Michael Ross wrote:
So the question is, how long does in rush take on a typical dc motor for an EV? The answer might save you a bit of money.
A motor draws its inrush current until it comes up to speed. That might take a fraction of a second; or many seconds. If something is holding the motor so it can't turn, it will draw that huge inrush current *continuously* (until something breaks or melts).
I have a GE Electrak electric garden tractor. It has a 36 volt PM DC motor, connected by a V-belt to the transaxle. The v-belt is tightened/loosened by the 'clutch' pedal (a classic garden tractor setup). There is also a switch on this clutch pedal. It is arranged so as you release the clutch, it first starts the motor (with no load, because the belt is loose), and then the clutch engages, and away you go!
For a disconnect you are more concerned with continuous use, and quenching arcs on opening. Are you planning to turn on a load with it? That is the job of the contactors.
A disconnect is typically an "oh, shit!" device; a way to stop the excitement in case of an emergency. It *has* to work; but it only has to work ONCE (because you have to fix it before you can try again).
A fuse is the classic disconnect device. So one way to set up a manual disconnect is a mechanical arrangement that lets you remove the fuse (like yank it out of its fuseholder). But you do *not* want to insert a fuse into a live circuit!
Arc quenching: Contactors built for DC motor control will have built-in methods to deal with contact arcing. They have definite maximum voltage and current levels that they can safely switch. Within these limits, they can switch 100,000 times or more.
But you can also add additional arc quenching. Classics are an MOV or ZNR type device, or an RC, or RCD snubber network. They reduce arcing, and so extend contact life.
-- "Obsolete" means nothing more than "the salesmen would prefer you buy something else". -- Dave McGuire -- Lee A. Hart, http://www.sunrise-ev.com/LeesEVs.htm _______________________________________________ UNSUBSCRIBE: http://www.evdl.org/help/index.html#usub http://lists.evdl.org/listinfo.cgi/ev-evdl.org For EV drag racing discussion, please use NEDRA (http://groups.yahoo.com/group/NEDRA)
