Rich Rudman wrote: > Isolate the Damn CAR!! It's easier, and cheaper and should be done > anyways with more than 96 volts of battery on board. Do the car > right.... and the charger is a NON issue. Adding in a Neg side > contactor to your Motor negative is all you have to do on most EVs > to keep the motor from becoming the ground fault.
I agree that it is possible to isolate the pack from the car well enough so a non-isolated charger can be used safely. But, it is by no means easy! UL expects products to pass a 1500vac hipot (high potential test) from input wires to ground. This is to insure that the device has sufficient insulation to withstand the kind of 1000+volt transients that routinely occur on the AC line. It is quite a challenge to insulate your batteries from ground thoroughly enough to withstand 1500 vac! They also expect you to have TWO independent redundant insulation systems, EACH of them able to withstand the whole 1500vac. This is what is called a "double insulation" system, commonly seen on outdoor electrical devices that must be safe even without a ground. To meet this standard, you can't put the batteries in a grounded metal box, because the battery's case only counts as one layer of insulation, no matter how thick it is. You'd have to put the batteries in a separate plastic box. The idea of double-insulation is that it is safe even if one of the layers gets damaged somehow (a crack or hole in it, for example). And, UL expects products to withstand 3500vac from input to output (where "output" is any wire or conductor that could be touched by a person). This is to insure that a severe surge on the powerline is going to punch through the insulation from input to ground, and not from input to output. It would take quite a contactor to provide 3500vac isolation between the pack (connected to the AC line via a non-isolated charger), and things like motor terminals that could be touched. Then you will have to deal with all the devices that are connected directly to the batteries, that wouldn't be disconnected by a contactor between batteries and motor or controller. Things like E-meters, your Rudman Regulators, DC/DC converters, etc. Meeting UL is not required for cars; the auto companies made SAE the only relevant standard, and they don't address this issue. However, the UL standards are reasonable ones to meet for anything connected to the AC line, auto or not. -- Lee A. Hart Ring the bells that still can ring 814 8th Ave. N. Forget your perfect offering Sartell, MN 56377 USA There is a crack in everything leeahart_at_earthlink.net That's how the light gets in - Leonard Cohen
