This is an ammeter . . . isn't it? And how do I use it?

CarreraS2 · 03-15-2006, 07:22 PM

See pic - this is an ammeter, correct?

I'm testing for current draw that is draining a battery. Supposed to connect the ammeter between the battery ground and the negative post on the battery.

Says a range of 0 to 100 milliampere is normal, a current of 400 miliampere (or 0.4 amp) may indicate something is drawing too much current.

Q: What do I set this thing at?? And what readings should I look for at that setting?

Fl Ted · 03-15-2006, 07:40 PM

Set it on the 200m (milliamp) scale initially. If it goes off scale ( display goes blank or flashes) youll have to use the 10 amp scale, which usually has different recepticles for the leads.

CarreraS2 · 07:52 PM

Thanks.

I set it at 200, it reads 112.3.

I take it that setting it at 200m is just setting a range.

So my 112.3 reading is 112.3 milliamperes of current draw.

That seems close enough to the acceptable range - my charging system is working fine (tests fine - 13.7 volts of charging), but the battery seems to weaken quite a bit if the car sits for 2-3 days.

Maybe a bad battery.

Fl Ted · 03-15-2006, 07:57 PM

Disconnect the ground cable and see What happens to the battery after sitting a few days.

Wil Ferch · 03-16-2006, 07:28 AM

You don't mention the year of your car....

For example..the 84-89 Carrera's should show no more than about 16 mA standby draw. The 964's have about 65mA standby....

- Wil

rick-l · 08:03 AM

My 88 cabriolet with a state of the art (for 1988), PO installed, CD and Alarm system ("step away from the car") draws about 80 milli amps with the key in my hand.

On an ammeter you should start with the highest reading first. You don't show all of your meter but hopefully the ammeter input requires you to move the test leads to a different input (maybe 2?).

The reason I say this is the fuse on my Fluke DMM (a cheap one) for the 200 milli amp scale costs $8 locally

I think it will interrupt 5000 amps.

Oh and another thing, is 13.7 volts high enough to completely charge the battery? I had the let it sit for 5-6 days it wouldn't start syndrome. Went through the same things you are doing and gave up. Didn't put it all together but I replaced the voltage regulator when I first got the car (all that was wrong was the brushes were worn but I didn't know that before I took it out. When the lights started flickering again after a couple years I got a new (rebuilt) alternator. Problems went away.

CarreraS2 · 03-16-2006, 09:03 AM

Thanks. This is on a 914, which should I suppose have just about no standby draw. It doesn't even have a clock. The only thing is has is a stock blaupunkt out of a mid 80s 911, that has a constant draw to keep the presets set.

So it sounds like maybe 112mA draw is more than should be expected for my car? If that sounds too high, I'll start pulling fuses to try to track down the draw.

Rick, yes, when I move to 10A position on the meter, I have to move the leads to a different input.

When I tested at the 10A position, it showed 0.112A.

Wil Ferch · 03-16-2006, 09:09 AM

Sounds high, then....

Wil

David E. Clark · 03-16-2006, 12:48 PM

You might want to take a look at a document called basic ammeter use. It's like ammeters for dummies. It helped me.

cmonref · 03-16-2006, 03:30 PM

SoCal911SC: You stated that you are testing between the ground strap and the battery ground. If you have multiple wires connected to the positive terminal, I suggest you do your testing between the positive terminal and each of its connected wires, one at a time. Disconnect all of those wires from the positive terminal and test them individually.

I did what you did and ended up removing ALL of the fuses without finding the drain. The drain was in one of the wires connected to the positive terminal, but NOT the wire that powers the fuse box.

CarreraS2 · 03-17-2006, 05:44 PM

Hey Brian, you were right on!

I actually hadn't checked back in on this thread, but went and pulled all the fuses.

Was still drawing around 120mA.

So I came back to post my results and saw your post.

Went to look at my battery, and sure enough, there was an added on connection on the positive post of the battery.

Traced it (this was all added by the PO), and as it turns out, it lead to an auxillary cooling fan. The fan is triggered by a relay. I noticed that if I touched the relay even slightly, it would click. Hmm.

Replaced the relay (with a neat fused one, BTW), checked the battery drain, and voila! 00.0 drain now!

Thanks, all. I know a lot more about ammeters and tracing battery drains now than I did a couple of days ago.

cmonref · 03-18-2006, 12:08 PM

SoCal911SC: Glad you found your problem! Like me, we both got a lot of practice in R&R of fuses. I actually went thru the fuses TWICE, thinking I missed something the first time.

I love to work on the 911, but I am sure glad I do not have to make a living doing it!

CarreraS2 · 03-18-2006, 12:14 PM

Luckily I didn't spend a huge amount of time on the fuses.

Rather than taking them out one by one and running to the battery to check the ammeter, I just pulled them all out at once and took the reading. I figured if I got a low reading with all the fuses pulled, I would then have the problem "surrounded" and could home in on it by replacing the fuses one by one.

Luckily there are only 12 fuses on a 914, too! Not the million like on a 911.

Anyways, thanks again, you saved me hours of headscratching. Drinks are on me next time you are in So. Cal.! (Thanks to the others, too, for learning me on how to even read the ammeter!)