Michael K Johnson via EV wrote:
I got lots of useful help here on my lawn tractor conversion project —
Glad we could be of help. Congratulations on getting the "EV grin" while mowing the lawn! :-)
silly idea that I could fit everything under the existing hood and it would look the same, just be quieter.
Yeah, the batteries certainly add bulk, and there's no place to put it. Skimp on the batteries, and they die young. I helped convert a Wheel Horse tractor. We first tried two 12v, because they fit under the hood. Mowing time was too short, and they only lasted one season. We crowded in three; that got the job done, but barely. Four would have been the charm.
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.
Installing muffin fans pulling cooling air through a reticulated foam filter (like they use for aquariums) to provide positive pressure cleaned air in a plenum around the motor was a good idea. The motor stays clean.
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.
Using plexiglass to make that plenum was a great idea.
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.
Talking myself into doubling my 4awg welding cable for the equivalent cross sectional area of 1awg was almost certainly overkill.
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.
Hooking up my power switch so that the charging cable is connected in one direction, and the contactor in the other, means that I can't accidentally try to charge it and run it at the same time
A good plan.
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 wanted to avoid a 12V house battery and run everything off of 48V
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.
it was hard to source the muffin fans
Another trick: Industrial EVs will wire lights, fans, etc. in series to allow use of 12v or 24v devices on 48v.
and the contactor solenoid draws more power than it otherwise would.
If that's a worry, 48v contactor coils are very common.
The MTD transmatic belt-and-pully variable transmission isn't as bad as I thought (it's not hydrostatic and by most reports it's more efficient than a hydrostatic), but it's really imperative to get the MTD belts and not belts advertised as "OEM replacement".
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?
Having two of the batteries cantilevered over the front tires requires excessive tire pressure and makes steering a lot of work.
The advice to instead mount them cantilevered off the back of the tractor was good; I didn't do it because it would get in the way of bagging.
Maybe the bagger can be moved back a bit? Or add wheel weights, or a counterbalance weight somewhere behind the rear axle?
My ElecTraks have half the batteries in front, and the other half under the seat. Steering is still heavier than a normal tractor, but not too bad.
I definitely expect to have to sharpen the blades often; they will draw more current if they are dull.
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.
longer life. I have not yet built a snubber, though on an oscilloscope I measured a 1ms -100V pulse from the contactor solenoid. Basically, that means that I got a 1ms -100V pulse with a 10MOhm 15pF RC snubber. ☺ I finally got an assortment of rectifier diodes and high voltage polypropylene capacitors so I can cook up a RCD snubber to put on the contactor solenoid thanks to Lee's excellent page on the characteristics of various types of snubbers.
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.
no need to snub the permanent magnet DC motor; I couldn't measure any back-EMF from it and I have a vague sense that's typical due to the permittivity of permanent magnets.
PM motors have less inductance, so less trouble with voltage spikes. Perversely, the lack of inductance makes them harder to use with PWM controllesr that depend on motor inductance for the current limit to work.
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.
I have not built the battery balancers. The batteries are all within .02V of each other so far.
That's good. Worry about balancing when they start to drift apart.
The one balancer I built was a pain to build. I can't figure out how Lee manages to solder the diodes to the lugs without overheating the diodes.
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.
My motor running alone on the bench was uncomfortably loud
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.
Now, the mower deck is much louder than the motor.
Isn't that always the case? :-) When we convert our ICEs to EVs, we no longer have the ICE noise. But then we notice all the other whines, whirrs, squeaks, thumps, and rattles that the ICE was covering up!
-- The definition of research: Shoot the arrow first, and paint the target around where it lands. -- David Van Baak -- Lee Hart's EV projects are at 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)
