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Old 07-09-2005, 05:05 AM   #1
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ALT charge

what does your alternator charge at. im just curious if i should replace mine. it charges at about 13.5 watts, but drops to 12 when i run the ac. any suggestions. yes i am running a system, i work in car audio so i theoretically have got to.
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Old 07-09-2005, 10:30 AM   #2
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It actually sound normal for me if the alt goes down when the a/c is on. You are pulling more from your engine, therefor at idle your engine won't be pushing as much. As far as the system thing, if you are in car stereo, you should know that alts do fry, and it's not fun when they do. Luckily, my alt in the mustang has held up very well, I went through 3 in my old car within a year.
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Old 07-09-2005, 11:11 AM   #3
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Your charging system is designed to maintain a certain voltage level. What that level is depends on temperature and load. The load is determined by everything that draws current, low battery, AC, stereo, etc. The temperature also affects charging rates, cold batteries do not like to be charged quickly.

Typically, the system voltage witht he engine running and the charging system working properly is 13.8V, even with a good load on it. A fully charged battery, without the engine running, is 12.6V.

If your system voltage is in the 12's with the engine running and the AC on then you have a problem.

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Old 07-09-2005, 12:41 PM   #4
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Eh ok, ignore me lol
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Old 07-09-2005, 01:16 PM   #5
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Owned by steve again.
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Old 07-09-2005, 01:28 PM   #6
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As long as it stays in the positive range it is ok. During the summer with the AC and lights and stereo on you will see occasional drops in charging. Best thing is to keep a healthy battery. Make sure water is full in it. I would go and get a hydrometer at a auto parts store or wal-mart/K mart and chechk each cell for its charging. Keep posts and terminals clean. A old tired battery will reduce performance of the electrical system
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Old 07-09-2005, 02:07 PM   #7
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thanks corey. might end up getting a new alt. any suggestions on what i should pick up.
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Old 07-09-2005, 02:12 PM   #8
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Quote:
Originally Posted by TBone
thanks corey. might end up getting a new alt. any suggestions on what i should pick up.
Before I get a new alt I would check that one all auto parts places have alt test benches. Make sure you go to a place yoyu trust because it is easy for them to fake a bad alt. First check the battery cells with a hydrometer. They cost around $5-$10. You might have a dead or week cell in the battery
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Old 07-09-2005, 04:17 PM   #9
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Assuming everything works as designed and you do not have any extra electrical loads (meg stereo, ton's of neon lighting, etc) then your system voltage should never drop into the 12's.

Like Corey says test your stuff before you replace it. A hydrometer is an easy way to test a battery, if and only if, you can access the individual cell's electrolyte. If it's a sealed battery then you can't do that. It can be load tested by most parts stores, which is fairly accurate as long as it is fully charged and does not have a weak or bad cell.

One quick and easy test you can do for a bad cell is to measure the battery voltage. Each cell contributes 2.1V to the total output of the battery. 2.1v times 6 cells equals 12.6v, assuming a fully charged battery. If you are reading 10.5V at the battery you have a bad cell. This test can't find a weak cell, only a hydrometer or load test can. If you are reading more than 10.5V but less than 12.6 you either have a less than fully charged battery or a weak cell(s). Put it on a charger overnight and remeasure. If it is still low and your water levels are all ok then you probably have a weak cell(s).

As for testing the alternator and regulator, that is easiest done with a charging system tester. Most parts stores can do that. Based on your readings I'd assume the regulator is working, for now. The alternator could be weak, but you could also have excessive corrosion in the wiring causing a poor signal to the regulator. The regulator looks at system voltage and commands the alternator to put out.

I am assuming your readings are being made with a meter and not the dash guage. The problem with voltmeters in cars is that it reads voltage, which can be misleading. It doesn't know where the electricity is coming from (battery or alternator). Whereas an ammeter will tell you exactly which way the electricity is flowing. If it reads positive then it is flowing from the alternator to the system, that's good. If it reads negative then it is flowing from the battery to the system, which means either your engine is off or your charging system has failed.

I would have your system tested before I replaced anything.

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Old 07-09-2005, 06:38 PM   #10
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I am not a big fan of sealed battery's. I have never had much luck. Because you cannot service the battery it just dies and there is nothing you can do about it.
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Old 07-10-2005, 02:23 AM   #11
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im getting the alt readout from my amp. it is an alpine v12 with a meter on it. what do i have to do to use this hydrometer.
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Old 07-10-2005, 08:30 AM   #12
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The best place to take the readout is at the battery. Your amp's wiring might be giving a low reading due to voltage drop.

To use a hydrometer is fairly simple. You will use it to suck up electrolyte from each cell and read either the little balls floating in the sampled electrolyte or the pointer floating in the electrolyte, depending on what style you have. Just remember to put the electrolyte back into the cell it came from.

The readings will tell you how charged that cell is and all the readings show be close to each other. If you have one or two cells that read substantially different than the rest then those cells are problematic. What you are actually measuring is the specific gravity of the electrolyte, which will vary based on what state of charge it is in.
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Old 07-10-2005, 02:19 PM   #13
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ok thanks
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