Outer Limits 4x4 Board

if i put a multimeter on my battery what should the expected reading be at idle.

as i am having issues with battery i.e. jump start all good go for a short drive am able to start the car and it dont feel like it is flat or labouring leave over night flat as a tack.

so i wanted to make sure it was charging when idling before i go get either alternator or battery looked at.


thanks

The way to go is to put your multimeter on with the engine off, and get a measurement. If it's a touch over 12V, battery is holding voltage (but in rare cases may still be stuffed; there are batteries that have good voltage until you put a load on them.) If it's under 12V, it may be stuffed, or it may just have gone flat because of a stuffed alternator.

Then start the engine. Measure voltage at idle. Depending on how old the car is this should be anywhere from 12.8 to 13.5V (roughly).

Then rev it up to 2500 or so and measure again. Voltage should be in the same range as above.

If it's not okay at idle AND at 2500, the alternator may be stuffed.

Sometimes it's okay when revving and not okay at idle. If it comes good at just a few hundred revs over idle it's probably still useable, if not it needs help.

Jason

well at idle the multimeter reads 12.8-9 rev to 2000rpm it went up to 13.5

the problem now is that it seems to be losing charge when off.

the alternator is still the standard nissan 50amp and battery was relitivly new.


Now would me installing and running a new winch have any issues in blowing up the alternator or battery.

Surely if your running a winch, you would have dual batterys? Is it petrol or diesel? If its petrol, I put a VT Commodore alt on my rx wagon, just had to make up a right angle bracket.(100amps). I wrote in a thread before, Take your positive lead off and put the multimeter on amps and put it from lead to bat + with the car off. Be sure nothing is dragging power.

ZAPPAGQ wrote:Surely if your running a winch, you would have dual batterys? Is it petrol or diesel? If its petrol, I put a VT Commodore alt on my rx wagon, just had to make up a right angle bracket.(100amps). I wrote in a thread before, Take your positive lead off and put the multimeter on amps and put it from lead to bat + with the car off. Be sure nothing is dragging power.

Not yet on the dual batterys - very near future

it is a petrol and when the dual goes in i was looking at upgrading alternator.

well done as above disconnected +ve lead and tested between lead and +ve terminal on the battery got a reading of 1 is this good or bad

What range was the multimeter on, ie. "1" what - Amp?

murcod wrote:What range was the multimeter on, ie. "1" what - Amp?

well here is a pic of what the multimeter was set on

new to this and was not 100% sure this was correct

Looks like the 20mA range - so it would have been 1mA ? (ie. 0.001 A)

That's nothimg to worry about.

well just brought a new battery will see if this one will hold charge over night.

fingers crossed it was only a dead battery and no alternator.

well i put a bosch 700cca battery in worked for a week no problems went to start this morning flat as.


so thought it may have been a half charged battery i jump started it and went for a drive for an hour.

what i am concerned about is whit engine off i only get a reading of 11.3 volts.

while idleing i get 12.8
and rev to 2000rpm i get 13.5

i am at a loss now.

anyone


oh and with the above picture am i meant to swap the black lead to the other plug when testing amps.

If you have just brought a new battery then it can only be one of two things............ either there is something drawing power when the car is off or the alternater is stuffed.

The fact that the volts went up suggests the alternator is ok........ but maybe not 100% ok.

A reconditioned alt is generally arround 100-150.......... altrhough I must admit thats for Commodores and maybe urs is not so popular...........ring arround.

Actually better still...........go to a auto electriciuan and ask them to checvk your alternater for you..........shouldnt cost anything.

Those voltages are too low: either your multimeter is reading low or your regulator isn't putting out enough voltage.

Even 13.5V isn't enough to recharge a battery properly. As Top Cat indicated, the fact that voltage climbs suggests the alternator is functioning. But voltage at the battery is wrong.

Another possibility is high resistance joints, probably in your earth path from battery to alternator body. Excess resistance anywhere along this path will cause voltage drop while charging, reducing the voltage at your battery. Try repeating your voltage measurements between +ve terminal on battery and case of the alternator.

Cheers,

Scott

If the battery is really low on charge then it's feasible the voltage will read low when it's first started- particularly if it's only a 50Amp alt. The current drain on the alternator would be causing the low level reading.

Fully charge the battery, then fit it to the vehicle and recheck the voltage after starting.

Best to take it to an auto elec and get them to test it, they shouldn't charge anything for just having a look.

well aouto elec has alternator now will wait and see what the outcome is.


thanks for all the input guys.

well aotu elec has done his thing will take for a driv tonight for an hour or so and we will see if it still has the same problems.


auto elec rebuilt and rewound due to bearing was close to shiting itself brushes were stuffed and i wanted higher output.

went from a 50amp to 60amp due to hiatachi alternator only allowing so much new thicker wire.

I have a similar issue with my battery losing charge however I notice the dash voltmeter that is normally just under the 14V mark jumps above the 16V mark now. If I turn the headlights on it drops back down to under 14V.

Could my regulator be stuffed?

Hi blkmav, if your volt meter is correct then you need to have the reg looked at quickly.

As your lights are pulling the voltage level down when you turn them on, this indicates that your battery is pretty close to fully charged so if you do any long distance driving with the voltage up at 16 volts you will most likely stuff your battery as it will not take high voltages like this except while charging the battery when it is low.

Cheers

Thanks, I had thought it was the regulator.

Here's my theory
- regulator is over charging
- battery doesn't like it and drops cell
- battery goes cold and won't hold charge
- try to start and battery doesn't have enough charge

I only have a 50A alt and can buy a brand new 70A from a later model cheap. I'll replace the whole altenator and looks like I'll have to replace both batteries as well.

Hi again blkmav, before you replace the batteries, get them tested.

Why waste money if they are still useable although I think you could be right but get them tested anyway.

The bigger alternator won’t go a miss.

Cheers.

Update - new alternator is in, regulator was farked in the old one. Fitted new Overlander 700 battery. All running fine now.

blkmav wrote:Thanks, I had thought it was the regulator.

Here's my theory
- regulator is over charging
- battery doesn't like it and drops cell
- battery goes cold and won't hold charge
- try to start and battery doesn't have enough charge

I only have a 50A alt and can buy a brand new 70A from a later model cheap. I'll replace the whole altenator and looks like I'll have to replace both batteries as well.

Hi Blkmav

Did the 70amp alt from the new model bolt straight in?

In the end it was a 60amp. Had to drill the mounting holes out and change the plug, other than that bolted straight up.