SPICA ALTERNATOR FIRE! (Copy)

You read that right. Here's what happened and how I fixed it. I reference an email from marine electrical guru Nigel Calder, who helped me figure out what went wrong - text of that email is beneath the video.

Hi Andy,

My guess is your rubber washer did not do the job! This would have happened sooner or later anyway because the back of these alternators gets really hot – above 100ºC – especially when charging into lithium-ion so the rubber would have softened and either melted out of the way or resulted in a loose connection and an arcing fault. That’s why there was a piece of hard plastic in there in the first place!!

Some rubber also has conductive elements – depends on the composition when it is formulated. I found this out when I set the rectifier for a 22kW DC generator on fire during one of our electric propulsion and hybrid experiments, at night and in a gale and in rock strewn waters off the west coast of Sweden (near Kungsviken) so quite a dramatic exercise. It happened because I used a piece of rubber from a truck tire inner tube as an insulator. It turned out to be somewhat conductive. There were a lot of flames and because it was night time it was quite dramatic and I thought ‘this would make a great photo’ but I chickened out and put the fire out and only afterwards realized I would have had time to get the camera. I was somewhat annoyed with myself, but not nearly as much as Terrie was with me!

Let’s assume it was a short with your alternator. You now applied reverse polarity to the diodes that are grounded through a plate connected to the case and blew the diodes. I’m surprised the fuse did not blow. Your rubber was probably working well enough to keep the current flow low enough for the short time before you broke the circuit (because of the time delay characteristics, it would take several hundred amps to immediately blow what I am guessing is an ANL slow blow fuse).

-Nigel