Clamp-on Ammeter Help

[Flapjack]

Let me preface this by saying, I consider myself to be a pretty decent electrician. There has been nothing I could not wire up in my car, house, etc... plus, I spent 10 years of my USAF career doing most of the electrical work in my fuel systems maintenance job (mostly 200-400 VAC, but also a lot of DC control voltage work as well).

I've used clamp-on ammeters in the past, but almost exclusively to check up on centrifugal fuel distribution pumps. These things put out anywhere from 300-600 gpm of fuel and drew quite a lot of amps. I'd use an ammeter to determine whether or not the motor before the pump was going bad (usually the windings).

So today, I go to pick up a Sears ammeter to help me troubleshooting a persistent battery drain my on 1997 Suburban. In the past, I've just disconnected a cable from the batter and jumpered the battery/cable to chase down current draws. I pull fuses to find where the draw is, which has worked every time. In the case of my Suburban, I was very little draw (in the neighborhood of hundredths of an amp). I've already had the battery and alternator checked. I don't drive the truck often, but I cannot leave the battery connected for more than a day or two without the battery being dead. I've replaced the battery twice.

Anyways, I ordered the ammeter online from Sears for in-store pickup. I screwed up and got an AC only one. Before I returned it, I had to try it out (of course). The first thing I tried was a lamp. It bounced between 0.02-0.03 amps. Finding that weird, I tried other things (TV, humidifier, obnoxiously bright halogen lamps in the garage, etc...). All read the same. So not only did I get an AC-only ammeter, I figured it was defective.

Later on, I switched for the next model up (link here) which does both
AC and DC. I read the manual, just to make sure I wasn't doing anything wrong (clamp works for both AC and DC... some only the leads work for DC, so I had to be sure). Same freaking thing. 0.02-0.3.

I tried the DC one using my phone charger which is rated at 1300ma (charges the high end "droid" phones very quick). My phone was nearly dead. I plugged it in and finally got the darn gauge to change (a little). It read 0.08 on the 40amp setting. Still, I know from reading on various phone forums that you can't use a crappy charger with these phones because they can pull over an amp while charging.

The final test, to make sure I wasn't crazy was to single out the highest amperage thing in the house... the dryer. I put it on the 40amp setting, as the label said ~30 amps at load. The reading on the meter? 0.02 amps.

So my question is... what am I doing wrong? Is it really possible that I bought two defective ammeters in a row??

 

[TexasKyle]

You cant measure amperage like that on a multiwire cable. You have to measure the amperage on a single wire. Trying to measure amperage on a multiwire cable, by clamping around the entire cable will result in the readings you got.

 

[Flapjack]

You cant measure amperage like that on a multiwire cable. You have to measure the amperage on a single wire. Trying to measure amperage on a multiwire cable, by clamping around the entire cable will result in the readings you got.

Someone on another forum just pointed that out. I will do some more testing, but I'm sure that's it.

 

[rojizostang]

You cant measure amperage like that on a multiwire cable. You have to measure the amperage on a single wire. Trying to measure amperage on a multiwire cable, by clamping around the entire cable will result in the readings you got.

i agree. it will work however with a hot and a neutral within the jaws. you may loose a little of the actual current readings from the return on the neutral, but it will still work, but i don't think it will work with two hot wires that aren't the same phase. never really had the occasion to use it around conductors that aren't the same phase

 

[Flapjack]

i agree. it will work however with a hot and a neutral within the jaws. you may loose a little of the actual current readings from the return on the neutral, but it will still work, but i don't think it will work with two hot wires that aren't the same phase. never really had the occasion to use it around conductors that aren't the same phase

So you're saying I probably should've seen something when I tested things like lamps and my TV? They only have a hot and a neutral...

 

[rojizostang]

So you're saying I probably should've seen something when I tested things like lamps and my TV? They only have a hot and a neutral...

it seems like it. we use this type of instrument to measure and identify current/conductors in the utility construction business. specifically, my crew uses them to measure amperage on corresponding ends of the same cable(among other things), and they(the conductors) have concentrically wound neutrals(wrapped around) and a semi-conducting shield, and we have no problems using them in this manner.

perhaps in your case since the neutral isn't concentrically wrapped around the conductor, maybe it won't work. I've never really tried it with a neutral and a hot wire just running "parallell" so to speak thru the jaws of the instrument. all that is to say i might be wrong about it working with the neutral and hot the way you did it.

just one conductor by itself within the jaws, or other conductors of the same phase simultaneously within the jaws of the tool should provide a fairly accurate reading.

try attaching the tool independantly to the hot wire and then to the neutral by itself. you should get a reading on each wire, with the neutral being significantly less, just as an experiment. of course if the amperages are very low to start with, you probably won't see a large difference, but it should be visible.

oh, and i don't think it makes a difference, but i've used this type meter on ac circuits only. we don't sell dc service

 

[Flapjack]

Thanks for the info. Unfortunately, I haven't had time to play with the tester more. Maybe this weekend...

 

[06whipple]

You're correct...can't measure hot and neutral together...have to test one wire at a time. If you are looking for the draw on your battery (with vehicle off) just take a current reading with a multimeter in series...most good meters can handle up to 10 amps DC. you don't need to buy a clamp on ammeter.

 

[Flapjack]

You're correct...can't measure hot and neutral together...have to test one wire at a time. If you are looking for the draw on your battery (with vehicle off) just take a current reading with a multimeter in series...most good meters can handle up to 10 amps DC. you don't need to buy a clamp on ammeter.

That's the thing... in series has always worked for me. This time, though, I don't get any significant reading (hundreths of an amp). I have replaced every part of the charging system (minus the starter) and am still having problems. I cannot let the vehicle sit for more than a day or two without the battery being completely dead.

I was hoping by having the batter connected beforehand (and not having to disconnect it), I might be able to tell if there's a draw that disappears after the battery cable is pulled (and doesn't come back until later).

I know it sounds unlikely, but I'm running out of ideas here.

The only clue I have is that Chevy replaced the directional airflow box underneath the dash. They had to take a significant part of the dash apart to get to it, including the stereo. The only (apparent) thing they did wrong was to not hook up the Pioneer add-ons to my stereo (must be done in series, ie: XM, iPod, Bluetooth). I fixed all that and checked all the other connections. They were all fine. I also did a cursory examination for what I could see under the dash molding. Nothing seemed out of sort.

I had hoped to shorten my troubleshooting down to a single circuit by pulling fuses until the drain dropped. Kinda hard to do when I'm not registering any drain.

 

[06whipple]

I would try getting a reading with just the interior light on just to see what kind of amerage it draws. Use that as a baseline for "too much" draw since that would kill the battery in a couple of days. Even though you are only seeing hundredths of an amp draw maybe over time that is enough to drain the battery. I don't know what the amp hour rating of a car battery is, but 20-30 milliamps continuous for a couple of days is pretty much.

 

[rojizostang]

well, i know you've replaced the battery twice, but since you can't find a draw anywhere, perhaps you should take the battery to autozone or someplace like that and let them put their tester on it.

also, is their any chance you have a bad ground somewhere? perhaps what appears to be a draw on the battery or a perhaps a bad battery is actually a bad/broken/loose/disconnected ground wire? i know bad grounds can wreak a lot of havoc when trouble shooting stuff

 

[Flapjack]

I would try getting a reading with just the interior light on just to see what kind of amerage it draws. Use that as a baseline for "too much" draw since that would kill the battery in a couple of days. Even though you are only seeing hundredths of an amp draw maybe over time that is enough to drain the battery. I don't know what the amp hour rating of a car battery is, but 20-30 milliamps continuous for a couple of days is pretty much.

Good idea. Will try it.

well, i know you've replaced the battery twice, but since you can't find a draw anywhere, perhaps you should take the battery to autozone or someplace like that and let them put their tester on it.

I have Autozone or Advance test it each time they charge it. It's so freaking dead, my home charger doesn't want to charge it in a reasonable amount of time. They usually charge it in 35 minutes. They always test it while they're at it.

also, is their any chance you have a bad ground somewhere? perhaps what appears to be a draw on the battery or a perhaps a bad battery is actually a bad/broken/loose/disconnected ground wire? i know bad grounds can wreak a lot of havoc when trouble shooting stuff

I've never heard of a bad ground causing a draw. I don't think there is a physical way for that to happen. Bad grounds can cause all sorts of other problems, yes. But killing a battery?

 

[rojizostang]

I've never heard of a bad ground causing a draw. I don't think there is a physical way for that to happen. Bad grounds can cause all sorts of other problems, yes. But killing a battery?

what i meant was that perhaps what appeared to be a drained battery was actually a bad connection. i didn't realize you had it to autozone each time and they charged and tested it. so, i believe you're right about it not being a loose or bad connection on the ground.

the battery is draining down with the key off....so if there's a draw behind a fuse, it would seem that only those fuses that are not effected by the key being on or off are the ones that would be the likely culprit, like the cigarette lighter fuses, and the dome light fuses, anything that is hot or can come hot while the key is off (like dome lights). you probably already figured that out anyway.

the other thought would be that the draw would be in any other portion of the vehicle that is upstream from the fuse box, like the main battery cable, starter cable, and maybe the alternator charging wire or even the alternator itself. you might need to remove all the fuses, and just hook up the battery hot and ground and see if there's any drain like that.

or, remove all the fuses, and isolate all your main cable ends from the starter/alternator/and all other devices that can ground a circuit thru a winding or filament and test for continuity on the main battery cable to ground. but that's going to be a lot of work and might not be worthwhile until a last resort.

if all else fails, there may be a place near where you live like we have here that is a automotive dc expert. we have a shop that rebuilds starters and alternators and are also experts at troubleshooting cases like yours.

i'm really interested in hearing back if you figure this out, let us know.

 

[Flapjack]

what i meant was that perhaps what appeared to be a drained battery was actually a bad connection. i didn't realize you had it to autozone each time and they charged and tested it. so, i believe you're right about it not being a loose or bad connection on the ground.

here's an idea. charge the battery completely and hook up the hot and ground connections. remove all the fuses. add one fuse at a time every other day or so while checking the battery voltage and see which one starts drawing the battery down. it might take a while, but perhaps that will work. if you can identify which circuit the fault is on, then it would be a matter of isolating sections of the wire/circuit to determine where it's shorted.

and then obviously if it's starts drawing the battery down before you start installing fuses, then the short would be upstream from the fuse box towards the battery. perhaps that's where the fault is to start with and why you're not seeing any draw as you check behind each fuse? that actually sounds pretty logical come to think about it. hook up just the battery with all the fuses removed and check to see if your getting a draw on your main battery cable upstream from any/all fuses...including the starter wire and alternator wires. not sure how your truck is wired, but if the battery cable goes straight to the starter and then to the fuse box you could have problems there or going back to the alternator also.

Definitely good ideas. I'll start with the basic test to see if there is any draw I wasn't picking up with my cheap multimeter.

I probably will have some time to work on it Thursday night. I'll post again then.

Thanks for all the help/advice.

 

[rojizostang]

hey....you quoted a post i edited a whole bunch....maybe worth taking another look...pm'd you

 

[Flapjack]

hey....you quoted a post i edited a whole bunch....maybe worth taking another look...pm'd you

I re-read your post. Definitely good stuff. I'll keep you update for sure. I'm really hoping it's something simple that I missed the first go around. I'm a damn good troubleshooter, but I probably haven't given this one the time it deserves (since I rarely drive it).

 

[Flapjack]

Ok, finally got a chance to work on it.

The clamp-on sucks ass. It read 00.39 any time it was no zeroed. I didn't budge when I put it over the positive battery cable. So I went back to my trusty old multimeter and tested with the probes.

This time, I got 0.14 amps steady. Still not sure if that's "too much", but I went through the fuses until I found the answer.

It was fuse #7, "Auxiliary Power". I pulled that and the draw went down to 0.01 amps.

So now I need to figure out what is using auxiliary power and where the problem is. Any idea on a GM?

 

[rojizostang]

no idea, really. i suppose i would leave the fuse out, and try to figure out what isn't working, as i'm sure you already figured out. did you find this draw with the key in the "off" position? probably a dumb question.

 

[Flapjack]

no idea, really. i suppose i would leave the fuse out, and try to figure out what isn't working, as i'm sure you already figured out. did you find this draw with the key in the "off" position? probably a dumb question.

No, I haven't tried yet. Got a bunch of other stuff to do (like put the 5.4L back in the Stang).

I'll keep you updated.

 

[rojizostang]

No, I haven't tried yet. Got a bunch of other stuff to do (like put the 5.4L back in the Stang).

I'll keep you updated.

i'd like to have a 5.4 in my stang also