Digital Multi meter probs Please help

[HKPolice]

I'm reading 12.37v on the 12v rail but BIOS/windows reads 12.03v
5.25v on DMM vs 5.13v
3.6v on DMM vs 3.5v

I tested the DMM on various other sources:
New AA 1.5v Duracell: 1.61v
New Generic 9v battery: 9.8v
New 1.55v Maxell made in Japan watch battery: 1.59v
Creative Muvo2 Lithium Ion 3.6v battery: 3.84v
Sanyo Cordless phone 3.6v battery: 3.92v
12v 200mA AC adapter for the phone: 16.47v?!?

Something didn't seem right, so I went out and bought a new DMM, but the readings are the SAME on everything.

WTF is going on here?

I did notice that on both DMM, it says 200mA max and the phone battery is rated for 600mAh - does that have anything to do with it?

Something isn't right here, how could both DMM give the same readings, which are always above spec?? Or is this normal for batteries? The AC adapter is the most confusing, how could the reading be SO far off?

Electricians, please help

[Ugly n Grey]

No the readings are correct, batteries always overvolt when in good shape. The wall adapter is a low quality and plainly sucks apparently.

Your DMM is perfectly accurate, software always reads less than what is there in my experience.

[craig588]

Without a load wall wart adapters put out much higher voltage than they are rated for. I have seen 1.5V batteries that have gotten pushed all the way up to 2.1V.

Also, without a load the batteries will also put out more voltage than they should. You can use a resistor with a fairly high value and it will be enough to make the right voltage show up.

[Thorry]

Actually simple voltage circuits converting for example 220 AC to 12 DC will always produce way higher volts when no load is applied. Try putting a load of about 75% of rated maximum then the voltage will be within 10% of rated voltage.

Also batteries work on a chemical reaction within (it's actually called a chemical cell), this reaction is juiced up with a catalist inside the battery causing the voltage to be higher then rated at the start (there is more of the catalist in there) and will slowly drop as the cell runs out.

With rechargable batteries it's worse, they can be about 50% above or below rated. Also not applying load can freak it out.

So your multimeter is just fine, it's just cheap circuits not producing exactly what is rated.

[join nbk]

yeah, i was at first gonna look at this thread and say


change the fuse in the dmm

but thats not the case here



case closed