A note about current clamps(inductive ammeters).... I just went out and checked the range on my Fluke clamp -- a pretty decent unit by most standards -- and the specs say the range only goes as low as 1 amp, usable(though not considered accurate) down to .5 amp. You're not going to find one that's much more sensitive than this for an affordable price IMHO, so consider the clamp to be a way to do a "quick check" to make sure the current does not exceed the rating of the hardwired ammeter that you intend to use for finer measurements.

 

Vely Intwesting. I will go read the dox on mine again. It is less than a year old and IIRC in the $75 range. It sure seemed able to display differences in current draw well below 1 AMP and has a zero calibration feature.

OTOH, absolute accuracy is probably not as important in this case as is repeatability and relative accuracy. For instance if the actual draw is .5 AMPS but the meter displays .4 AMPs and if the draw is .3 AMPs and the meter displays .2 AMPs as long as those measurements are repeatable then even a meter with absolute inaccuracy (but with the above repeatability) is sufficient for purposes of finding and eliminating current drains. Afterall, as long as the draw is going down as you find and eliminate drains then the primary purpose is served. The problem would be when to stop looking for drains if the absolute accuracy of the meter is +/- 0.1 AMPs or more.

 

REMEMBER - if you're NOT using the 'clamp', but rather using a regular meter 'in-line'...DO NOT turn the key on....if you do - the draw will be such that you will likely fry your new VOHM meter!

 

Thanks everyone for the advice. I've got a VOM at home so I'll test the amperage draw - fuse by fuse. I'll work on it this weekend and report back my findings

 

If you have a kid or kids...it is a great project to involve them with. So that you don't have to run 6-foot extensions off of the meter, or keep climbing in & out to check...Have them read out the meter to you as you pull fuses.

 

" The battery disconnect is a last resort."

It worked for me.

I bought a $30 dollar Moroso battery disconnect switch, and i havn't had a dead battery since.

Go figure...

 

""For 'drain' checks you want to measure current. Put down the multi-meter - even though it claims (read the fine print in the manual) to be able to measure current - go to Sears/Radio Shack and buy one of the inductive ammeters - the kind that have a spring-loaded 'loop.' You close the loop around the wire that is carrying the current you wish to measure and look at the display. Easy as pie.""

""Beats the heck out of messing with the multi-meter, crossed prob wires, fragged fuses in the MM....I'm surprised.""

I could swear earlier posts recommended using a multimeter with the Milliamp current setting. But I'm sure you are correct, because I hooked up that blasted multiment every way imaginable and never ever got a reading. I even bought a new one thinking the old one went bad.

I will either go buy an inductive ammeter tonight or maybe wait until the Frenzy for a grown-up to show me what to do. Thanks for the clarification.

 

Steve, that's sweet, so I'll give it a try. Go to http://us.fluke.com/usen/products/Fl...keUnitedStates and buy this or one like it. Notice the front panel near the botom it has connector holes for mA and A? That means Amps measurement. You MUST have a multimeter that has the mA or A connector on the front of it regardess of Mfg, model.

This is because you must have the electron flow THROUGH the meter, unlike a voltage measurement which simply samples the electron flow. Think about it, were going to measure a flow now not a potential for flow.

Okay, got the meter in your hands? Right then, you will need something to clamp the probes to the battery area. For the post, I recommend a small visegrip plier. for the ground strap, maybe another vicegrip or a large forceps.

Loosen but do not remove the ground strap clamp bolt. Insert the RED probe wire into the connector marked A. Insert the BLACK probe wire into the COM on the meter. Take the other end of the RED probe and clamp it using the vicegrip to the grounding bolt behind the tool cover. Here's the hard part. Take the BLACK probe tip, and while loosening the ground lug on the battery, slip the probe under the ground clamp, and make contact with the battery - (minus)terminal. Do not pull the ground clamp off the battery yet!

Make sure all your car appliances are off. Key off, lights off, alarm off. Now carefully lift up the ground clamp from the battery while maintaining contact with the BLACK probe. If your interior lights are functional, they should remain on throughout this step. Clamp the BLACK probe tip to the battery lug, and set the cable asideso that it does not touch the battery at all.

Ready? Turn the meter selector **** to A with the solid line over the dashed line (DC Amps). Wait for the meter to do self test, and voila! You are now measuring the current flow from your battery. If the interior lights are on, it might read about 5-6 amps.

Lay the meter down, close all the doors and wait for the lights to go off. The meter will go down to a very low number that is probably nearly off the low scale for the A connector. If it does go down a lot, you will need to change to the lower scale, by moving the RED probe from the A in the meter to the mA connector. But before you do that, look at the wording under the mA connection. It says "4000mA Fused". That means there is a 4 amp fuse in that circuit that will blow if you open any of the doors with the meter in the mA connector.

So, while still in the A connector, go around a turn off all your little interior lights to get the reading well below 4A before proceeding. Once that's done, temporarily reconnect the ground cable to the batt lug while not moving the meter probes. Now, move the RED probe connector to the mA hole. You can then take the ground cable back off, and you will be reading on the milliAmp scale. 4000mA = 4A. The 'milli' prefix multiplies by 1/1000, or 0.001.

At this point you are ready to start sleuthing for current draw. You may get in, close the doors, wait for the timer to go off (15-30seconds), and this is your resting current draw. Pull all of the fuses, however you want, and make a chart of current load with all fuses pulled, and as you insert each fuse. This will tell you what circuits are drawing what current. Once you do that, publish the results here for all to share. If you still have similar current draw with all fuses pulled, your problem is beyond the scope of this procedure, and you will have to come on down the Foat Wuth, Teyxas to let me hash it up.

Things not to do: With the meter in the mA hole, NEVER turn on the key, roll up a window, play the radio, etc. This will draw too much current and blow the fuse in the meter, which is user replaceable. Do not worry about the far right digit flopping back and forth, you are looking for trends here on the order of 2-10mA (milliAmps, or thousands of an Amp). If you put in a fuse, and the right digit flops around a bit, it's no problem. look for increases that are sustained when you insert a fuse. Don't start with a low battery, the VOLTAGE should be nominal at around 12.7 volts when you start testing.

Have fun, you can't get shocked unless you lick the terminals. Let us know what you find.

Doc

 

You can do the current measurements with a MM. (See docmirror's excellent step-by-step above.) BUT, read the fine print of the MM manual too. The cheapo MMs have time-based limitations in addition to the 'capacity' limitations the good Doc spells out. For instance, IIRC, one of my meter's dox reads something to the effect of "15 seconds of testing every 5 minutes" when doing current tests. You get to do four measurements per hour. BAAH! I got SO fed up with these limitations that I bought the inductive meter. It's much simpler to use. But, Dave (Sharkskin) brings up a good point about low-current measurement accuracy of these units - so you'll need to read the print on those before you buy. I'll take a look at mine too - tonight since I'll be doing some electrical diag anyway.

 

Steve, you blew the internal fuse I mentioned on the mA setting. Open the meter up and change the fuse.

Dave, the time limitations on testing current relate to the heat produced by the internal shunt on high settings. When measuring less than 200mA, you can test continuiously with the Fluke model. At higher current settings, say, above 2 amps just be aware of the current flow through the meter. There is value in buying the best tools.

Clamp on ammeters are notoriously inaccurate on low settings. They work inductively, and there is a large variation based on the insulator, distance from the current flow, dimeter of the wire, direction the clamp is placed, etc. Mainly a clamp on is just to determine if there is current flow at all, and approx what amount. Fluke offers the clamp appliance with the auto kit, and it's usefull to see the charging current or the cranking current. Those values are in the 10s of amps, we're looking for stray milliAmps, the clamp-on just won't do it.

ps to my instructions, the Fluke has the handy little analog bar scale along the bottom of the display. This is really, really useful for trend analysis.
Doc

 

Wow, terrific step-by-step directions, Doc. Thanks VERY much. Dave, I will check on my meter's time limits. Thanks. Will report back.

 

Mmm... Crow.

Yup we would be here. A drain of .2 AMPs will kill a battery in a week or two. The precision of my inductive meter is 0.1 amps. I couldn't find the manual. Other users believe the meter to be accurate to +/- 100mA. So, given the questionable accuracy it IS NOT a great tool to deal with the last 200mA of drain. Essentially, you cannot know when you're into the ~sub-200mA draw range.

But, it was a great tool to find the mis-wired audio amp (thanks PO) in my '89 that was killing the battery in three days.

So, the good Doctor and Sharkskin are correct: the inductive meter is a good tool to use to get the draw into the range where you can use the MM for continuous current testing.

EDIT: Crap. I editted over the original post (partially quoted above.) That was not my intention.