digital multimeter question

smokinbasser · Oct 11, 2003

In a post else where here. A DMM is being used to measure battery power as opposed to just voltage ,by using the current mode. I am not able to even get a reading across the pos and neg terminals of a 123 batt. If it was a little cheap DMM I could see the potential for no readings but this is fluke 78 meter. It has auto ranging and I am wondering if that is what is causing the problem in my failure to get a current reading. Thanks. /ubbthreads/images/graemlins/help.gif /ubbthreads/images/graemlins/help.gif

georges80 · Oct 11, 2003

If you put your fluke on current range (esp the 400mA range) and connected it across a 123 battery - you just blew the fuse! You generally can't measure the current across batteries with a fused meter without blowing the fuse (unless the battery is quite discharged). You 'may' get away with it on the 10Amp range if the battery can't deliver 10A into a short circuit (which is essentially what your DVM is behaving like on the current range).

To measure current capability of a battery - you should use a sufficient wattage resistor as the 'load' and measure the voltage across the resistor. Not sure what you're trying to test for here - state of battery? Current capability?

There's a way to check if the fuse is blown without opening the case (at least on the 87III) - read the manual (it's also online at Fluke's website).

george.

smokinbasser · Oct 11, 2003

thanks you just answered my question and am trying to check current capability.now to find a replacement fuse and a testing resistor

CM · Oct 11, 2003

Check inside the case, my fluke has a spare fuse inside.

smokinbasser · Oct 11, 2003

I wasn't that lucky mine didnt have the spare and it looks like I am in for a search either tomorrow or monday Only place that has one so far is Grainger and they're not a weekend store , radio shack and automotive parts stores just gave me THAT look. You know the look just after you ask them for a double action single throw paraflafla with positive grounding.Its a KTK15 fuse most definitly not a run of the mill item. I'm buying 2 or 3 when I do find them.

snuffy · Oct 11, 2003

Around here you can find them at Lowes, Menards, etc.
Look in the electrical dept. They are common 600 volt AC fuses. Good luck

Traut · Oct 12, 2003

I am impressed! Accurate, concise, directive.

turbodog · Oct 12, 2003

The fluke 78 says 10a range, but if you will read the manual it also says the 10a range is good for 20a for limited time (15 seconds or so). I routinely used mine in the 14-16 amp range with no problems.

Ferrous · Oct 12, 2003

I don't know about yours, but on mine (23 I think) the low range gives a 6 ohm load or so. This is good enough for any battery that's 1.8V or less. Once you replace the fuse, check the resistance of the low current range of your meter so you can figure the maximum voltage battery to use it as a "mild load" test for.

The_LED_Museum · Oct 12, 2003

In any case, you don't want to put the meter probes directly onto any battery's (+) and (-) terminals when the meter is in ANY current measuring range, or else that fuse will pop in no time flat. /ubbthreads/images/graemlins/jpshakehead.gif

smokinbasser · Oct 12, 2003

My manual says 20 amperes for 30 seconds maximum, My mistake was in touching the probes directly to the battery +and - terminals and not using a resister to jump and read off it quick enough so as not to"use up" the battery life.BTW Thanks to snuffys lead I bought two fuses and now know where to buy more. lol And all this due to nothing more than curiousity on my part on flash amps of various 123 batts.