Am I nutz? Electrical question

[Bonnewagon]

A fairly new battery is getting weak slowly. After charging the battrey seems good, shows 12.5 volts, and you place a load on it with a carbon pile tester, it drops to 11.5 volts. Good battery, right? Now, I start the engine, test the battery, and it jumps to 13 volts right away. Alternator is good, right? BUT, when I put a load on it with the carbon pile tester, voltage drops to 9 volts. Alt doesn't look so good now. So I take the alt to my old school family run auto electrical re-builder guy. The old timer is busy, so a younger guy helps me. I explain the situation, and he keeps saying he thinks the battery is bad. But the battery was replaced less than a year ago. The last one had a bad cell, under load it went right to 10 volts. This new one re-charges immediately, and only gets weak after being operated for a week or more. I think the alt is not keeping the battery charged properly. I think this alt is OEM and about to hit 100k so I don't mind getting it re-built. Side note- an engine oil leak has been quietly dousing the alt with crud. I can easily see that causing trouble. Am I right? Or am I nutz?

 

[64nailhead]

I'll say you're nutz (I've seen the joke of the day thread haha).

Regarding the alternator, amps is the concern, not volts. An amp clamp would be your friend for determining the root cause of the issue. But from your description about the alternator, I'd say you're on the right track.

 

[Bonnewagon]

I knew someone would agree I am nutz. Everyone around me does. I am old enough to remember when cars had ammeters on the dash. Now all I see are voltmeters, if even that. I think this alt is producing power, but the regulator is not directing it enough to properly charge the battery. Either way, the alt needs to be freshened up if for no other reason than to eliminate it as the problem.

 

[86 Salon]

To properly load test a battery, you need to apply 1/2 the CCA to a fully charged battery for 15 seconds. The battery should not drop below 9.6v. If you don't have an adjustable carbon pile, you're just guessing.

 

[Clone TIE Pilot]

I knew someone would agree I am nutz. Everyone around me does. I am old enough to remember when cars had ammeters on the dash. Now all I see are voltmeters, if even that. I think this alt is producing power, but the regulator is not directing it enough to properly charge the battery. Either way, the alt needs to be freshened up if for no other reason than to eliminate it as the problem.

That is why many say to run the volt sensing wire for the regulator to the starter solenoid terminal instead of the battery teminal on the alternator.

 

[ck80]

A fairly new battery is getting weak slowly. After charging the battrey seems good, shows 12.5 volts, and you place a load on it with a carbon pile tester, it drops to 11.5 volts. Good battery, right? Now, I start the engine, test the battery, and it jumps to 13 volts right away. Alternator is good, right? BUT, when I put a load on it with the carbon pile tester, voltage drops to 9 volts. Alt doesn't look so good now. So I take the alt to my old school family run auto electrical re-builder guy. The old timer is busy, so a younger guy helps me. I explain the situation, and he keeps saying he thinks the battery is bad. But the battery was replaced less than a year ago. The last one had a bad cell, under load it went right to 10 volts. This new one re-charges immediately, and only gets weak after being operated for a week or more. I think the alt is not keeping the battery charged properly. I think this alt is OEM and about to hit 100k so I don't mind getting it re-built. Side note- an engine oil leak has been quietly dousing the alt with crud. I can easily see that causing trouble. Am I right? Or am I nutz?

You can also both be right, and nutz, at the same time. Not saying that is the case here though. Regardless the oil crud isn't helping things either so I'd clean that up and fix the leak too while you're poking around.

 

[Bonnewagon]

I don't have one so I am still guessing. But here is what happened. My old timer re-build guy called me and said the alt was just fine. The brushes look brand new and it puts out everything it should. This would not be normal for a 100k mile alt. Then he said, are you getting oil on the belt? Well, he was right. The timing cover seal was weeping oil, not a lot, but over time enough to contaminate the belt with oil so that when under a big load, the belt slipped and the alt could not put out. This was insidious as it took a LONG time to wear down the battery. What I feel really happened was the prior owner had the alt and belt replaced at a shop, but they never addressed the root cause, the oil leak. So I was right, the alt was NOT keeping the battery charged. And I AM nutz for working on everyone's car but mine. What is that they say, the shoemaker's kids go barefoot?

 

[John Canon]

. . . What is that they say, the shoemaker's kids go barefoot?

But look how happy they are, while Dad is twisting his oily fan belt in knots.