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Battery / Alternator Blah Blah Blah

justin911

By justin911,
in General Maintenance

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justin911 Grand Master

justin911

Posted
Posted

my battery keeps going flat... I had a bit of a search bout alternators and what not and did some tests with the ol multimeter... im just not sure wat the results mean :laugh: Also i had the battery replaced about a yr ago.. for one of those racv ones... but evan with the new one it would go flat if u just sat in the car for like 30-45 mins...

anyways so i jumpstarted the car to get her going just now.. and hooked up the multimeter to alternator.. it sat on a constant 14.5v.

Then i slapped it on the battery in the boot and that was also showing 14.5 or so (as was the pfc hand controller)

so yeah... what does that mean ;) ??

thanks ppls ;)

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mad082 Grand Master

mad082

Posted
Posted

the battery that you got might have been sitting there for a while before you bought it. cold weather is the true test of how good a battery is. if the alternator is cactus then the battery would lose power as you drive from using the brake lights, indicators etc. i'd go and buy a century battery. that way you have the 3 year warranty or however long it is.

blind_elk Grand Master

blind_elk

Posted
Posted

When you test the voltage output of the alternator, you are presumably testing at idle. Try raising revs to, say , 2000 and measure output.

It should remain the same voltage (ie around 14V). If it increases, then the alternator is kaput - it is overcharging the battery, and overcharged batteries don't hold charge.

wilch Grand Master

wilch

Posted
Posted

I always thought that if you raised the revs and the voltage didn't increase then your alternator is gone.

ie. If you start the car and it stays at 12, and if you rev the car and it stays at 12, then the alternator isn't working at all.

ToF Experienced

ToF

Posted
Posted
cool thanks guys ill give her a rev and try it 2nite again :P

but ya still abit confused.... if i rev is it meant to stay the same or go up... ?

As blind_elk said, when you rev it should stay the same.

If it goes up then it's overcharging your battery, which is bad.

justin911 Grand Master

justin911

Posted
  • Author
Posted

ok well im gonna buy another battery..

just out of curiosity tho.. cause i dont understand the hole battery/alternator thing... atm my battery is at 11.x volts and it wont start... but somebody else was telling me there battery is also 11.x volts when the engine isnt running... so like.. why the hell wont my start if its the same as other ppls :dry: ???

I woulda thought if the battery was flat it'd be below 11.. or woteva the normal voltage is when the cars not running.. ??

topper Rookie

topper

Posted
Posted

Justin,

a fully charged battery should show 13.2 volts, engine not running and no load(6 cells times 2.2volts per cell)

truth is you will rarely see that. Start your car, and at the battery you are looking for @ 13.8 - 14.5 volts at approx 2000rpm, if it reaches 15 volts or higher it is being overcharged, less than 13.0 volts poss crook alternator or possibly voltage drop between the alternator and battery(bad wiring). Take your car to an Auto Electrician and ask them to load test your battery.

The other possibility is that something is draining your battery when the car and all accesories are tuned off, eg boot light staying on, glovebox light staying on, relay drawing power etc.

Dont just go and by a battery add hoc, it may be a waste of money.

Topper

Craved Grand Master

Craved

Posted
Posted

anyone know what the settings are on multimeters to check the AMPs drain on a battery while the cars are off..

trying to remember but cant, also the points on the battery and earth to check this would be helpful too.

Shayde Mentor

Shayde

Posted
Posted

Don't buy anything until you are certain what the problem is. There are a various tests you can do to see if the alternator is failing or not. Just do a few google searches. You're mainly interested in the impedence/resistance between a few particular points.

Also: The battery will show whatever voltage what battery is supposed to output unless you put a load on it. A multimeter won't do much in determining that, unless it has a dummy load also.

topper Rookie

topper

Posted
Posted
anyone know what the settings are on multimeters to check the AMPs drain on a battery while the cars are off..

trying to remember but cant, also the points on the battery and earth to check this would be helpful too.

Set the multimeter to amps dc, start at around a 10 amp range, disconnect the neg battery terminal and put one lead of meter to neg batt terminal and the other to the battery lead(the one you disconnected). With doors closed everything off you should have less than .2 of an amp drain. DO NOT try and start the vehicle or turn on any high load items whilst doing this test.

justin911 Grand Master

justin911

Posted
  • Author
Posted

well i noticed my racv battery had a 2 yr warranty.. so i got em to come round and replace it for free :) they did some tests and rekon its def the battery... (allthough when my engine blew up they rekon it was just out of petrol :P)

anyways ive got another concern though. How much cranking power thingy (or woteva its called) should a battery for a skyline have ??

I noticed mine is only 370 which doesnt realy sound like a lot.. ??

I dont have have a big audio setup or anything though... pretty much just the head unit.

thanks again for all the help :D

benl1981 Grand Master

benl1981

Posted
Posted

370 should be ok. Little on the low side. I think the one I replaced was 270cca..so I think you have bigger than the stock one..

If youre not runing a big system I reckon it should be ok for a couple of years or so. Just dont leave your lights on or parkers for too long with the engine off.

Craved Grand Master

Craved

Posted
Posted
Set the multimeter to amps dc, start at around a 10 amp range, disconnect the neg battery terminal and put one lead of meter to neg batt terminal and the other to the battery lead(the one you disconnected). With doors closed everything off you should have less than .2 of an amp drain. DO NOT try and start the vehicle or turn on any high load items whilst doing this test.

cheers for that,

exactly what i was after :(

mine will be a huge drain though :)

550cca battery and too low to crank the engine after 2 days

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