what's a normal draw on a car battery?

[Scootin159]

I'm having a problem with my battery going dead, so I checked the alternator...fine, but the battery wouldn't store a charge for more than 3 days, so I just got a new battery. Thing is though now with the new battery it's still doing it just the same. Is it just a new (dead) battery, or do you think there is a draw on it?

I'm gonna go hook it up to my ammeter & see what the draw is on it (without anything running), but what is an acceptable value? I know there will be some because of the stereo storing the time, etc, but what will kill a battery in 3-4 days?

 

A real quick test for excessive battery draw is to go out and buy a cheapo 12 V test lamp, disconnect the negative battery terminal with the ignition key removed from the ignition.
Connect one end of the test light to the disconnected battery terminal and the other end to the negative battery post.
If the light illuminates, there is excessive draw, now remove one fuse at a time until the light goes out, this is how you pinpoint the circuit that is killing the battery.


(Don't forget to close the doors or the interior lamp will cause the test lamp to light)

 

[Evadman]

parasitic load must usually be under a 1/4 of an amp.

 

[Scootin159]

Originally posted by: Roger
A real quick test for excessive battery draw is to go out and buy a cheapo 12 V test lamp, disconnect the negative battery terminal with the ignition key removed from the ignition.
Connect one end of the test light to the disconnected battery terminal and the other end to the negative battery post.
If the light illuminates, there is excessive draw, now remove one fuse at a time until the light goes out, this is how you pinpoint the circuit that is killing the battery.


(Don't forget to close the doors or the interior lamp will cause the test lamp to light)

That's pretty much exactly what I was going to do, except I was gonna use my ammeter instead of the test light (I have an ammeter, no test light). I'll probably use a test light as it would be easier to read from the other side of the engine bay (where the fusebox is), but if I can't find one would you happen to know about what load that would be?

 

[Scootin159]

Originally posted by: Evadman
parasitic load must usually be under a 1/4 of an amp.

lol, thanks, you answered before I even asked

 

[Scootin159]

Originally posted by: Roger
A real quick test for excessive battery draw is to go out and buy a cheapo 12 V test lamp, disconnect the negative battery terminal with the ignition key removed from the ignition.
Connect one end of the test light to the disconnected battery terminal and the other end to the negative battery post.
If the light illuminates, there is excessive draw, now remove one fuse at a time until the light goes out, this is how you pinpoint the circuit that is killing the battery.


(Don't forget to close the doors or the interior lamp will cause the test lamp to light)

I just checked out that VW in your profile, that thing is awesome. Never knew those were that big inside, but don't they have like a 90hp engine or something like that? Does that top leak at all? Either way, looks like a fun vehicle.

 

[Evadman]

I just checked out that VW in your profile, that thing is awesome. Never knew those were that big inside, but don't they have like a 90hp engine or something like that? Does that top leak at all? Either way, looks like a fun vehicle.

Not when you replace the stock motor with a Corvar that has been cleaned and prepped beyond all imagination.

 

[Zenmervolt]

Gotta be the 944. It's not shorting on the hood, is it? That's been known to happen, though that's usually a sudden thing and not recurring. The draw on the battery should only be a few milli-amps. You said that the alternator was OK, how'd you measure it? You should be getting 14 volts across the battery terminals when the engine's running. As for what will kill a battery in 3-4 days, it would have to be a fairly considerable draw. I think you'll definitely be able to tell if you're drawing more amperage than you need to run the clock and the radio. Remember that about 1,600 milliamp hours will power a digital clock for a really, really long time.

ZV

EDIT: Knowing how much Roger loves that bus, I'm willing to bet that the top doesn't leak at all. Which is more than I can say for the top on my 914. (26 year old rubber doesn't seal really well.)

 

I just checked out that VW in your profile, that thing is awesome. Never knew those were that big inside, but don't they have like a 90hp engine or something like that? Does that top leak at all? Either way, looks like a fun vehicle

Thanks for the props, click on my website again, then click on "more power"

By the way, the stock engine produced 55 BHP, this in a 5,000 lb vehicle

Yes Zem, my top does not leak a drop

 

[Scootin159]

Alright, I'm frozen, but I just checked it & let it run for about 15 min to charge the battery a little.

It's been 4 days since I've started it, average temp about 15* I'd guess.

I checked voltage accross battery: 11.9v, wow, it's actually got power. Last time after leaving it a week it was at 8.2v (after a week of 0* average temps).

I then disconnected the ground terminal & put ammeter inline: ~3.3mA
When I connected/disconnected the ammeter I would hear a relay click, so I diagnosed which relay it was & pulled it (secondary connections, whatever that is): now ~3.0mA
Pulled radio/alarm/clock fuse (been having issues with the alarm, so wondering if it was draining it): ~2.7mA

I also heard a little clicking around the headlight motor area. After my accident I had to prop the headlights up manually & then I disconnected the fuse for the motor. My guess is that there is a relay that is telling the motor to run & pull the lights down. The motor isn't running because I pulled the fuse for that, but the relay must still be getting power. Would a relay be drawing enough juice to do this? If so, good, I'll have them fixed monday (along with the rest of the bodywork). This and the combination of the 0*(highs) weather might have been enough to kill the battery in a week or so, you think?

I then re-connected the battery & started the car. Checked voltage: 13.7v, alternator must be good.

 

[Scootin159]

Originally posted by: Roger

I just checked out that VW in your profile, that thing is awesome. Never knew those were that big inside, but don't they have like a 90hp engine or something like that? Does that top leak at all? Either way, looks like a fun vehicle

Thanks for the props, click on my website again, then click on "more power"

By the way, the stock engine produced 55 BHP, this in a 5,000 lb vehicle

Yes Zem, my top does not leak a drop

Yeah, I remember our neighbor had one & he would have to go down to 2nd gear to make it up the hill in front of our house. After looking over what you've done with it though, I'm very impressed. That would actually be a lot of fun for road trips.