Batt/Alt/VR Head Ache

[cmann250]

I was thinking something died and was stinking like sweet hell in my truck until I discovered it was coming from my battery. Thank you Mark, because I made the connection from one of your posts. I blamed the stupid pigs for a while too.

This is the 2nd O'Reilly Super Start battery that I have had go bad. Key off I have 13.86V, key on 13.76V, and idling -14.87V. What the heck does a negative reading mean??? Alternator is an Advanced unit ~1 year old, voltage regulator is about the same age, and battery #2 is under 6 months old. Battery #1 split, spewed acid, and was returned. I changed nothing after battery #1 split. The ammeter in the dash has never worked. The only reason I replaced the alternator was because I didn't have a multimeter at the time and I was a chronic noob. I don't think it's the battery because 2 different ones have gone bad. I've never had a starting problem either.

What gives?

[Mark Nixon]

NEGATIVE 14.87, from a POSITIVE state of ~13.86, seriously?
I've never heard of an alternator being able to reverse charge a battery that has a normal state of charge.
I suppose it's possible if the rectifiers are at issue.

I'd certainly have that alternator checked, at the VERY least.

Mark.

[Tacoclaw]

A negative reading generally means that the person running the DMM had switched the leads and has the red lead on the ground side.

14.7 is where my truck idles at, so that sounds about right.

[ellis93]

A negative reading generally means that the person running the DMM had switched the leads and has the red lead on the ground side.
.

Yep

Wonder if that alt is dumping a huge amount of amps.

Just for giggles put your multimeter on ac volts and measure battery voltage again. ANY ac current and the alt is bad

[cmann250]

Well I did have the leads backwards But to make things even more interesting I just fired it up and it's reading 17.6-7V.

Ellis, I have 38.xV of AC current

[Mark Nixon]

I'd say you have a munched alternator.
That it's pushing 17+ volts means that it may have gotten the voltage regulator, too.

Mark.

[Tacoclaw]

Yup, I welded on my truck with the battery connected and burnt my regulator up. Fired it up and the volt gauge was pegged. Got the stinky battery syndrome and everything. Try throwing another regulator on it before you spring for anything more expensive.

[ellis93]

Ahh, buy(warranty)both. Any ac volts is bad news. That's what the rectifier in the alt takes care of. It knocks the top and bottom off of the ac current to make the dc current.

That's the crude explanation I received on it anyhow.

[Hansen01]

id say get yur alt. checked, then good or bad, replace the voltage regulater and the plug. i was going threw regulators like crazy for a while until i put a new plug on my regulator. Ya know if you got your ammeter working correctly youd know if your voltage regulator goofs occationally

[cmann250]

I had a reading in the 19's after the drive home for lunch and in the 15's after I quit for the day. It's about a 5 mile drive. Nothing like inconsistancies. Of all people, the Amish have a good alternator, starter, and electric motor repair shop about an hour away. Mark, I read in one of your posts about beefing up grounds. Where do I need to look and how thick do these need to be?

Hansen, I was just thankful that everything else worked

[Hansen01]

when my plug and regulator were bad mine would go to 20
One ground i know they told me to add was one from the battery to the regulator, size wise, i just went with the biggest one i had lieing around

[cmann250]

I took a 2 hour trip yesterday and once I got to my destination, the battery was sizzling and smoking. I got a battery off of revemup15 and didn't have any trouble on the 2 hour drive home. The battery wasn't even warm when I got home. This leads me to believe the rest of charging system is fine.

I drove for a while with out a battery. All lights worked, but suddenly it shut down. How does the FSS work? Power=open and no power=closed?

[CumminsPower59]

How does the FSS work? Power=open and no power=closed?

YUP!

[cmann250]

Did it have residual power hiding in the system to keep it open? I bet I drove 20 miles with no battery

[CumminsPower59]

I don't know on that, but years ago when I had my 91 W350, I lost the alternator coming home from my 2nd shift job, it ran the whole way home with very little power. I don't think it takes much to energize the FSS. I gutted the one on my 92 for two reasons, one for the above (loss of alt, batt, etc.), and the other because I was running a cranked up pump with stock IC injectors. Pull cable shut down is the only way to go