Recently Shawn Lawless posted some comments about “thermal events” aka a controller blowing up and I realized that this is something that everyone installing a controller should really consider since this is a major safety issue.

Controller thermal events can happen on any EV running any controller. Fortunately Zilla controllers have been very reliable and failures have been rare. Unfortunately this means that most people are not familiar with what a controller thermal event can do. Now that many Zillas are passing the ten year mark (and some 15 years) and people are pushing them harder than ever we can expect more units to fail.

So what’s it like when a Zilla fails at full power? Sometimes it’s only a small pop and a little smoke leaks out. Other times it can mean a severe amount of explosion, fire and plasma. Remember what the carnage looks like on those old C type 1221 controllers that used to blow rather often in the 1990s? Those 120V 400A units that we used to think had power!? Maybe you were not playing with EVs then but I remember end covers blown off and flames shooting out the end, molten copper and aluminum dripping off the ends. Burnt paint and lots of carbon was common. Well, you can take that mess of flame, molten metal and carbon and multiply it by about ten for a high power Zilla setup. Forceful plasma balls can melt through plastic covers like there was nothing there and burn sheet metal shields enough to roast the paint on the other side. Preparing to minimize such an event is essential.

My point in all this?
Be prepared and don’t let this potential failure cause injury. Here are a few tips to consider when installing a controller:
* Never install a controller power section in the same compartment with the driver or passengers.
* Consider what would happen if a large ongoing fireball where to shoot out of the end of your controller. Would your vehicle still be safe?
* Be very careful to use the correct size semiconductor fuse in the battery circuit. This will have a lower current rating than the controller, usually less than half the peak rating of the controller. Be sure to use the fuse I/T curve to select the smallest current rating that will do. The fuse must also be rated to break the maximum DC voltage of your system at full charge. AC ratings are not enough.
* Always use a safe main contactor rated to carry the maximum expected current for the required duration without welding on, and then to break the maximum possible fault current. On a Zilla this will allow the Hairball to do it’s job and quickly shut off power in case of a failure. Beware of the continuous ratings of Kilovac and Gigavac contactors. I think they are deceptive in that they rate them with absurdly large cables attached to cool the terminals. If you don’t have those large cables, the contactors will weld on at those “rated” currents. They often do not list ratings for the smaller 2/0 cable we often use on the battery loop.  See my Faq for more on contactors.

EV’s are a lot of fun and games until someone gets hurt. Please, let’s be safe out there!