I was driving home in the rain today w' the windshield wipers on, stock headlights, and an aftermarket set of 55w driving lights.

After 20 mins of driving, I noticed the battery light flashing on and off, and the battery voltage gauge dropped to ~10 (usually it's ~12-14). I turned off the fogs, the headlights, and windshield wipers which raised the battery voltage back to its normal range.

Is this normal?

Are the foglights THAT much of an extra strain on the electrical system?

The battery is brand new.

The only other considerations are:
-I just put in a 10" sub and amp...maybe it's draining power (although it was OFF when the battery voltage dropped)
-I just replaced the belts, so maybe there's not enough tension to spin the alternator properly.

Any ideas?

 

No, I wouldn't call it normal. Did it only happen when you idle I hope? 10 is VERY low and it sounds like some kind of charging problem.

 

x2...

id get a test done on that alt

 

yep...and the problem STILL went on today...

If I turn on the windshield wipers with the headlights, (no sub, no fog lights) I'll watch the voltage meter just drop while I'm driving.

So yes, the battery voltage drops both during idle, and during driving.

So it needs a new alternator, eh?

 

That is the most likely conclusion. Should be tested though.

 

when the truck is on, the alternator should keep the voltage at the same level no matter what. Unless your battery isn't accepting the charge (it better be if it's brand new) then I would say alternator. Swing by Advanced Auto Parts, they do alternator testing for free.

 

Ok...so I think I found the problem. A week ago we put new gatorback belts on her, but had trouble with the manual tensioning because all the bolts are frozen. We tensioned it to spec the best we could, and left it.

So yesterday, I popped the hood, and checked the freeplay. Pushing down on the belt with my finger allowed me to move it ~3/4". Is that bad? Not entirely, but the book recommends around 1/4" of freeplay, tops. So I loosened the locking bolt, ignored the tensioning assembly, got a good grip with pliers, and yanked the alternator as hard as I could while tightening the locking bolt with my other hand.

I checked the tension...MUCH tighter than before.

I started the truck and tasked the hell out of the charging system (high beams, wipers, foglights, stereo, brakes). Better this time! The needle only moved slightly.

So I think that could be it: the belt wasn't tensioned enough to spin the alternator properly, thus the charging system wasn't doing its job. I drove it again today, and the needle stayed in the 14v range the whole time.

Sound conceivable?

Or is it all in my head?

 

It sounded like an alternator problem to begin with, so, yeah, it's believable. I would keep a close eye on your battery if I were you though.

 

It sounded like an alternator problem to begin with, so, yeah, it's believable. Maybe the belt was slipping? Did you notice any loss of HP? I would keep a close eye on your battery if I were you though.

 

I suspect the alternator is just bad and this has nothing to do with the belt.

 

I would still have the alternator tested. It doesn't sound like something that could be caused by your belt WITHOUT any other symptoms (squealing, easily identifiable belt wear?)

Also, one quick note, the voltage reading WILL go down with the more load you put on it, although 10 volts is really low. The lowest you should see is 12. The voltage regulator should keep the voltage at the alternator terminals at about 14, but the more current your pulling from it, the more the voltage drop will be at the battery because of the electrical resistance (and therefore power consumption) of the wiring.

-

 

I figured it was an alt problem.....but when i see people driving with thier 55 watt off road lights ON i give them 150 watts of real power in thier face.....

But if no one was around disregard my statement...

Rocky

 

At night in the rain in the summer, I have no voltage drop:

260 watts off-road lights
130 watts stock high beams
130 watts fog lights
Air conditioning compressor load
Blower on high
Windshield wipers
Throw on a bunch of emergency lights and siren

I still hold steady around 13 volts minimum. Something is definately wrong with your alternator if you are having this problem.