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Alternator output voltage?


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14 replies to this topic

#1 freedster

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Posted 22 September 2005 - 12:06 PM

Hello all-

I was worried that my 87 GL only seemed to be putting out a little over 12 volts at highway speed, and would often dip below 12v when I was idling at a stoplight with only a couple of accessories running. I never had problems with getting the car started, but I figure that's because I put in the biggest battery I could fit back in December and that engine isn't much to turn over anyway.

So, to allay my fears, I picked a factory alternator out of a 75k 92 Loyale at the boneyard, and once installed it seems to be doing exactly the same thing.

1) Is this a problem with all Subaru alternators, is my volt gauge wrong, or do I just have 2 marginal alternators on my hands? Should I just not worry about it?

2) Is there some external voltage regulator to the system that I don't know about?

3) I've got an Alternator from an S-10 that I can drop in. It has a serpentine pulley on it so I haven't done it yet, but would that fix the issue?

4) I also bought an ammeter dash gauge that I haven't installed yet either because I'm not quite sure how to wire it in. Should I bite the bullet and go ahead and install it?

-Freed

#2 Bobby_boucher

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Posted 22 September 2005 - 12:11 PM

i would use a multi-meter first and check the charge at the battery rather than trust the in car amp meter.

#3 stephenw22

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Posted 22 September 2005 - 01:19 PM

I agree. There are times my cars show 12v at the voltmeter on the dash, but a multimeter on the battery shows 14v.

Depending on your idle speed the accessories you run at idle, it could also be bringing down the alt voltage. I usually keep my idle speed near 1000rpm, just because it seems to keep the alt voltage more stable at idle.

#4 zyewdall

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Posted 22 September 2005 - 04:27 PM

i would use a multi-meter first and check the charge at the battery rather than trust the in car amp meter.


I agree. If the battery is still doing fine, I suspect it is getting charged enough, and the meter is just off. I have also had the opposit problem -- car ran terrible, and wouldn't start, and when I put a voltmeter to it, I was running on 7.8 volts because the alternator wire had come loose and wasn't charging any more. The idiot light didn't come on though....

My meter (different car than the one above) does sit just above 12 at idle (I always have the headlights on too), but goes up to 13 while driving, so I figure it's okay.

#5 Cougar

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Posted 22 September 2005 - 04:32 PM

If the reading you give is from the dash meter you may find that the meter is about 1 volt lower than the actual battery voltage. This is due to voltage drop in the wiring to the meter.

A ammeter needs to be installed is series with the accessories power wire to the battery. To me, it is not worth doing. If you know where 12 volts really is on your meter you can always refer to that and know what the state of the charge system is for the most part.

#6 Syonyk

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Posted 22 September 2005 - 07:21 PM

i would use a multi-meter first and check the charge at the battery rather than trust the in car volt meter.


100% agreed. The voltmeter on mine doesn't ever show above what I would assume to be 13v or so, but I get a solid 14.5-14.7 at the battery terminals, so I don't worry about it.

Check the battery terminals with a voltmeter. If it's above 14.3v or so at the battery terminals while the engine is running, the charging system is fine. It should ideally be 14.7v or so, but anything in that area is fine. Much below 14.3v, and much above 15v spell trouble.

-=Russ=-

#7 82bratavenger

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Posted 23 September 2005 - 12:51 PM

I'm having the problem of running below 12v more like 8-10v and when I turn on the lights it drops pretty good. The alt. is new and I hve tried two others with the same thing. Checked all connections and they are good and I have full power to the battery. Do I have a short maybe some where that you all might suggest I look first. The car had an alarm system at one time before I bought it and all the crap is still under the dash. Maybe there?

#8 zyewdall

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Posted 23 September 2005 - 01:10 PM

Checked all connections and they are good and I have full power to the battery.


What do you mean by full power to the battery? Do you mean it has good voltage, and the 8-10 volts is measured somewhere else, or that you measured charging current at the battery, or what?

#9 BoostedBalls

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Posted 23 September 2005 - 04:36 PM

I wouldn't trust the meter on the dash, it has been in a vibrating environment for a long time. Think of it as a little better than an idiot light.

Check voltage at the battery teminals as the car is idleing. Then move the + lead to the big connection on the alternator, 13.5vdc is good. They should be very close to the same voltage, if they are and the reading is over 13.5vdc, you are golden. If it is quite a bit higher at the alternator, you have a corroded connection or maybe a frayed wire. Usually at the alternator post. Voltage regulators are internal to the alternators and very robust.
The GM alternators are a better unit IMO, but require some modification to the bracket.
You could also take the NEGATIVE lead off the battery while the engine is running and check voltage again. This will take the battery charging load off the system.

#10 Cougar

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Posted 24 September 2005 - 11:21 AM

To 82Bratavenger:

Check to see if the alternator warning light turns on when the key is turned to the ON position to test the warning lights. If it doesn't check to make sure the bulb is ok. If that is ok then check the voltage to the small white/red wire to the alternator with the key to the ON position. You should see close to battery voltage there. If it isn't, you need to find the bad connection in the line. This wire ties back to the warning light and to power. Make sure all the fusible links are making good contact also.

#11 82bratavenger

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Posted 26 September 2005 - 04:26 PM

I will test the voltage output at the battery and at the alternator. By 8-10v I am going by the gauge. It drops dramatically when I turn the head lights on and actually bounces when I turn the turn signal on. As for the warning light, it goes on with the ignition and goes out when I start the car. It is good.

#12 zyewdall

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Posted 26 September 2005 - 05:07 PM

It drops dramatically when I turn the head lights on and actually bounces when I turn the turn signal on.


Ha ha :D My old '85 wagon the whole dash lights (for the digital dash) would randomly flash on and off with the turn signals.... the old subaru's were pretty notorious for having electrical gremlins, although I had an '84 wagon without any problems at all...

Zeke

#13 torxxx

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Posted 26 September 2005 - 06:33 PM

As long as there is +12 volts at your battery with the car running, you've got NO problems. Subaru has some of the worse dash gauges I have ever run over.

I've changed 3 instrument clusters in my car in the time I've had it. Oil press slipped the first time. Temp stopped the second and the third time the voltage gauge quit working completely.

#14 Cougar

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Posted 26 September 2005 - 08:22 PM

Be sure to check the fusible links for a connection problem. Your voltmeter is reading too low, even though they normally read low due to the wiring. Somewhere between the power accessories wire from the battery and the voltmeter in the dash is a bad connection.

Another thing is there may be a problem with the ground that is causing this problem. To check that out you can make a long ground jumper and tie one end to the negative battery terminal. Then touch other end to suspected bad ground points to see if things change when you touch them with the jumper.

#15 82bratavenger

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Posted 28 September 2005 - 12:37 PM

I checked the grounding points just by tightening and cleaning them , but will try the longer wire to the neg post. Thanks




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