[techhelpbb]

To extend this...

If you look at page 21 of the manual you'll see that VM+ is actually not across the motor output...but between the current shunt on the high side and the high side MOSFETs.

If you note the top of page 22 under the heading 'Voltage Sensing' you'll note that they refer to VBUS with regards to this voltage.

I should like to point out that if you look at that current shunt named R23 in the BOM, you'll note it's: 0.001 Ohm, +/- 1% and only 4 Watt.

Now...the Jaguars claim they can withstand 100 Amp at motor startup.

If we take Ohm's law: E = I x R.

If I = 100 Amp and R = 0.001 Ohm.

The voltage (E) across that shunt will be: 0.1 Volt
(I should like to point out that in older analog current meter applications it was quite common to see current shunts designed to produce maximum voltage drops of 0.05 Volt or 0.1 Volt...this is likely not an accident.)

So the Wattage across that shunt will be: P = E x I
(I'm using DC analysis here...so I'm cheating a bit)

Therefore the Wattage would be: 10 Watts.

Now...why the mere 4 Watt resistor?

Well...the Jaguar only says 100 Amps at *startup* and once the motor starts moving it'll not need so much current to keep moving...or that's the theory.

So basically they hope you won't cook that resistor until it opens the circuit. If you did cook that resistor the only voltage that would appear on that analog to digital converter (for reading VM+) would be driven there from the converter's input bias current...and that might be very low since the low side of the voltage divider will pull to ground pretty hard.

In another topic up here I was talking about monitoring the circuit current with a shunt (resistor). Oddly I designed a whole circuit for this application...then went back and took a good look at the Jaguar schematic and noticed they used the same part (INA193). Only thing was...I designed it with a 0.002 Ohm resistor, +/-1% accurate, 30 Watt resistor. I assumed someone *would* draw upwards of 120 Amps through that circuit and often enough it would be a problem otherwise. I came to this decision because the CIM motors often used can pull over 120 Amps when stalled...and they'll survive that abuse for a good long time.

In your case...if you've beaten up the Jaguar often...you've been effectively testing the response time of your current limiting systems. So maybe you 'got lucky' and finally did some lasting damage. If you can check that resistor you might want to.