Quote:
Originally Posted by techhelpbb
Have you considered inspecting the MOSFETs inside the unit?
|
Dude,
This is not always the failure mode on the Tan or Black Jag. Your calculations on the current
sense resistor are mostly correct and it is likely the source of the failure if nothing else went sour at the same time. I have noted that many tan Jag failures occurred when the current sense became so hot, it unsoldered itself from the board and in the movement of the robot actually moved off it's circuit pads. This opens the current flow inside the Jag. Just to be accurate, CIMs draw 133 amps in stall which would dissipate about 17.6 watts in the current sense resistor. Over an extended amount of time, this would cause severe heating of the resistor. Normally, CIMs are run at 40 amps or less so normal dissipation is about 1.6 watts.
The current
shunts in analog meters (and many digital meters with current measuring) is to prevent damage to the meter (either causing the pointer to wrap itself around the pins or damaging analog to digital convertors). The more sensitive an analog meter, the less current it would need to go full scale. I have an old Midland analog meter that has a full scale current of 60 microamps. In order to measure current the meter needed a current shunt across the terminals to prevent damage. Say you wanted to measure 10 amps full scale, then the shunt had to be sized such that 9.99994 amps flowed in the shunt. This shunt is not the same as the series current sense resistor used in the Jags. My Fluke uses a #10 wire as a shunt on the high current (10 amp) range.