[Al Skierkiewicz]

Jim,
The spec sheets for the breakers we use can withstand 600% over current for several seconds prior to trip and can withstand something near 200% indefinitely. So for the 40 amp breakers, periodic stall currents are not enough to trip the breakers. As they are self resetting, the reset takes place almost immediately, and with sustained trip currents, the breakers will actually buzz. The drawback is that these devices are thermal by nature and so get hot under trip conditions. The main breaker is similar in design and function except it is not self resetting.

Tech,
The chip is called a shunt current monitor in that it was designed to be used in that application. The resistor in the Jag is merely in series with the output and as such is not really a shunt since it is the only path through which current flows. It is a convenient chip to use in this application since the gain is fixed, it is designed for single power supply and can swing to within 0.2 volts of the positive power rail. The output current of the battery is speced at around 600 amps for a few seconds and is primarily limited by the internal resistance of the battery which is .011 ohms. While it is easy to say currents in the Jag are normally around 50 amps, that is not correct. Many teams design mechanical systems that draw significantly higher currents. There has been at least one post in the past few days where the team started out draining their battery in less than two minutes. For the black Jags, the manufacturer states that the current monitor will fault the device based on current over specified time. I believe that the black Jag is more aggressive at current monitor due to the reduction of MOSFETs in the output stages. The Victors do not use a current monitor for a variety of reasons. I believe this is due to the fact that the sense resistor limits current delivered to the load, adds to the parts count, and is not needed with three 40 amp FETs in parallel in each leg of the output circuit. While the FETs have a higher series resistance than the Jag, in most of our applications, the added resistance is minimal as it amounts to about the resistance of two feet of #10 AWG wire. Please remember that the power rating on a resistor is based on it's temperature rise and sustained temperature over time. A 1/2 watt resistor can handle 10 watts for a few seconds while it can never handle 1 watt over a several days.