Small tractor conversion

[JLux]

I attended the August 10 SEVA meeting last night to begin finding some answers for a project to convert a small Farmall tractor I have to an EV. I found that the general trend is of conversation and systems that are far more complex than I want. You guys really know your stuff, but high tech and complexity is not a direction I want to go. Design criteria purportedly used for the Citroen 2CV is more of what I want to achieve. Please hold your laughter until you've read to the end. Then you can have at it.

I have read the good info on the Allis Chalmers G conversion done in eastern WA and while it is intriguing I want to come up with a simpler system than that. Specifically I want to forego any controller and use only a mechanical on-off switch.

My rationale is that this tractor idles at 450 and has a max no-load rpm of 1600. Working max rpm is probably no more than 1450 or 1500. While there is a theoretical engine rpm range of about 1000, the engine really has only one speed when working. One does not "run through the gears" in a tractor to gain speed; you start from a dead stop in any gear. When the original IC engine is not being worked it is either idling (waiting to work) or off. In EV terms the motor would either be on or off with no in-between. Desired differences in working speeds would be handled by the transmission. The only need for a variable electric motor speed would be in the case of 4th gear where a velocity of less than top speed might at times be useful. But in actual use 4th is only used on roads where a top speed is desired. So I don't see where any variable speed is necessary. Nice, perhaps, but not necessary, and nice takes second place to simplicity for me.

I would retain the original clutch and transmission. A subframe containing motor mounts and thrust bearings for the original flywheel would be constructed to replace the IC engine, which in this tractor is a stressed member joining the transmission to the front wheel assembly. The electric motor would attach directly via a flex coupling to the flywheel, or via a gear reduction unit depending on the rated output rpm of the motor. I have a heavily built 5.9 Boston Gear reduction unit but the nameplate seems to indicate it has a 1.5 hp maximum (seems low to me), and I would not want to run an input rpm more than 3600. A dry chain and sprocket reduction seem the most likely right now. The motor would have a single master on-off switch.

Original horsepower of the IC engine is 20 at a max rpm of 1600; no torque figures available. This suggests a dc motor of 10-14hp. A desireable battery capacity is something I don't know how to estimate, but I would like to be able to mow 2+ acres of 24" grass between charges. This kind of load might also be seen as a variable 10-15 hp load for 2 to 4 hours. The current original engine (not new by any means, and probably making only 15 hp now) can mow up to 4' grass.

I would particularly like to have a conversation with someone doesn't mind momentarily stepping back from the leading edge of EV technology to a project that emphasizes extreme simplicity, that might well appear to many of you to be a great step backwards. If anyone is so interested I would much appreciate a contact.

By the way, on a related topic, I grew up on a farm in the 1960's and spent some thousands of hours on early Bobcat skid loaders. The second echelon design of that system used a variable speed, non- or semi-centrifugal CVT to offer speed changes. A hydraulic pressure bleed from the main pump was used to actuate a cylinder that moved the driven pulley sheaves together to obtain a higher speed (about 2:1) by moving a hand-operated lever forward. Though I may be wrong about this, and though the hydraulic system had other double acting cylinders, I think this was powered in only one direction, meaning that hydraulic pressure pushed the sheaves together, but there was no reverse pressure to move the sheaves apart. Pulling the lever aft simply allowed the pressure to escape, and springs in the variable sheave forced the sheave apart. I bring this up because the simple (not complex) CVT's we see today are entirely centrifugal, and the idea of manually variable sheaves might no longer be an commonplace idea, though they might be useful in some applications.

[trackman]

I also am interested in converting a tractor to electric. you have an interesting idea using the clutch and trans. I have an agricultural mechanic background. I am familiar with the variable speed sheeve. John deere used it on their combines. particularly on the 8820 combine. hyd. fluid is used to open the pulley sheaves, and spring tension closes them again when the hyd. fluid pressure is released. this system was used to drive the threshing cylinder. There was also another variable speed belt driving a cleaning fan where the drive pulley sheeve was open and closed by turning a threaded rod, and the driven pulley was spring loaded.