Alternator charging rate

[grannyknot]

I checked my alternator while the engine was running and it's putting out 16.8 v at the alternator and the battery, that's way to high isn't it?

Thanks,

Chris

[grannyknot]

Maybe I have the sense wire mixed up and the alt thinks the battery is flat. I hate electricals.

[grannyknot]

Even with sense and field wire disconnected the alt is still putting out 16.8v

Blown regulator?

[Captain Obvious]

Yeah, I think 16.8 is too high.

Is this something that just started, or has it always been like that? Also, is this an internal or external regulator?

[grannyknot]

The alternator is a 3 wire GM unit, 140amp, internally regulated. Not sure how long it's being doing this, I had it rebuilt 4 yrs ago and tested it after I installed it and it was fine then. The ammeter  reads dead center of the gauge most of the time and the needle only moves to the + side a bit when when I turn something on like the the blower or headlights. I only checked it yesterday because I'm trying to figure out a tach problem.

I have Zsonthebrain's diode fix installed,(the white cap from MSA) also Dave's recommended 8ga wire from the positive output on the alt. to the starter, the unit is well grounded with a dedicated grounding wire.   All I can think to do is pull it and take it to a rebuild shop to be tested.

[Captain Obvious]

I've not messed with the GM three wire upgrade, but I thought it was pretty bulletproof.

 

I thought that the sense wire needed to be connected though.. If it's disconnected, the alternator will try to put out more voltage to increase the sense feedback?

What happens if you run a jumper wire directly from the sense to alternator output lug? Does the voltage stay at 16.8 or does it drop down to a more reasonable level?

[Zed Head]

I would measure voltage at the alternator plug with the key On.  Both should show battery voltage.  You don't even need to know which is which.  Unless one has no voltage.  

Could be that your alternator has had the L circuit shorted at the B post, to eliminate the need for one wire.  That would explain why it still charges.  Could also be that your three-wire is actually a one-wire.

I think that ammeter only shows charge and discharge from the electrical system.  No indication of voltage at all.  Probably why everyone switched to voltmeters and a charge light.

Edited March 29, 2016 by Zed Head
added alternator, changed three to two.

[grannyknot]

Thanks gents, I'll give that try when I get the car back in 2 weeks, having some paint chips and panel alignment done.

Chris

[Captain Obvious]

Good luck and let us know what you find. Don't run it too long at that high of a voltage. I'm no battery expert, but I believe you can damage them if you run too high for too long.

[Zed Head]

Yes you can.  They overheat and boil fluid out with unregulated voltage (that's a good sign of a bad regulator).  Then, if you have a 1974 Dodge Dart Sport, the electronic ignition module will die like somebody shot it, after you replace the external regulator, as you're heading in to town.  If you're lucky a local mechanic will be standing in his yard and come over to tell you what happened after you describe the recent problems.

 

 

[rossiz]

74 dart was my first car that i never drove - my grandfather gave it to me 6 mo. before my 16th birthday and my brother took it to college since i couldn't drive it. i had fancy wheels and a cool paint job all picked out for it (rattle can of course) but unfortunately the car never came home...

threadjack over ;}

[Captain Obvious]

Zed, Haha!! Nice story. Not that something like that happened to anyone here, right? 

I think maybe the first car I ever drove was a 72 or 74 Dart or Valiant. Don't remember. Those were the family cars.

Don't think my Dad ever found out...