The weather here has been crap, the last two weeks. It has either rained, or threatened rain every day. The rain, when it comes, has been drizzle on and off all day, or overcast all day, with a brief but violent downpour. If this becomes a trend, I will need fenders.
Last Tuesday, I was pacing around all day, watching little storm cells appearing and vanishing all over the map. I'd finally had enough at 3:30 and decided to go for a short ride. I got about 15 miles from home with big clouds stacked up ahead of me the whole way. But I started to notice dark clouds building fast behind. I arced around and headed for home. I switched from WOT in position 2 (21-25 mph), to WOT in position 3 (28-32 mph). It was looking real nasty about 10 miles from home. By 4 miles, it was raining pretty good. By 2 miles I had my glasses pulled down my nose, squinting between the glasses tops, and my cap brim. The sky was pitch black, swirling, with cracks of lightning too near for comfort. At the entrance to our road, the power cut off. I looked at the CA and the voltage was 35 and dropping fast. Something was obviously wet, and shorting out. Probably the controller, or the BMS. I cut the power switch, downshifted to a low gear, and started grinding out the last bit over one mile to home. I turned on the power switch every minute or so. The CA would boot up. The voltage would read in the low 30's, and start dropping fast. I finally pushed the bike in the back door with water running out of my shoes, soaked through. I haven't been that wet since falling out of a kayak. I pulled the soggy, black polyester cover from the battery. I had been meaning to urethane the inside, but hadn't gotten around to it yet. The BMS and battery were damp. I unplugged the battery from the controller, and the BMS balance lead plug from the BMS. I checked the pack voltage at the main pack terminals, with my VOM, and read 53.4 volts, about what it was before the rain hit.
The backside of the BMS had an insulating layer of black posterboard/cardboard, held on with the nuts for the six tiny screws that held the aluminum heatsink to the front. Paul, at EM3ev, had warned me not to count on it, so the BMS sat on a piece of black neoprene foam from a mouse pad. However, the posterboard was completely soaked, and now conducted well enough to cause a small drain on some part of the BMS. The CA, reading a low voltage, was cutting power. I was able to peel the wet cardboard off the back of the BMS, leaving little bits under the mounting nuts. I put a floor fan on high, and let it blow over the electricals all night. The next morning, I carefully removed the tiny nuts, one at a time, and replaced the scraps of posterboard with small nylon washers. I then glued a 4 mm thick piece of white, closed cell packing foam to the back of the BMS to replace the cardboard, and neoprene foam. This, and the urethane coating I now have in the bag, should prevent the problem from reoccurring. With two rides, and a charge since, everything seems fine.