DC Digital Ammeter with shunt

[furqankaimkhani]

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?

 

[barry]

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.

 

[cupoftea]

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.

 

[danadakk]

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
conductivity.


Regards, Dana.

 

[FvM]

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.