First of all, I am always thankful to Roy for his safety ideas and experiences. I really feel (and actually am) a lot safer using certified gloves and tools (via mail order from CIPro) that he recommended while working on the 312V systems on my US Electricar S10. Victor also is very careful, and that's one reason I like working with him.
Secondly, I always like to have 2 or 3 reasons why I won't die messing around with this high voltage stuff. Some of us that are old enough to have worked with vacuum tubes are lucky to have survived. Add the high currents, and fact that you can't turn batteries off, one can never be too careful here. Besides, I'll let Plasma Boy do the plasma stuff--I'll be content to learn from the experience without paying the tutition of actually going through it. Yes, I'm looking at this mostly as a servicing safety measure, so your point about not needing to interrupt the current is a valid one. However, if I can't find a fairly cheap, light, DC-rated switch, reasonably priced contactors still seem very attractive. Normally, I expect that the motor and charger will be already off when this contactor is opened. Of course, this has to be done carefully to ensure the HV doesn't go back thru the 12V signal wire to the car ground (and we certainly would want to turn the contactor off when not doing anything to avoid draining batteries). Once I consider contactors, I can think of emergency cutoff applications that might be very useful. For example, one could cut off the pack if the battery box temperature gets too high from overcharging batteries, a ventilation system fairure, or fire (LiIon electrolyte may be flammable); or if hit hard during an accident (using the gen I airbag sensors). My batteries will be in metal boxes with another layer of insulating material and air ventilation if I use NiZN, LiIon (but I like water cooled NiCD, if I go that way). I see that Kilovac Czonka-III's are supposed to handle 320V, 250A continuous, 400A for 100 seconds, 600A for 10 seconds, and can break 2000A (hopefully at least once), while using only 1.7 watts at the 12VDC coil. And the price is very reasonable. However, I am concerned with Roy's reports of exploding contactors. Did they explode on making or breaking? Could there have been hydrogen buildup in the box? Some impact resistant barrier around the contactors may be in order! Perhaps I'll just go with higher rated contactors, even though they may be more expensive. A bit of cost is still cheap insurance. Regards, Gary Victor wrote: > Roy Nutter wrote: > > > > I don't know of any switches that will take 330 V and 300A that are > > light. We use the Kilovac Bubba's for our Formula Lightning. The > > Czonka's were giving some of the teams problems by exploding at these > > currents a few years ago. The only problems that we have had with the > > Bubbas have been related to too many too fast pre-charge cycles (student > > accidents aren't always accidents :-)) burning the contacts and causing > > sometime sticks in the on. Even with that, it still is the safest > > disconnect that we could come up with. It is the only ne used by the > > teams that I am aware of although some may still be using czonkas. > > We do use anderson connectors at these voltages and currents. We have > > had no problems with them. The anderson connectors seem to add about > > 0.002 or less ohms per single connection. (We use a version by SMH.) The > > electric bus we have also uses anderson type connectors at 330 V and 600 > > Amps at no apparent problem.> > > Actually, I don't think the switch should be rated to interrupt 300A > current. It should conduct it, but not interrupt. When servicing > EV, the current at the moment you want to disconnect the batteries > is zero. A properly sized Anderson will do the same job nicely. > > Only emergency switches should *interrupt* max current. > Gary weren't asking for emergency ones, you wanted service > disconnect inside the boxes to break in 60V sections, is this correct? > > Victor
