Quote:
Originally Posted by Kevin Sevcik
That would provisionally work, yes. The issues I'd want thoroughly addressed before I'd use it:
1. How reliable is it under FRC service conditions? We're talking pretty exciting bumps and crashes, and available voltage dipping into the 9V range under heavy current draws. And you have that diode dropping .7V of your available voltage for energizing your coil. It'd be unfortunate if the coil dropped out under those conditions when an unmodified Jag would hum merrily along.
2. I don't have the Jag schematics up at the moment, so I can't say that one of these will work. You may need two to completely disconnect the H-Bridge to actually protect everything important.
3. You do realize you're proposing to slap a 1" cube into the Jaguar's innards? The Horribly Oversized and Oppressively Bulky Jaguar? If this turned out to be the solution, I think I'd take a leave of absence from CD for a year to save myself the howls of outrage.
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1. No doubt...testing is absolutely critical. Some of the Panasonic 40A relays seem to have drop out voltages well into the 7VDC and below range. Not sure that's really a good idea as a contact rating, but there are plenty of choices.
2. At some point either on the positive supply side, or negative supply side of the H-bridge you should only need to disconnect one contact to break the circuit. Course there is a current monitor resistance in that circuit, but breaking the circuit should protect that as well.
3. As I pointed out above, the idea in my mind was to consider this as a purchasing option. Frankly, with reservations, I agree with other mentors here that damaging something by powering up wrong can be a good lesson. However, I could easily see how it could be a painful lesson for poorly funded teams (even a show stopper). I don't think we should all pay for mistakes we might not make (in power, in size, in weight). Then again if someone has concerns like this perhaps there is value in considering the possibilities if they are willing to pay for it.
Additionally, I'm not sure you can escape the whole extra cubic inch issue. Even if you use a MOSFET(s) in the existing available space in the Jaguar the space involved seems to approach that size. Perhaps it could be built as a module outside the existing Jaguar and attached by someone that won't get it backwards? In that manner the Jaguar itself is the same...but sadly you'll not be able to power up the Jaguar at all like that (I had entertained the idea of having the Jaguar being able to even communicate on the CAN bus that the power is reversed).
Perhaps a connector could be made available on the outside of the Jaguar. Designed so that what plugs in there can't be plugged in with the wrong polarity. At that connector you could either plug in a 'jumper' which is merely a piece of sufficent gauge wire, or you could plug in the reverse voltage protection module which itself is designed to mate that connector with guarenteed polarity. The idea being that a team that has this concern could buy the modules if they want them, have them attached to the Jaguars, and then remove them later and put the 'jumpers' in their place (after they are sure they haven't made a serious error).