Help on DC amp clamp meters

DJuan222DJuan222 Posts: 24Registered Users ✭✭

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  • jonrjonr Posts: 1,033Solar Expert ✭✭✭✭
    I think it does what the description says - both AC and DC.
  • littleharbor2littleharbor2 Posts: 979Solar Expert ✭✭✭✭

    2.1 Kw Suntech 175 mono, Classic 200, Trace SW 4024 ( 15 years old  but brand new out of sealed factory box Jan. 2015), Bogart Tri-metric, 700 ah @24 volt AGM battery bank. Plenty of Baja Sea of Cortez sunshine.

  • DJuan222DJuan222 Posts: 24Registered Users ✭✭
    OK now that I got the meter I feel dumb...well kinda

    Cant figure out why I can get the clamp to work and the lines from the panels + and the + from MPPT to batteries ( accurate to what the mppt reads )  but I cant get it to work on the 12 v 300amp line from the batteries.  its like 0 ga unshielded cant get any V or A even on the end where connected to inverter. Yes its set to DC, the system works been the a year. get 0 reading on car battery also

    what am i doing wrong on the 12v stuff ??
  • BB.BB. Posts: 27,699Super Moderators admin
    When measuring volts--You are using the +/- leads from the meter? (some meters have an AC non-contact voltage sensor--But that will read zero volts if trying to non-contact sense DC voltage).

    If you are using the leads, put one lead on a battery - terminal and keep it there. Use the other + lead to probe each connection point in your system around the battery bank. See if everything "makes sense" or not.

    If you have a 12 volt system... Get a (cheap) 12 volt Test Light from the auto parts store (looks like a clear screwdriver with a sharp point and a clip lead out the back).

    When using DMM meters--They draw very little current (millionth's of an Amp). It is possible to read across a "bad connection" with a DMM and read "good voltage". But as soon as you put a small load on the connection, the voltage drops to zero (and why test lights are sometimes better for debugging power connections).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • PhotowhitPhotowhit Posts: 4,662Solar Expert ✭✭✭✭
    edited May 23 #6
    Okay, so I guess you bought a clamp meter?

    Are you clamping only 1 wire? They work of fields so if you clamp 2 wires they neutralize each other.

    ...also with some of these new inexpensive meters you set the strength with the dial the select either AC or DC by pushing a button.
    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Prosine 1800 and Exeltech 1100, ForkLift battery. Off grid for @13 of last 14 years. 1000 watts being added to current CC, @2700 watts to be added with an additional CC.
  • DJuan222DJuan222 Posts: 24Registered Users ✭✭
    let me be more specific

    when set to DC I can read amps off the panels and + wire off MPPT to the batteries

    when i try to read the 12v 300A single unshielded cable from the battery bank to the inverter I get 0

    the setup has worked a year and the single red wire off the car battery reads 0 also on amps

    it seems to be a problem when i try to read from batteries??
  • PhotowhitPhotowhit Posts: 4,662Solar Expert ✭✭✭✭
    Is the inverter on with a load? Perhaps an inexpensive clamp meter wouldn't pick up a minimal draw in sleep mode? @BB. Bill will likely know... Also is the car on, pop on the headlights should work as a load.
    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Prosine 1800 and Exeltech 1100, ForkLift battery. Off grid for @13 of last 14 years. 1000 watts being added to current CC, @2700 watts to be added with an additional CC.
  • BB.BB. Posts: 27,699Super Moderators admin
    I am unclear if the Inverter is working or not (no voltage on the DC input to the inverter?).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • jonrjonr Posts: 1,033Solar Expert ✭✭✭✭
    You have the DC amps range set to 600A?   Test it when you know you have a few amps of load.  

    Don't attempt to measure volts using the clamp.
  • DJuan222DJuan222 Posts: 24Registered Users ✭✭
    Yes!! I had to let the refridgerator come on then it read a load and It finally gave me 6 amps :)

    question though, to test batteries amps at rest how do you check 100amps?  all of my DMM max at 10amps?
  • BB.BB. Posts: 27,699Super Moderators admin
    What do you mean by "test batteries amps at rest how do you check 100amps"....

    Batteries at rest have no current flow--So no Amps to measure.

    Are you asking how to test a battery to see if a 100 AH rated battery actually 100 AH capacity? Are you trying to figure out if a battery is XX% state of charge?

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • DJuan222DJuan222 Posts: 24Registered Users ✭✭
    Yes Bill I guess thats what Im asking mainly XX% because I have had several gel batteries have 12v and lose amps so couldn't even start motorcycle

    John

    Are you asking how to test a battery to see if a 100 AH rated battery actually 100 AH capacity? Are you trying to figure out if a battery is XX% state of charge?
  • EstragonEstragon Posts: 2,633Registered Users ✭✭✭✭
    There are two different amp ratings; amp-HOURS, which is the capacity of the battery to sustain a load of 'X' amps for 'Y' hours before a cutoff low voltage is reached, and cranking amps, which is the capacity of the battery to supply current at 'Z' amps instantaneously. Most deep cycle batteries are rated in the first (AH) way. Most starting batteries are rated in the second (CA and/or CCA and/HCA) way. 100AH capacity is not the same thing as a 100CCA capacity.

    Which are you trying to test?
    Off-grid.  
    Main daytime system ~4kw panels into 2xMNClassic150 370ah 48v bank 2xOutback 3548 inverter 120v + 240v autotransformer
    Night system ~1kw panels into 1xMNClassic150 700ah 12v bank morningstar 300w inverter
  • BB.BB. Posts: 27,699Super Moderators admin
    GEL batteries are sensitive to charging current--And over charging voltag. And probably have a somewhat shorter life than a typical (similar quality) flooded cell deep cycle battery.

    Since GEL batteries are sealed, you cannot use a hydrometer to measure the specific gravity. You are left with measuring the resting voltage and doing load tests (try to find a voltage vs state of charge chart for your batteries)..

    From a practical point of view--A battery bank has "failed" when it no longer does the job you need it to do. If it used to work for you and some years later does not now--Then it is time for replacement.

    Load testing, both when new where you log resting voltage, and probably maximum load and what the voltage of the battery bank is. And run the same test once a year and/or on your "failing bank" to figure out what you need for your bank (I would suggest that if your bank is ~50 state of charge and you are running your maximum expected load--not surge load--That you want the voltage to be over ~11.5 volts (for a 12 volt bank).

    For my car, I crank the engine with the headlights on--If the lights stay reasonably bright when cranking, all is OK. If the lights dim substantially and/or the cranking sounds slow--Then check charging system and battery voltage while charging--If OK, then the battery is probably starting to fail.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • DJuan222DJuan222 Posts: 24Registered Users ✭✭
    thanks guys, its my 100AH AGM batteries, i thought there was a way to measure what they still " have "

    for example if 1 of 3 has gone low on amps but ok on volts, since in a solar system I cant crank it, not sure how to figure out which battery to replace...isnt it true the other 2 good batteries will go bad faster trying to help that weak battery??
  • EstragonEstragon Posts: 2,633Registered Users ✭✭✭✭
    Yes, one battery gone "old" before its time can "age" the others faster, especially in parallel.

    A couple of things I'd try to identify a suspect; check the temperature of each battery with an IR thermometer towards the end of charging - a bad one may be hotter or cooler than the other two, and check current from each under a decent load with DC clamp meter - a bad one may be supplying less current that the others.

    You could also disconnect each (fully charged), let it sit or apply a load to get resting voltage to ~12.8v (to disipate any surface charge), then apply a load of known size and draw voltage down to ~12.2v. A bad battery will go down in voltage faster - capacity will be roughly 2x the amp-hours used by the load.
    Off-grid.  
    Main daytime system ~4kw panels into 2xMNClassic150 370ah 48v bank 2xOutback 3548 inverter 120v + 240v autotransformer
    Night system ~1kw panels into 1xMNClassic150 700ah 12v bank morningstar 300w inverter
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