Voltmeter wiring
Discussion
Previous owner installed a voltmeter and it is wired up to the green and black wires in the dash from one of the other instruments.
For it to show the voltage at the alternator then everything else must be off, as when, for instance, I put the ac and heater fans on it shows something like 9-10v. As I am only interested in whether my alternator and battery is working properly would wiring it up directly to either the battery or the rear terminals of the alternator make it so that turning on ancillaries does not effect the gauge reading?
Turn on the lights too and I can't help wondering if I am draining the battery rather than charging it.
Brand new Odyssey battery and alternator here btw and fresh wiring and earths in engine bay btw.
For it to show the voltage at the alternator then everything else must be off, as when, for instance, I put the ac and heater fans on it shows something like 9-10v. As I am only interested in whether my alternator and battery is working properly would wiring it up directly to either the battery or the rear terminals of the alternator make it so that turning on ancillaries does not effect the gauge reading?
Turn on the lights too and I can't help wondering if I am draining the battery rather than charging it.
Brand new Odyssey battery and alternator here btw and fresh wiring and earths in engine bay btw.
Don't know if this helps or not.
I have a cheap Chinese digital voltmeter (plenty of them on Ebay) that plugs into the fag lighter socket and gives good readings at all times. That socket is also the way that some trickle chargers connect.
If you can trace the fag lighter wiring back into the main body of the car, could that be a good place to connect your gauge?
I have a cheap Chinese digital voltmeter (plenty of them on Ebay) that plugs into the fag lighter socket and gives good readings at all times. That socket is also the way that some trickle chargers connect.
If you can trace the fag lighter wiring back into the main body of the car, could that be a good place to connect your gauge?
If the voltage rises with the engine running above what it was then your alternator is in theory charging. Doesn't matter if you try it with headlights on or off to start with as long as the voltage rises in the same condition with the engine running it will gave current flow to the battery. Yes there will be a tiny voltage drop at the end of a long wiring run on load but nothing major compared to at the battery.
Generally you'll be at 12.3 to 12.4 v perhaps on a charged battery and the alternator running should lift it above 13v at any point you test it. If it does it's charging generally. From your description it may be wired into the resistance wiring for the fan controller but you could still pick up 12v anywhere really under the dash.
Generally you'll be at 12.3 to 12.4 v perhaps on a charged battery and the alternator running should lift it above 13v at any point you test it. If it does it's charging generally. From your description it may be wired into the resistance wiring for the fan controller but you could still pick up 12v anywhere really under the dash.
Edited by 200Plus Club on Wednesday 9th August 07:51
Edited by 200Plus Club on Wednesday 9th August 07:52
When the engine is running it shows around 13v, about 0.2v less than I get at the back of the alternator.
With the ac and heater fans on it will drop to about 10v, add the fan in the driver's footwell and I am seeing 9v. I will measure at the alternator with everything on to see what that shows, but if that also drops down to the same level then I can't see the point of the voltmeter, unless you turn everything off each time you want a reading.
With the ac and heater fans on it will drop to about 10v, add the fan in the driver's footwell and I am seeing 9v. I will measure at the alternator with everything on to see what that shows, but if that also drops down to the same level then I can't see the point of the voltmeter, unless you turn everything off each time you want a reading.
If the voltage at the battery is dropping to 10v with the engine running your alternator is f
ked. Hopefully thats not the case. If the real voltageat an actual 12v terminal inside the car while running thereis unacceptably high resistance somewhere which may overheat. Best scenario is your gauge was wired by an idiot.
ked. Hopefully thats not the case. If the real voltageat an actual 12v terminal inside the car while running thereis unacceptably high resistance somewhere which may overheat. Best scenario is your gauge was wired by an idiot.jazzdude said:
When the engine is running it shows around 13v, about 0.2v less than I get at the back of the alternator.
With the ac and heater fans on it will drop to about 10v, add the fan in the driver's footwell and I am seeing 9v. I will measure at the alternator with everything on to see what that shows, but if that also drops down to the same level then I can't see the point of the voltmeter, unless you turn everything off each time you want a reading.
to me it does sound like someone picked up 12v on the actual fan motor winding, ie with the resistance of the winding in it, so that under load you are seeing motor voltage. just move the +12v wire to anywhere else under the dash, ie the instrument binnacle, or a 12v radio feed etc.With the ac and heater fans on it will drop to about 10v, add the fan in the driver's footwell and I am seeing 9v. I will measure at the alternator with everything on to see what that shows, but if that also drops down to the same level then I can't see the point of the voltmeter, unless you turn everything off each time you want a reading.
put a voltmeter across the battery to test it and if you dont see the voltage drop the same then that is the answer i guess, not an ideal spot to pick up 12v for a voltmeter across the blower motor fan winding.
earth can go anywhere, so just find another 12v spot on the car, it will all show the same voltage give or take.
if the battery voltage drops to 10v with the engine running and the electrical loads switch on then you have a duff alternator or battery potentially
As I said, battery and alternator brand new, and new super thick wiring and earths as battery moved to boot.
Seems very likely that positive from somewhere in the instrument panel is the cause and the answer is to run a positive to the alternator directly and an earth to the alternator mounting bracket to be on the safe side.
If I also use thickish wiring then hopefully the reading will be on the gauge as near as damn it to the alternator.
Just a quick question, what is the best way out from the instrument pod into the engine bay without needing a contortionist?
Seems very likely that positive from somewhere in the instrument panel is the cause and the answer is to run a positive to the alternator directly and an earth to the alternator mounting bracket to be on the safe side.
If I also use thickish wiring then hopefully the reading will be on the gauge as near as damn it to the alternator.
Just a quick question, what is the best way out from the instrument pod into the engine bay without needing a contortionist?
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