Question for the Electrical Gurus.

[mirose]

So I have been tweaking my windshield wipers so they will work without a hitch at my inspection in a few weeks. So in order to test them, I had the key in the ignition in the ACC position. And for about an hour I occasionally tested the wipers. After I was done, I forgot to take the key out of the ACC position and spent another two hours doing other things on the car. As I was cleaning up I realized the key had been in the ACC position and I turned it off. I have a trickle charger and I figured I would charge up the battery since it had been drawing for a few hours. My forearm brushed up against the Alternator while hooking up the charger, and the alternator case was VERY warm.

So my question is this: Even though the car was off, is there any reason that the alternator should have gotten warm just from having the key in the ACC position??? (and no, I haven't driven the car in 24 hours, so its not just warm from a recent drive). I just find it weird, but maybe the electrical gurus can explain why its not a big deal. Thanks - Michael

[josrodes]

I noticed that my battery would drain if I left the master cutoff on, i have a ron francis harness, after some testing, I narrowed it down to the alternator, after doing some research it seems to be an indication of a bad alternator, I haven't change mine, it seems to work fine otherwise, I haven't notice if mine gets hot when the cutoff is on but could be given the readings I got.

To eliminate alternator I measured amp on the circuit with/without alternator.

[steve_mk4]

I have not looked at schematics of that circuit in years (I assume you have an alternator with an internal regulator) but I beleive the regulator is in the circuit when the ignition/acc is on so having it get warm after being on for a while would be expected.

[Thumper135]

I notice the one on my 70 Chevy truck will do that. If I have the key on for some time, the alternator will get worm, I couldn’t find anyone that could explain it any better than Steve did, and it really hasn’t given me any trouble over the last ten years. This will be a good one if anyone here can give us a “scientific” answer to this one. Personally, I stopped worrying about mine after about a month, and haven’t given it any thought since. It still works…….
Yea, I know, I said that Chevy word. The truck came with the wife.......and it's pretty cool in itself.

[steve_mk4]

OK, here is a simplified scientific explanation. The regulator in a car does 2 things. One is convert AC to DC which in the case of the engine not running is out of the picture. FWIW, it does this using 4 diodes in a bridge rectifier configuration.

The other task is to regulate the voltage from the alternator to an acceptable level to charge the battery and run accessories (typically 13.7 to 14.5 volts). When the car is off and the ignition is on, the battery voltage is only around 12.7 volts (or lower) so the regulator senses this and is turning on some circuits (i.e. transistors) in the regulator to try to increase the voltage coming from the alternator to charge the battery. When a transistor is on, it is dissipating heat and that is why it gets warm.

HTH,
Steve

[edwardb]

Was going to say the same thing as the others -- this is the regulator in the alternator that is getting warm. They have to dissipate heat -- as described -- that's why there are cooling vents and a small fan on the belt drive. I'm not 100% clear why it's on when in the ACC position, but if others say this is normal I believe them. I have a RF harness in mine and I don't recall exactly how ACC was wired. Doesn't matter in my case though. No accessories. But whether the alternator is getting too hot, e.g. defective or shorted, might still be a question. If it's working OK, e.g. showing the right charging voltages on the gauge, charging your battery OK, probably not an issue. Easy enough to get checked at one of the big parts places, e.g. Autozone, Advance, etc. if in doubt.

[rich grsc]

Here is a simple test, turn the ignition to ACC on your daily driver, check it in about 3-4 hrs.

[mirose]

Great explainations. I appreciate it. I am sure that is all it was then.

Michael

[Bob Taylor]

not all of them this might be dumb and probably is butt.... my cutoff switch passed away this year and was stuck on. Also if you have a "live wire fused jumper" for memories or radios that may be enough ? ayone check the voltage at the fat alt wire while this was happening .Call me Shultz on this one " I know nothink" Bob

[Cheapsnake]

Your alternator depends on an "exciter" voltage to get it charging and that should be fed from the "on" position of your ignition switch. With the swith in the "acc" position your alternator shouldn't see anything.

[mirose]

Originally Posted by Bob Taylor

not all of them this might be dumb and probably is butt.... my cutoff switch passed away this year and was stuck on. Also if you have a "live wire fused jumper" for memories or radios that may be enough ? ayone check the voltage at the fat alt wire while this was happening .Call me Shultz on this one " I know nothink" Bob

Bob, Im thinking you might have had a few too many before posting this reply...I didn't know a cutoff switch could "pass away". but maybe you can explain. I get your point though, this might not be a totally benign issue...but it makes some sense that the electricity is "conditioned" through the alternator and that creates the heat. Everything is working fine in the car, but I am going to keep my radar up until I feel sure that its supposed to get warm in the ACC position.

Originally Posted by Cheapsnake

Your alternator depends on an "exciter" voltage to get it charging and that should be fed from the "on" position of your ignition switch. With the swith in the "acc" position your alternator shouldn't see anything.

I hear what you are saying....do you have any idea what the other posters are referring to regarding the alternator "conditioning" the electricity even when the car is off?

I am going to look at the wiring diagrams again and see if I can figure out if the alternator gets any juice in the ACC position the way I set it up.

Thanks for the input. I am going to keep on this until I know for sure whats up

-Michael

[mirose]

Ok, here is a page of the R.F. harness manual...in the second bullet not in picture #1 below it says "If you are using an EFI Harness with the Chassis Harness, hooking up the Alternator Ignition power is not necessary"...Well I have EFI

And if you look at the second picture...its the portion of the diagram showing the alternator ignition power wire goes from the ACC to the Alternator....so that must be the wire that is sending power to the alternator...and the manual says its not necessary. That being said, I did also follow this schematic (picture #3) from Mark at Breeze after I bought the alternator from him...it does show something being hooked up to the brown alternator ign wire (see handwriting at top right of third picture) So maybe Mark can give me some info about why his schematic says to hook it up.

I am a bit hesitant to remove that wire now as my inspection is coming up in 2 weeks and everything is working just fine and I don't usually keep the car in ACC mode much, if at all. However, after inspection I am going to remove that wire as a test and see what happens.

[Cheapsnake]

I think the reference to "conditioning" is the conversion from AC to DC.

Your diagram does indeed show a feed from "acc" to the alternator, but I can't fathom the logic. It may be that the acc position is hot whenever the key is in the on position, which would then provide the exciter voltage. If this is the case and it poses a problem, a simple solution is to move that brn line to the on position of your switch. That way you can have your accessories on all day and it'll never touch your alternator.

Tom

[steve_mk4]

You have it wired correctly from what I can see. I'll be honest and agree I don't know why the battery is connected to the regulator when in the acc. position. I could understand in the "on" position. The three connections on the regulator (A, S, I) are:
A - Connect to alternator battery cable terminal
S - Connect to alternator stator terminal
I - Connect to key switch acc.

Your schematics show it connected correctly so I would not worry about it.