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It will be interesting to see how bad the parasitic losses will be by using the electric motor to drive the hydraulic drive system vs a direct drive electric system. Circulating fluid with the pump while not moving (idling) would be my concern with losses.
 

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How much run time are you expecting out of this? 51Ah doesn't seem like it'll be very much with that strong of a motor.
Agreed. At full load and assuming 100% efficient that calcs out to about 15 minutes. To understand the real run time one would have to better understand the power lost in the hydraulic system and how much power is needed for the specific task.
 

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while idling, other than for cooling the oil, why would you need to keep circulating the oil? Hydrostatic units stop flow when idle so I don’t see much need to keep it moving other than a little cooling. I would see this as a bonus for ev, the hydraulic pump isn’t generating more heat (unnecessarily) while sitting idle and your parasitic loss would be zero.
The drive system on our tractors is hydraulic, NOT hydrostatic. In our systems the pump circulates a fixed amount of fluid on each revolution. Fluid does not stop, but is only re-directed via the valves. As such, any energy needed for the pump to idle and push fluid through any non-drive circuit is what I am considering parasitic. As long as the motor is spinning, the pump is spinning and thus losses exist.

A good description of the difference between the two systems can be found here:


Even with a hydrostatic system the charge pump is always moving some oil for cooling, thus some loss. For that matter, spinning the fan to move air over the cooling radiator consumes energy.
 

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I understand ours tractors are hydraulic and not hydrostatic and since we have gas engines running all the time, fluid never stops. But in an electric setup you have better control so lower the motor speed or stop it when not needed. Your loss would be minimal at best. I still see this as a win for efficiency. Even running a small fan on the radiator would be minimal.
Based on the above it would be far more efficient to simply ditch the hydraulics and go direct drive electric. Under the above scenario one would need to throttle the electric motor to reduce flow in the system but that would be no less cumbersome than working the throttle to "hypermile" a gasoline engine while still controlling motion with the hydraulic valve. A 7 1/2" electric cooling fan draws about 5.5 amps at 12v. That's somewhere between 2 - 2.5% of the OP's storage capacity.

Don't get me wrong, I think it's a cool project I just wonder how much will be lost using the standard hydraulic drive system. One will see losses in:

1.) The pump
2.) Friction losses of fluid through the lines and valves
3.) Drive motor
4.) Gears in transaxle
5.) Cooling fan

Yes, all those losses exist with the factory ICE, but they would not exist with a direct drive electric motor.
 

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You still need reduction gears in the transaxle, but everything else is a loss. Although getting enough reduction in the trans for an electric drive motor might prove a challenge.
DC motors have lots of torque, that's why electric cars are so quick. I would expect them to need LESS gear reduction than an ICE. I could be wrong.
 

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Dc motors have gobs of torque but not compared to the hydraulic motor on a Case transaxle. Would take a very large electric motor to replicate the low end torque of the present drive motor. My buggy has 12 to 1 reduction behind an aftermarket torque motor and that is with 22" tall tires, and while good, still won't pull like my 446, at least continuously.
Gotcha. I just looked at the torque specs of the OP's motor and that of a K321 - similar, and not that much. Only 22+/- ft*lbs. Certainly lots of gear reduction needed.
 
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