[george kujanski]

here are some pix of a fluke multimeter showing the settings and probe jacks for voltage and current measurements.

Pix are better than text to describe how to measure current draw, etc.

To measure voltage, the probes are connected directly to the volatge source; i.e. to measure bat voltage, just connect red to pos and black to neg, while the battery is still connected to the car.

To measure current with this type of meter, you need to disconnect the wire or cable you are measuring and insert the meter probes in series, i.e. to measure current draw from a battery with the key off, disconnect one of the battery cables (such as the pos), and then connect the red probe to the bat post and the black probe to the end of the pos cable.

George

[OrigOwner77]

I've always wondered, George, how you can measure current draw on a newer car w/one of these w/out blowing it up (newer cars having the computerized gizmos and so many more electronic thingamabobs). Doesn't this essentially power the entire vehicle through the multimeter? Eg. if you hook it up in series between the cable and battery, can't you theoretically hear the door chime/buzzer, honk the horn, etc?

Also, should you measure current draw via the (-) or (+) post? I've always heard to use the negative cable.

[george kujanski]

True enuf, think of the multimeter in Amps function as just a piece of wire. The meter pictureed tho only has a 10 fuse max so if you draw more than that you will blow the meter fuse.

For measuring leakage or current thru a light load, 10 A should be good enuf.

Certainly don't try to start the car with the meter connected 300 Amps or more. There are clamp on meters that clamp around the cable and can withstand hundreds of amps.

George

[wrench]

Hey George, are you a Teacher? It is one thing to be good at diagnosing and repairing automotive electrical problems. It is a whole different Ball Game to be able to teach it to others (especially beginners). You seem to be great at both! Have you ever considered writing a book on the subject?

[george kujanski]

No, I'm not a teacher, but i want to be one in my next life.

My wife is an educator and she gets summers off. That's what I should have chosen as my career..oh well. "the 3 best things about teaching...June, July and August"

Years ago my son was diagnosed with cancer and missed a lot of school when he was in high school. My wife and I did a lot of home tutoring to keep him from falling behind; she did the soft topics and I did the math and sciences. I got a lot of practical teaching experience during those years.

Thank you for the compliment.

I have begun to write some short papers on certain recurring topics in these forums, one of which is a intro to, and explaination of ignition systems, currently in progress.

George

[george kujanski]

Orig/owner: you can use either post; what ever current leaves the battery on one post comes back into the battery on the other post.

Modern multimeters will display a (-) sign on the readout if you connect it backwards.

Assume you disconnect the positive cable from the post. If you attach the red probe to the post and the black to the cable, a current draw will show as positive. If you switch the probes, it''l show up as a negative value, but the number will be the same.

So either way you connect it, with the key off, you should get a very low current draw, less than 50 mA.

One advantage of using the neg cable is that if your wrench slips and touches body metal while still in contact with the battery, you won't melt the wrench because the wrench and body are at the same voltage

George

[OrigOwner77]

Originally Posted by george kujanski

Orig/owner: you can use either post; what ever current leaves the battery on one post comes back into the battery on the other post.

Modern multimeters will display a (-) sign on the readout if you connect it backwards.

Assume you disconnect the positive cable from the post. If you attach the red probe to the post and the black to the cable, a current draw will show as positive. If you switch the probes, it''l show up as a negative value, but the number will be the same.

So either way you connect it, with the key off, you should get a very low current draw, less than 50 mA.

One advantage of using the neg cable is that if your wrench slips and touches body metal while still in contact with the battery, you won't melt the wrench because the wrench and body are at the same voltage

George

Thanks for explaining that George. I know not to start the car w/the multimeter connected. Hehe.

Reason I was asking so in-depth is my Dad's 93 vette constantly goes through batteries. After a few weeks, it is totally dead. So I'm going to use this info to try to check the current draw. First I'll pull the dome light fuse, then start pulling fuses to drop the number the meter reads until I get a near-zero draw. Sound correct?

[george kujanski]

Yep, if you suspect a current draw while the car is off. There also are circuits that are connected directly to the battery without going thru the fuses; you need to check those.

Make sure it's also charging correctly, if it's not you never replenish the energy from the battery and the batt is always in a state of discharge.

George

[chuckmnv]

Thanx, George. I've been having the battery in my 95 GMC die over time. Of course, I don't drive it much. It is a new battery, after having replaced the old one because of a dead cell less than six months ago. I've been following this testing info, but now it makes more sense. I'll have to give it a try soon.
cm

[chuckmnv]

George -
Another thing I haven't figured out and my multimeter manual is of no help as the authors seem to think that everyone who wants/needs to use one is an electrician, or whatever. Please 'splain all the symbols. I don't want to set my meter to the incorrect reading and trash it.
Thanx, again.
cm

[dracowizard]

Hey George,great info,good to recieve the measure in series for draw.But please let me get this straight. No draw and you have 0. But if there's a draw and theres some measurement,then next is pinpointing the source. I'm assuming that this is by doing a test from the battery cable.....and a reading shows theres a draw....what may be the first and/or following steps to isolate the source?

[BILTIT]

I would check which circuit is drawing the current by pulling one fuse at a time while having the meter hooked up. When the amperage drops below 50ma or to zero then you know the last fuse you pulled is the offending circuit. Be sure to check circuits which attach directly to the battery (not through the fuse panel) aswell, as george mentioned.

[BILTIT]

Originally Posted by chuckmnv

George -
Another thing I haven't figured out and my multimeter manual is of no help as the authors seem to think that everyone who wants/needs to use one is an electrician, or whatever. Please 'splain all the symbols. I don't want to set my meter to the incorrect reading and trash it.
Thanx, again.
cm

I hope george doesn't mind me jumping in.

Starting from the bottom left and going clockwise.

OFF=OFF
~V = AC voltage/Frequency
-V = DC voltage
-mv = DC millivoltage
horseshoe = resistance (ohms)
arrow = not sure, continuity? (don't use this one myself)
ma = milliamps
ua = microamps
COM = common (ground)

[dracowizard]

BILTIT,thanks for the tip....and figuring how resourceful george seems to be,i doubt he minds your sharing a lil info.This could be a great help,for one as i hope to finally work on my 65 project after completeing my garage this summer.Next,i think my brother may benefit as well,for his 72 lemans draws the batt down over a long time period.Got him a bargain on a used batt tender lately to help him,but now we can check for other possible problems!

[chuckmnv]

BILTIT -- This is what I have. Looks to me like too much information. It was a Christmas present from my wife, and I'm still trying to figure it out.
cm

[johnsma22]

Originally Posted by BILTIT

I hope george doesn't mind me jumping in.

Starting from the bottom left and going clockwise.

OFF=OFF
~V = AC voltage/Frequency
-V = DC voltage
-mv = DC millivoltage
horseshoe = resistance (ohms)
arrow = not sure, continuity? (don't use this one myself)
ma = milliamps
ua = microamps
COM = common (ground)

I have, and use the same Fluke 87 True RMS meter that George pictured. Continuity is also performed from the ohm function. The arrow function is for checking diodes.

[LPete]

Chuckmnv, it looks like yours tests capacitance (nF=nanofarads, uF=microfarads) and has a transistor tester built in (hFE is the beta measurement of a transistor). That's a cool meter!

[george kujanski]

The more information, the better!

I attached a marked version of the meter pointing out some more stuff.

The (~) symbol means AC measurements. AC voltage changes polarity like the symol infers. Wall outlet voltage is AC at about 110 volts

The ---- with the solid bar over it means DC measurements, DC is a steady, non-varying voltage like you get from a battery.

The sound wave/ arrow symbol is used for resistance maesurements; if the resistance is low, near zero, it'll beep to indicate good continuity, as if you were checking a wire end-to-end to see if it's broken. Sometimes it's easier to listen than to glance at the meter.

The diode resistance is used for checking a diode; a diode should have very low resistance in one direction, and if you reverse the probes, it should have a high resistance. For diodes you use this function instead of the normal resistance function. Also, for proper checking you need to disconnect one of the diode leads from the circuit it's in, otherwise you may be measuring the circuit instead of the diode alone.

George

[BILTIT]

Ah yes, the diode symbol, I should have known that one. I think working 46 days straight is getting to me, haha.

[chuckmnv]

So, is the button up on the right to be used for diode testing?
Anyway, this thing has more than I'll ever use, I think.
Thanx for all the info, guys. Like someone's tag line, "I'm just learning as I go."
cm