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Ammeter Span adjustment

Discussion in 'Troubleshooting and Repair' started by driver06, Jan 21, 2021.

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  1. driver06


    Jul 14, 2019
    I have a 24v 0 - 60 amp digital ammeter that reads about 30% of the correct reading. There is no access to or information on the shunt. Should I be able to adjust span to a known load? I tried doing so on an indicated 5 amps, but maximum change over the whole range of adjustment is only 0.5 amps.
    Is the pot faulty maybe?
  2. Bluejets


    Oct 5, 2014
    My car won't go...can you tell me how much to fix it and where I can get the parts.??

    See the problem where near enough information, links, photos, model numbers etc. etc.
    davenn likes this.
  3. Harald Kapp

    Harald Kapp Moderator Moderator

    Nov 17, 2011
    Check the battery.
  4. driver06


    Jul 14, 2019
    Make unknown. 24v dc. The span potentiometer is bottom right. Its a general question. Does a Span potentiometer normally give a greater change in reading than 0.5amp on a digial reading of 5amp, please? ammeter S1120006.JPG
  5. Harald Kapp

    Harald Kapp Moderator Moderator

    Nov 17, 2011
    Usually not. The pot is there to compensate slight inaccuracies of the fixed resistors.
  6. kenny256


    Jan 4, 2020
    You would only adjust the span at the full load, just as you adjust the zero at no load.

    If you have a multimeter you should measure and check the values of the resistors and the pots. That is the one sure way to determine if the pot is bad, measure the resistance while you turn the knob.

    Looks like the shunt would read out 1mV per Amp.
  7. Harald Kapp

    Harald Kapp Moderator Moderator

    Nov 17, 2011
  8. Kiwi


    Jan 28, 2013
    I assume this is out of a marine dash panel?

    The meter requires the correct external 60mv shunt to operate.
    The meter and shunt must have the same rating.
    Example: A 100A shunt will have a 60mv drop across it with a current of 100A. A meter calibrated for 100A will go to full scale at 60mv and display 100A.
    The span pot allows you to fine tune the reading for accuracy. About 5%
    Does the shunt current rating match the full scale of the meter?

    My guess would be that the shunt rating is three times the meter setting.

    Check the details written on the shunt and compare them to the link on the other side of the board(150,250,500,600,1000).
    Both should be the same.
    Harald Kapp likes this.
  9. 73's de Edd

    73's de Edd

    Aug 21, 2015
    Sir driver06 . . . . .

    I had initially started on this MUCH earlier, but then had to break away for more urgent Sattidy tasks.
    In the interim I see that . . . der KIWI . . . meister, has added on his :

    My guess would be that the shunt rating is three times the meter setting.

    Check the details written on the shunt and compare them to the link on the other side of the board(150,250,500,600,1000).
    Both should be the same.

    Those statements also mirror my same exact suspicions.

    I am now going to go into even further and exacting depth in responding to those two presumable factoids.
    Now, with you knowing the necessary facts related to the externally connected ammeter shunt block, as if the proper one is being used.
    The use of a known load connected in series with the power source and its remoted shunt should permit you to use a DVM in its . . . probably . . . lowest DC Voltage range, to measure across screw terminals connected to wires 1211 and 1210 . The readout should be in millivolts as directly related to amps then passing thru the completed current curcuit.
    If that is then in disagreement with the instruments interpretation of amps passing . . . . .in its being low, as you say . . . .
    Then there is need of checking out the instrumnents range scaling.

    Lets examine some things . . . .

    I initially see that near the left white display LED cluster / pack, PCB midpoint, is an option of AC or DC operation, with a solder blob spread connection now enabling the DC mode.
    A short distance down, will be what I think are being three dummy / production change TA and Sample and Hold solder pads.

    NOW ! . . .My kingdom for the purveyor of the correct relevant info on / as to the cryptic "TA" mode aspect.

    S o o o o o o o . . . . . nowsomewhathoweveranyways . . . . . if you will then look a bit further to the right of that trio of pads, you will see that mode function is being engaged by the pesence of yet another solder blob spread connection at ANOTHER foil etched SH mark up . . . with no TA involvement..

    Now . . . for the real MONEY shot . . . . . look at the opposite end of that mentioned TA and SH options stakes and then see the starting off of 100.0 * 60.0 * 50.0 * 25.0 and 15.0 * paired sets of stakes exposed solder to foil pad joints.
    Therewith I am fully expecting some series arranged and selected values of surface mount resistors on the unviewable side, to be daisy chained between the sets of stakes for creating range selectors for the differently required millivolt range scales.
    Viz . . . .15mv - 15 Amp . . . . . 25mv - 25 Amp . . . . . 50mv - 50 Amp . . . . . 60mv - 60 Amp and the final 1000mv - 100 Amp, you just need to be sure that you are using the proper remoted current shunt and then push on a jumper plug for the set of stakes related to your required millivolt range.
    With your experienced low readings, I am expecting that it is now improperly scaled / jumpered for a 1000mv readout . . . . . . thus the resultant low side error.

    Since the other PC board sides view was not being offered . . . .are the below units being the same / correct parts ?

    Strip of breakaway Dual Row Header Pins

    Shorting plug for use between header pins

    I'm expecting use of Gold flashed pins for weatherability / reliability . . . and expectimg the PROPER installation of a shorting plug across the 60.0 set of pins.
    HOWEVER the 1000 range might be a real mystery to affirm . . . without confirmational TESTING . . . .because it could be with a shorting plug installed at the 1000 set of pins . . .OR . . .with NO jumper plug being used on the unit at all !
    All . . . . . leading back to the possibility that some production line new hires . . . . . Sally Jean Johnson / or / Missy Ling Ting Tong . . . set up the wrong meter voltage scaling on that unit of yours.

    Check the battery.
    I'm seeing this unit being direct hard wired into MAIN system battery via wires 1212/9 and -B1P/9A.

    Tha a a a a a a a s s s s s s it . . . . . .

    BTW . . .poster . . .what is ? . . . . . this monitored equipment . . . that uses 24VDC . . . . at maybe 200AH instant capability ?

    73's de Edd . . . . .

    As I am a' seein' it, this a' here . . . Tact . . . thang. . . . . . . is being the capability of convincing people that they know more than they actually do.

    Last edited: Jan 24, 2021
  10. driver06


    Jul 14, 2019
    Thank you everybody for all the answers and information. However I am pretty lost with all of this, so am going to pass all of the information over to my mate who is an electrician. Will keep you informed.
  11. driver06


    Jul 14, 2019
    My mate decided the "new" ammeter was faulty. The supplier changed it and the new on works fine. Thanks again everybody for your comments.
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