can I check alt this way? HELP!

[Drivir8]

Not a Jeep... just a rice-burner but I drive it daily...
Not sure if my alt is charging.... do's not seem to be or a brand NEW battery has stopped taking a charge... can I take both battery cables off and put a meter on them? Also, it jump starts and drives just FINE on just the alt when I KNOW the battery is dead.... maybe the regulater is bad?????

[dnixon]

hook up a voltmeter to the battery while in the car (car not running) check the voltage. Then start the car and while its runing the voltage should jump up to about 14.XX if it stays at the level of just the battery (12.XX) then it isn't charging.. So check the connection to the alt.. stop the car find a ground and then go to the postitive cable on the alt and see if the connect is getting the same (roughly) volatage as the battery is putting out.. hope this helps!!

*edit*
Oh and if you see that the battery is good and the alt is charging then you may have a constant drain on the battery when you shouldn't... then it will be a pain trying to trace that to the source of the drain..

[ December 08, 2002, 02:42 PM: Message edited by: dnixon ]

[Nobby]

see my post on this thread.
never disconnect or reconnect a battery with the engine on i.e when charging.

I just pasted it to make it easier.

I advise against turning a battery off or then on
again with the engine running. In fact i say never do this. This is a surefire way to blow your alternator. It is possible to get away with it in certain cases but the usual result is a blown alternator. What happens is you create a momentary high voltage spike ( several hundred volts) which blows the diodes and regulator.
Not a great way to troubleshoot. Use a meter.
Still I guess if you wrongly suspected the alt. when it was fine and then blew it testing it like so, did you really loose anything? ;)

Take a voltmeter and put it across the battery terminals read the battery voltage, do this with the engine off all loads off. Now fire up does the voltage go up? yes, good. Its important to remember if you have a bad/flat battery your volts will not rise markedly but they should go up. Say 11.8v before start up and then rising to say 12.4v. If you leave it setup for a while if the alt. is working correctly and the battery is accepting a charge the volts should slowly steadily rise.
Does it go up to 13.4v or more even better. Now turn on a load such as heater fan or high beam lights. Does the voltage stay above 13v volts even better. Does drop below 13v and stay well you may well have regulator issues. Depending on how rough/ low your idle is it usually pays to raise the idle during the test a little bit to a 1000 rpm to make sure the alt. is turning fast enough.
Does it go into the high 14'sv maybe 15v well you may well be overcharging and cooking your battery once again faulty regulator. This is a rough test but at least it lets you know whether you should invest in a more accurate test at a shop.
hope this is clearer than mud.
These figures are approximate to give an example do not take them literally.

[ December 08, 2002, 03:30 PM: Message edited by: Nobby ]

[andy d]

uhhmn, just put the voltmeter across the battery terminals with the battery connected. a fully charged battery should read about 12.4-12.6 volts dc. start the engine. a good charging system should,make a volt reading of around 14.5 vdc across the terminals. despite advice to the contrary, i wouldnt take off a battery cable to test for alternator output. ive done this and all sorts of other things to prove a GENERATOR out. i wouldnt try this with a solid state regulator for fear of letting the smoke out of it. least thats what they say on the bmw page i also hang out at.

[Nobby]

IMHO 14.4v is the upper limit for charging a battery.
Alot of vehicle alternators drive batterys at 14.3-14.5v when the battery is fully charged. This is due to the very basic crude one step regulation of an average vehicle alternator regulator. This is still O.K. in that the only way to make it better is to move up to more expensive 3 step smart regulators. Charging a battery at 14.4v once fully charged will slowly degrade it. Its a case off its cheaper to make the owner replace the battery once every couple of years then it is to smarten up the charging system.
Yes you can expect to see 14.5v on an O.K. system however the point i am trying to make is that thats as high as it should go 14.8v and thats not good.
Im sorry if this sounds kinda petty it just really irks me that with todays technology some vehicle alternators are still rather crude battery abusers.

If you have a battery which is not sealed I.e you can check the electrolyte level it does pay to occasionally check the level and top up with distilled water if necessary 14.4v at full charge gases the battery, and despite the supposed re-condensing cap design of modern batterys the level can still go down.

[2nd Day]

just a thought.....my dad has an old dodge van and his battery was being drained becuase his glovebox light was staying on when he closed it....