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DC Digital Ammeter with shunt

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Member level 4
Sep 10, 2010
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I have a DC digital Ampere meter. It has a tag of DM3-100A. Other than that, there is no diagram or brand names etc. It's Chinese made perhaps. It's light and small with this red 7segment type display. I connected it to measure the current for a 12 volt 12 watt bulb. I connected it and it gave 1 amp. Later I disconnected it and connected it on the shunt but in reverse polarity. It started showing 17 amp and then gradually lesser... I flipped the polarity again but now it's giving 13 amps or so .. which are obviously wrong. My question is, did the reverse damage it? Is it logical and normal?

I suppose somebody could make a digital ammeter that could only read positive currents and could be damaged by reverse current. But it would be a piece of junk.

Did you switch off then back on again, then try again?
It does sound like its broken though...well it obviosuly is, it measures 1 Amp as 13A.
Is there any zero-ing buttons on it?

Maybe in the past it was connected to a higher voltage than it could stand?....that woudl kill it.

Other possibility, if it has a range switch maybe contacts need cleaning. If its
range is controlled by relays maybe clean their contacts. Check solder joints to
the shunt as well, and just a general PCB inspection of solder joints. Use a mag-
nifying glass, enables one to see cracks in joints which can thermally alter their

Regards, Dana.

Or simply connected incorrectly. Seriously, without some more information about the device and how you connected it, it's a useless discussion. What do you mean with "connected on a shunt"? Show a sketch or photo of the setup.

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