Forwarded from Otmar Ebenhoech : 9/21/10
IMPORTANT ZILLA SAFETY ANNOUNCEMENT
I think it is very important that we expound a bit on what a
"thermal event" can entail since this can be a major safety issue.
Controller thermal events can happen on any EV running any controller
and I believe a little review for safety is in order.
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 a
small pop and a little smoke leaks out but it can also be a pretty
severe amount of explosion, fire and plasma. Remember what the
carnage looked like on those old Curtis 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!
I'll be posting a edited version of this on my FAQ shortly in case
you want to refer to it.
-Otmar-
914 EV, California Poppy, Zilla research vehicle.
http://evcl.com/914/The Zilla factory.
http://www.cafeelectric.com/Zilla Support is still at:
http://cafeelectric.com/Ssupport.php
