On Tue, Jul 29, 2014 at 1:30 PM, Lee Hart <[email protected]> wrote: > Michael K Johnson via EV wrote: >> I'd seriously consider getting together with friends on a scavenged >> Volt battery... > > That could be fun as an experiment, but could cost more and require more > finesse to get it all to work. Dumb old lead-acids are easier, and a > reasonable first-EV solution.
Well, a few months after I bought my batteries, a friend bought a few scavenged volt batteries, and it literally would have cost me less than the $1K I paid for the SLAs to have more capacity with greater available discharge. So I'm not being crazy here. I would have needed a different charger for lithium, though. That's where the money would have gone. > Putting the motor in a pressurized box is an interesting solution. The foam > filters apparently have a low enough pressure drop to work with > propeller-type fans. The more common approach uses a squirrel-cage blower > with a higher-drop filter element. The plenum exhaust area is about 2x12" and the frame around it stays clean; it's clearly moving a lot of air. I do brush off the filter after each mowing session because it collects detritus around the intakes. I sized the frame just small enough for a good interference fit. > Is it "real" plexiglass (brittle acrylic), or the more common polycarbonate > (slightly flexible, nearly unbreakable)? Polycarbonate is so strong that > even 1/8" would be indestructible. Acrylic. Polycarbonate is more expensive and really hard to work, as your point about the indestructibility of 1/8" stock attests to. If I had gone with 1/4" acrylic for the whole box, I could have used simple butt joints and screwed the pieces together and it would have been far less work. I did find out a couple weeks too late that I could have brought the acrylic to a friend and co-worker who would have cut it for me with his laser cutter. Maybe next winter... ☺ > Well, it's a small matter. Your wire lengths are short, so not a lot of loss > no matter how you do it. What ulitmately matters is that the wire doesn't > get hot, and you've certainly achieved that. It's a small amount of extra money in the grand scheme of the conversion, and I don't really regret it. I'm merely recording for the next person that my impression was that it was overkill for the tractor. I don't think these batteries can source enough current to overheat 4awg; they start noticeably sagging around 140A-150A. Might be different with lithium. >> Buying SB50 anderson connectors for charging at 48V 6A max was silly; > > But, they are very robust and will last. They can carry 6a even when dirty, > worn, and corroded. Maybe you'll get a higher current charger someday. (Your > AGMs might like higher-current charging anyway). I cut the female end off a C15-C15 extension, and used the male C15 end of the cord for my charging circuit. I used liquid electrical tape (many layers) to cover the conductors coming out of the cut-off end of the cord, and keep the male end plugged into that cut-off plug to keep the male connector clean when I am not charging the traction batteries. But if I ever make one of the open source chargers that can dump more than 6A into the batteries, I'll keep the SB50s in mind, of course. $1200-1400 for the EMW kit is more than I want to spend on that right now. I'm still recovering from blowing the budget in the first place. > 48v input to 12v output DC/DC converters are pretty common; the Telco > industry used them in quantity. You can probably find one surplus for > $10-$20 that can run fans, contactor coils, and your amphour meter. As it turns out, the old 12V battery is toast. But I have some SLA batteries that UPS units were complaining about but which have lots of life left in them and I'll use them for house. Even cheaper than buying an isolated converter. Of course I don't have a 12V charger handy, so I cobbled together the power supply from a dead laptop, a buck converter with a CV regulator, some wires scavenged from a dying coffee mater, and my meter to make sure I'm within spec, and voila, a charger! Someone else could use a converter to run fans and contactor coils, but since I have 48V fans and contactor coils, I'd have to replace them to switch, and that doesn't seem worthwhile. The 48V fans came out of telco gear where 48V is, as you point out, common. > If that's a worry, 48v contactor coils are very common. That's what I have. I just seem to recall that the 48V contactor coils drew more current than the 12V in the same series (Alltrax). > On snowmobiles and other users of this variable-pulley-size method, they > sometimes use metal belts (chains) with little friction pads on the sides. > They are more efficient than the typical rubber v-belts. Maybe one is > available for the size needed here? I doubt it. This is a long belt and needs to flex and runs through frankly poorly-guided space. I'll stick with OEM and would suggest the same for anyone trying to convert similar tractors. > With EVs, an ammeter makes it easy to *tell* when it's using more power. > With an ICE, there's no way to tell it's burning more gas. Well, I could certainly hear the difference in sound from the ICE when it was loaded. I could definitely tell. It's just easier to ignore the problem when you can just pour more fuel in the tank than having to stop and recharge overnight when you are "out of juice". > Glad it helped! An oscilloscope is the perfect way to pick the snubber > parts. You can easily see when you have good values. Add capacitance until > the peak voltage is reasonable, then add resistance until the ringing is > just about gone. That's the clearest description I've seen yet of the experimental process for building an RC snubber! >> I'm considering making a simple PWM motor controller for the fans > > For this to work, they have to be simple motors -- not brushless DC motors > with electronics. Almost all small fan motors are now brushless DC. > > To use a PWM controller with a brushless DC fan, you'll have to add your own > series inductor and filter capacitor on the PWM output (a proper buck > converter) so you get smooth filtered DC out. Indeed, they are brushless. Not much point. Thanks! > I fold the diode lead back along the body. Insert the diode into the lug > (the folded lead holds it in place). I solder the end of the lead wire to > the inside of the lug with a BIG soldering iron, which can heat the lug up > quickly. Add solder to solder the wire to the inside of the lug. It then > cools quickly, because only that one small area of the lug was heated to > soldering temperature. Ah, and with curved hemostats I can then heat-sink the diodes while soldering. I feel better with that design. But I might still buy them from you anyway. ☺ > That's surprising. It should have sounded like a vacuum cleaner motor; not > particularly loud, but perhaps annoying because there's a whistle-like pitch > to it. I think I'm more sensitive to noise than most; I find vacuum cleaners annoying too. It sounds similar to the videos that Joe posted of his conversion. I don't think it's a faulty motor sample. _______________________________________________ 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)
