24V Light on Power Distribution Board

[Matt Krass]

Originally Posted by Al Skierkiewicz

joachimbean,
The 24 volt power supply will operate down to about 4.5 volts on the battery. If you haven't charged the battery, it is possible for the battery to fall to less than 4.5 volts when you try and power the robot. However, there is always the possibility that one of your batteries has been wired backwards. It happens all the time at the beginning of the season. Check all batteries with your voltmeter to be sure. The battery connector is marked with a + and - as well as the PD. Measure the voltage right at the input to the PD to be sure you have the correct polarity and a battery that is well above 4.5 volts.

Is the PD protected against reverse polarity?
Also, he said the 5V and 12V outputs were working, which would imply that he currently has the correct polarity, but if the board isn't protected a reverse wired battery may have damaged something.

Do we know exactly what boost converter they use for the 24V rail? I'm curious what its datasheet says about reverse polarity.

EDIT:
I realized after I asked all the schematics are on the FIRST website here: http://usfirst.org/roboticsprograms/....aspx?id=16337

The boost converter is based on the LM3478 chip, and I pulled its datasheet up from NI. I admit I only skimmed it, but it doesn't seem to have any reverse polarity protection, nor does the PD board seem to have. It does have built in short circuit protection, so a short shouldn't have hurt it, but there is a 15A fuse in line with it inside the PD board. If you shorted it, I'm not sure if that fuse would go before the SCP in the LM3478 would kick in, so it's possible that blew I suppose. I guess this is a viable possibility if you guys can't find any batteries wired in reverse.

EDIT2:
I actually think that it's not a fuse but a self resetting internal 15A circuit breaker. I should probably not try to read schematics when half asleep....