearings just once.

 

[Nick M]

Not really believing the datalog, I went inside and grabbed my DVM and plunked the probes on the battery posts, sure enough 11.5V! Then, as I stood there with the probes on the battery I heard the tone of the alternator change and the voltage jumped up to normal 14.2V. Weird, I drove to work and the battery voltage was normal the whole time.

And your alternator is how old? Mine is so old, the ND sticker is hard to read. Mine did something like that last summer. The B+ stud is on the rectifier as you know, so I ordered a new one, brushes, and regulator and did a "rebuild". Then my intermittent charging problem went away. The stud was broke but I didn't notice it right away. It had some corrosion on it, but I just didn't get around to dealing with it until it wouldn't charge.

 

[IJ.]

Work out the ratio, mine died after a few months of 8300 at the crank
(was my original 86.5 NA one so no surprise)

 

[3p141592654]

Thanks everyone. I thought this was going to be some intermittent nightmare, but sounds like it is a common symptom. It will stay parked until I get the new brushes installed.

 

[onemancrew]

Can brushes be worn out even if they don't look worn?

i got similiar problem except the alternator keeps whining as well.... pulled it out and it all seems to be fine! brushes are good. expensive thick earth cables attached to block and everything. It still seems to be charging battery fine, but i can hear it load up when extra accessories are on, say heater and headlights it whines like crazy! Supercharger style.

Its doing my head in!!

 

[jetjock]

Could be a bad diode. Check for ripple by setting the meter to AC millivolts.

 

[3p141592654]

And your alternator is how old? Mine is so old, the ND sticker is hard to read. ......

22 years old! Damn, I thought it was going to last forever like the light bulbs on this car. With a few exceptions, every light bulb on the car is original!

 

[onemancrew]

Could be a bad diode. Check for ripple by setting the meter to AC millivolts.

Thats what ive been told, the thing is though, The trouble is, i don't even know what the diode looks like, like I said before, i pulled it apart and there isn't that much in there..lol Has anyone got a pic of a diode??

, im usually pretty good with mechanical things, but once i get to electrics i kinda get confused, i don't own a digital multimeter, only an oldschool analog one.

Is there any way to check millivolts with an Analog Multimeter?

 

[Nick M]

22 years old! Damn, I thought it was going to last forever like the light bulbs on this car. With a few exceptions, every light bulb on the car is original!

So now the low bid crowd can see why the OEM alternator is $600 USD, and not $19.95 like at Autozone.

 

[jetjock]

oneman: if you possess neither the tools or knowledge it'd be simpler to install a new alternator.

Jon: it may not be brushes. Could be a bad field connection at the slip ring or a loose stator connection. If it were me I'd tear it down. You'll need a rattle gun for the sheave nut.

Other than heads and fogs all my bulbs were also original. I always thought that was strange but guess not.

 

[3p141592654]

Gary, it's on the bench now. Thanks for the pointers. I'll give it a thorough going over.

 

[3p141592654]

The brushes were pretty near gone. More worrying, the brushes were riding in deep grooves. Is this normal, or are my slip rings fubar? Other than that, it seems to be okay, unless there is a temperature sensitive issue that I can't see.

 

[onemancrew]

:ugh: Thats what my slip rings looked like when i pulled mine apart,,, i thought they were ok since they still had a copper colour to them, I hope i was right. lol it still charges fine but still seems to have a definite slight whine still. :wtc:

 

[Dan_Gyoba]

That's what the rings looked like on my alternator when I replaced the brushes... 220,000 km ago.

 

[3p141592654]

Toyota allows 1.6mm of wear down to 12.8mm dia, and mine were at 13.6mm, but even in spec it still looks scary.

 

[Nick M]

I see corrosion on that rectifier stud.

 

[jetjock]

Those are worn but should be OK. At least you got to them before the brush springs did. Polish 'em lightly, bed the brushes in (or not), and it should be good to go. Blow out what the old brushes used to be or pull it apart and do it. That way you can tighten up/eyeball everything and change the front bearing. It's a standard #6204 or a Koyo 333. Same difference.