Voltage: How High is Too High?

[NathanR]

I've been trying to figure out if I have other problems that may have contributed to several consecutive heater blower fan failures. Measured the voltage in my car today, at the cigarette lighter.

Engine Off: 12.4 v
Engine On (1500 rpms): 14.5v
Engine On w/load: 14.3v

My bentley manual says "voltage much above 14.2v indicates a bad voltage regulator". Is
14.5v too high???

regards,
N/

[911_Dude]

I dont think 14.5 V would cause the failures. But 14.5 would be my limit.

[john walker's workshop]

me too.

[NathanR]

Thanks guys. I'll stop worrying about it for now.

BTW, I checked it at 3000 rpm, and the voltage was the same - 14.5v

[darrin]

nathan -- my 86's VR would generally show relatively normal voltage, but would occasionally spike to closer to 20 volts. This would manifest through the more commonly observed "dimming" of headlights/gauge lights (dimming from super-bright to "normal" at the end of a voltage spike) and/or illumination of my seatbelt warning light for no reason. The overcharging also caused (what I now understand to be) a nice sulphur smell as the battery boiled away.

So, it might be a good idea for you to both a) rig a voltmeter more constantly to see if you're spiking (I use a feature built into my escort/passport radar detector) and check your battery to be sure it's not boiling out/low on fluid)

[drleah]

Not a mechanic, but when I got my '82 911 the tach started bouncing. So took a mm and tested per Bentleys thinking maybe something in the charging circuit. Cleaned up new battery new hold down etc. stopped bouncing then started again. My voltages were very similar (within 0.1 V). Pulled the alternator and VR. The brushes were worn by at least 1/2. New VR installed. I am sure that this is/was caused by multiple issues (floating/bad ground, shorts etc) and I am digging through them methodically. But I wouldn't discount the voltage regulator yet...


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[NathanR]

Darrin,

Good point. I'll have to think about how to do that. I wonder if that defect would be detectable if I took the alternator to a shop to checked? It would probably be just random whether it did it while on test bench.

I've not noticed lights dimming and I don't want to pry the lid off the battery at the moment. I'll see if I can't borrow a plug-in voltmeter and observe.

Thanks,
N/

[RDM]

Nathan,

Wasn't there something going on with your headlights, too?

Stop by for the voltmeter. I'm home.

[NathanR]

The switch is a little hinky. Sometimes jiggling it makes the lights and dash illumination go out altogether. I don't think it's related to the charging system. I'll give you call sometime tomorrow about borrowing the voltage tester, and your tap and die set too, if you're willing...

[wwest]

Originally Posted by NathanR

I've been trying to figure out if I have other problems that may have contributed to several consecutive heater blower fan failures. Measured the voltage in my car today, at the cigarette lighter.

Engine Off: 12.4 v
Engine On (1500 rpms): 14.5v
Engine On w/load: 14.3v

My bentley manual says "voltage much above 14.2v indicates a bad voltage regulator". Is
14.5v too high???

regards,
N/

A fully charged lead acid battery will have 2.25V/cell, 6 X 2.25 = 13.5 volts/static.

During charging peak voltage might be above 16 volts, but average ~14.7 at most. Lots of MM will read peak which will be misleading. With a battery being, needing a heavy charge or a heavy current load, headlights, blowers, etc, the voltage back in the engine compartment may be somewhat extreme.

[Bob Kontak]

Originally Posted by NathanR

I've not noticed lights dimming

When at 3,000 rpm and you read 14.5 volts, how much does the voltage vary? Same test at idle.

The one or two V-regs I have suspected and replaced (with dimming headlights) demonstrated a one half to one volt variance at battery. Once replaced, the variance was one or two one hundredths of a volt.

[dshepp806]

No worries at that voltage. I'd just watch it,..and double-check with a different meter.

Doyle

[NathanR]

Bob,
Using Dru's plug-in voltmeter while driving, the voltage varied between 14.0v and 14.5, but was usually around 14.3v. Based on your observation, this VR may be on its last legs but I don't think this is frying my blowers.

I may replace it as preventative mtce, given how much of a PITA these blowers are turning out to be...

Thanks,
Nathan

[T77911S]

mainly depends on the type of battery you have in there.

[Mighty2.0]

I'd love to have 14.5 at my battery with engine running - struggling with voltage loss.

[Flat6pac]

With a Carrera, too much voltage will fry the brain.
Bruce

[NathanR]

Went ahead and ordered a new VR, will install when it arrives.