Jump to content


Welcome to Ultimate Subaru Message Board, my lurker friend!

Welcome to Ultimate Subaru Message Board, an unparalleled Subaru community full of the greatest Subaru gurus and modders on the planet! We offer technical information and discussion about all things Subaru, the best and most popular all wheel drive vehicles ever created.

We offer all this information for free to everyone, even lurkers like you! All we ask in return is that you sign up and give back some of what you get out - without our awesome registered users none of this would be possible! Plus, you get way more great stuff as a member! Lurk to lose, participate to WIN*!
  • Say hello and join the conversation
  • Subscribe to topics and forums to get automatic updates
  • Get your own profile and make new friends
  • Classifieds with all sorts of Subaru goodies
  • Photo hosting in our gallery
  • Meet other cool people with cool cars
Seriously, what are you waiting for? Make your life more fulfilling and join today! You and your Subaru won't regret it, we guarantee** it.

* The joy of participation and being generally awesome constitutes winning
** Not an actual guarantee, but seriously, you probably won't regret it!

Serving the Subaru Community since May 18th, 1998!

Guest Message by DevFuse
 

Photo
- - - - -

low voltage-- battery, alternator fine


  • Please log in to reply
24 replies to this topic

#1 myfinalcoffinx

myfinalcoffinx

    Eat, Live, Breath Subaru

  • Members
  • 259 posts
  • SF

Posted 13 November 2005 - 07:37 PM

I retract my earlier proclaimation that I'm getting a new battery. Although I'm still having trouble with my lights dimming. My voltage meter in the dash reads about 8 before I start it up, but when I test the battery with a tester it reads 12.69--- right where it should. When I start the engine, it jumps up to about 11 on the dash, and then as I turn accessories on, it starts to drop off along with my dash lights, headlights and my idle rpm.

Also, sometimes it takes a little bit longer of a crank than it should to finally get the engine running.

Like I said, I've tested the battery after it sat for a couple days, still at 12.69, and I tested the alternator by pulling the positive contact from the battery when the car was running, and it just kept chugging along. What else should I check, and what could be the cause of this problem?

Thanks,
Kevin

#2 jeffast

jeffast

    f*** im 24

  • Members
  • 2,029 posts
  • midwestren

Posted 13 November 2005 - 07:38 PM

what kind of mods are you running sterio flood's etc?

#3 myfinalcoffinx

myfinalcoffinx

    Eat, Live, Breath Subaru

  • Members
  • 259 posts
  • SF

Posted 13 November 2005 - 07:46 PM

I have a CD deck in my dash but I've had that longer than I've had the battery, and nothing modified anywhere else. No floods, no lights or anything.

Only thing electrical that has changed recently was when I fixed my rear defrost grid from 0 lines working to all lines working, and I installed a new ignition coil.

what kind of mods are you running sterio flood's etc?



#4 jeffast

jeffast

    f*** im 24

  • Members
  • 2,029 posts
  • midwestren

Posted 13 November 2005 - 07:49 PM

on my six my voltage regulator went bad and it caused my lights to flicker when at idle but my voltage gauge would constantly go crazy while this was happening have you tested your regulator also take your alternator to checker or autozone and they can test it out of the car and tell you if it has any problems

#5 rallyruss

rallyruss

    Subaru Master

  • Members
  • 1,653 posts
  • San Jose CA

Posted 13 November 2005 - 07:53 PM

I retract my earlier proclaimation that I'm getting a new battery. Although I'm still having trouble with my lights dimming. My voltage meter in the dash reads about 8 before I start it up, but when I test the battery with a tester it reads 12.69--- right where it should. When I start the engine, it jumps up to about 11 on the dash, and then as I turn accessories on, it starts to drop off along with my dash lights, headlights and my idle rpm.

Also, sometimes it takes a little bit longer of a crank than it should to finally get the engine running.

Like I said, I've tested the battery after it sat for a couple days, still at 12.69, and I tested the alternator by pulling the positive contact from the battery when the car was running, and it just kept chugging along. What else should I check, and what could be the cause of this problem?

Thanks,
Kevin


the old pull the cable off the battery and it still runs test.
please forget you ever learned that trick. it is a very poor test. for one thing it can ruin an ECM due to the voltage spike introduced into the electrical system when pulling the cable off.
if you are running a stock Alternator with all those accesories it is most likely on its way out. they cannot handle much over the stock load. I think they are only rated at 45 amps. not much at all. sometimes they will still output some amperage but not enough. you need to have it load tested. also verify the ground and power connections are good still. look up how to perform voltage drop tests. it will help you out greatly.

#6 zyewdall

zyewdall

    Subaru Master

  • Members
  • 2,136 posts
  • Ward, CO

Posted 13 November 2005 - 08:09 PM

Sounds like bad connections or too small of wires. Run a new #8AWG wire from the alternator output directly to the positive battery terminal, and a 8AWG wire from the alternator bracket bolt to the negative battery terminal, and see if that helps it. Could be a bad ground to the engine too -- I think the EA81's didn't have a large guage wire going directly to the starter like the EA82's, but not sure.

#7 Snowman

Snowman

    Midnight Passenger

  • Members
  • 3,538 posts
  • Haines

Posted 13 November 2005 - 08:15 PM

Use a volt meter to test in the following places:

1. On the battery terminals with the engine running, test with all factory electrical loads on. The voltage should read at least .5 volt above the voltage with the engine and everything off (open circuit voltage), generally between 13.5 and 14.5 volts. This will tell you if there's a problem or not. If there's a problem, proceed to the next steps.

2. Place one lead on the alternator case and one on the terminal on the alternator, with the engine running and all electrical loads on. Like above, the voltage should read at least .5 volt above open circuit voltage. If it doesn't, your alternator is failing.

3. Place one lead on the battery positive and one on the terminal on the alternator, with the engine running and all electrical loads on. Voltage should read less than .5 volt. If it's more, there's a bad connection between the alternator and battery.

4. Place one lead on the battery negative terminal and one on the alternator case with the engine running and all electrical loads on. Voltage should read less than .5 volt. If it's more, then you have a grounding problem.
Those tests should give you a decent idea of what's going on. You can further pinpoint problems in the power and ground cables/connections by using the method described in steps 3 and 4 to test the voltage drop across individual cables or connections.

Hope this helps.

#8 Cougar

Cougar

    Elite Master of the Subaru

  • Members
  • 6,342 posts
  • Anchorage

Posted 13 November 2005 - 08:46 PM

The fact that you read 8 volts on the dash meter before you start the engine and you can still start the car means the battery has enough charge, as indicated by your voltage readings at the battery. The problem you are having with the low dash meter reading is due to a bad connection between the battery and accessories. The smaller wire from the battery supplies the power to the accessories. Also check the fusible links for a bad connection there. Even with good connections the meter may read about 1 volt lower than the actual battery voltage. This is a common characteristic of the system due to wire losses.

#9 hush777

hush777

    More Subarus than Kids!

  • Members
  • 391 posts
  • Idaho

Posted 13 November 2005 - 08:49 PM

My son's brat had a similar problem.

Voltage was fine during the day, dropped and fluxuated with the lights on.
Would work really good if you pulled up on the clutch pedal...:rolleyes:

Turned out he forgot to hook up the negative side to the body ground and it would only work good if it could ground through the clutch cable, pulling up on the pedal caused the cable housing to flex just enough to make the ground connection.

Check the ground.....:D

Hush

#10 zyewdall

zyewdall

    Subaru Master

  • Members
  • 2,136 posts
  • Ward, CO

Posted 13 November 2005 - 09:15 PM

Great writeup on voltage testing Snowman. I always keep a voltmeter in all my cars -- about $10 for one, and helps SO much with troubleshooting.

Z

#11 edrach

edrach

    RIP 6/28/14

  • Members
  • 12,326 posts
  • Bothell, WA

Posted 13 November 2005 - 09:46 PM

I'm with Russ on DON'T DISCONNECT THE BATTERY WITH THE ENGINE RUNNING. Very bad for the car in general; aside from taking out your ECU (if your car has one) this is a good way to fry the alternator also. Hopefully, everything is still working. The likely cause of the lamps dimming is poor grounds or corroded connections along the way. Not an uncommon problem on a 23 year old car. Hard to find, but they can cause a multitude of problems.

Snowman's testing writeup is right on the money. One of the deceiving factors in testing battery voltage is that you were testing it without a current load on it. Even a dead battery can test with good voltage readings under no-load conditions; put a load on it and the voltage will drop like a stone. Almost any auto parts store will test your battery and alternator for free. Of course they'll want you to buy one of their replacements which leads one to suspect the testing. Try taking it to two or three places and if all of them come up with the same faulty component, it might be time to replace that part.

All that being said, I still think you have a bad ground or bad connection somwhere.

#12 nipper

nipper

    Semi Elite Master of the

  • Members
  • 17,634 posts
  • Long Island NY

Posted 13 November 2005 - 11:08 PM

Why dont you start with the simple and obvoius .... replace the old battery cables, both pos and negative. Its not alot of money, and if they are original probably wouldnt be a bad idea.


nipper

#13 myfinalcoffinx

myfinalcoffinx

    Eat, Live, Breath Subaru

  • Members
  • 259 posts
  • SF

Posted 13 November 2005 - 11:15 PM

Why dont you start with the simple and obvoius .... replace the old battery cables, both pos and negative. Its not alot of money, and if they are original probably wouldnt be a bad idea.


I did that a little less than a year ago, and I've checked every single ground connection in the compartment.

Tomorrow afternoon I'll for sure take both the battery and the alt. into a couple auto stores and see what they have to say.

The symptoms come and go, and for now, they are gone. But cold nights and icy mornings tend to bring them back, so we'll see how this plays out.

Also snowman: I got proper results back for the first three tests, but on the fourth test (negative battery, alt. case) i got something like 9 OHMS... huh?

thanks,
-kevin

#14 zyewdall

zyewdall

    Subaru Master

  • Members
  • 2,136 posts
  • Ward, CO

Posted 13 November 2005 - 11:20 PM


Also snowman: I got proper results back for the first three tests, but on the fourth test (negative battery, alt. case) i got something like 9 OHMS... huh?

thanks,
-kevin


Hmmmm. Sounds like a bad ground. A resistance test should show 0.1 ohms or maybeg 0.2 or 0.3, but not higher than that.

#15 Mark Humble

Mark Humble

    USMB Regular

  • Members
  • PipPipPip
  • 119 posts
  • Lewiston Ca.

Posted 14 November 2005 - 12:15 AM

Snowman has it right, the voltage drop test is the best at finding a bad connection. It works on both the pos side and the neg side. Many people who have heard of this test will test the pos side and ignore the neg side. This is also one of the best tests to find starter circuit problems. I have found 2 different pos cables bad right in the middle of the cable, other wise looked fine. Something to check might be the voltage to the headlights. Maybe there is a problem in that circuit only. Remember also, when a alt load test is done, the alt should put out about 50% more than they are rated for. Thats why you should take it to someone who has the equipment to do a load test. Turning on everthing in the car won't put that much load on it. Oh yes, don't do the pull the battery cable to see if it stays runing trick, it could cost you a lot of money. Know a guy who did this on his boat. Only he ran the engine up to 5000 rpm first. Poof. He blew everything, and I mean everything. Raidos, ignition, ect.

#16 zyewdall

zyewdall

    Subaru Master

  • Members
  • 2,136 posts
  • Ward, CO

Posted 14 November 2005 - 12:21 AM

Oh yes, don't do the pull the battery cable to see if it stays runing trick, it could cost you a lot of money. Know a guy who did this on his boat. Only he ran the engine up to 5000 rpm first. Poof. He blew everything, and I mean everything. Raidos, ignition, ect.


On old cars with generators and mechanical voltage regulators and points and condenser ignitions, it didn't hurt anything. But alternator diodes and electronic ignitions and computers really don't like voltage surges..... Newer cars (newer than 'early 60's) are just too sensitive for it to be a recommended proceedure any more.

#17 myfinalcoffinx

myfinalcoffinx

    Eat, Live, Breath Subaru

  • Members
  • 259 posts
  • SF

Posted 14 November 2005 - 12:33 AM

oops:banghead:

On old cars with generators and mechanical voltage regulators and points and condenser ignitions, it didn't hurt anything. But alternator diodes and electronic ignitions and computers really don't like voltage surges..... Newer cars (newer than 'early 60's) are just too sensitive for it to be a recommended proceedure any more.



#18 Snowman

Snowman

    Midnight Passenger

  • Members
  • 3,538 posts
  • Haines

Posted 14 November 2005 - 12:36 AM

I did that a little less than a year ago, and I've checked every single ground connection in the compartment.

Tomorrow afternoon I'll for sure take both the battery and the alt. into a couple auto stores and see what they have to say.

The symptoms come and go, and for now, they are gone. But cold nights and icy mornings tend to bring them back, so we'll see how this plays out.

Also snowman: I got proper results back for the first three tests, but on the fourth test (negative battery, alt. case) i got something like 9 OHMS... huh?

thanks,
-kevin


Try doing a voltage drop test from the alternator case to the engine block and to where the ground cable(s) attach to the engine. If you've replaced the ground cables, that's probably where the issue is. I ran into the EXACT same problem on a bus this summer... no continuity from the alternator case to the engine block resulted in no charge.

And as been said by others, a voltage drop test is much better than checking the ohms of resistance. (For example, the tiny current that an ohm meter puts through the wire to test it can easily be carried through one or two strands of a battery cable even if the rest of them are toast, and the ohm meter will still read fine. Testing the voltage drop across that same cable would clearly show that it's faulty.)

#19 rallyruss

rallyruss

    Subaru Master

  • Members
  • 1,653 posts
  • San Jose CA

Posted 14 November 2005 - 12:53 AM

Try doing a voltage drop test from the alternator case to the engine block and to where the ground cable(s) attach to the engine. If you've replaced the ground cables, that's probably where the issue is. I ran into the EXACT same problem on a bus this summer... no continuity from the alternator case to the engine block resulted in no charge.

And as been said by others, a voltage drop test is much better than checking the ohms of resistance. (For example, the tiny current that an ohm meter puts through the wire to test it can easily be carried through one or two strands of a battery cable even if the rest of them are toast, and the ohm meter will still read fine. Testing the voltage drop across that same cable would clearly show that it's faulty.)


I never thought the day would come when so many people would agree on good testing procedures. I must be dreaming. well you are better informed and on the right track. good luck

#20 Cougar

Cougar

    Elite Master of the Subaru

  • Members
  • 6,342 posts
  • Anchorage

Posted 14 November 2005 - 01:29 AM

Also snowman: I got proper results back for the first three tests, but on the fourth test (negative battery, alt. case) i got something like 9 OHMS... huh?

thanks,
-kevin


Are you saying that you measured 9 ohms between the negative battery post and the alternator ground? If so, that is a real problem. I'm not sure why you stated ohms for a reading doing step 4, as the test was checking for a voltage drop and should be measuring volts. Did you see a drop and then check the resistance? If you did that then you would also have to isolate the battery so there would be no voltage tied to the circuit while measuring the resistance.

If the ground checks out ok, read my post #8 if you haven't already. The problem with voltage drop is in another area.

#21 myfinalcoffinx

myfinalcoffinx

    Eat, Live, Breath Subaru

  • Members
  • 259 posts
  • SF

Posted 14 November 2005 - 04:18 AM

I'm not sure why it registered in OHMS for that one. my meter automatically switches between volts and ohms as approproiate (except it's not so approproiate in this case.)

I'll pick up the nice one from work tomorrow, and see what I can come up with. In the mean time, can anyone clue me in on how to perform this "voltage drop test" or point me in a direction to where I can learn?

Are you saying that you measured 9 ohms between the negative battery post and the alternator ground? If so, that is a real problem. I'm not sure why you stated ohms for a reading doing step 4, as the test was checking for a voltage drop and should be measuring volts. Did you see a drop and then check the resistance? If you did that then you would also have to isolate the battery so there would be no voltage tied to the circuit while measuring the resistance.

If the ground checks out ok, read my post #8 if you haven't already. The problem with voltage drop is in another area.



#22 Snowman

Snowman

    Midnight Passenger

  • Members
  • 3,538 posts
  • Haines

Posted 14 November 2005 - 06:27 AM

I'm not sure why it registered in OHMS for that one. my meter automatically switches between volts and ohms as approproiate (except it's not so approproiate in this case.)

I'll pick up the nice one from work tomorrow, and see what I can come up with. In the mean time, can anyone clue me in on how to perform this "voltage drop test" or point me in a direction to where I can learn?


Sorry, I should have clarified. The voltage drop test is what I described for checking the ground cables, connections, etc. You are checking the voltage that is "dropped" from point A to point B, in a cable, connection, or whatever. The voltage drop is the amount of voltage required to push the needed amps from point A to point B.

In a hypothetical situation, if you had a bad ground connection and the battery needs 13.5 volts to charge it properly, the alternator may be putting out 15.5 volts but 2 volts are required to complete the circuit on the ground side, so they don't make it to the battery. In this situation, if you put one probe on the negative terminal of the battery and one on the alternator case and set the meter to read volts, it would read 2 volts, which is the "voltage drop".

I hope that made some sort of sense.

#23 Cougar

Cougar

    Elite Master of the Subaru

  • Members
  • 6,342 posts
  • Anchorage

Posted 14 November 2005 - 10:28 AM

Another way to say what Snowman is telling you is this. Whenever there is resistance in a circuit, and current is flowing through that circuit, there will be voltage drop across that resistance.

(The circuit in this case is the wiring between the battery ground an the alternator ground and current being used by whatever loads are turned on)

Since the two ground points should be tied together with a good ground wire (zero resistance) there should be zero voltage drop between the two points. Any current that has to pass through a ground lead that has a resistance will cause a voltage drop. The amount voltage drop will change depending on the amount of the resistance in the lead and the amount of current flowing through it used by the other loads. This voltage then is robbed from the devices it should be going to. The bad wire becomes a load 'in series' with the other loads. Because the bad lead resistance is in series with the other loads it takes away voltage that should be dropped across them.

The test is simply checking for voltage across two points that should ideally be tied together with no resistance between them and therefore no voltage drop across them. One key point about this kind of test is there must be current flowing through the suspected trouble areas while testing. If no current is flowing then no voltage drop will take place.

Doing a little study of Ohm's Law and basic DC circuits will be of great benefit to you. You will be able to track down problems like this with ease. It would be time well spent and you will use it all through your life.

#24 myfinalcoffinx

myfinalcoffinx

    Eat, Live, Breath Subaru

  • Members
  • 259 posts
  • SF

Posted 02 December 2005 - 08:09 PM

As was previously suggested earlier today, I'm updating the status of this problem that never got resolved on here.

I pulled the alternator, and when I was in there fiddling with it, I grabbed the belt, and it was super loose. Tightened that baby right up, and away we went. I assume that the problem is solved, as none of the symptoms have been back. I do however, have a new alternator on hand, just in case...

I feel kinda dumb now, but thanks a ton guys!

Oh, and Cougar, I've been doing a lot of reading about DC circuits lately and my electrical engineering major buddy is helping me figure some stuff out, so thanks for the tip!

#25 Cougar

Cougar

    Elite Master of the Subaru

  • Members
  • 6,342 posts
  • Anchorage

Posted 02 December 2005 - 10:19 PM

Good deal. You will be able to use that knowledge in many areas. You will be glad you spent the time studying this.




0 user(s) are reading this topic

0 members, 0 guests, 0 anonymous users