digital voltmeter advice

[martx007]

Hi Folks
just got a digital voltmeter (see pic) for my battery but having difficulty get it to work.
It says the yellow wire is the measuring voltage, black common negative and red power supply (7-25v)
i connected the red and black to a spare 12v battery, the yellow to the +ve of the 36v battery and the -ve of 36volt battery to the common -ve but doesnt work. As it came from hong kong thereś no instructions so does anyone have a diagram for this or know the wiring technique.

many thanks
martin

 

[oigoi]

Does it have a chip with a number on it on the circuit board? Perhaps if you could get a data sheet for that chip it would help understand how it should be connected, often data sheets have example circuits on them

 

[10mph]

I would have certainly tried connecting as you have - no real alternative. You could try it on just the 12v battery - both yellow and red to plus 12.

A few days ago I ordered a very similar looking module from HK intending to use it as you are. Mine is DC 4.5V To 30V RED Digital Volt Panel Meter Voltmeter . My battery is 23V to 29.4V so I can use the two wire system of this model and won't need a separate power supply. I hope it works when it arrives - but under £6 so no big risk.

When I was reading some of these panel meter description, it is clear some don't have reverse polarity protection, so it is important not get the leads the wrong way round!