Electrical question

[drohweder]

Finally got around to testing the truck. I kept the digital meter. First on the using a 20V DC setting, the battery was at 10.6v. I jumped the truck (didn't take much) and retested with the engine at idle. The battery was above 13 and the output cable off the alternater was 14.8V. After 20 minutes of driving the battery was at 13.4V. I took off the negative cable and went to bed for the night assuming battery is OK, the alternater is charging adequately. When I tested it again this morning the voltage had dropped to 11.3 volts and the truck barely started. What does this mean as the battery was not connected overnight--not possible to drain when the ground is disconnected right?

So I run the truck and the voltage is again above 13 on the battery (tested to fame ground and between posts). QUESTION--will a battery not have enough juice to turn the starter below some threshold number (i.e. 12 volts)? Its not like my battery is dead becuase all I need to do is place jumpers from my 80 (engine off) and it fires up first turn of the key.

I disconnect the + cable and place the meter leades between the post and terminal. Set to the 20mA setting with the leads switched up I get a reading of 0.5 with the key off and out. I start removing fuses and the only change is when I take out the lighter fuse and it drops to 0.2 (is this a significant drain?). Shouldn't I be at 0.0 if all is well anyway? So problem solved right? I leave the fuse out (now my interior lights and high beam indicater don't work (tipped off from the wiring diagram) but thats ok. The truck sits for about an hour and when I go to start it up it turns over a few times, I pop the clutch and am off to work....now the truck is parked on a hill and I am writting this post.

Any tips? What physically happens to cause a drain? It an exposed hot wire grounding out on metal---what should I be looking for? Remember, if I drive this truck consistently (don't let it sit for a couple of days then I never had this problem (took 8 months for me to realize it as I drove another car for a week). Thanks for the help.

 

[IDave]

Yes it sounds like you have a slow drain, which is probably a grounded wire or switch. It may also be that your battery is old and not holding a charge well.

 

[drohweder]

Battery is a new (<6mo) Optima Red Top. Must be a drain somewhere.

 

[hammerhead]

If the voltage is dropping with the batt disconnected then I would be suspect of the batt. You stated that the batt is only 6 mos old. Check your mfg date on the batt. I'll bet it is alot more than 6 mos old. Point is just because you just got it doesn't mean it's new. We stock our lead/acid batts dry and fill them at the time of purchase. Can't do that with an optima.

Not saying you don't have a drain but if you eliminate possibilities then you get closer to the problem.

 

[IDave]

That's what I'm thinking: as Hammerhead sez, you shouldn't be losing charge with the battery disconnected. You could definitely have 2 problems.

 

[Desertdave]

In my experience the red top Optima batteries don't take too kindly to being seriously discharged. They also don't like being charged at 15V. Your battery may now be bad if it doesn't hold a charge overnight, diconnected from loads.

I have gotten over 8 years of use out of the two former red top Optimas in my Cruiser. I have killed one in my Ford when the alternators internal regulator would malfunction when hot. I have gotten years of use after a single deep discharge on the red top in my daily driver, I am just very careful to not leave the interior light on in the garage over the weekend!

 

[Klunky Chris]

In my experience the red top Optima batteries don't take too kindly to being seriously discharged. They also don't like being charged at 15V. Your battery may now be bad if it doesn't hold a charge overnight, diconnected from loads.

Thats a big 10-4!

I strongly suspect that your optima is toast from a slow discharge. I have had 3 optimas die from this and recently diagnosed a similar problem in Scott Simmons 80. Optimas are great, but don't deep cycle them or they die wierdly and are hard to figure out. My experience is that if an optima is less than 11v it's gone. Your voltage drop while disconnected overnight verifies this.

It also sounds like you've got a bad connection between your alternator output and the battery. With a good connection you should only see maybe .1v -.4v difference between the alternator + nut post and the + of the battery. Check your batt post connections first, this is a notorious area to cause resistance, even if it *looks* clean.

Find your drain, fix it, and check your battery and most likely replace it.

You're on the right track!