Battery test

Post by **philhoward** » Mon Apr 16, 2018 8:57 am

That would give a more accurate reading - I assumed the loom was staying as standard.

Post by **scimjim** » Mon Apr 16, 2018 1:04 pm

peter freeman wrote: ↑
Mon Apr 16, 2018 8:56 am
There is a problem in that the meter gets its voltage from the middle of the loom - hence why I wired it directly to the battery terminal - via a "ignition on" relay - you can wire the relay to the "normal" gauge supply. Calibrating the meter for the full load situation will only make it read wrong ( high ) when the load ( no fans or lights etc ) is low.

Massively overcomplicating things Peter - just calibrate the gauge to read correctly ie 12v at a stable 12v input etc.

Post by **peter freeman** » Mon Apr 16, 2018 1:13 pm

Under what circumstances do you calibrate it Jim - everything off or everything on. Given the wiring loom and resistance therein you will get a different result. Wiring direct to the battery will give the same result everything off and everything on.

Post by **philhoward** » Mon Apr 16, 2018 1:19 pm

I always thought calibration meant it was right within a certain range (i.e. 10-90% of FSD)? Should be reasonably easy to calibrate it to read the correct voltage at 1) Ignition on, engine and everything else off (about 12.5V?) and 2) Engine running and charging battery (all other equipment off) - about 13.8-14.4V? Anything lower is definite discharge and anything higher indicates a charging fault.

Post by **peter freeman** » Mon Apr 16, 2018 1:38 pm

Yes correct - but not if the calibrating voltage changes. You have two circumstances no load and load so the "calibrating" voltage changes so you cannot be right with both conditions.

Post by **scimjim** » Mon Apr 16, 2018 4:50 pm

Why on earth would you calibrate at a random load condition? Calibrate off load and leave the wiring alone.

Post by **peter freeman** » Mon Apr 16, 2018 5:04 pm

Then it will read low on load which can be worrying - our 6A would go down to 11v with the heater fan lights etc were on when the voltage on the battery terminals was 13v hence I changed the wiring. If you want it to read the battery voltage ( which is what it is for ) then wire it directly to the battery ( via a relay ). If you don't believe me then check its reading with everything on then remove the green wire from it and replace it with a wire to the battery - compare results.

Post by **scimjim** » Mon Apr 16, 2018 5:44 pm

If the voltmeter was supposed to just read the battery voltage it probably would have been wired to the battery. By reading system voltage it tells you if there’s other problems, long before it gets bad enough to register at the battery (particularly as its being charged by the alternator).

The standard system shouldn’t read 13v off load and drop to 11 on full load - that’s proving my point exactly.

Post by **peter freeman** » Mon Apr 16, 2018 6:05 pm

You obviously believe that the voltage drop from the battery to the point where the gauge is connected is zero, maybe close to zero but not when a load is applied.Its a lot easier to connect the gauge to a close by wire. You have not proved your point - basic electrics.

Post by **scimjim** » Mon Apr 16, 2018 6:07 pm

I didn’t say it should be zero?

Post by **peter freeman** » Mon Apr 16, 2018 6:25 pm

Using your logic you should have a voltmeter on every circuit so you can see when you have a problem anywhere.