Alternator Questions

[theholycow]

I'm 99% sure that the SG measures voltage itself. I seem to remember it displaying voltage properly when I was using a 9v battery to power it while I input long XGauge codes.

[bowtieguy]

thanks guys...all posts appreciated.

think i'll keep an eye on it and see if any symptoms(none yet) occur. makes me wonder tho, why the previous owner bought a new battery.

[GasSavers_Erik]

Originally Posted by trollbait

Is this a recent development?
What I gathered from an HHR site, is that alternator will put out 14+ volts only when in charge mode. Presumably when the computer decides the battery needs to be charged.

I know you stated the battery is new, but how long did it sit on a store shelf? Perhaps it didn't have a full charge going into the car.

I think this is a good point- maybe you are just seeing the results of the ECU managing the alternator's output.

[VetteOwner]

easiest way to test to see wtf its doing is get even a cheapo multimeter and set to DC volts and measure at the battery terminals.

my s10's volt gauge would spike down to under 9 for no reason and i was thinking the alt was taking a crap. hooked up a multimeter and layed it on the windshield, when the gauge fluctuated the meter stayed constant 14v

[bowtieguy]

new observation: it seems to run consistently at 14 volts when the engine is cold. as it warms (near full warm-up), the fluctuation begins; again never dropping below 12.

is there a possible heat soak issue?

[bobc455]

There is some intentional thermal effect, yes. The design theory is that the battery needs the most recharging when the engine has just been started (and therefore the regulator is cold).

However, cheap aftermarket voltage regulators don't have good control of temp vs. voltage and might drop too low.

On my Buick, I spent the money for a GM voltage regulator (internal to the alternator) because it has proper temperature circuitry. When I replace the alternator every 3-4 years, I disassemble the alternators (old and new) and keep my GM voltage regulator, because it works correctly.

The GM regulator cost like $35, and a cheap rebuilt alternator (using ultra-cheap parts, including an ultra-cheap/poorly designed regulator) will typically cost $40-$50. Therefore they are probably buying some $3 imported regulator...

Having said that, as long as you are maintaining a minimum of 13.3V, even when hot, things should be just fine. A more normal range is 13.6 - 13.9, and some cars will maintain 14.2 (which is really higher than you need) when hot. But if you are seeing voltage below 12.6 while running, then you have a problem.

-BC

[bowtieguy]

thanks Bob. i'll have to watch where in the 12 volt range it drops to more closely. the alternator has a honda label, so it COULD be the original. the car has nearly 200k miles, but the previous owner bought OEM replacement parts so...

def would look to use OEM denso to replace it if necessary. made up my mind, the location dictates that i do not wish to do this more than once!

[VetteOwner]

yea some parts on any car can be goofy, my s10's was charging fine but had bearing failure at 140 somehtingK styarted that growl then a high pitched squeal haha yea time to swap it out...

[bowtieguy]

Originally Posted by bobc455

But if you are seeing voltage below 12.6 while running, then you have a problem.

well, it does drop very briefly to 12.5, even .4, but generally stays above that.

[Ford Man]

There's a chance you just need new brushes. My '88 Escort with nearly 515K miles still has the original alternator, all I've done to it is replace the brushes once since the car was new. I'd suggest looking to see if the brushes can be removed and changed if needed without removing the alternator. A new set of brushes would probably set you back about $5.