How to use clamp meter?

bmetbmet Solar Expert Posts: 630 ✭✭
I went to Sears yesterday and purchased an AC/DC clamp meter that B.B. has referenced on occasion. I had no trouble measuring DC current, placing the clamp around the positive lead of my battery cable, but that doesn't work for AC cords. I guess I am better off using the KillAWatt meter for that value?

Comments

  • nsaspooknsaspook Solar Expert Posts: 396 ✭✭✭
    Re: How to use clamp meter?
    bmet wrote: »
    I went to Sears yesterday and purchased an AC/DC clamp meter that B.B. has referenced on occasion. I had no trouble measuring DC current, placing the clamp around the positive lead of my battery cable, but that doesn't work for AC cords. I guess I am better off using the KillAWatt meter for that value?

    On a cord, with both the hot and neutral wires next to each other the fields cancel. It might not be possible to easily get to just one wire so the KillaWatt meter is a great tool for that.
  • BB.BB. Super Moderators, Administrators Posts: 32,019 admin
    Re: How to use clamp meter?

    Several issues...

    1. Did you set it to AC Current?

    2. As NsaSpook said--you need to measure the current in one wire at a time... If you measure +/- (or Line A and Neutral) as pair, their magnetic fields cancel each other out...

    You have a couple options, one is to purchase a special plug that breaks out the wires:

    480172 - AC Line Splitter Allows clamp meter to measure AC Current on a 2-wire or 3-wire power cord

    The other is just to get a short AC extension cord that you can gut the outer sleeve off and expose the black/white/green wires so you can clamp on them directly.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • BB.BB. Super Moderators, Administrators Posts: 32,019 admin
    Re: How to use clamp meter?

    I forgot to add... DC Clamp Meters read + or - on the current meter depending on which direction the current flows through the clamp (if you flip the meter over, the sign will reverse).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • bmetbmet Solar Expert Posts: 630 ✭✭
    Re: How to use clamp meter?

    Yes, I did switch the meter to AC current. Thank you for that point. I am experienced with voltmeters in general, but clamp meters were never part of my toolbox, and my range was usually in the mA s.

    It's nice to be able to measure the current my panel is outputting at any given light intensity. It lets me see just why charge controllers are necessary. Thanks.
  • bmetbmet Solar Expert Posts: 630 ✭✭
    Question for B.B.

    This Sears clamp meter is giving me confusing readings, and I wonder if it may have to be exchanged for another. With nothing in the 'clamp', i get a reading of around 0.8 vdc. I can push the 'zero' button, and it will null out, but only as long as the 'zero' button is engaged. With the 'zero' button disengaged, the 0.8 value returns to the display.

    When you recommended this meter, is it because you own one, or because it is the least expensive DC clamp meter you found?

    Remember that I started out with crappy parts to make a cheap power-pack, then upgraded everything (except my charge controller). I wanted the clamp meter to verify the name plate values, but am unable to get solid reading on the current. Here is my attempt from yesterday, an overcast day.

    I put my cheap $7 voltmeter across the charge controller inputs, and got 19-20 vdc (everything is connected). I then switched the meter leads to read Amps, and placed it in series between the panel and charge controller, and measured a fluctuating value from 2.5 - 4.0 Amps(overcast). When I placed the clamp meter around the + wire coming from the panel to charge controller, it varied between .2 and 1 Amp. ???

    I want to trust the $60 Craftsman over the $7 Harbor Freight Tool, so I must be doing something wrong. Why would the clamp meter read a current with nothing in the clamp? Why won't the display stay 'zeroed' after disengaging that function?

    Just as a by the way, my Costco marine battery is being floated, the voltage is at a fairly consistent 13.2 - 13.3 volts. Sometimes I see it as high as 13.6. , my charge controller is always a tenth of a volt higher than the battery.

    Am I using the clamp meter incorrectly? As far as the dvm, voltage is across the wires, and current is in series with the wire, right? What am I missing? Thank you.
  • BB.BB. Super Moderators, Administrators Posts: 32,019 admin
    Re: How to use clamp meter?

    I have one and others (before me) have purchased them before too...

    The "zero" button for the current seems to be a bit confusing to me too... And the manual is less than clear.

    First, select DC or AC amps at correct scale.

    The way I use is, with the current clamp not connected to the wire, push the Zero Button Once to get the ZERO on the LCD--That sets the display to 0.0 amps

    Now connect to ONE Wire (not both black and red wires--the "sum of the current" from the + and - leads will add up to zero).

    You should read + or - (depending on direction of DC current flow through clamp) X.X amps.

    If you go from non "ZERO" to "ZERO" on the LCD with a wire connected, it sets whatever current flow the zero and the meter will display the difference in current (higher or lower) than the "zeroed" current flow.

    I am not quite sure what the meter is displaying when no "ZERO" on the LCD when measuring DC current....

    Active hall effect transistors (I am guessing) used for sensing DC current flow are not that stable and tend to drift. Normally, you have to adjust zero current with DC clamp meters to offset the drift of the Hall Effect device(s). Depending on accuracy, you may need to re-zero the meter every few minutes (or more often).

    Beware that nearby strong magnetic fields (such as stereo speaker magnets) can affect accuracy too.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • BB.BB. Super Moderators, Administrators Posts: 32,019 admin
    Re: How to use clamp meter?

    And yes, votlage is across the wires and current is through the wire (cut wire, place DDM in series to measure current).

    Regarding your 0.1 volt higher at controller measuring float voltage...

    I am not quit sure I understand what it is you are measuring at the meter vs at the battery... With your meter you are measuring 13.5 volts and at the charge controller you are measuring 13.6 volts? If so, you have a bit of voltage drop between the charge controller and the battery bank... Hard to tell how much--What is the wire gauge and length?

    If the DMM measures 13.5 and the Charge Controller displays 13.6 volts--probably within the margin of error.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • bmetbmet Solar Expert Posts: 630 ✭✭
    Re: How to use clamp meter?

    B.B.

    Thank you for the quick response. My steps, in order.

    separating + and - wires.
    zero the meter
    disengage the zero button (display reads 0.8 )
    place clamp around one wire, display reads low ( 0.2 - 1.0 A)

    unclamp meter from one wire (returns to 0.8 )

    zero the meter (displays 0.0)
    disengage the zero button
    display reads 0.8


    I have to believe my panel is putting out some current, or else my battery wouldn't be at float value. The panel is connected to controller by #12 solid core wire that has a vinyl coating. The odd thing about the wire, is that it is not copper-colored. Could it be aluminum? It's fairly stiff.
  • BB.BB. Super Moderators, Administrators Posts: 32,019 admin
    Re: How to use clamp meter?

    The Zero Button is a "toggle"... One push flips the current state, and so on...

    From my experience, Press the Zero Button once and look at the display... If the "ZERO" icon is not on, press the Zero Button once more and you should see "ZERO" and the display should read pretty close to 0.00 amps.

    Now, place the meter on the wire.

    The blank "ZERO" with 0.8 reading is the "offset" that needs to be zeroed out... If you had 0.8 reading on the meter it may add +0.8 to your current reading or subtract 0.8 from your current reading (offset) depending on the polarity of the current through the meter.

    If you are using the meter correctly, you should be able to clamp on and read read +1.20 amps, then unclamp and flip the meter over, and clamp on again and read -1.20 amps (note the sign change).

    If flipping the meter over does not read close to the same current reading, then you may not be using the Zero Button correctly.

    You can also try the same thing with your car... Turn on your lights on for a few minutes. Then start the car... You should measure around 10 amps charging the battery from the alternator when idling.

    Regarding how much current your array is loading into the battery bank... Details? Array voltage, battery voltage, DC current reading... Is the controller in "float mode", etc...

    -Bill

    Does the wiring say ALU or something on the vinyl? Scrape the wire a bit (or look at the cut end.... Some copper wire is tin coated and may look silvery. Unless you go some old house wiring (out of the 60's or 70's)--it would seem to be unlikely you got aluminum electrical wiring (unless this is some special stuff).
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • bmetbmet Solar Expert Posts: 630 ✭✭
    Re: How to use clamp meter?

    The measurement was made at both battery terminal, and the controller output terminal. The meter is a HFT cheapie, so I expect it to have a little error.

    My lack of experience with clamp meters show, but when I f first got this it was working great. The display would show 0.01, and give consistent currents for my inverter use. Now, with this residual value coming up every time I tun it on, I am not sure what I am really measuring. The location is remote country field with no local electronics except my Treo.

    Only other thing I noticed, is that when I upgraded to my current panel, my charge controller began ticking louder as the sun gets into high sky. I thought it was just the pwm circuit working really hard (is that stupid of me?)
    BB. wrote: »
    And yes, votlage is across the wires and current is through the wire (cut wire, place DDM in series to measure current).

    Regarding your 0.1 volt higher at controller measuring float voltage...

    I am not quit sure I understand what it is you are measuring at the meter vs at the battery... With your meter you are measuring 13.5 volts and at the charge controller you are measuring 13.6 volts? If so, you have a bit of voltage drop between the charge controller and the battery bank... Hard to tell how much--What is the wire gauge and length?

    If the DMM measures 13.5 and the Charge Controller displays 13.6 volts--probably within the margin of error.

    -Bill
  • BB.BB. Super Moderators, Administrators Posts: 32,019 admin
    Re: How to use clamp meter?

    The 0.8 with the zero "off" is the offset of the flux sensor (my guess). It may also be temperature sensitive (hot meter, more offset--have not tested that theory on mine).

    Basically, you need to "zero" the DC clamp meter before each use.

    And, try it on a few cables on your car (battery, alternator, etc.) so you get a feel how well it is working.

    The cheap DMMs seem to be pretty accurate (I am still happy with my ~30 year old off-brand cheap DMM). At least until something goes wrong--then it is a good idea to double check against a known good meter/voltage source to confirm all is well and the battery is good (we had at least one thread here on debugging a solar setup that came down to a flaky DMM lying about voltages--The readings were consistent, but not correct--really strange).

    You can have issues measuring current when you place your DMM in the circuit and the shunt adds additional resistance. However--where you placed yours (between solar panel and charge controller) should be relatively insensitive to any change in resistance--So I would trust it's reading assuming that you have the scale set correctly and plugged into the right sockets in the meter (been there, done that :roll:).

    Also, if you have a known DC current you can clamp on and check--it will increase your confidence on using the meter... Measuring a head lamp, charging the car battery, etc... For me, with a somewhat discharged battery on two different Honda vehicles always showed very closely to 14.2 volts and 10 amps maximum charge rate.

    You can have somebody crank the car and measure the high range current setting too (hmmm... I need to do that--knowing the "good numbers" makes diagnosing starter/wiring problems down the road easier when I have numbers that I don't know if they are good or bad).

    Flipping the meter over (changing current flow direction) and making sure that it still reads about the same value but with a sign change is a pretty quick way of confirming that zero/offset issue has been addressed.

    -Bill

    The PWM "ticking"... Don't know... It would be handy if you had your basic system description in your signature (you need to turn on your sigs next time you post--check the check box)... Watts of panels, charge controller, battery bank voltage/Amp*Hour rating and such.

    The ticking could be a slow "on/off" type controller and changes in magnetic field causing a bit of wire/sheet metal noise...???
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • mike95490mike95490 Solar Expert Posts: 9,363 ✭✭✭✭✭
    Re: How to use clamp meter?
    bmet wrote: »
    ...The odd thing about the wire, is that it is not copper-colored. Could it be aluminum? It's fairly stiff.


    The aluminun wire I installed last spring (6 ga) was very nearly butter soft. The insulation was stiffer than the wire inside was. very strange stuff.
    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 ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    solar: http://tinyurl.com/LMR-Solar
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  • bmetbmet Solar Expert Posts: 630 ✭✭
    Re: How to use clamp meter?

    B.B.

    Thank you for the correct procedure. I misinterpreted the readout, thinking a measurement could not be taken as long as the word 'zero' was present on the display.
    Now I see that it requires a couple of seconds to register a value after the clamp is applied. The numbers are more believable (altho being overcast for the 2nd week in a row sort of prevents me from knowing the full output). :cry:
    BB. wrote: »
    The 0.8 with the zero "off" is the offset of the flux sensor (my guess). It may also be temperature sensitive (hot meter, more offset--have not tested that theory on mine).

    Basically, you need to "zero" the DC clamp meter before each use.

    And, try it on a few cables on your car (battery, alternator, etc.) so you get a feel how well it is working.

    The cheap DMMs seem to be pretty accurate (I am still happy with my ~30 year old off-brand cheap DMM). At least until something goes wrong--then it is a good idea to double check against a known good meter/voltage source to confirm all is well and the battery is good (we had at least one thread here on debugging a solar setup that came down to a flaky DMM lying about voltages--The readings were consistent, but not correct--really strange).

    You can have issues measuring current when you place your DMM in the circuit and the shunt adds additional resistance. However--where you placed yours (between solar panel and charge controller) should be relatively insensitive to any change in resistance--So I would trust it's reading assuming that you have the scale set correctly and plugged into the right sockets in the meter (been there, done that :roll:).

    Also, if you have a known DC current you can clamp on and check--it will increase your confidence on using the meter... Measuring a head lamp, charging the car battery, etc... For me, with a somewhat discharged battery on two different Honda vehicles always showed very closely to 14.2 volts and 10 amps maximum charge rate.

    You can have somebody crank the car and measure the high range current setting too (hmmm... I need to do that--knowing the "good numbers" makes diagnosing starter/wiring problems down the road easier when I have numbers that I don't know if they are good or bad).

    Flipping the meter over (changing current flow direction) and making sure that it still reads about the same value but with a sign change is a pretty quick way of confirming that zero/offset issue has been addressed.

    -Bill

    The PWM "ticking"... Don't know... It would be handy if you had your basic system description in your signature (you need to turn on your sigs next time you post--check the check box)... Watts of panels, charge controller, battery bank voltage/Amp*Hour rating and such.

    The ticking could be a slow "on/off" type controller and changes in magnetic field causing a bit of wire/sheet metal noise...???
  • BB.BB. Super Moderators, Administrators Posts: 32,019 admin
    Re: How to use clamp meter?

    Bmet,

    It took me a couple of days of playing with the unit for me to figure out what the heck was going on too...

    If I understand the operation correctly, that non-"ZERO" display is

    Very confusing.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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