The Stovebolt Site Forums The Shop Area The Electrical Bay Basic Electrical System Question for Generator/Regulator Systems

When I first converted my truck to 12V, the ammeter needle would seemingly vibrate. I interpreted this to be the regulator cutting in and out. More recently, it doesn't do this. The ammeter indicates steady charging above idle. At low/idle speed, it drops to discharge.

I've put a voltmeter on the system and read approximately 15V. This reading does not change with speed.

My simple understanding of these systems and Ohm's Law suggests that the system is not over charging because 15V is the running system voltage and to overcharge, there has to be higher voltage present in the system to drive additional current.

Does the described system behavior sound normal? Was the needle "vibration" right after the system rebuild an unusual behavior that has since corrected itself?

Thanks in advance for the comments/help.

Bill

first thing to remember about these trucks is they were not equipped with scientific precision instruments - once you get things functional you need to evaluate over time what the gauge is telling you .... if it shows a real charge it means the battery is low, or being charged from starting the truck, should decline to neutral soon, not stay at real charge for an extended period, although slightly above 'neutral' may be your 'normal' reading above idle .... a reading of slightly below "neutral" at idle is likely fine, that might be the 'default' position for that particular gauge, especially if you have any electrical things active, like any lights [foot on the brake?] - note what it reads when the engine is off and key is on

Bill

15 volts is on the ragged edge of too much voltage. With a fully-charged battery the max voltage should be around 14.7. After cranking, and especially if the battery has been loaded heavily, charging voltage at the battery posts can be anywhere from about 13V to 14.5 or slightly more. The state of charge of the battery, NOT THE VOLTAGE REGULATOR determines what voltage the charging system develops. The regulator ONLY functions to set the maximum charging voltage against a fully charged battery.

If your voltage is going to 15V immediately after startup, you probably have a shorted regulator and it's capable of boiling the battery dry.
Jerry

I re-checked with the meter I had originally used and found it had about a 2V offset.

I drove the truck today with a different voltmeter on the battery. Here are the results, I don't think there is an issue:
Before start: ~ 12.3V
After Start, fast idle: ~ 13.5V
At idle: ~ 12.3V
Running (during the drive): 13V - 14V

Also, during the drive I turned on the heater to put a load on the system and the voltage held. I think the system is performing well, no over-charging.

Thank you Jerry and Bill for the input.

Best regards,

Bill

Those numbers look good. After the initial startup, the charging voltage will be slightly lower due to the drain on the battery from the starter. As the battery recovers, its resistance increases and the charging system responds by raising the voltage. When it reaches the cutoff point built into the regulator, the regulator comes into play and prevents overcharging. Basically, a generator has two functions, wide open or off. As it reaches the preset voltage, the regulator starts working to prevent too much of a good thing!
Jerry

Jerry,

Thanks for confirming.