Brief voltage drop when releasing gas

[Svein]

Went for a longhaul in the dark this xmas, and noticed that my headlights dim slightly and the voltmeter drops a bit when I release the gas. I thought this might be me having a mismatch between number of off road lights and the alternator, but it seems to happen when I´m running low beams only as well. My two batteries are about a year old, not the same brand, but same size and newly charged. Any Ideas what I should look into? New alternator? Bigger one? Or just have a look at the grounds?

Cheers,
Svein

 

[Brandon Schnautz]

Could be the voltage regulator in the alternator, also it's never a bad idea to clean your ground lugs and add a little dielectric grease before you tighten them back up.

 

[Svein]

There you go! I might have to look into getting a new (bigger) one before it all goes **** up then!

 

[RichLo]

Does the RPM drop below normal idle RPM when this happens? I've noticed on other cars/trucks that if I have a high load or the AC is running it'll dropa few hundred RPM below idle for a second before catching up and that low RPM causes the alternator to drop output and dim the lights. I've never 'fixed' it, just gotten used to it (mainly on manual transmission vehicles).

 

[Svein]

I havent noticed that - but Ive Been keeping my Ehe on the voltmeter and not the rpm. Hmm. Gonna keep an eye out for that!

 

[wheelman]

Fan belt slipping when you let off the gas.or something dragging on it.

 

[Ken K]

Check you dash volt meter using a DMM at the battery to compare the two. The dash gauges are close enough for horse shoes & hand grenades. Use that DMM at the alternator B+ with one led, the other at the battery while running at idle. This is a voltage drop test and both B+ & ground will read about the same which is 0.50 volts on higher amperage circuits. Once you have this reading, turn on the headlights, blower fan, wipers and re-check battery voltage. Compare it to reading with everything off. Alternator's produce less amperage at low speeds, but just to make sure there's no other problems. Your can upgrade to an AD244 real easy. There is video on this at alternator man.com. Snag one at the bone yard, change the connector and you may have widen the holes a little, but do some research to get 180 amps from the newer style alternator. Just be ready to identify them.

I drove a car with vacuum operated wipers too, they did not work well going uphill in the rain.

 

[98 Nitro]

Fan belt slipping when you let off the gas.or something dragging on it.

This or in my case the tensioner was worn.