Ammeter barely reads

[Alan Fox]

My ammeter barely reads a charge or discharge , I bead blasted the shunt and all the fasteners and wire ends attached to it... When I load the shunt electrically  the microvolts for the estimated load are in line with the specs on the shunt..(60 amps 50 millivolt) I checked the resistance of the wires to the guage and it is negligable ..  Has any one had the instrument rebuilt with good results , any suggestions I like the strip guage and would like to keep if possible...

[Jerry 5TJ]

So, have you tested the meter?   You know it should read 60A with 50 millivolts, so apply a known 25mV across the meter and see if it indicates 30A. 

If you don't have a precision millivolt source, how about a 1.5V battery with a resistive divider -- say 47K and 1K ohms to pick two commonly available values -- which should give 31 mV across the 1K resistor if the battery really is 1.5V.  That should move the needle up to about 37 amps.  {(31mV x 6/5) ~ 37 amps}

If that shows the meter is OK, and since you know your shunt is good,  then perhaps your charging system really is not charging?   Check your plane's schematic to see what the ammeter indicates -- some show generator output, some show battery current (charge/discharge).

 

 

[Alan Fox]

Thanks for the input , that was the nest step , tried a rheostat but it didnt work , and radio shack stinks for semis any more .....Will let u know thanks Alan