Alternator/battery high voltage at high rpms

[dre]

My friends 1991 obd0 b18 civic 4 door was having probs today.
When we were cruising his lights get brighter at 4k rpm and up.
It only happens 4k and up. Everything would get bright like the cluster and headlights get very bright like its pulling a lot of power.

So we got the alternator replaced 3 times and even tested same prob still. Will use a volte meter and it idles at 14 volts. When idle goes to 4k voltage goes up to 18-19 volts. Could it be the alternator or something grounding.

Topic

[steven jacobsen]

sounds like a shorted battery to me, the alternator keeps thinking it needs more charge. when it gets to higher rpm the alt. can really pump a charge.

[John B Kobberstad]

You may have a bad voltage regulator. Does your alternator have internal regulator or is there an external regulator? Did you replace alternator with 3 new ones or 3 used ones? How was alternator tested and what kind of testing was performed?

[college man]

I’m with the voltage regulator.If its internal to the alternator
then I suggest an OE unit.

[dre]

changed all the 3 with reman. None of them are used.
and the alternator is internal regulator.
also will the battery be the prob?

[college man]

The battery produces 12v The job of the alternator is
keep the system charged.The regulators job is to regulate
the system voltage.

[EricTheCarGuy]

That alternator does have an internal regulator but the computer can alter voltage output. It uses a component in the under hood fuse box called an ELD (Electric Load Detector). I’ve never seen one cause overcharging however. You may have a wiring issue somewhere. You’d need to track down a wiring diagram to see if the computer is sending a signal to increase alternator output. If that’s the case then the ELD, or a wiring issue could be the cause.

[twiggy]

Check that you have good ground connection between the alternator and battery. I would do this by measuring the voltage between battery ground and alternator ground. It’s should be 0V.

[Josh]

I would also check for corrosion at your battery terminals. If you have a lot of it, your computer might not be seeing your battery put out so it might be having the altenator compensate for it. I would just make sure your terminals are clean of corrosion too.

[EricTheCarGuy]

[quote=”twiggy02919″ post=49339]Check that you have good ground connection between the alternator and battery. I would do this by measuring the voltage between battery ground and alternator ground. It’s should be 0V.[/quote]

I don’t think a connection problem would cause overcharging. To me that seems like it would be caused by a control issue. The alternator grounds to it’s mount so you could check it by doing a voltage drop from the negative battery cable to the case I suppose.

[Author]

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