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Old 09-05-2013, 08:44 AM   #1
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How do parts stores test your battery and alternator?

Hey everybody, I've never had to have a battery tested or my alternator tested before and was wondering how its done. Can I leave them hooked up to my jeep and them come out and test them or do I have to take them off and take them into the store to have them tested? reason being my jeeps throwing a code for high battery voltage and I was told to have them both tested.

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Old 09-05-2013, 08:52 AM   #2
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You have to take it off and bring it in (from my experiences).
They typically bolt it onto a fairly large upright machine with a belt and dc connections. They turn the machine on and spin the alternator. Machine records level of output from the alternator onto a screen. The test is pretty fast.

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Old 09-05-2013, 08:54 AM   #3
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They can test the battery in the jeep but the alt you have to take out. And at that point you might as well take out the battery as well.
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Old 09-05-2013, 09:05 AM   #4
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Ugh of course lol... anything to take more time that I already dont have lol. I'll get into that when I put my new o2 sensor in then. Thanks a lot for the fast responses! Now I heard if that isn't the stock alternator and it's got a higher ampage it would over charge the battery. If that is true wouldn't I just need a new battery to handle the voltage of the alternator?
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Old 09-05-2013, 09:15 AM   #5
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Ugh of course lol... anything to take more time that I already dont have lol. I'll get into that when I put my new o2 sensor in then. Thanks a lot for the fast responses! Now I heard if that isn't the stock alternator and it's got a higher ampage it would over charge the battery. If that is true wouldn't I just need a new battery to handle the voltage of the alternator?
If you're taking your battery out anyway, pull out your battery temp sensor in the bottom of the tray, unplug it from the harness, and put an ohm meter across the two leads of the sensor. It should be between 9000 and 11000 ohms at room temperature (75-80 degrees). If it's outside that range, replace it.
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Old 09-05-2013, 09:16 AM   #6
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A higher capacity alternator will not overcharge a battery if everything is working properly. Alternators are load controlled and only put out the current that is required from them. Current is pulled from them they do not push it.

All automotive alternators operate at the same voltage, you don't need a different battery for an high output alternator.
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Old 09-05-2013, 09:23 AM   #7
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Yep if a battery only needs 20 amps to recharge it, it'll only get that 20 amps whether your alternator is the factory 117 amp alternator or an aftermarket 180 amp alternator. Like a battery, alternators only put out as much power as they are asked to provide.

Like a car capable of going 180 mph doesn't have to drive 180 mph, it only goes as fast as it is told to by the accelerator pedal.
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Old 09-05-2013, 09:46 AM   #8
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Ah I see I understand now. About the battery temp sensor.. The PO moved the battery to the trunk when then installed the flat fenders because there wasn't room for it in the engine bay anymore. Where would the temp sensor be?
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Old 09-05-2013, 09:52 AM   #9
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Since few know what the battery temperature sensor is or what it does, it is highly doubtful it got moved to the rear with the battery. The temp sensor sits on the bottom of the battery tray so the battery can sit directly on top of it. It is a small round black plastic part with a wire coming out of it.
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Old 09-05-2013, 10:00 AM   #10
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you cant test the alternator by doing this:

1) start the jeep
2) with the jeep running, take a flat blade scredriver and hold on the BACK of the alternator armature bearing (little silver cap in the center back of the alternator).
3) if the alternator is working, the center cap will be magnetized and pull the screwdriver blade to the bearing cap.

thei test will not tell you the amount of voltage that the alternator is putting out, only that it is putting out a charge. to have it tested for actual charge, you would have to take it off and have it hooked up to a machine at the local parts store.
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Old 09-05-2013, 10:17 AM   #11
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alright because the battery tray is gone lol. is it like a black plastic rectangle? with a like a 90 degree elbow lookin thing with a wire running into it? sorry for the shi**y details lol. Ill take a pic when I go home for my lunch break of what I think it is you're talking about and you can let me know if that's it or not if that would be easier lol
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Old 09-05-2013, 10:31 AM   #12
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Ah I see I understand now. About the battery temp sensor.. The PO moved the battery to the trunk when then installed the flat fenders because there wasn't room for it in the engine bay anymore. Where would the temp sensor be?
The temp sensor normally sits in the battery tray under the battery. The sensor monitors the temperature of the battery and sends the info to the PCM. The PCM includes an electronic voltage regulator (evr) and it uses that info as one of the values to determine the regulated rate of charge. I have no clue what was done with yours, and I'm not entirely sure how not having it hooked up or having it at a constant temperature would effect your charging rate, but it would make me ask the question, "Did the high voltage code start when the battery was moved, or has it been a more recent occurrence?"

Did a quick check of the FSM, and it states that, "System voltage will be higher at colder temperatures and is gradually reduced at higher temperatures." Seems to me that if your PCM never sees the higher temps, that it would probably remain charging at a higher rate...just something to think about...
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Old 09-05-2013, 10:47 AM   #13
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The alternator will charge without the temperature sender being operational. What you lose without the battery temperature sensor being operational is the protection it provides the battery by it telling the alternator to slow down its charge rate when the battery starts getting hot from too high of a charge rate.
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Old 09-05-2013, 10:57 AM   #14
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The alternator will charge without the temperature sender being operational. What you lose without the battery temperature sensor being operational is the protection it provides the battery by it telling the alternator to slow down its charge rate when the battery starts getting hot from too high of a charge rate.
Exactly...that's why I'm wondering if that's where the high voltage code is coming from.
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Old 09-05-2013, 11:00 AM   #15
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That high voltage code can often be the result of a dirty, loose, or generally poor battery connection.
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Old 09-05-2013, 01:06 PM   #16
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thanks guys I'll look at it tonight when I get home while I'm looking to see if I have an exhaust leak, or a vacuum leak hopefully I don't have either and if I do I hope its easy to fix, but I really hope it's not either of them and it's just my o2 sensor going bad. Also I'll take a picture of the box I was talking about when I get home. I didn't have time to on lunch.
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Old 09-05-2013, 03:37 PM   #17
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Okay I attached those pics of where the battery used to be

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