powr dist. board/cRIO puzzle - please advise!

[Steve Compton]

I'll let Chad Spackman, wjo is really the brains behind this add in when he can, but today he wired up a bench system - battery to distribution panel to victor. Shorting a 15 amp fuse on the power distribution panel immediately shuts down the cRIO,just like we saw on our robot. On this nech system, no possibility of CRIO being in contact with metal frame, no possibility of wiring gluitches with victors, etc. A simple short to the power distribution board and the cRIO folds.

[Alan Anderson]

Originally Posted by Steve Compton

A simple short to the power distribution board and the cRIO folds.

Since the power being distributed by the board is coming directly from the battery, this should not be a surprise. If battery voltage drops low enough, the 24v boost supply for the cRIO shuts down. A breaker does not respond instantly, so the battery will likely be loaded long enough for the cRIO to lose power and reset after the breaker trips and the voltage comes back.


Your description of the testbed has a couple of problems, though. There should be no "15 amp fuse" anywhere in the system. Shorting a fuse should have no effect unless the fuse is blown and there is another short elsewhere. I'm going to assume you're talking about taking the positive side of a circuit powered through a 20A breaker and connecting it to the negative side, and not worry about it.

[Steve Compton]

Thanks!. This is exactly why I said I will have Chad start talking on this forum... I am sort of shhoing in the dark here and he knows what he's talking about...so beofre I say anything else half-educated, I'll pass it over! Again to ALL of you, thanks for the ongoing conversation.

Steve

[spack]

Thanks to all for suggestions.

What I know through monitoring and through some tests before crating are:
- It's not a comms issue.
- It is an interruption or disturbance of power to the CRio due to a high upstream branch current, or some nasty EM kick. The CRio reboots.
- The internal resistance of the battery is far and away the largest feed resistance in the circuit and the (very slow acting) auto-reset breakers are not meant to protect the CRio from an IR drop due to hard short, so no surprise there. Having said that, I did like the alternate battery approach we used to have to help when a battery may have gotten mismanaged. Also having said that, there is no way to know if there was or is a hard short without the robot in front of us. We can only theorize at this point and do what follows figuring that it probably is such a thing or that the commutator is stuffed.

We will be replacing the motor, victor, and using an alternate breaker port out of hand. And we will arrive with new batteries. Isolation will be checked.

I did some bench testing with a surge load while monitoring the 24v supply with a scope. Frankly I don't like the approach. I'd rather the CRio stayed up while our robot was billowing smoke rings.

Thanks again,
Chad

[Al Skierkiewicz]

The Crio is intended to inhibit output when the battery voltage falls below 5.5 volts. The Crio power supply quits when the battery voltage falls to 4.5 volts. the sense lead for this is the jumper you insert in the analog module.
What did you see when scoping the 24 volt supply?