Burned by clamp-on ammeter

PNjunction
PNjunction Solar Expert Posts: 762 ✭✭✭
in Off Grid Solar & Battery Systems #1
Ok, not physically burned.

I use a clamp-on ammeter a LOT just to check on my systems during charge. Not as accurate as a shunt, but good enough. The one I'm using is very inexpensive, and the internal battery voltage affects that. Best accuracy was obtained by using a non-rechargeable AA lithium primary cell.

I was pulling my hair out looking for a non-existent problem in the system - it was that my clamp wasn't perfectly meshed together at the tip. A teeeny piece of plastic from my toolbox had lodged itself in one side of the clamps tip, so that when it *looked* like it was closed, it truly wasn't.

The difference was only about a 2A discrepency from normal, but enough to make me go nuts until I found it. That and the fact that the clamp spring itself is getting looser means I'm going to put a gentle squeeze on the clamp tips by hand prior to measurement when it encircles the wire, rather than just rely on the thumb-loaded spring.
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  • vtmaps
    vtmaps Solar Expert Posts: 3,741 ✭✭✭✭
    #2
    Re: Burned by clamp-on ammeter
    PNjunction wrote: »
    The one I'm using is very inexpensive, and the internal battery voltage affects that.

    Brand and model? --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
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  • zoneblue
    zoneblue Solar Expert Posts: 1,220 ✭✭✭✭
    #3
    Re: Burned by clamp-on ammeter

    Well all i can say is dont even think about using one near motors or water pumps. That will drive you really demented.
    1.8kWp CSUN, 10kWh AGM, Midnite Classic 150, Outback VFX3024E,
    http://zoneblue.org/cms/page.php?view=off-grid-solar


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  • PNjunction
    PNjunction Solar Expert Posts: 762 ✭✭✭
    #4
    Re: Burned by clamp-on ammeter

    It is the Radio Shack True-RMS Digital Clamp On multimeter, model 2200172 #22-172.

    Even though the lowest range is 40A, it does quite well down to single digit amperages. Well, within reason to see if baseline specs are being met.

    The "zero" function has a quirk if you aren't used to it. To zero it, you push the zero, and leave it activated ("zero" in the display) when you take your measurement. I expected it to be a toggle to zero and toggle back out. Not so. And, depending on how much junk it detects in the environment, you may have to zero it more than once. I tend to zero it when close to the wire that I'm going to clamp around.

    I noticed a drift of accuracy with battery voltage when I compared readings when swapping out a fresh alkaline and a freshly charged quality nimh rechargeable. They have different inherent voltages, and the current measurements differed. The most accurate seemed to be the alkaline, but instead I used a AA non-rechargeable lithium.

    The voltmeter is ok, but since I want better accuracy, and now deal with Lifepo4 cells, I use my Fluke 87V as a standard for volts.
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,613 admin
    #5
    Re: Burned by clamp-on ammeter

    That "zero function" sounds exactly the same as the Sears meter I link too...

    It is "different". I suggest for new users to play around with their car's electrical system and do things like measure current with the headlights on/off, motor running/stopped.

    You will quickly see how it all works together.

    Note with DC current meters, you can measure the current direction (+/- on LED display, or possibly just bank/-).

    So if you are trying to figure out the direction of current flow, if you flip the meter 180 degrees on the wire, you will get the +/- direction change in current. Or if the current in the battery changes from charging to discharging, you will see a sign change too.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • mike95490
    mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    #6
    Re: Burned by clamp-on ammeter

    The Zero function, should be activated once per measurement and with the meter in the same orientation as the reading would be take. But no wire inside the clamp. then release . If you leave it active while you measure, you are removing the measurement.
    Zero nulls out any residual magnetic field, and then you open the clamp, and put the wire in it, and close it.

    If you leave it active while you measure, you are removing the measurement.
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
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  • PNjunction
    PNjunction Solar Expert Posts: 762 ✭✭✭
    #7
    Re: Burned by clamp-on ammeter

    That's the way to do it, but these cheap meters do it differently. That difference is what drove many of us nuts when we first got them, and even quite a few bad reviews and returns for not functioning like we think they should.

    Many of us old-timers and even newcomers who know the difference, are flabbergasted at how they programmed the button sequence because it is just not logical as you indicated above.

    Yet this procedure works, (for these cheapo's). First thing I did was use my Fluke 87V across a shunt to make sure the cheapo clamp-on wasn't giving me totally inaccurate readings after using this quirky procedure.

    My next clamp-on will definitely be a Fluke for sure, and will solve that funky button sequence!
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