Voltage Drop

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  #1  
Old 10-15-06, 09:03 AM
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Voltage Drop

Why would my voltage drop when i rev the engine or take off? Batt and Alt is Brand New
 
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  #2  
Old 10-15-06, 09:30 AM
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Take a voltmeter to your battery with the engine running, and NO accessories on, that means no lights, radio, heater, etc. You should have at least 12.5-13.5vDC. If you don't, your alternator is not charging right. With accessories on, your battery should not fall below 11.5-12vDC. Check your alternator cables, specially the grounds for good contact. Check your battery cables for good contact as well. Also, did this happen after the batt and alt replacement?
 
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Old 10-15-06, 01:38 PM
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Also check that the pulley belt is tight. If the belt slips on the alternator pulley when the engine revs, the voltage will drop until the alternator catches up to the belt speed.
 
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Old 10-15-06, 07:57 PM
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Originally Posted by HotinOKC
Take a voltmeter to your battery with the engine running, and NO accessories on, that means no lights, radio, heater, etc. You should have at least 12.5-13.5vDC. If you don't, your alternator is not charging right. With accessories on, your battery should not fall below 11.5-12vDC. Check your alternator cables, specially the grounds for good contact. Check your battery cables for good contact as well. Also, did this happen after the batt and alt replacement?

alt is charging at 14.3 with accessories on
it just started happeing a month after installing them
 
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Old 10-15-06, 07:58 PM
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Originally Posted by goldstar
Also check that the pulley belt is tight. If the belt slips on the alternator pulley when the engine revs, the voltage will drop until the alternator catches up to the belt speed.

replaced the belt today because it broke but still does it
 
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Old 10-16-06, 08:27 AM
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Explain your loss of voltage, your dash lights and everything dim down?
Trace all your cables to make sure they are good. Make sure they are grounded at the proper points. A bad ground will do this.
 
  #7  
Old 10-16-06, 02:52 PM
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Was your belt old and past due? Or is a bearing on a different pulley dragging and this causing your problems? Just a thought.
 
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Old 10-16-06, 05:59 PM
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Originally Posted by HotinOKC
Explain your loss of voltage, your dash lights and everything dim down?
Trace all your cables to make sure they are good. Make sure they are grounded at the proper points. A bad ground will do this.
everything dims
 
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Old 10-16-06, 06:00 PM
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Originally Posted by DAN75321
Was your belt old and past due? Or is a bearing on a different pulley dragging and this causing your problems? Just a thought.

yes. all pulleys move easy
 
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Old 10-16-06, 07:19 PM
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What kind of accessories? Does it happen with just the headlights on and no other accessories on?
 
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Old 10-16-06, 08:09 PM
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Originally Posted by jeff67
What kind of accessories? Does it happen with just the headlights on and no other accessories on?

just basic things, nothing that pulls alot of power, the lights are real bright when you first start the van but after some time driveing it goes down just right above yellow mark and every gets dim, and when i rev it up te voltage drop and the lights dim a little. but when i put a voltmeter on the batt(when running) it says 14v

how could i tell if theres a bad ground?
 
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Old 10-17-06, 07:16 AM
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Have you checked the voltage with a voltmeter when you rev the engine up and the lights dim? If it drops, test the alternator itself by connecting the positive end of voltmeter to alternators bat connection, and other end of voltmeter to ground. If voltage still drops, it's a bad alternator.

Like already noted, it could be a loose or corroded ground connection.
- Grap the wires at the rear of the alternator one at a time and try to twist them to see if any are loose.
- See if any wire leaving the rear of the alternator is hanging loose somewhere. Look around for any other wire that's loose, or any screw hole inside engine body area that looks like it's missing a screw (might be where the ground used to be).
- See if the black wire running from the battery to a screw on the body is loose or corroded. If so, remove the screw holding it to the body and clean it with a wire brush. Rub the area it screws to with sandpaper to ensure a good metal to metal connection.

Consider taking the vehicle to Advance Auto and get them to check the battery and alternator.

Good luck.
 
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Old 10-17-06, 07:33 AM
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Originally Posted by bigfred
Have you checked the voltage with a voltmeter when you rev the engine up and the lights dim? If it drops, test the alternator itself by connecting the positive end of voltmeter to alternators bat connection, and other end of voltmeter to ground. If voltage still drops, it's a bad alternator.

Like already noted, it could be a loose or corroded ground connection.
- Grap the wires at the rear of the alternator one at a time and try to twist them to see if any are loose.
- See if any wire leaving the rear of the alternator is hanging loose somewhere. Look around for any other wire that's loose, or any screw hole inside engine body area that looks like it's missing a screw (might be where the ground used to be).
- See if the black wire running from the battery to a screw on the body is loose or corroded. If so, remove the screw holding it to the body and clean it with a wire brush. Rub the area it screws to with sandpaper to ensure a good metal to metal connection.

Consider taking the vehicle to Advance Auto and get them to check the battery and alternator.

Good luck.
voltage stays the same when reved, all grounds look fine. mine has two so the service manual says, one body, one engine. advance auto always tells me the batt is bad because its there alt and they dont want to exchange it if it bad
 
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Old 10-17-06, 05:02 PM
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Take it to autozone or somewhere else you trust that would give you an unbiased diagnosis of the battery and alternator.
 
  #15  
Old 10-17-06, 06:59 PM
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Originally Posted by jeff67
Take it to autozone or somewhere else you trust that would give you an unbiased diagnosis of the battery and alternator.
napa said battey is fine, alt is chargeing fine but can take a load so im out 150 for a alt
 
  #16  
Old 10-17-06, 08:43 PM
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Originally Posted by chevyastro4x4
napa said battey is fine, alt is chargeing fine but can take a load so im out 150 for a alt
Did you mean it CAN'T take a load? Did you get another alternator yet? If not, just a suggestion...have it tested again at one other place, then go back to advance and tell them 2 places told you the battery tested good and the alternator failed when load tested. It sounds like the problem is intermittant so it may not have shown up on their test or are they just being jerks about the whole thing?
It would help if you can duplicate the problem when you're at advance.
 
  #17  
Old 10-17-06, 09:46 PM
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Originally Posted by jeff67
Did you mean it CAN'T take a load? Did you get another alternator yet? If not, just a suggestion...have it tested again at one other place, then go back to advance and tell them 2 places told you the battery tested good and the alternator failed when load tested. It sounds like the problem is intermittant so it may not have shown up on their test or are they just being jerks about the whole thing?
It would help if you can duplicate the problem when you're at advance.

i tried that and they put there stupid machine on it and did the load test and it said bad battery like always and they said we cant exchange it
 
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Old 10-18-06, 02:41 AM
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"napa said battey is fine, alt is chargeing fine but can [can't] take a load "

"i tried that and they put there stupid machine on it and did the load test and it said bad battery like always and they said we cant exchange it"

Since NAPA's tester is saying it's a bad alternator and Advance's tester is saying it's a bad battery and won't replace the alternator, and since you bought the alternator at Advance, I'd go to another Advance store to get it tested. Hopefully you won't have too far to drive. I'd be hoping that the tester at the first Advance store is defective, and the one at another store will say it's the alternator.
 
  #19  
Old 10-18-06, 07:37 AM
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Originally Posted by bigfred
"napa said battey is fine, alt is chargeing fine but can [can't] take a load "

"i tried that and they put there stupid machine on it and did the load test and it said bad battery like always and they said we cant exchange it"

Since NAPA's tester is saying it's a bad alternator and Advance's tester is saying it's a bad battery and won't replace the alternator, and since you bought the alternator at Advance, I'd go to another Advance store to get it tested. Hopefully you won't have too far to drive. I'd be hoping that the tester at the first Advance store is defective, and the one at another store will say it's the alternator.
i'll give that a try
thanks
everyone
 
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