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15.3 Volts - too much?

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Texvet

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Discussion starter · #1 ·
I checked the battery (before starting) after the car sat for a few days and it showed 12.93 V. I started the car and the volt meter showed 15.4 +,-. I drove the car on the outerbelt for a 1/2 hour and the reading at the battery (engine running) was still 15.1. I shut the car off and the battery showed 13.3, but started dropping slowly, then settled at around 12.6.

I assume the alternator is making up for the lost charge on the battery (running at 15+V) - but I would think it should make up the difference and head down towards 13.5 to 14 after the 1/2 drive.

The battery and alternator are both new - I feel like the battery is the issue because of it dropping after stopping the engine?

What do you guys think?
 
#2 ·
Yes it is too much. I'm not sure if you should look at the battery or the alternator. My first guess with high voltage is the voltage regulater that is built into the alternator. I would take it out and bring it to autozone to get tested.
 
Discussion starter · #3 ·
I just got back from Autozone and they checked it on the car - and it showed 15V and that the diodes we good. I questioned the 15V and he said it's a little high "but better than too low"!!

Would a "bench test" of the alternator give a better reading?

I am going to take the new battery back and have it checked - I'll report back what they say.
 
#4 ·
I would have the bench test done. I would also think about going to a new autozone. a guys saying "but better than too low" is a little scary; he should have checked the acceptable range of alternator output for your car. I would look in my factory manual, but I'm at work right now. Maybe someone else can chime in with the factory max voltage value...
 
#5 ·
Actually everything i see eletrical related says dont exceed 12 volts... so no fuses blowing at 15 volts is a little scary.
 
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Discussion starter · #6 ·
I will pull the alternator tomorrow and take it another place for a bench test.

I just got back from having the battery tested and it's good. I am think maybe there is dead short some where?

If I remember right - the way to test for a short is to disconnect the negative cable and hook-up a test light - if it comes on there's a short some where?

Will, I did that and the light did not light up. I tested it + to - and the bulb is good... BUT I grounded it (test light) to the block and touched the positive teminal on the battery and it didn't come on?

SO - I grabbed the old multi-meter put it to the disconnected positive post of the battery and grounded it to the engine and I got a low 8V reading. Does that indicate a short?
 
#7 ·
Texvet said:
I just got back from Autozone and they checked it on the car - and it showed 15V and that the diodes we good. I questioned the 15V and he said it's a little high "but better than too low"!!

Would a "bench test" of the alternator give a better reading?

I am going to take the new battery back and have it checked - I'll report back what they say.
Click to expand...
autozone guy is a moron.. your voltage regulator is going bad.. (inside alternator) Soon it will spike to 15+ and blow headlight bulbs, etc.. I've seen it done on my car before.. Replace the alternator..
 
#8 · (Edited)
Burnett03 said:
autozone guy is a moron.. your voltage regulator is going bad.. (inside alternator) Soon it will spike to 15+ and blow headlight bulbs, etc.. I've seen it done on my car before.. Replace the alternator..
Click to expand...

This Happened to me...

Fix it before you are driving on the Ben Franklin Bridge(4 lanes and no shoulder) and the Alt. spikes 17volts killing your eprom ecu and a few other wires and fuses...

Change the alt. quick!
 
#9 ·
2 things ussually cause hi voltage, one your battery is bad and the alternator is trying to compensate, or 2 the regulator is bad and is trying to F&$% up your ride. if it's the regulator is can mess crap up like mentioned above, and it can ruin your battery,, constant over-charge. so change that bastard before it messes something up.
 
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#10 ·
I agree that the regulator is bad. Take it to a more reputable parts house and have it tested, but I think it's pretty safe to say you'll need a new alternator.
 
Discussion starter · #11 ·
I took and had it bench tested this morning - it was showing 14.9 - 15V. The guy wanted me to leave - but I told him I wanted him to pull another one and bench test it to see what it put out. He had to order one from the warehouse, and it will be in @ 3:00. I will see what it tests at.

When you say regulator - you mean the one built in to the alternator - correct?
 
#13 ·
I have never seen so much B$ in one thread before... B$ and Ignorance..
The output voltage of the alternator is well within industry specs, with a range of 12.9v-16.5v when opperating. When you hook a voltmeter up to the battery, and notice the rate constantly changing (say sweeping from 14v to 16.2v) that you need to be concerned- thats how you tell your VR is going out, that or the voltage read at the battery drops when the headlights/ A/C is turned on... I don't know who educated these fools telling you that 15v is too much, but go to your local dealership with your voltmeter, and test any brand new car- I'll guarantee you that it will read higher than 13.5v when running.

EngineBuilder

-Certified mechanic since 1999, DSM'er since 1993
 
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#14 ·
Texvet said:
I will pull the alternator tomorrow and take it another place for a bench test.

I just got back from having the battery tested and it's good. I am think maybe there is dead short some where?

If I remember right - the way to test for a short is to disconnect the negative cable and hook-up a test light - if it comes on there's a short some where?

Will, I did that and the light did not light up. I tested it + to - and the bulb is good... BUT I grounded it (test light) to the block and touched the positive teminal on the battery and it didn't come on?

SO - I grabbed the old multi-meter put it to the disconnected positive post of the battery and grounded it to the engine and I got a low 8V reading. Does that indicate a short?
Click to expand...
With the car off, and all accessories turned off, (be sure to disconnect the light in the engine compartment, if so equipped) remove the negative battery cable, and connect a multimeter between the connector for the cable, and the battery, how many volts are read? This tells you how much latent draw there is on your battery. To find out what system is drawing this power, you will need to isolate which system is drawing it.. This is done by removing fuses one at a time, until you notice that the voltage significantly changes. Once you have isolated the circuit that is causing the problem, check the grounding areas for that cirucuit, cleaning any rust/corrosion that you find. (this info is in your service manual, you DO HAVE A SERVICE MANUAL RIGHT?- oh wait, if you did, you'd know that 15.3v is acceptable.. Get a manual..) If that doesn't solve the issue, check the various wires within the circuit for shorts- you do this by using an ohm-meter, (using the setting on your multimeter that shows the sign for Omega) place one end of the probe at the ground for the circuit, then begin working your way back through the circuit- when you notice a significant increase in resistance, you have found the section where your short is.

-EngineBuilder
 
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Discussion starter · #16 ·
EngineBuilder - Thanks for the information - and the scolding. I think the "fools" you refered to were simply trying to be helpful based on their experiences. Not everyone is as knowledgable as you - and thankfully, not as arrogant.
 
#17 ·
-Tex
Perhaps your right, maybe they were just trying to be helpful. I applaud their effort. I appologise for being overly critical of people trying to help. Spreading misinformation in an effort to be helpful is anything but. With people saying things like "It happened to me, change the alternator quick" I felt I should clear the air a bit.

With that said, have you checked to see if there is a latent drain on your battery?

If you are concerned with the alternator overcharging the battery, check the battery after a short trip. (half hour-45mins) If the battery feels warm to the touch, then there is a good possibility that the alternator is charging when it isn't needed, and the regulator would be the culprit in that instance.
It is highly that the regulator would fail in this manner; the majority of regulator failures include problems such as the headlights dimming when you turn on the A/C, or other types of power drains which the alternator is no longer able to compensate for.


-EngineBuilder
 
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#18 ·
This is what I get from my DSMCD.

Factory sevice manual
1997 eclipse/eclipse spyder
volume 2: Electrical
mitsubishi motors

on page 355

"Regulated volage at each temperature near the battery V
-20 C 14.07-15.07
0 C 13.89-14.89
20 C 13.58-14.58
40 C 13.15-14.15
60 C 12.84-13.84"

I doubt it was -20 C when you measured the voltage; so it looks like you ARE out of range. I don't think anything has changed with the alternator from '95 to '97.
 
Discussion starter · #19 ·
EngineBuilder - I haven't gotten to the possible short issue yet - I will put things back together today and see how it goes.

The votage debate continues.... The guy at AutoZone had 2 alternators brought to his store from the warehouse and both showed the same 14.7 - 15V reading when benched tested. The paperwork that comes with the alternator - stated that voltage out put up to 15.3, sould be considered normal. I am beginning to find some comfort with the higher than expected voltage output.

I also took my battery in to be tested. Before testing it he mentioned it looked "small" pointing to the 420 CCA rating. It tested as being OK. Rudy and his partner at the parts counter, strongly suggested that the size of the battery was contributing to my problem. They looked up the battery specs and said I need a minium of 520 CCA.

Let me expose my ignorance again by asking..... Does the CCA have anything to do beyond getting the car started? Would a lesser than spec CCA put a burden on the charging system and cause the Battery, Brake & Anti-locks to come on? Being that the batery was 2 months old - I went back to Walmart asked them to recheck to see if my car called for a different battery - and it did. They gave me a new 630/520 CCA battery.

I am headed out to reinstall the alternator and new battery - I'll report back. Thanks for all your help and feedback.
 
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