In rush is not nearly 8 seconds, msec probably, but I am new to DC motoring myself. I come at this from doing manufacturing engineering 20+ years ago on motor contactors and such. We would always try to keep switch closures shorter than 3sec (all mechanical contacts bounce), so in rush would not chew up the contacts too bad. I managed a lighting contactor that was used for parking lots full of incandescent lamps (I can't even remember what lamps like that looked like now). The higher end unit was 600A (continuous BTW). Big silver chunks on the end of big copper fingers for contacts. I digress - the inrush was done in an AC half cycle or 8 msec with lamps.
It is just the inductors taking on their current the first time, once they are charged up they resist change and things are "calmer." 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. 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 contractors. This is just a brain dump. I hope someone else more cogent chimes in. On Sat, Nov 2, 2013 at 10:30 PM, Michael K Johnson <[email protected]>wrote: > On Sat, Nov 2, 2013 at 9:23 PM, Lee Hart <[email protected]> wrote: > > Second, you can wire the two contactor coils in series. Wire your "start" > > switch (that pulls in only the start contactor) so it applies power to > both > > coils, *and* shorts the coil of the "run" contactor. That means it > applies > > the full 48v to just the "start" contactor coil. Full power, so it pulls > in > > quickly. > > > > Then a moment later when the motor has started, open the switch that > shorts > > the "main" contactor coil. An interesting thing happens at that point. > The > > contactor coils are inductors. The "start" coil insists on keeping the > same > > current flowing; so it *forces* the current in the "main" coil to the > same > > current. Thus *both* contactors turn on at full current. > > > > A moment later, the inductive energy in the "start" coil is used up. > Ohm's > > law then divides the voltage according to the resistance of the two > coils. > > Assuming they are the same, each coil gets 1/2 the pack voltage, or 24v > > each. This is plenty enough to keep them pulled in (they won't drop out > > until the voltage falls to 10-20%). And at half voltage, they draw half > > current; thus you're holding two contactors on with only half the > current. > > :-) > > Clever! I'm too used to thinking in binary... > > I'm going to wire some safety switches in. Including the seat sensor. > If I register as momentarily off the seat, both contactors would then > disengage and the mowing would stop. And I'd have to go through a > whole start sequence to get the system going again. > > So I'm trying to understand whether there is a simple circuit that > will accomplish the start sequence merely by power being supplied. > In that case, as I sit back down on the seat, power is applied and > the sequence you describe happens. It's designing that simple > circuit that I am not confident I would do right. > > I suppose the right answer is to debounce the safety system with > a capacitor of sufficient size. If I do that, even with a single contactor > I'll have many fewer cycles on the contactor and prolong its life. > > > Write me off-list if you need one. I have piles of surplus contactors at > > good prices. > > Thanks! I have one contactor already; I'd guess that to make this work > I'd need one with a similarly-rated coil; otherwise they won't balance > that way. I'll think about that if I find that the simple circuit is > available... > > > An SB350 takes a heck of a strong pull to separate it. You probably don't > > need one nearly that big anyway, but if you have it, it's fine. But you > may > > need a foot switch rather than a finger switch to pull it apart. > > The things I don't know... I was worried about an SB350 behind a 400A > fuse being a little too small (all I saw was 350A), but I wanted to make > sure > I had an emergency disconnect. I now found the product data at > http://www.andersonpower.com/products/multipole-sb.html > SB120 isn't available above 2awg, which won't work with my 2x4awg. > SB175 can handle inrush of about 8 seconds at 400A with 1 awg. > > All my anderson disconnect experience is with UPSes which I suspect > are all SB50. According to their datasheets, that should be 10-15 lbf; > the SB175 25 lbf, and the SB350 30 lbf. > _______________________________________________ > 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) > > -- Put this question to yourself: should I use everyone else to attain happiness, or should I help others gain happiness? *Dalai Lama * Tell me what it is you plan to do WIth your one wild and precious life? Mary Oliver, "The summer day." To invent, you need a good imagination and a pile of junk. Thomas A. Edison<http://www.brainyquote.com/quotes/quotes/t/thomasaed125362.html> A public-opinion poll is no substitute for thought. *Warren Buffet* Michael E. 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