Using Sears Clamp meter

Rybren
Rybren Solar Expert Posts: 351 ✭✭
I have one of the Sears clamp meters that is often recommend here.

I find that measuring DC current with it is rather confusing. When I press the zero button, ZERO is marked on the display and it reads 00.00 A. If I then place the clamp over the +ve wire from the CC to the battery, it will read a value somewhere less than 1A. If I then press the Zero button again (so that the word ZERO is no longer displayed), it will read a value of anywhere from -1.5A to -3.0A. (This is on a 60W PV system with a cheap shunt-type CC). If I run thru the same procedure, but test the -ve wire from the CC to the battery, I get the same results (-ve current reading)

I am very confused.

Comments

  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: Using Sears Clamp meter

    The ZERO button works like "no other" Zeroing button I have ever used.

    I think I figured out how to use it on this meter.

    "ZERO" off--Displays uncorrected readings from current clamp meter.

    When you push "ZERO ON", the meter does two steps. First is "measures" and stores a sample of the current reading (normally you have the clamp with no wires in its jaws). Then it takes that value and subtracts it from active reading and displays the results from there on (while LCD says "ZERO".

    You can "ZERO" at any time (say it displays 10amps). And now you have an "offset" (while display a current value over/under the 10 amp offset current). I.e., if you put the meter on the cable to measure current on--And push Zero On, the meter will read zero until the current in the cable goes up or goes down.

    Note that DC Clamp meters will indicate the direction of currrent flow (some will just display a "-" sign only). AC meters cannot "show current/power flow direction".

    When you turn off zero, it again displays the uncorrected current.

    DC Current meters use a Hall Effect Transistor which drifts over time/temperature/etc... And you should rezero every couple of minutes (more or less) for the most accurate readings. I have not played with it set to AC to see if it has the same drift issues or not.

    One other thing to remember is that the clamp measures the "total current" flowing through the jaws. If you have two wires with 5 amps flowing, the meter will display 10 amps. If you have two wires going to a load (AC or DC), the current flow "out" from one wire will cancel out the "return" flow with the other wire, and the meter will always read near zero current.

    If you want to measure (or example) the current in an AC appliances. Get a short extension cord and (carefully) separate the wires so you can clamp on one wire at a time to measure the current flow in that wire.

    You can also purchase a "test tool" that breaks out the wiring too (you clip on different "bars" to measure black/white/ground currents):

    Attachment not found.

    Another thing I have not played with is if the ZERO Button also functions with other readings (voltage, current, etc.)... (don't have meter handy at the moment).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Rybren
    Rybren Solar Expert Posts: 351 ✭✭
    Re: Using Sears Clamp meter

    Bill,

    Thanks. It is a very confusing device - especially when it reads a negative value regardless of whether it's on the +ve or -ve wire from the CC to the batt.

    I'll play with it some more this weekend and maybe even check it against the batt cables on my car to see if I get similar results.

    Cheers

    -Jerry
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: Using Sears Clamp meter

    I cannot remember if it reads "negative" if the current goes from top to bottom or bottom to top in the clamp... I have to try it on something that I know the direction of current (such as car with headlights on and engine off) to re-learn the direction of current on the meter. :blush: Just don't use a meter in my life that much anymore.

    And then there are the semantics--Is a battery recharging positive current flow, or is it discharging positive current flow. Is it the polarity/sign different if I am measuring the the current flow from a Primary (non-rechargeable--discharge is positive flow) cell vs a rechargeable cell (recharging is a positive flow)? :p

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Rybren
    Rybren Solar Expert Posts: 351 ✭✭
    Re: Using Sears Clamp meter

    I'll have to try different configurations to see if the results change.

    Thanks Bill - now my wife will have one more reason to yell at me. "Why are you playing with that old solar system? Why aren't you working on the new one?" Oh joy :cry:
  • inetdog
    inetdog Solar Expert Posts: 3,123 ✭✭✭✭
    Re: Using Sears Clamp meter
    BB. wrote: »
    And then there are the semantics--Is a battery recharging positive current flow, or is it discharging positive current flow. Is it the polarity/sign different if I am measuring the the current flow from a Primary (non-rechargeable--discharge is positive flow) cell vs a rechargeable cell (recharging is a positive flow)? :p
    l

    For me, the important thing to remember is that positive current on the plus lead means that the power is flowing in the same direction as the current. Beyond that whether current into the battery or out of the battery is positive is a matter of convention. :-)
    And I have been to several of them.
    SMA SB 3000, old BP panels.
  • PNjunction
    PNjunction Solar Expert Posts: 762 ✭✭✭
    Re: Using Sears Clamp meter

    BB - I just picked up a Radio Shack #22-172 clamp meter and it works the same way - but confusing at first.

    I too had a hard time until I figured out that for dc current measurements, you just *leave* the meter in the zero mode and then open and close the clamp around the cable. And like you said if you want to measure an offset, zero it while current is already going through.

    Like so many, I thought I had a bad one, but now I really like it. Compared to a Fluke 87V multimeter, the dc voltages are about .07 volts too low, and I don't have a calibrated shunt for seeing how good the current calibration is. But for general-purpose stuff, I think I'll keep it!
  • Rybren
    Rybren Solar Expert Posts: 351 ✭✭
    Re: Using Sears Clamp meter

    The thing that I don't like about my Sears meter is that all readings on voltage or current jump around continuously when not connected/measuring anything. They do tend to stabilize somewhat when connected, but it doesn't give me a warm, fuzzy.
  • ggunn
    ggunn Solar Expert Posts: 1,973 ✭✭✭
    Re: Using Sears Clamp meter
    Rybren wrote: »
    Bill,

    Thanks. It is a very confusing device - especially when it reads a negative value regardless of whether it's on the +ve or -ve wire from the CC to the batt.
    It doesn't matter whether you are on the + or - conductor; the + and - current readings indicate which direction the current is flowing through the clamp.
  • PNjunction
    PNjunction Solar Expert Posts: 762 ✭✭✭
    Re: Using Sears Clamp meter
    Rybren wrote: »
    The thing that I don't like about my Sears meter is that all readings on voltage or current jump around continuously when not connected/measuring anything. ...

    Don't sweat the jumping - even my Fluke does it when I wave the leads around with no voltage. Speaking of which, I got the Fluke so I could at least have some reliable standard to set and measure my solar gear to. If I had relied solely upon my clampmeter, it is .07 volts too low. For most purposes that might be ok, but for critical voltage setups in the solar game, I think it is worth investing in at least a medium quality Fluke so you can calibrate everything else against it and apply offsets if necessary.

    Without any lab-gear calibration around, the Fluke is my gold-standard. Other brands might also be very accurate, but out-of-the-box the Fluke was something I could trust. One doesn't even have to go as far as an 87V either ..
  • Photowhit
    Photowhit Solar Expert Posts: 6,002 ✭✭✭✭✭
    Re: Using Sears Clamp meter

    The jumping around is normal, it's nice having the zeroing button, my Amprobe have an analog pot(?) to adjust the zero! Very touchy. kinda glade my sears clamp meter is working again. It was giving me an OL (over load?) reading when I turned it on. I replaced the batteries 2x, no luck. I put it away and took out my old Amprobe and used that. when I moved it over to the new place, I gave it a try and it turned on to near zero. I reset it and tried it out and it's working again... guess it just needed a vacation!
    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Magnum MS4024, Prosine 1800(now backup) and Exeltech 1100(former backup...lol), 660 ah 24v Forklift battery(now 10 years old). Off grid for 20 years (if I include 8 months on a bicycle).
    - Assorted other systems, pieces and to many panels in the closet to not do more projects.
  • PNjunction
    PNjunction Solar Expert Posts: 762 ✭✭✭
    Re: Using Sears Clamp meter

    Watch out for voltage drop! Use *fresh* alkaline or non-rechargeable lithium. Mine takes 2 AA's.

    Measurements all around me started dropping beyond normal on standard output devices. When the measurements got 2 amps below normal, I got to thinking about it and turns out that it only takes a very small voltage drop to reduce the accuracy.

    I swapped out my beloved fresh Sanyo Eneloop lsd rechargeables that I treat like gold for fresh alkaline, and wala - current reading are back to normal, and even the voltage accuracy compared to my fluke multimeter improved from .07v low to only being .05v low.

    As much as I like using RE batteries, in my meters I'll be sticking to alkaline or perhaps non rechargeable lithium for more accurate measurements.
  • PNjunction
    PNjunction Solar Expert Posts: 762 ✭✭✭
    Re: Using Sears Clamp meter

    Quick update - popped in Energizer non-rechargeable AA lithiums. Now the voltmeter is just about as accurate as my Fluke so no more mental compensation. Amperage measurements are up too, but I don't have a calibrated shunt to test against.

    Seems that these cheap meters are not very well regulated, and even the slightest drop of voltage causes inaccurate readings. Both the nimh and alkaline dropped ever so slightly, and the meter noticed it immediately. So far, the voltage of the lithiums is holding up so I guess in my meters that's what I'll be using.