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Old 06-18-2012, 05:23 PM   #26
Cougar4
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Doing a voltage test at idle isn't a real good test to do and doesn't tell you much about the charging system. Most alternators will not be able to show a normal voltage level at idle speed. You should perform a voltage test while the engine is at least running at 1,500 RPM.
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Old 06-19-2012, 09:09 AM   #27
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You already know that your system is charging properly. If the battery and alternator are good, and the wiring is good,it's a mechanical problem. Either the wrong pulley or the belt is slipping.
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Old 06-19-2012, 05:40 PM   #28
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Originally Posted by LIChuck View Post
You already know that your system is charging properly. If the battery and alternator are good, and the wiring is good,it's a mechanical problem. Either the wrong pulley or the belt is slipping.

I think it may be a issue with the Blower motor. Only when the blower motor is on will it drop to 11's and not come back up. Anything else I can turn on and the alternator will fight to bring the voltage back up at idle.

Belt is not slipping, not sure about the pulley until someone can post the size on the stock pulley.
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Old 07-22-2012, 12:52 PM   #29
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I have this exact same problem, voltage (via TT readout) drops to under 12 when the A/C is on and blower motor is turned to high. Turn down the blower from 4 to 3, voltage goes up to a little over 12, turn down to 2, voltage is 12.3, turn down to 1 voltage is between 12.5 and 13. It's such a significant draw, I think I'm going to just order a new one.

So was the ten year old blower motor the problem, and did you get yours replaced?
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Old 07-22-2012, 03:01 PM   #30
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The trouble most likely isn't with the blower motor. There may be a bad ground that is the cause of the voltage drop you are seeing. The higher the current flow through the load the higher the voltage drop will be across the bad ground point. Before replacing anything it might be a good idea to clean your battery connections and the main grounding under the hood. Have the alternator capacity checked also to make sure that is ok along with the battery condition if it is suspect. A trick you can do to check for bad gronds is make a jumper lead long enough you can tie one end to the negative battery post and then touch the other end to suspected bad ground points. If there is a change in the operation then you have found a bad ground point. The trouble could also be in the wire connections on the power side of the circuit.

Last edited by Cougar4; 07-22-2012 at 03:08 PM.
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Old 07-22-2012, 03:05 PM   #31
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Thanks for the response. I've already been through all of the ground connections, the battery is less than a year old. The alternator is something I have not checked, and may be part of the equation, but turning on the blower is such a dramatic difference compared to other accessories, that I was hoping it would be a simple diagnosis. For a change.
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Old 07-22-2012, 03:17 PM   #32
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Good work. Since the grounding seems to be ok check the voltage on the fuse for the blower and see if you measure the voltage drop there also. If you don't see about the same drop in voltage there then there may be a slightly resistive connection point somewhere down the circuit.

The alternator is another possibility and may not be able to produce the amount of current output it is rated for so it might be good to have that checked out. Make sure the connections to it are ok and have no signs of heat damage. If you work on the main output lead of the alternator be sure to remove the battery ground connection first since the lead is hot to the battery at all times.

Last edited by Cougar4; 07-22-2012 at 03:23 PM.
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Old 07-22-2012, 04:06 PM   #33
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I should specify, I've been through the grounding points in the engine bay. If there are any in the interior, I have not checked anything there. Alternator is the next bit, should I just take it to an auto parts store to check it or can I do it myself? I do have a multimeter, but if I were a superhero, electrical systems would be my kryptonite.

When you say to check the voltage at the fuse, do you mean across the fuse connections (which if I have it correctly would only measure that point in the circuit, not its voltage relative to the system), or from the fuse to a grounding point on the frame?
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Old 07-22-2012, 08:18 PM   #34
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The grounds under the dash are probably ok. To measure the voltage at the fuse I mean to say, check the fuse for the blower motor in the dash panel using a good chassis ground point for your meter reference. See if the voltage change happens there.

If the voltage across the battery is below 13.8 volts while the engine is running around 1500 RPM then the alternator may not be working as good as it could be.
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Old 07-31-2012, 12:18 PM   #35
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Thanks for helping this thread hijacker.

Apparently, visually inspecting the grounds was not enough. I disconnected them all one by one, cleaned them and put conducting grease on them, and much voltage weirdness has disappeared. The real problem was with the grounding kit I'd installed nine years ago, the wire attaching to the passenger side shock was corroded below the washer and likely the main cause of the issue. Replaced the two extra grounding wires, scrubbed the attachment points and it's much much better. Still probably need to replace the alternator, because it won't keep up with everything, but at least I'm 13 volts or more at idle now.
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Old 07-31-2012, 02:07 PM   #36
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The strut tower is the lousiest place to pick up a ground. The bolt goes into a rubber strut mount. Don't connect a grounding wire there.
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Old 07-31-2012, 04:32 PM   #37
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I've actually got the ground in contact with the frame at that point. Paint has been removed, and I'm using a steel washer to contact the frame, so the connection should be fine. Unless I'm missing something, which is ENTIRELY possible.
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Old 05-05-2016, 03:05 AM   #38
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When you say the light on the cluster, you mean the battery light? And what color is the wire that powers that lamp, and then goes to the exciter? Can someone point me that?
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Old 05-05-2016, 11:00 AM   #39
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My info shows the wire color is blk/wht for the exciter and warning light.
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Old 05-05-2016, 01:29 PM   #40
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Alright, thank you Cougar4, will have a look tomorrow.
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Old 01-10-2017, 09:24 PM   #41
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Sorry to revive a dead thread, did OP find a solution to his issue?
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Old 01-11-2017, 09:42 AM   #42
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Quote:
Originally Posted by bassman12350 View Post
wrx_02, your alternator should be charging the system at between 13.8 and 14.2 volts, or somewhere in that general area. If the output of the alternator is dropping to 11 volts at the output wire terminal on the alternator, it is not charging the system properly.

You've basically checked everything in the charging system and it is doubtful you'd get two bad alternators in a row, but I have heard of it happening. All that aside, I'd start checking for bad grounds. The main problem points would be:

1. Where the battery ground cable connects to the chassis.
2. Any grounding straps between the engine block and the car "frame" or body.
3. Any smaller ground wires on your car which tie back into the charging circuit.

Once you've gone through and cleaned the ground connections, I'd check the charging circuit again with a voltmeter with the engine at idle - - turn on any accessories you can think of; all lights, A/C (fan on high), stereo, etc. Alternator output should be around 12 volts with the full load, possibly just lightly under. 11 volts is too low. Then run the engine up to about 1500 - 2000 RPM; alternator output should be around 14 volts.
This is precisely how I fixed my problem. +1
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Old 01-16-2017, 08:41 PM   #43
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2002 WRX 90k miles Optima Red Top Battery
Stereo installed since 2004 with no issues

Voltage started to drop into the 11's and even 10 volts when I am at lights with the AC on. So I go down to the auto parts store and have the Alternator checked. They say it's bad so I get one from NAPA. Replace it with a 2006 STI Reman 90AMP.

Voltage still drops into the 11's so I suspect the battery may be bad from the stock alternator going out. Get my Optima replaced with a new one. Still getting the same issue.

Take the Car into Cobb for a timing belt and have them check for a draw in the system. They couldn't find any wires with a high resistance or draw on them. Suggest it is the Alternator.

I go back to NAPA and have them test the new alternator, they tell me it is not charging the system. So they order me another one. I put it on and still get 11's sometimes but they told me it tested as good. So I charge my battery last night thinking it was low from driving it around. They told me the battery tested good also.

Car finally hit 14's this morning but it was really cool outside, as it gets hot the Volts drop. Anyone have experience with the NAPA remand alternators of the Bosch? I can upgrade to a Bosch 110 but am not sure the issue could be somewhere else. Could the discharged battery cause the alternator to kick out less volts?

hi, double check the voltage at the alternator and the battery. had a car charging low volts... so i put another alternator in still the same. check that there was full charging volts at alt , but very low volts at bettery., the charging cable from alt had a break in it.

mark
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Old 11-10-2017, 11:39 AM   #44
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The 90A Alternator from NAPA was a piece of ****.
I ended up getting either a 110 or 120AMP Bosch and it did the trick.
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Old 01-27-2019, 06:02 PM   #45
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I have a similar problem with my 04 WRX
When i turn on the engine the voltage goes to 14,1v, and after some seconds goes to 12,5-12,7 in idle

If i turn on the light, the AC or other , the voltage goes to 14,5


If i rev, the voltage remain stable to 12,5 or 14,5(with something turned on)



I don't think this is normal, any suggestions?
I've already changed the alternator with another toke from a junkyard
Do you know where the ground cable are?


Thx
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Old 01-29-2019, 01:16 PM   #46
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The voltage readings you gave are really not a problem in my book and you may have no real problem here. Battery voltage should be around 12.6 volts normally. If there is no load then the battery isn't getting discharged. When there is a load the charging voltage goes up slightly and keeps the battery topped off. If there is a problem I suggest you check the battery 'sense' wire that ties between the alternator and the battery. There should be battery voltage on that wire. It lets the alternator know the charge condition of the battery.
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Old 01-29-2019, 03:07 PM   #47
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no your voltage should be in the 13-14 range whenever the engine is spinning. if it drops into the 12s when the engine is on then something is wrong. make sure the aluminum is clean where the alternator bolts on, make sure the positive is clean and tight, make sure all grounds are clean and tight, clean and tight battery terminals... you get the idea.
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Old 02-02-2019, 02:26 AM   #48
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I had a big issue with voltage as well! I got the run around from shop to shop, but it was my dash cluster battery warning light. [A red battery symbol on the dash) IF THAT LIGHT GOES OUT, THE ALTERNATOR CANNOT CHARGE THE SYSTEM! Definitely make sure that bulb is good.
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Old 02-13-2019, 12:48 PM   #49
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Quote:
Originally Posted by Chrisjinn View Post
I had a big issue with voltage as well! I got the run around from shop to shop, but it was my dash cluster battery warning light. [A red battery symbol on the dash) IF THAT LIGHT GOES OUT, THE ALTERNATOR CANNOT CHARGE THE SYSTEM! Definitely make sure that bulb is good.
The reason the warning light needs to work is because it is in series with the exciter windings of the alternator. Current passes through the lamp and to the exciter. If the exciter has no power getting to it then the field windings will not work, no charging. I learned this lesson many years ago while trying solve a charging issue on a Ford truck. After numerous hours of time spent trying to figure out the problem I found out the warning light didn't work. Lesson learned the hard way.
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