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Old 11-09-2017, 11:09   #1
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Alternator good, not charging battery

I took the battery to an alternator shop that bench tested the alternator and said it was good.
When I reinstalled the alternator, the battery voltage is 12.40 and does not rise when the engine is running (at idle or higher rpm). Any ideas?
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Old 11-09-2017, 11:21   #2
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Re: Alternator good, not charging battery

ore info. Internal regulator or external? It sounds like a regulator issue, but if internal and they checked... then that doesnt make sense.
Is the ground cable to the engine block clean? This can be a source of loss of contact... although your engine starts evidently. Is the start battery grounded at the same spot? Battery switch in the right position for charging? Defective battery switch?
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Old 11-09-2017, 11:28   #3
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Re: Alternator good, not charging battery

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ore info. Internal regulator or external? It sounds like a regulator issue, but if internal and they checked... then that doesnt make sense.
Is the ground cable to the engine block clean? This can be a source of loss of contact... although your engine starts evidently. Is the start battery grounded at the same spot? Battery switch in the right position for charging? Defective battery switch?


The alternator is internationally regulated. The engine is only hooked to the start battery, not a house bank. Alternator and start battery are both ground to engine block, connections are clean.
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Old 11-09-2017, 11:30   #4
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Re: Alternator good, not charging battery

Check and clean all electrical connections between the alternator and the battery bank including all negative connections.
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Old 11-09-2017, 11:33   #5
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Re: Alternator good, not charging battery

... and clean the battery posts. Sometimes they can be "wet" inside and not show any obvious corrosion. I had this occur on a car. Charge light came on. Nothing wrong. The posts had grey/wet on them inside the cable clamp..
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Old 11-09-2017, 11:33   #6
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Re: Alternator good, not charging battery

One of my engines ate 2 batteries in 2 years . I checked the out put ,good checked the battery connections ,clean checked every thing I could think of . Will fitting new battery this year one of the really professional looking connections on the battery line fell off . It looked perfect . Yank on every joint and take nothing for granted
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Old 11-09-2017, 12:11   #7
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Re: Alternator good, not charging battery

All connections are suspect. I usually run a ground and don't depend on the mount for ground. I had an issue where an known good alternator wouldn't charge that was eventually traced to automotive battery cables. When cut open, corrosion ran throughout the cables. Somehow the heavy current of starting would blast thru, but the smaller charging amps would not.
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Old 11-09-2017, 12:19   #8
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Re: Alternator good, not charging battery

Test voltage at the alternator. If you're getting 14 at the alternator, you know it's between there and the battery. Sometimes, a self exciting alternator needs a kick start. One wire, or two going to the alternator?
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Old 11-09-2017, 12:50   #9
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Re: Alternator good, not charging battery

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Test voltage at the alternator. If you're getting 14 at the alternator, you know it's between there and the battery. Sometimes, a self exciting alternator needs a kick start. One wire, or two going to the alternator?


I've taken cleaned every connection between the battery, engine ground and alternator. Still nothing.

I took a picture of the alternator before disconnecting and hooked up the same way......could it be wired wrong?Click image for larger version

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Old 11-09-2017, 13:18   #10
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Re: Alternator good, not charging battery

Non self exciting, so that takes care of that. Like was mentioned earlier, you could have a corroded cable under the insulation. Do you have a multi meter? If so, you should be able to test right there at the positive and negative posts on the alternator. Unhook it from the battery so you get a "clean" test. You should get 14 volts, give or take a couple of tenths. 20volt DC would be the best setting on your meter(if you have one) to test.
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Old 11-09-2017, 13:21   #11
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Re: Alternator good, not charging battery

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Originally Posted by Fence Man View Post
Non self exciting, so that takes care of that. Like was mentioned earlier, you could have a corroded cable under the insulation. Do you have a multi meter? If so, you should be able to test right there at the positive and negative posts on the alternator. Unhook it from the battery so you get a "clean" test. You should get 14 volts, give or take a couple of tenths. 20volt DC would be the best setting on your meter(if you have one) to test.
Do NOT do this unless you want to replace your diodes.
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Old 11-09-2017, 13:46   #12
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Re: Alternator good, not charging battery

Check voltage at alternator pos and neg with engine off. Do you get 12.4 there? If not. You have a bad cable or blown fuse.

do again with engine running See what you get there. If you have 12.4 there. Alt is not charging. If you have 14.4 there and 12.4 at battery. You have bad cables.

One of those small wires is probably ignition. And should also have 12v while running. Otherwise it will not charge.
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Old 11-09-2017, 13:57   #13
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Re: Alternator good, not charging battery

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Do NOT do this unless you want to replace your diodes.
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Old 11-09-2017, 14:17   #14
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Re: Alternator good, not charging battery

Quote:
Originally Posted by Fence Man View Post
Test voltage at the alternator. If you're getting 14 at the alternator, you know it's between there and the battery. Sometimes, a self exciting alternator needs a kick start. One wire, or two going to the alternator?
I'm not sure this will work if the alternator is not being "excited" ..... ie: no low voltage to sense so it doesnt kick on and put out 14+ volts...?

I would also be careful about auto parts store testing... IIRC I had a starter that tested fine, but under load it didnt work. Been awhile...
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Old 11-09-2017, 14:47   #15
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Re: Alternator good, not charging battery

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Originally Posted by smac999 View Post
Check voltage at alternator pos and neg with engine off. Do you get 12.4 there? If not. You have a bad cable or blown fuse.

do again with engine running See what you get there. If you have 12.4 there. Alt is not charging. If you have 14.4 there and 12.4 at battery. You have bad cables.

One of those small wires is probably ignition. And should also have 12v while running. Otherwise it will not charge.


Engine running or off, 12.4V at alternator and battery.
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