Volt meter question

[76bonanza]

can someone explain what readings are good an bad. I would say right now I am reading about 15.00 volts or 3/4 mark on gauge is this good or bad? I have heard to low or to high is bad?

Thanks

[rockman20]

Is this the stock gauge? I know that the gauge in my truck is off by almost 2 volts. It says that it is up around almost 18 volts but if you test with a good multimeter, the alternator is right around 16 volts.

My Cutlass runs around 16 volts as well and I have never had any issue with it. (Going on 2 years now like that) In fact, my MSD ignition components and electric fans sure seem to like the extra voltage.

[hotrodhomi]

sounds high but the stock gauge is not that accurate. do you have a voltmeter you could check it with? the alt should charge at roughly 13.5 to 14VDC

[76bonanza]

Yes stock gauge. when I check it do I just put the meter on the battery?

[1987SierraClassic]

Yes, you can measure across the battery, just make darn sure that the meter is set correctly...I've seen people dead short the battery through a meter...once you let the smoke out of them, they don't work so good!
Also, voltage too high is bad. It can boil the battery dry. 16 volts sounds high. I agree with HOTRODHOMI....13.5 to 14 volts is about right

[rockman20]

Keep in mind that I am always testing at the Alt. I am now interested in testing across the battery to see what kind of voltage the battery is actually seeing. I would assume there has to be some voltage loss.

My pickup has a 1,000 CCA @ 32* battery with serviceable cells and I check the fluid levels around every 3 months. So far I see no level drop.

[76bonanza]

If I test at the ALT. do I just check the two wires on the plug? Or how do I test at ALT?

[76bonanza]

Hey rockman love your saying under your name that is one of my favorite movies as well.

[76bonanza]

It would read no higher than 14 at battery. I noticed whill I was stuck in trafic my gauge backed down. If my battery is losing charge would it make the guage read high untill it was back to full charge?

[86-C10-V6]

Idealy, lead acid batteries should be float charged to 13.8 volts. The open cell voltage of a fully charged battery should be 12.6 volts (engine off not charging). The alternator will try to regulate its output to 13.8 but this level will vary slightly with temperature.
The alternator is not a perfect DC source and will contain some AC ripple on the output, this may cause common volt meters to read slightly high(incuding the instrument panel meter). The battery is the best location to test the level of charging since the capacitance of the battery will have some averaging affect on the ripple voltage. If the altenator output is greater than 14.4 volts for any extended period of time, it will cause gassing of the battery and with open cells will cause a water loss as well(sealed batteries have less problems with this).
Generally speaking the alternator should be able to regulate the output to 13.8 volts regardless of the load but the altenator output is rated at high RPMs and therefore at engine idle some loads will cause the voltage output to drop.(like when you turn on the AC or the fan on high).
The instrument panel meter may also be affected by the loads within the cab. As an example if the heater fan is running on high, even though the battery may be at 13.8 volts, the voltage at the fuse block may be lower due to thermal losses in the wire between the battery and the fuse block. Same goes for the lights and AC.

A good test would be to turn all electrical devices off and check the voltage at the battery with the engine at idle(with a charged battery, voltage should be 13.5-14 volts). Then turn on lights, AC, high speed fan and rev engine to 2000 RPM, voltage should still be in same range maybe slighly lower.
Remember, alternator RPMs can be as high as 4 to 5 times the engine RPMs so high reving engines will wear alternator bearings and armature brushes much faster.

[cliffsta]

14.4 is an *official* number that ive heard and its what i get normally, but my battery is toast. Anything much less than13 should be watched. with my lights, foggies, whipers, and radio with the toast battery (the alt is still good though) it falls all the way to 10. when i put the key in it barely registers on the volt meter

[rockman20]

Hmmmm......I wonder why my readings are so high then. Maybe I can't read the digital read out on my meter.

My pickup, I have been kind of thinking about and I guess that when I tested that, I had just started the vehicle and it was cold and had sat for a while so it did crank for a while before starting. I usually test the Alt at the batt terminal on the alt.

But reading this thread, I can see where the battery is a better place to test.

76bonanza, I had to get that movie on DVD. I watch it a lot. It takes a certain sense of humor to appreciate that movie though. Most of the people I know do not like that movie at all.

[cliffsta]

easiest way to test alternator: get voltage off the battery (should be 12.6) with the motor off; then start it and let it run a couple minutes and check voltage again with the motor running. If it goes up, then the alt is good.

[76bonanza]

Hey rockman I know what you mean about the movie do you also like Dogma? It is off beat also but I like it.

[rockman20]

Honestly, I have not watched Dogma. I wanted to watch it once, but I had a girlfriend at that time and I somehow ended up watching something else instead.

But, the girlfriend is gone now, so I suppose I have time to watch it now!

[76bonanza]

Good movie if you can watch it and not take it seriously some people can not.