Partial Jag failure?

[techhelpbb]

So I was digging around in the older Jaguar schematics and discovered in the older gray (grey) model they used a 0.0005 Ohm, 2 Watt resistor (labeled R35) for measuring the current.

http://www.luminarymicro.com/products/rdk_bdc.html

The schematic and BOM in question is in the:
"Brushed DC Motor Module and RDK Design Package Rev B" dated 1/19/2010

The user manual in question is in the:
"Brushed DC Motor Control Module and RDK User's Manual" dated 1/19/2010

Additionally, instead of being on the high side (+ side) of the motor control circuit it's on the low side (- side) of the motor control circuit. This would have made it very hard to measure the reverse current that they don't measure anyway.

This altered resistor value, at half the Wattage still limits the safe operating current to 63 Amps or less continuous. However, it's lower resistance also limits the range of the voltage it will achieve across that resistor.

In that circuit they used an operational amplifier not designed for this purpose (not a big deal...except it might limit it's ability to survive overload).

That operational amplifier is configured as a non-inverting amplifier with a gain of 40. So any voltage that appears across that resistor will be multiplied by 40. So at maximum it'll report a voltage of about 1.26 Volts at 63 Amps. Still safe for the 3.3V microcontroller. However...this means that older Jaguars have a slightly reduced ability to measure current and still have the same possible failure situations.

Again...if that resistor burns out or becomes desoldered the circuit will still fail and you'll still read 0 Volts from it.
So my post above applies whether you use the gray (grey) or black Jaguars. Just modify it with the older Jaguars to disconnecting the low side (- side) of the motor driving circuit.