# Help w voltmeter units

Hey I’m trying to set up a led arduino on a 12 volt battery and I don’t know how many amps the meter reads. Is it 36 milliamps or 360 milliamps. I can’t figure it out for my battery. I’m trying to figure out how long a 10 Ah battery should last for it. Thanks in advance.

Hello
Check the operations manual of die DMM how to make measuremts of amps.

Hi,

Your DMM manual will tell you that 20mA range reads up to 19.99mA.
So 0.36 is 0.36mA.

Tom...

Hi @qkedarg
I couldn't tell you what you're reading, as you selected the scale from 0 to 20mA, but put the probes in COM and 10A.

In this case;
End of scale 19,99 mA
its measurement maybe 0.36 mA = 360 uA

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Good catch...
Tom..

So I was aware it was the “wrong” port but on the “right “ port I get a 1. Unfortunately new member can only post one photo at a time …I get a 1 on 2000u and 20m as well. and I get o.00 on 10 and the light turns off.

Hi,

Try
Plug the DMM lead back to the 10A input and com, select 10 on the meter scale selector and see what it says.

Does the LED light assembly have any power consumption on a label somewhere?

Thanks.. Tom...

It says .34 on ten amp setting. I think that means it is 340 m amp. It seems like a lot of amps for only the first ten inches of a several foot 12 volt led strip …

Strangely 20 m reads 0.35 and 200 m reads 3.5. Not sure why changing the upper limit limit without changing the units changes the reading by a factor of ten. That was what was really confusing me. But I think 340 milli amps is my current.

Assuming you know Ohm's Law you can hook-up a resistor to confirm what your meter is doing.

And if you're just driving those LEDs, as a "sanity check" you can assume a maximum of about 20mA each. (They will light-up with less and if LEDs are in series they will "share" current). But several LEDs at less than 1mA is unlikely.

P.S.
Clean that solder-splash off of your meter!!!

Hi,
What is the voltage rating of the LED strip?
How many LEDs are illuminated?
What is the output volts of your battery?

Thanks.. Tom..

That is because you are still using the 10A socket and not the 400mA socket.

10A socket is for the 10A range ONLY.
400mA socket is for the other lower mA ranges.

DMM-AM33D.pdf (694.3 KB)

Tom...

The short circuit output of the battery currently reads 13 volts.

The led lights are supposed to run on a 12 volt dc adapter

17 leds are on the strip I’ve cut out.

So I’m figuring that the battery will last 10 ah/ .35 amps = 28 hours.

Hi,
17 LEDs at approx 20mA = 17 * 0.02 == 0.34 A or 340mA sounds about right.

I hope you mean open circuit voltage of the battery is 13V.

28 hours theoretically.
You need to Google your battery part number and see the performance graphs.

Tom...

1 on the 2000uA (2 mA) scale means 1 mA
1 on the 20 mA scale means 1 mA
1 on the 200 mA scale means 1 mA
On the 10A scale (after switching to the 10A input) you would get 0.00 since your 0.001A won't fit in the two digits after the decimal point.

Measuring on any but the 10A scale when using the 10A input will get you nonsense.

Hi,
@qkedarg is seeing on his meter is the number 1 in the extreme left handside of the display.

Tom...

If you want to read currents lower than 200mA, you have to use the "V Ohm mA" socket;
if you want to read currents higher (or equal) than 200mA, you have to select "10" (A) and use the "10A" socket!