I had SUSPICIONS about this!!

[gmrulz4u]

OK...hopefully you've all read my previous posts regarding my charging system...

 

Well for a while now, when I get up in the morning, and it's about 30-40 degrees F, before I start my car, I would plug my digital voltmeter into my cigarette lighter socket, and the voltmeter would show 10.6volts or so. I would turn the key, and the car would start perfectly! SO, I started to suspect that this $15 voltmeter was not always accurate!! And tonight my suspicions came true. I went outside, my car had been shut-off for about 6 hours or so, it was about 40 degrees F out, I plug in the voltmeter and sure enough it says 10.7volts. So I pop the hood, get out my newly purchased digital multimeter, and place the leads on the + and -, and sure enough, the multimeter says the voltage is 12.07!!! So that's a difference of 1.37volts, which is quite HUGE!

 

So now for my questions:

 

1) Is the fact that I'm plugging this voltmeter into the cigarette lighter socket cause the voltmeter to give false readings??

 

2) Does the power going to the cigarette lighter socket go down more and more the longer the car is shut off? Because it's strange, at around 5pm, the voltmeter was saying 11.8volts, 5 hours later, it's saying 10.7??? Even though the car has been shut off!?? This makes NO sense to me?? How it can go down when there's no power being sucked from the battery? And, keep in mind, I never leave the voltmeter plugged in, unless I'm in the car, so it's not even draining anything either(which obviously would be very little anyway)

 

And just so you know, the cheap-ass voltmeter I'm using right now is shown here:

http://store.yahoo.com/rodi/powpvm804.html

 

I think I should just get this one by Dakota...I've seen this one in a lot of mags:

http://www.dakotadigital.com/Detail.cfm?Category=5&PartNumber=ODY-05-3

And maybe this as well:

http://www.dakotadigital.com/Detail.cfm?Category=5&PartNumber=ODY-20-5

 

THANKS EVERYONE:)

[GnatGoSplat]

Hmmm, sounds like your voltmeter is crummy and is affected by temperature.

You can make sure by using your multimeter to check the voltage at the cig lighter plug. If it's 12-something and your voltmeter still says 10-something, you've got a crummy voltmeter!

Power at the cig lighter should be close to what you find at the battery. It may be slightly lower due to resistance of the wiring, but the resistance should be very low so the voltage should be real close.

The only other thing I can think of - make sure the contacts in your cig lighter jack are clean. If you (or the previous owner) has ever used the cig lighter for lighting cigarettes, it's likely the contacts are crusted up. I'd clean them with some steel wool if they're real crusty. Better yet, a Dremel wirebrush. If they're not real crusty, try a pencil eraser. Be sure to pull the fuse before attempting cleaning or you might need to buy a new fuse!

I'd try the cleaning first, it's possible you just have dirty contacts and the voltmeter is fine. I'd definitely compare the voltmeter to your multimeter though.