Trying to measure amp draw. What am I doing wrong?

[Martinjmpr]

Trying to measure amp draw using a multi meter. Followed instructions I found online and made a simple 12 V socket with bare wires on the positive side.

The idea is I'll plug one end into the 12 V socket and plug my appliance into the other. I'll hook up my multi meter in between in order to measure amp draw.

According to the instructions I found this should be possible but when I connect my multi meter according to what I see in the pictures there's nothing showing on the multi meter and power doesn't flow to the socket from the power source.

The photos below show my adapter directly connected with power flowing and connected through the multi meter with no power flowing.

So I'll ask the gurus here what am I doing wrong.

In this picture you can see power is flowing from the jump starter to the voltage meter.

And in this picture you can see I've connected the multi meter but power is not going through it and nothing is showing on the multi meter.

Any thoughts on what might be going on?

 

[Martinjmpr]

I suspect your meter is faulty. Perhaps its internal fuse is open, its leads, or just its 10amp scale you are switched & plugged into.
If the meter works on ohms or volts, that can rule out its leads.
Using that plug in voltmeter as a load, it draws very little power. On 10amp scale your meter may not be able to display that low, thus it displays zero, but even if it cant display that low, that meter should still pass current and illuminate your "load" (voltmeter).
Thus, suspect the meter faulty.
Had you tried measuring current on its 200ma scale ??

I've tried pretty much every combination of switches moving the leads to different locations etc. The weird thing is the meter works just fine for showing volts. It's just when showing amps that it doesn't seem to work. I guess I could try with a different meter and see if that makes a difference.

I think what I was really looking for was just a reality check that I had made some dumb rookie mistake.


Sent from my iPhone using Tapatalk

 

[IdaSHO]

Most meters use a fuse to protect the ammeter.

You probably just popped the fuse due to over-current.

 

[Martinjmpr]

Most meters use a fuse to protect the ammeter.
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You probably just popped the fuse due to over-current.

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Would the fuse for the ammeter be separate from the fuse for the multi-meter itself? Because as I said, the voltmeter portion works fine.

 

[IdaSHO]

Yes

Generally, the ammeter is the only fused protected setting on such a meter.

 

[dwh]

First of all, the meter has two places to plug in the red probe. One is for measuring amps, the other for everything else. If you can measure volts but not amps, then you have the red probe in the wrong hole on the meter.

If you have the probe in the hole for measuring amps, and have the ammeter wired in series, but aren't getting anything, then you've almost certainly blown the fuse that protects the ammeter section.

Good meters will have two fuses, one to protect the main board, and one to protect the ammeter. Really good meters will have spare fuses inside.

Cheap meters...good luck.

 

[Martinjmpr]

I opened up the meter last night and you are correct - there are two glass fuses in there. Unfortunately, they have paper over the glass so I can't tell which one is blown.
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The fuses look identical but one reads 8a 250v, the other one reads 500h 250v. Don't know what "500h" means but would it be appropriate to replace both with an 8a fuse? Reason I ask is that supposedly the meter measures up to 10a.

 

[AndrewP]

They need to be the same fuse that you take out. I would guess the 500h is how they designate 500miliamps, ie 0.5 amp. So don't go putting an 8 amp fuse in there unless you want a new DVM.

Everyone with a multimeter has blown the ammeter fuse at one time or another. I keep spares inside the battery compartment-they are usually extra small glass fuses.

 

[another_mike]

What device do you have plugged in at the time that you're trying to measure amp useage from?

 

[dwh]

I opened up the meter last night and you are correct - there are two glass fuses in there. Unfortunately, they have paper over the glass so I can't tell which one is blown.

Do a continuity test with another meter. But you already know the mainboard fuse isn't blown.

The fuses look identical but one reads 8a 250v, the other one reads 500h 250v. Don't know what "500h" means but would it be appropriate to replace both with an 8a fuse? Reason I ask is that supposedly the meter measures up to 10a.

Um. 500h probably means it's a half-amp (500 milliamp) fuse. That'll be the mainboard fuse. The 8a (probably slow blow) will be for the 10a ammeter section.

 

[Martinjmpr]

Do a continuity test with another meter.

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If I had another multimeter I wouldn't need to fix this one would I?

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Um. 500h probably means it's a half-amp (500 milliamp) fuse. That'll be the mainboard fuse. The 8a (probably slow blow) will be for the 10a ammeter section.

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Makes sense. I'll put them back in the MM to figure out which is which. That will also tell me which fuse goes where.

 

[Martinjmpr]

What device do you have plugged in at the time that you're trying to measure amp useage from?

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Right now I just have my simple plug-in voltage meter, but that was just to test the concept and see if it worked. Eventually what I want to be able to do is plug it in between my refrigerator and a 12v source so I can measure actual the amp draw.

 

[another_mike]

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Right now I just have my simple plug-in voltage meter, but that was just to test the concept and see if it worked. Eventually what I want to be able to do is plug it in between my refrigerator and a 12v source so I can measure actual the amp draw.

How many amps do you think that voltage meter should be drawing? Wouldnt your 0.00 reading of amps being drawn be accurate?

Edit: never mind. Didn't realize the device isn't getting power

 

[Martinjmpr]

You can test your fuses with that plug in voltmeter thing you are experimenting with.
Those two wires you were attempting to measure current thru. Put a fuse there, if that voltmeter lights up, the fuse is good.
If voltmeter does not light up,,, fuse is bad.

Doh! You're right, of course I could!

 

[john61ct]

What model fridge?

As a freezer? Or what is target fridge temp?

How hot is ambient?