The Stovebolt Site Forums The Shop Area The Electrical Bay Not charging?

Firstly: 12v system, new battery, new alternator, new complete wiring harness.

Anyway, I took my truck out for a long drive today. I noticed on the voltage gauge, the whole time I was driving it was reading about 11.5 volts. The battery is brand new, and I checked the voltage before I left this morning, about 12.7.

I thought that when you're driving, the alternator is charging the battery and it should read over 13 volts when driving. Mine was around 11.5

As an experiment, when I was about 10 miles from home, I turned on the electric fan, headlights and heater. By the time I pulled into the driveway, it was down to 10 volts.

So, my guess is that the battery is not charging when I'm driving, and that when I'm running my accessories they're running off the battery and not the alternator? The alternator and battery are brand new. It's a 3 wire, externally regulated alternator. I don't know the age of the regulator.

So what do you think? It's my understanding that the accessories don't actually run off the battery, but rather the alternator is supplying the voltage. The battery is just for supplying the initial juice to start it up.

So after a long drive and running a few accessories, a battery started the day with a reading of 12.7 volts, and now is around 10 volts.

Could I have hooked up the alternator incorrectly?

Note: I just went out to the garage to check the voltage on the battery after the truck has been sitting for about an hour, and it was 12.3 volts. wtf?

Yes, you've probably connected something incorrectly, or the alternator has a problem. Which alternator are you running? If it's a GM 10-SI, there only needs to be two connections, a 10 gauge main charge lead going from the 1/4" terminal stud on the back of the alternator to the battery cable connection at the starter, and a jumper wire from the big alternator terminal to the #2 blade terminal on the perimeter of the alternator housing. The #1 terminal does not need anything connected to it unless you're running an idiot light on the dash. The battery terminal voltage with the engine running should be between 13 volts and 14.7 volts, depending on the state of charge of the battery, and how many acessories you're running.

The voltage will recover slightly after the battery sits awhile with no load on it. It will drop again as soon as something is turned on.
Jerry

This is how I have it wired, according to the diagram link below.

https://lh6.googleusercontent.com/-EF5uel8cUlw/TqSESSGU_xI/AAAAAAAAB0M/ciIQwofADVw/s826/Untitled.jpg

I'm using a brand new 3 wire alternator. The main power goes to the power lug, and the other two wires come off the F and 2 terminals of the voltage regulator. The other two wires of the regulator are just like in the picture, both split off of the white Excitor wire.

Do you think I should get the other type of alternator that is pictured in the diagram and ditch the regulator? It looks simpler and eliminates the regulator.

Your diagram doesn't show up, at least with the link in your post. The internal-regulated 10SI is a much better alternator, more charging capacity and much simpler wiring, also. They're a lot easier to find at parts stores than the earlier style, and they cost less most of the time. Before making the swap, try running 12 volts directly to the "F" terminal at the alternator with the engine running. If the voltage goes up to 13 volts or more, the alternator is OK. That eliminates the regulator and allows you to decide whether the problem is in the alternator or the regulator.
Jerry

Edit: I finally got the diagram to show up. Neither one is right, according to the way I like to wire alternators. The lower diagram will work with the 10SI alternator, but the "exciter" wire isn't needed.
Jerry

Thanks Jerry. I actually picked up an internally regulated alternator, the kind that uses the flat connector rather than the square. The guy said it was for mid 70's GM, so I think that's the one I want.

So this way I can eliminate the voltage regulator and run just the power and alt excitor wire to the alternator.

I'll swap it in on Friday and see if it makes a difference.

One more question, I don't need a DA connnector, do I? I'm using a 69 GM column and ignition switch. My understanding is that you only need a DA plug when you're converting 6 to 12 volts and using the stock ignition switch.

I'm not entirely sure what a "DA" connector is- - - -must be a new term on me. There were some problems with engine run-on after shutting off the switch unless a resistor was wired into one of the regulator leads when using an ammeter instead of an idiot light with the old external regulated alternator, but I'm not aware of similar trouble with the internal-regulated 10SI. There was some discussion about connecting a constant 12 volts to the "exciter" connector which usually grounds the idiot light. That's NOT the connector that needs the constant 12 volts- - -it's the connector marked with the number "2". On factory-original wiring diagrams, that connection gets unswitched battery voltage in all the diagrams I've been able to find.
Jerry

Problem solved. I picked up an internally regulated alternator for a mid-70's GM, bypassed the external regulator, ran the alt excitor wire straight to the alt, used the flat plug and wired according to diagram, and voila- it never drops below 14volts while the engine is running, plus my battery isn't dead the next morning.

I'm very happy now.