Hi I'm running twin battery's and alternator set up on my discovery 1, I have bought a couple of volt gauges off ebay they just have a live and earth on them. So if I connect to the battery they are on all the time how can I wire them in so they onky come on and go off with the ignition?
timtheenchanteruk
Well-Known Member
ideally it should be 12.6V when not running, 14.5 when it is, but tbh unless you spend a fortune on car gauges, they aint that accurate, as long as you know whats normal for YOUR setup the actual reading isnt that critical.
Voltage drop on 12V is quite high, so shorter overrated cables are the best, I just tapped into a live feed and earthed mine tbh, I know what it should be, so if it varies i know.
Voltage drop on 12V is quite high, so shorter overrated cables are the best, I just tapped into a live feed and earthed mine tbh, I know what it should be, so if it varies i know.
brian47
Well-Known Member
Those of us who use electrical meters as part of the job will know that a voltmeter is a very high impedence device, that is it should draw very little current from the circuit under test.
For instance the old AVO 8 multimeter has a spec of 20,000 ohms per volt, so on the 20 volt range used to measure at 12 volts the impedence would be 400,000 ohms. Modern digital voltmeters are in the range of 6 to 10 megohms per volt.
That would mean that the guage or length of wire used for the measurement inputs to your voltmeter is of little importance, since there is very little current flowing along them.
Just fit your voltmeter where it looks good and use some sensible wire to connect it to the electrical system.
The above applies to voltmeters, the world of high currents and ammeters is different.
For instance the old AVO 8 multimeter has a spec of 20,000 ohms per volt, so on the 20 volt range used to measure at 12 volts the impedence would be 400,000 ohms. Modern digital voltmeters are in the range of 6 to 10 megohms per volt.
That would mean that the guage or length of wire used for the measurement inputs to your voltmeter is of little importance, since there is very little current flowing along them.
Just fit your voltmeter where it looks good and use some sensible wire to connect it to the electrical system.
The above applies to voltmeters, the world of high currents and ammeters is different.
