General Maintenance & Repairs - How accurate is voltage gauge?

How accurate is the voltage meter for our cars. I have a 98 Formula and it kinda seems like my voltage is fluxuating all over the place while the car is running. It tends to fluxuate mostly between 13 and 13.5 volt but it has gotten as bad as like 12 to 13.5. Maybe this is normal or maybe not just something I noticed that bothered me a little bit

My voltage gauge seems accurate and it does not fluctuate. However, if I ever wonder if the alternator is working correctly, I just put a volt meter across the battery terminals with the car running and make sure it's around 13.5 to 14.0 volts.

If your battery is a few years old I'd check the connections/bring it to Autozone or somewhere and have it load tested. When my voltage started dropping below 13 at lights with the AC on I ignored it for a while - then it went completely dead, got up one morning and keyless entry wouldn't even work.

My battery voltage went low, like 12volts when driving, and put an occiliscope on the battery, there were huge voltage spikes, these were being caused by the alternator. I spent an hour getting the alternator off, took it to a garage to get checked, it checked out okay, spent about 2 hours getting it back on the car.

Took the car to a garage, they confirmed it was the battery. The spikes were coming from the alternator, struggling to bring up the voltage of the battery. got a new battery and now all is fine.

Best get your battery checked.....

Not to sound like a bonehead, but borrow someones volt meter and just check it Your voltage will go up and down with load, thats normal You dont want to see under 13 volts. Right now in the desert its HOT, and with everything on, when the compressor kicks in the voltage does bang around alittle.
I just changed my alternator, only because the voltage with the ac on dipped to 12.6 and my lights started fluttering. I read some posts about light flutter and they were 100% right it went away with the new alt. My voltage never dips below 13.1 now and charges usually at 13.4

My voltmeter doesnt read the same as the ones on my capacitors. I dont know if it supposed to be the same but mine goes between 13.5 and 12.5 on the caps but it seems to always stay above 13 on the gauge in the cluster.

the cap barely uses any power from the batt to stay charged.

The gauge is pretty accurate. I have verified this several times while I have been working on my stereo and other projects.

hmmm. does anyone ever have their guage lights dim when sitting at a stop at night with stereo (i have monsoon system, and an extra 400 watt sub) playing and all other accesories on? It only happens at a stop. Is this normal?

Well the only reason I ask instead of just investigating it further is because when I first got the car about a month and a half ago it was totally stock (Except the missing muffler) and now I have put an entire new stereo in it. Before I put the new stereo in there was no fluctuation in voltage. and now I have a 600watt amp in my trunk and my voltages are acting wacky. My battery is a little old so I thought maybe that new stereo pushed it over the edge. As of right now everything seems to be behaving but I am going to get the battery checked out so I dont end up stranded someplace.

Thanks guys

is it fluctuating with low bass notes? If so thats pretty normal. It takes a lot of power to make those frequencies.

in my case it just dims at a stop, no flickering, then brightens up when i go. the battery is new.

do you have an underdrive pulley on your car?

no, not that i know of

Dimming lights with a big stereo at a stop is normal. Your power breaks are engaged, AC running, stereo blasting,....its normal. When your driving your alt spins faster providing more current. Have you ever concidered going to a 200 amp alt?? Or adding a big cap to your stereo to take the load off the alternator?? I sell 1, 2.2++++ farad caps for guys with stereos all the time to take alternator load off.( plus it makes the bass hit harder, and tighter) I own a electronics business. E-mail me with questions (I answer emails 10x faster then PMs!)

hmmm. does anyone ever have their guage lights dim when sitting at a stop at night with stereo (i have monsoon system, and an extra 400 watt sub) playing and all other accesories on? It only happens at a stop. Is this normal?

sure the hell is for me...ever since the u/d pulley if I turn it up I'll run as low as 12V when cruising at 2000rpm, even with an o/d alt pulley...the rockfords and the JL's tend to chew up power, and I imagine if you're pushing 400W to a sub you're in the same boat

It doesnt seem to fluctuate much with the stereo for me because I have tested it driving around with the stereo completely off and it flutters around a bit anyway. But I did notice that after my voltage stayed around 13 volts for a couple days and I took it out one night to try to convert my ricer friend into a muscle car guy ( which basically involves opening her up on the highway) when I got back home I noticed my voltage gauge was back up at a solid 13.5 where it stayed for a while... (BTW he just put a fart can on his Accord so I guess I didn't do a good enough job)

hmmm. does anyone ever have their guage lights dim when sitting at a stop at night with stereo (i have monsoon system, and an extra 400 watt sub) playing and all other accesories on? It only happens at a stop. Is this normal?

What kind of amp? I have a 55x1 Alpine and a 500x1 Hifonics amp in my car and sitting at a stop light with the bass pounding the lights never dim. However, in my old Formula I had a 150x2 MTX amp bridged into one channel powering the subs and with that amp the lights would dim even going down the road. I've heard bridging a Class A/B to power subs draws a lot more current then having a mono Class D amp, but I don't know if that's true.

My amp is a 2way bridged and my lights dont dim its a rockford fosgate RF2002

Martingale- correct, thats because a class D amp is more efficient.

I used to run a rf 801s(2400w max) and a rf801x(2400w max) in the same car with a stock alternator, 200 amp cb and a good battery. The lights would dim on occasion and one time it actually shut off the car (damn electronic distributors) but in general it wasnt too bad. My actual RMS usage was around 1000w. by the way these are both class A/B amps. 4awg wire running 15 ft with that kind of power is scary.