Charging voltage is fluctuating rapidly

[colinnwn]

I have a Scangauge II and one of the gauges I keep up is the voltage meter. When the truck is running, it has started rapidly fluctuating between 11.6 volts and 14.1 volts, and every value in between.

 

It will change dramatically every few seconds, probably related to the Scangauge refresh rate. I haven't noticed any other symptoms of low or fluctuating voltage with the truck. When the truck is off, the battery is stable at 12.6 volts, though I haven't tried to test it under load.

 

Not long ago, I replaced the OEM alternator that died after an excursion to 19 volts, with a Malaysian built 13900 replacement from a junkyard. That was just to limp me along to get the OEM alternator looked at, which I've done. I had it cleaned and the brushes replaced and tested, so it is supposedly good to go back in if I wanted to.

 

When I installed the junkyard alternator, it tested good at a part store. Is there any reason to suspect anything besides that junkyard alternator or voltage regulator in it dying? I wouldn't want to go to the work of replacing it for the 3rd time in 6 months, and it not be the problem.

 

One other item of note, I had the firmware in the Scangauge updated for the first time in 7 years. I'm thinking that was a mistake. I haven't found a setting where it doesn't occasionally turn off when driving, or turn on when I open the door with the car off, or quit responding. It never did this with the old firmware. I also see a noticeable shimmering of the display when looking at it, like horizontal shadowy lines rapidly moving from top to bottom. I never saw this with the old firmware either. But so far all of the ODBII reported values look right when the Scangauge is working, which is 95% of the time. So I don't think these voltage readings are inaccurate from the Scangauge.

 

 

 

[Slartibartfast]

I can't think of what else would be causing that kind of fluctuation besides a flaky alt or loose connections, though I'd probably screw around with a voltmeter on the battery and see if I could witness the fluctuation on that for confirmation. Of course, the refresh rate on a digital meter or inertia of the needle on an analog meter might make this tricky. If you've got a rebuilt alt on the shelf, you might as well chuck it in and see.

 

I'd also be interested to see if eliminating the electrical noise of a failing alt from the charging system resolves any of the Scangauge's issues, though it doesn't sound like the two problems started at the same time.

[Alexey_Maruschak]

Если скачки напряжения связаны с величиной оборотов, то скорее всего регулятор напряжения вышел из строя.

Для этого не нужно менять весь генератор. Работы с заменой стабилизатора обходятся как правило 1/6 цены генератора.

Их ремонтируют как правило в тех же местах где есть ремонт турбин. У них есть каталоги по всем аналогам. Делается это быстро.

Мне 3 года назад (~ 75000 километров назад) поменяли - до сих пор работает.

[Citron]

Loose belt, loose connections, corroded terminals can all cause erratic voltage.

[colinnwn]

Loose belt, loose connections, corroded terminals can all cause erratic voltage.

The belt is tight and not squeaking. The connections on the alternator are tight. I forgot to check the tightness of the battery terminals, thanks for the reminder. But they aren't corroded. I don't know of any other suspect terminals to check. I think the alternator positive feed comes directly in to the battery terminal.

 

Sent from my FRD-L04 using Tapatalk

[colinnwn]

Well stupid me.

 

I replaced my alternator again without verifying the voltage readings using a 2nd method. I didn't imagine the ScanGauge could be reporting the wrong data. The ScanGauge is still showing rapidly fluctuating voltage. I put a voltage meter on the truck and it is rock steady at 14.4 volts.

 

I think the ScanGauge is screwed up. But to be sure the truck isn't reporting the crazy voltage, I'm going to get another cheap OBD2 reader. I'll start another thread. But if anyone is reading this and has a cheap and nice OBD reader, they like, let me know.

 

Thanks.