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 Post subject: Electrical Problems?...Testing battery and alternator.
PostPosted: Sun Nov 22, 2009 11:18 am 
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Joined: Thu Sep 03, 2009 1:13 pm
Posts: 22
Location: Jackson, TN
Someone else posted...
Headlights Dimming When Using Power Windows???
At night when I have my headlights on I’ve noticed that if I use my power windows my headlights will dim. I haven’t said anything to my passengers to see if they notice and most do not, my buddies who are ‘gear heads’ pick it up immediately though so I know I’m not crazy. This isn’t a huge problem, but its one of those things that kinda annoys a conscious Jeep owner.

Anyone else notice this problem?



I posted...

it may be normal, however, if it is a significant dimming, you may want to really look hard at your connections. when it comes to battery and alternator, it can be difficult to determine the chicken or egg.

Battery State of charge: (Engine OFF) always remove surface charge from batteries. To do this
either, attach a carbon pile and load the batteries at 25% of the total CCA rating for 15 seconds or switch the
headlamps on; select high beam for 2 to 3 minutes per battery, then switch off head lamps. Allow the batteries
to recover for 30 seconds, then test the batteries true state of charge with a volt meter. When surface charge
has been removed and battery voltage is found to be below 12.40 volts, charge or replace batteries before
proceeding

Battery voltage verification at alternator terminals. Ensure that battery voltage is present when
measured at the alternator positive (+) and negative (-) output terminals and between the negative (-) and
“S” Remote Sense Terminal. This should be inspected with the engine off and all electrical accessories in the
off position. This voltage should be the same as battery voltage measured in the above step. If the volt meter
indication is .50 volt less than battery voltage, complete individual cable voltage drop test on the positive and
negative cables. Correct voltage drop before proceeding.

Alternator voltage test. Connect the test leads of a volt meter to the alternator output terminals. Note:Most alternators have isolated ground rectification. Always connect tester / volt meter
directly to the negative output terminal of alternator or your test will be inaccurate.
• Start engine, increase to high idle (1500 RPM): The volt meter should now indicate that the alternator
output voltage has increased to a range from 13.8 volts to 14.2 volts. (Ensure that all electrical accessories
of the vehicle are in the off position.) If voltage increases but is out of range, inspect to see if alternator has
an adjustable regulator. If so, reduce engine speed to idle and adjust voltage to a setting of 14.0 volts. If
voltage is higher than 14.7 volts and cannot be adjusted below 14.25 volts, or if voltage is lower than 13.8
volts and cannot be adjusted into range then replace alternator.
• Inspect if voltage does not increase: If the alternator incorporates an ignition (IGN) terminal this
terminal must have battery voltage present above 12.4 volts. If not; inspect circuit for open and
repair. If all is verified and alternator voltage has not increased or is out of range replace alternator.

Performance Test. Set engine speed to 1500 RPM.
• With either a carbon pile or with truck accessories apply a current load equal to 75% of rated output capacity
of the alternator and maintain load for 5 to 10 seconds (see box 4 below). Test voltage after 10 seconds
with a volt meter at the alternator output terminals (enter voltage into box 5 below) If truck accessories are
utilized for current loading this must be monitored with an inductive current device on the positive output
cable of the alternator. (Note applying a load greater than 80% of rated output capacity of alternator
will cause the test to be inaccurate.)
• Properly functioning alternators will have a voltage drop of no more than .50 volts from no load to
loaded states (see value from box 6 below). If the voltage drops more than .50 volts the alternator
is considered to be defective.

Hope all of this helps you. If you do not understand a little in here, I or someone may be able to help.


I also posted later in thread about possible electrical upgrades...
2 mods that can be done... add a higher capacity battery for large loads. get a higher capacity, higher performance alternator (this helps when towing or using larger loads). also, a capacitor isn't usually considered, but that will probably get rid of your dimming problem as well. 1 farad audio capacitors would be a good addition. Anyone disagree?


This is a very important thread, as electrical issues are very common, and connections, battery, and/or alternator account for a good majority of them.

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08 KK Sport
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 Post subject: Re: Electrical Problems?...Testing battery and alternator.
PostPosted: Mon Jul 15, 2019 9:26 am 
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LOST Newbie

Joined: Thu Jul 17, 2014 3:38 am
Posts: 22
Good day guys,

On my 2009 Jeep Cherokee/Liberty, the alternator is charging too high, roundabout 15,2V. Just want to know if it has a internal or external volatge regulator?
And if it is adjustable?

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2009 Jeep Cherokee (SA)
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