The Stovebolt Site Forums The Shop Area The Electrical Bay Charging 17 volts- whats best fix

1954 Chevy, original 235 six and GM single wire alternator, served by Enos Blackbox wiring board. The truck ran and started good for years- still does. But I just added a fancy new radio and 6 disc CD changer- and they both promptly burned up. Now in checking I find that the alternator is producing 20 amps on start, and the voltage at the circuit board is 17 volts which falls to 15 volts on running. How can I fix this guys- I really like to have a fancy new electronic radio.

microbe,

I think the internal regulator looks at system voltage through its one and only single wire, and adjusts voltage accordingly.

This can only mean the regulator is defunct, and needs to be replaced, although it might also mean the voltmeter used to check the voltage was out of whack.

I haven't a clue what a Enos Blackbox is. Could this have toasted the alternator regulator, or could it be giving you a false reading. More detective work is in order.

Stuart

I'm not sure what you mean by,
"20 amps on start, and the voltage at the circuit board is 17 volts which falls to 15 volts on running."
What do you mean by, "on start"?
Do you have a "single wire alternator", or do you have an alternator that is wired improperly?
The standard 10SI or 12SI has an internal regulator that needs to be told what the battery needs, so that it can adjust the alternator output accordingly.

Enos blackbox is simply a circuit breakerboard made up for streetrods- make the wiring simple and neat.

If I check Amperage at the alternator- it will be 20 when I start the motor. If I check voltage- its 17 volts when motor start which then falls to 15 volts- still plenty to cook a radio. Yes single wire GM alternator- motor starts and battery remains well charged. VOM meter is OK.

Put one of your Volt meter leads on the battery negative post (on the battery). With the other lead, check to see if you have voltage at every place on the vehicle that you think is a ground. In other words, you should have "0" volts at the engine, frame, firewall and dash grounds.
There are alternators that are sold as "One Wire Alternators". You are using the term, "single wire". Are you sure of that we're talking about the same thing? Do you have a wire from the #2 pin to the Bat post or is yours suppose to work without it.

Speaking of terms.

Please use terms like
"Key Off" ,or
"Key On, Engine Off" , or
"Key On, Engine, On"

terms like "on start" or "motor start", make me wonder if you mean during "Key In Start, Engine cranking", but just aren't saying that.

If the grounds are good, then the internal regulator is probably bad.

microbe,

Don't spend any energy trying to measure current output on your alternator, it's not relevant to its health.

The most you should see in your system for voltage when it is charging is 14.7 volts...this is pretty high, but it's considered OK by auto electric shops. This is pretty close to your 15 volts, and with a inexpensive meter, maybe this is what you are actually reading/getting.

After reading your later posts, it almost sounds like everything is high, but OK. Again, don't be concerned with 'amps'...this is a function of the connected load.

My only question would be, where is your alternator BATT wire connected, and is it a clean connection that can see the battery and all accessories well. This single wire is the only feedback the regulator has to monitor things.

I'm curious, what device did you use to measure your 20 amp 'start' load with??


Stuart

OK here's the latest with overcharging alternator. I took it off and down to NAPPA- they tested it and said it was bad- don't ask me- the machine lit up and said "BAD". So replaced it with a new single wire- one wire alternator. Naturally they wern't exactly alike-had to buy a new bely, rig a new bracket- BUT ANYWAY- when I got it on with engine running VOM said 16 volts -down from 17 volts with the old bad" alternator.

Atomarc: I measured amperage with my VOM meter in series with the alternator output terminal.

microbe,

So your handy dandy new alternator shows a output of 16 volts...! That's too much. The regulator should top out at 14.7 or so.

You must have a beastly VOM to measure 20 amps. I have a plethora of meters...Simpson to Fluke, and they max out at 10 amps. Did you series some type of shunt when you measured this.

Something is haywire...16 volts is way too much.

Stuart

This is strange. Check all the grounds. Do you have a good ground cable or strap from the engine to the frame? It is possible the bat. is defective. Stick a bat. in out of another vevicle to try it. You shouldn,t drive it till this is solved. You can harm bulbs & components.

Just my own opinion here, my own experiences with single wire altenators was not very good. I would suggest that you go back to the std wireing for the alternator. It's only 2 or 3 more wires, much more accurate vootage control and quicker pick up than the single wire.
i do suggest that you check all grounds. Especially check for proper grounding of the alternator itself. It grounds through the case to the bracket, then on to the engine/engine ground. May need to run a direct ground from the alternator itself to the frame. I wouldn't think that a bad battery would do it, but this whole situation is odd, so anything is possible.

I'm not a alternator tech, so this might be OTL, but I was under the impression that the solid state regulator was somehow built/configured to only be able to put out a programmed max voltage.

Nothing external should make the alternator put out more than it is regulated to do. A shorted battery or anything else should only allow a maximum charge of around 14.7 volts.

If the output voltage goes beyond this, it seems like it would be a internal problem, a regulator problem. Does this theory sound right?

Stuart

stuart- that sounds right. i went back to NAPPA and they measured the volts- they got 15.

I think you may want to take your vom and check the voltage on another vehicle battery and see if your meter is ok. I have never seen a one-wire put out more that 14.7 volts no matter what you did to it.

It,s true the regulator controls the voltage at about 14 volts. The battery serves as a ballast. Without a battery or a defective battery the voltage can run away. The internal regulators are known to short & charge infinitly, although pretty rare.

I think a bad battery is possible-seems like if it has a problem internally it won't get fully charged,and thus your alternator's going to keep working overtime trying to get it up to a full charge.Of course that'd be an amperage issue more than a voltage issue. My GMC's doing kinda the same thing,and I still haven't got IT sorted out. I think in my case it's just a byproduct of 50 years of "ranch-wiring".I do agree that weak grounds account for a lot of electrical problems,so that's a good place to start.
Speed

Sounds like the regulator inside of your alternator went south.....ideally the alternator should be charging between 13.8 and 14.2 volts and no more. Any more and costly solid state things like radios and cell phones have a short lifespan.... as you sadly experienced firsthand. The amperage load should have nothing to do with you voltage output, it should still always be between 13.8 and 14.2...Thanks Randy