Parasitic Battery Drain... Alternator?

[legokcen]

I've got a '97 V6 and a few days ago, in the morning, the battery was completely drained. Everything was good the evening before when I parked it, but in the morning, it was completely drained. I charged it and took it to autozone thinking I may need a new battery and asked them to check it.

The first said my alternator was bad, but then told me it was just the battery. So, I buy a brand new battery and replace the 4.5 year old one that was in it thinking I'm good. Drive the truck home, then take it to work the next day and back. The following morning (this morning), I got get in for work and it is completely drained again. Nothing.

I trickle charge it while at work and this evening took it to another store to check, thinking maybe it's the alternator. When tested, the no load voltage was 13.21V and the loaded voltage was 12.69V. I was told this was ok, but it could be the problem. I thought it should charge at a higher voltage than that.

I head back home (I'm gone for the next few days so buying it now would be no help), and after shutting off the car, the voltage is 12.06. About 30 minutes later, it's 11.88. I've disconnected the batter to keep it from getting all the way down.

When I put the multimeter on positive and then on the casing of the alternator, I get a voltage reading. Is this indicative of a short? Should I replace the Alternator?

The 11.97V picture attached is the alternator casing to the pos battery cable. 11.99 was a few moments after cutting the truck off. When I came back 30 minutes later, it was 11.88V.

Any help would be greatly appreciated.

 

[LittleCaesar]

Can you multimeter read amps? If so, then switch to mA, hook it in series between the negative battery cable and post and see what reading you get.

Alternator original?

 

[legokcen]

Yes, it can. I’ll do that. Thanks!

I’m pretty sure the alternator is original. I’ve had the rig for 10+ years.

 

[TheDurk]

Why don't you start by unplugging alt plug and unscrewing the big wire*? Then see if the drain disappears, either by using the meter as suggested or watching the battery voltage drop as you did before.

If it's not the alt, there are lots of how-to's on how to chase a parsitic drain. If it is the alt., and it's a factory Denso, get it rebuilt--probably a bad regulator. A puppy dies every time someone trades a factory Denso as core on a crap reman.
__________
*Don't let that big wire contact ground(i.e. any metal), that could ruin your afternoon.

 

[Unner]

If it is the alt., and it's a factory Denso, get it rebuilt--probably a bad regulator. A puppy dies every time someone trades a factory Denso as core on a crap reman.

I'm only posting here to reinforce this. Don't replace your Denso with garbage Chinese parts.

 

[19963.4lsr5]

Depending on the temp of the engine bay the battery post voltage should be 13.5 to 14.5v with engine at idle and no accessories on. And it should have no problem maintaining that same voltage with headlights on and the fan on at the same time.

My one alt had a problem maintaining voltage just running the engine. Turn on the lights and the alt fell on its arse. Ended up being a bad diode in the bridge.

Another alt had low output and it was the brushes. They were worn to the point they were not touching the two copper rings on the rotor properly.

Brush holder assemblies are around 23 dollars and easy to replace. The regulator and diode bridge are much more expensive if you buy them OEM. I mean much more.




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[Scramble]

If it is the alt., and it's a factory Denso, get it rebuilt--probably a bad regulator. A puppy dies every time someone trades a factory Denso as core on a crap reman.

I'm only posting here to reinforce this. Don't replace your Denso with garbage Chinese parts.

Agreed! Or a POS GM CS 144. :lol:

 

[LittleCaesar]

As others have said it sounds like the alternator, that the brushes have gone and the alternator just isn’t working anymore. Never saw the battery light come on?
https://m.youtube.com/watch?v=71_kBhg6_-A

 

[fourwd1]

To answer your question, yes an alt can cause a parasitic drain and still be able to partially charge the battery. One of the diodes in the diode trio can short and cause that.

 

[wcjeep]

Alternator casing is usually Ground. Check for resistance from alternator casing to negative on the battery. Should be very low resistance.

12.69 DC Voltage while running is bad. Each cell of a lead acid battery puts out about 2.1 DC Volts. This means a new battery at rest should be about 12.6 DC Volts with no major draw.

Engine draws about 20amps just running.

 

[Ron Burgandy]

check every switch in your cab. i went through this with my duramax. ended up being the passenger seat switch was stuck and was sucking the life out of both batteries.


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[19963.4lsr5]

As others have said it sounds like the alternator, that the brushes have gone and the alternator just isn’t working anymore. Never saw the battery light come on?
https://m.youtube.com/watch?v=71_kBhg6_-A

Good question on the battery light.

My battery light did come on for the 80a alt with the brushes worn.

On the 70a alt with a bad diode (open) no battery light. And the alt wined under load.




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[legokcen]

So, I've done the parasitic test and was pulling 46.3ma with everything off. I've found the culprit and will have a figure out why that circuit (something I put in) isn't happy anymore.

With that circuit out, I'm seeing a 0.17 ma draw with everything completely off. I wanted to ask this group if I need to continue to hunt. I see how the big drain would have done it, but wasn't sure if 0.17 ma needed more looking.

 

[19963.4lsr5]

46ma should not kill a group 24 battery overnight.


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[LittleCaesar]

So which circuit is it.? But no, such draw will not kill a battery overnight.

Have you removed the alternator and had it tested? Sometimes if the alternator is at the point of no return, and not just in need of a brunch replacement, it will be very hot to the touch.

 

[legokcen]

Truck started up fine this morning, so the drain is gone. It was the circuit I disconnected.

It was a constant 12V circuit I tapped to install relays for the rear LED lights and the eLocker. It's been fine for about a year now so something happened in the last week to cause a short. I'll look into it this weekend. Right now, they're both unhooked.

I replaced the alternator due to what I feel now is a misdiagnosis and now am conflicted on whether I should return it or not. It charges at about 0.5 V higher than my old one.

 

[thegipper]

Hopefully you didn't get rid of your OEM denso alternator for some POS parts store alternator.

Aftermarket alternators (and starters) for these trucks are junk.

Glad you found the problem though!

 

[LittleCaesar]

As [MENTION=116387]Unner[/MENTION] said, if it isn’t a Denso alternator, return it and just buy some new brushes for your old one.

The draw must have been there for some time; the 35m amps isn’t great, or enough to kill a healthy battery nightly.

 

[TheDurk]

Truck started up fine this morning, so the drain is gone. It was the circuit I disconnected.

It was a constant 12V circuit I tapped to install relays for the rear LED lights and the eLocker. It's been fine for about a year now so something happened in the last week to cause a short. I'll look into it this weekend. Right now, they're both unhooked.

I replaced the alternator due to what I feel now is a misdiagnosis and now am conflicted on whether I should return it or not. It charges at about 0.5 V higher than my old one.

Check your relay wiring. It is possible to miswire one so that the coil is permanently engaged and the switch directly controls the load. It works perfectly (until the switch melts) but the relay coil is sucking power 24/7 even with key off. One way to check is to disconnect the battery with key and load switch off--if you hear a relay click--that's your culprit.

This happened to me when Hella sold me a fog light harness with the wires installed incorrectly in the relay plug. Really pissed me off. It took me a year to figure out I had the drain since I drove the truck every day, everything worked, and the battery never went dead. Then the switch melted.

What may have happened is you had the drain for a year, but then the alt. started going bad, and all of a sudden you did not have enough charge to start the next day. Occam's razor, at this point.

BTW, coil draw on a typical Bosch 12V relay is about 30mA.

 

[Floydp]

I have a 98 that battery dies overnight, draw coming from Efi fuse there is a ton of things on that circuit. Started unplugging each one with no drop so I’m stuck any help?