Michael, I converted a John Deere 112 tractor last spring, and mowed all summer with it. I'm super happy with it! It'll easily climb a 30+% grade starting from a standstill in 4th gear with the blades running, and I have used it pull small stumps with the 400:1 first gear (with a big stump it did a slow motion burnout on concrete!). Here are some of my experiences:
I first converted a hydrostat MTD. It took 200 Amps to barely move. With work I got it down to 160 Amps. I think the tranny was shot, I hope that wasn't normal! My John Deere takes about 80 Amps to mow, around 65 downhill and about 100 A uphill. I get regen down a steep hill or briefly if I suddenly slow down. I am impressed in that this tractor has alot of 1/4 inch steel on it, and weighs 650 pounds (300 kg)! It has 2 transmissions: A four speed transaxle (1, 3, 5, and 7 mph) and a variator that varies the speed range over a roughly 1:3 range. I think this is more efficient than a hydrostat. Here is the motor I used: http://www.cloudelectric.com/product-p/mo-es-10e-33.htm . The hottest it has reached is 77C with just the internal fan, on a 100+F (38C) day. Since your motor is 1/2 the weight but rated for the same power, I suggest keeping a close eye on temperature so you don't overheat it. I run the armature on 48V and the field on 12V, which gives a perfect 3300 rpm. The motor barely slows going uphill, and barely speeds up going downhill. I just grabbed wire I had available, 2/0 in the positive line and #1 in the negative line. The wires and battery terminals stay very cool. I like the idea of oversizing the wires a bit, as I think the cables then act as a heat sink for the lead battery terminals. Lead melts well before copper melts. I think Roland's suggestion to double up on the #4 wire is a good one. I mow 30%+ grades, so I am rather concerned about tipping over! I have the batteries in a little trailer for now. I'm in the process of making racks. The 1/4 inch steel has hooks for hanging farm implements, so I'll have no problem hanging battery racks front and rear. If you have hills to mow, here are some considerations: o Keep the CG low so you don't tip over o Do AGM batteries so the battery acid doesn't slosh out o If you do a battery trailer, a heavy tongue will help put some weight on the rear wheels, and help it climb hills without wheel spin o The sheet metal on a lawn tractor won't be very strong, be careful where you attach the battery racks My "controller" is just basically a contactor switch. I found just switching 48V directly gave a pretty good spark at the brushes. It likely would have been OK, I'm only doing around 100 turn-ons a year. What I did is something similar to what Lee Hart suggested with a starting resistor on one contactor and then full pack voltage via a 2nd contactor. Right now I do the switch manually, but I bought a "delay relay" and my plan is to have the starting resistor on for 2 seconds, and then full voltage. This way if someone switches it on in gear (I do that sometimes on purpose now to avoid using the clutch) it has a couple of seconds to get everything moving before hitting full voltage. I had thought to do Lee's suggestion with a capacitor and resistor RC circuit, but my fear was the relay might pull in or release slowly, causing bounces or arcing in the switch (any comments on that, Lee?). I went with the manual switch, and soon the delay relay, so the contactor coils will get fu ll voltage suddenly. (Advanced comment for the greater audience, doesn't apply to your motor, Michael): My field goes on first. I wrapped the field wire twice around a reed switch (a security alarm window sensor). Once the field is up to current, the reed switch turns on the starting resistor, and then the human (soon delay relay) turns on full voltage. This way it guarantees there is field current before the armature is engaged, and will drop out the armature if the field ever fails for some reason. I have old Optima blue top 55 Ahr batteries. I have nearly 1/2 acre to mow with some fairly steep hills. When the grass was growing slowly early and late in the season I could mow in 2 charges. When the grass was growing fast it would take 3 charges (1st one to 100%, the 2nd and 3rd to 80% to charge faster). This 43 year old tractor is better than my old gasser tractor was on day one! It mows much faster, and the cut is flatter. I can charge into the tallest grass at full speed and the electric JD doesn't slow down. The old gasser tractor I had to go either very slow, or cut 1/2 width strips for tall grass, or it would stall. The electric JD also has way way more pulling power. The only way the old mower would spin the tires was on ice -- the electric JD will spin the tires on concrete if it is held back! ----- Original Message ----- From: Michael Ross Sent: 11/02/13 08:56 PM To: Electric Vehicle Discussion List Subject: Re: [EVDL] Michael's 48V lawn tractor/mower conversion: sanity 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 quenc hing 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 be ing 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 i s 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. Ross (919) 550-2430 Land (919) 576-0824 <https://www.google.com/voice/b/0?pli=1#phones> Google Phone (919) 631-1451 Cell (919) 513-0418 Desk [email protected] <[email protected]> -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://lists.evdl.org/private.cgi/ev-evdl.org/attachments/20131102/18064763/attachment.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) -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://lists.evdl.org/private.cgi/ev-evdl.org/attachments/20131103/a48e977d/attachment.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)
