Voltage light

4

4AU4LIFE

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16 June 2002
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Jacksonville
Ok so here is my problem. I hope someone can point me in the right direction.
Come out to my car after it sitting in cold temperature (35 deg) for a few hours and start it up.
Driving home and everything is fine (25 mins) until I get to the last stop sign. The dash lights go dim and the voltage light comes on and the voltage gauge drops to midway. It normally is 3/4 way up.
I rev it up a little and the light goes out but volts don't move. Upon idle the light comes back on.
I drive the rest of way home without incident.
I start car next day and let it run while I wash other car. I periodically look at dash and everything is fine. Then the same thing happens again.
I have measured the battery with engine running and get a constant 12.0-13.0 volts.
Took the 4 pin connector off back of alternator and started car and light didn't come on so I can assume the light is working correctly(per Helm manual).
I don't have a load tester but am I safe to say that the voltage regulator is bad?
The battery does have a little corrosion on the positive terminal.
 
Sounds like your Alternator output is weak. One or more of the diodes have failed. Alternators are not hard to find on the used market. Any one that installs a CT supercharger ends up with one sitting around.
 
Last edited:
It could be a loose belt. 12.0 volts is a bad alternator. 13.0 volts is a good one.
the battery static voltage is 12.6 volts, anything over that is charging the battery.
What was the engine speed when you took your measurement?
If the voltage is low at idle but then comes up past 12.6 when you rev the engine, a loose belt is a possibility.
I'd check for that.
 
What was the engine speed when you took your measurement
Click to expand...
At idle.
If the voltage is low at idle but then comes up past 12.6 when you rev the engine, a loose belt is a possibility
Click to expand...
Would it just loosen all of a sudden?
I also put a load on just the battery. Lights, depressing brake pedal, stereo on and interior lamps on without engine running and volts got down to 9.4 in a matter of a couple of minutes.
 
Its always slipping thats why it goes away when you speed up the engine, the alternator gradually starts spinning enough to make up for the load even with the slipping belt because the engine is turning fast enough to compensate for the slip.

An easy way to tell is the belt is loose is if you can spin the alternator pully by hand when the engine is shut off, its loose.

The faster they spin, the more current alternators supply, up to their rating.

Most alternators I'm familiar with reach their rated output current at around 5000 rpm measured at the alternator. Due to the gear ratio of the smaller pully on the alternator, that maximum typically occurs somewhere around 3500 engine rpm.

So if you have lower output at lower speeds, a diode or two could fail in your alternator, it will show up at lower speeds also.

There are typically 9 diodes in the ouput section of an alternator, 3 phases with 3 diodes in each phase. So one or two can fail and it will still work but at lower current levels.

If one of the diodes in your *diode trio* fail, you will see your battery idiot light on your instrument cluster glow real dim all of the time. You can't see this in daylight, only total darkness, its dim.
The diode trio is separate from your output diodes, it powers the spinning part in your alternator, the rotor, which is what creates the magnetic field that spins and creates the 3 phase AC voltage that your output diodes rectify into DC for your charging system.

I almost forgot.... the first thing I would do is clean your terminals at the battery... if they are dirty, your battery won't be getting charged optimally. If you want to verify you have dirty terminals, measure the voltage at the alternator and at the battery, they should be within a few tenths of a volt.
 
Well after following the test procedure as spelled out in the Helm manual the culprit is a bad regulator.
Luckily the alternator is a snap to take off and take apart. Now just have to hope the local Honda, Acura store has it.
BTW, Thanks to all those offering help and assistance to me.
 
Kinan said:
Hey just a thought... does the new regulator come with a new set of brushes??

You might want to make sure they are in good shape.
Click to expand...
No, the brushes do not comes with a regulator. I did check them already and they are in good shape.
Thanks for the tip though.
Kinda surprises me that the regulator went bad in an alternator that is only a couple of years old. :(
 
Kinan said:
Have you used jumper cables lately?

tried to jump of been jumped?
Click to expand...
I had never been jumped in it before. I did the other night to help rule out the possibilities of what was wrong.
Then my father and I followed the test procedure in the manual and determined that the regulator in fact is bad. I plan on replacing the battery at same time.
 
*generally* jumping is what causes regulators to go bad -- unless the design is prone to heat related failure.

I haven't heard of many regulator/alternator failures on Prime so not very common (?).

Lets hope this fixes it and isn't just following the failure flow chart because it failed when you jumped and then some other underlying prob still exists after you change it out.
 
re

ok another question,

Is it normal to have the voltage meter almost pegged? Its not max but 1 bar from max. And its consistantly that high..
 
mul1gan, check your battery and terminal connections, that could be the problem.
 
re

will do.. If I had to buy a new battery, Is there one better then the other? I think i've heard of a lightweight battery mentioned on the prime.. Anybody have any experience with that?

thanks
 
If it is indeed over 14 volts your reulator is most likely the culprit, as its no longer *regulating* the voltage. Now more in the free run mode. The faster the alternator spins, the more voltage is put out.
 
Re: re

mul1gan said:
ok another question,

Is it normal to have the voltage meter almost pegged? Its not max but 1 bar from max. And its consistantly that high..
Click to expand...

My voltmeter is also almost pegged. It has been since new.
 

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