Electric Drive Motor Retrofit

[MossRoad]

 

[4570Man]

no, By that logic, a 2 cylinder 2 stroke gas engine rated at 20 HP should need a 10HP electric motor to replace it!..

In either case it’s a stupid logic that doesn’t work. If you were converting something like a wood splitter that only sees occasional and brief high load the undersized electric motor will probably work. If it’s a continuous duty load there’s no reason why a considerable amount smaller equal rpm electric motor could do the work. If it can then one the ratings was flawed.

 

[radios1]

In all reality, a 20hp engine and a 20hp electric motor both make 20hp. Horsepower is horsepower is horsepower.

the DC electric brushed motor makes power during the full rotation, each time the commutator aligns with a brush, torque is produced so you get more torque than a gas engine, which relies on a flywheel to keep the engine turning.. it's only single phase AC induction motors that only make torque each 180 degrees, and three phase AC induction motors make torque each 120 degrees. I did not yet correct my original post on this.

 

[4570Man]

the DC electric brushed motor makes power during the full rotation, each time the commutator aligns with a brush, torque is produced so you get more torque than a gas engine, which relies on a flywheel to keep the engine turning.. it's only single phase AC induction motors that only make torque each 180 degrees, and three phase AC induction motors make torque each 120 degrees. I did not yet correct my original post on this.

A 1750 rpm electric obviously has more toque than a gas motor. The 3600 rpm electric shouldn’t be much difference. Your logic is stupid and flawed. Does a 50 hp 2 cylinder gas do less work than a 50 hp 4 cylinder gas? If so where does the 50 hp 6 cylinder stand? The toque rise of the electric is much greater than the gas motor but it’s continuous duty load shouldn’t be any different. If a 20 hp electric motor could continuously do twice the work of a 20 hp gas motor than the rating is flawed. The gas motor either less than 20 hp or the electric was more then 20 hp probably both. Don’t confuse brief power rise with higher power.

 

[MossRoad]

the DC electric brushed motor makes power during the full rotation, each time the commutator aligns with a brush, torque is produced so you get more torque than a gas engine, which relies on a flywheel to keep the engine turning.. it's only single phase AC induction motors that only make torque each 180 degrees, and three phase AC induction motors make torque each 120 degrees. I did not yet correct my original post on this.

Now you're talking torque and that's different than HP. HP is HP and if they are both rated at 20, they'll both make 20. No way around it.

How bout we stop poking each other and get back to the OP's project.... :thumbsup:

 

[SpringHollow]

For an electric motor, the power it produces is a function of rotational speed relative to its rated speed. But the torque is the same throughout its speed range. I have seen the plots online before. (At near stall conditions, I do believe torque might increase as the motor draws more power.) So an electric motor can respond to an instantaneous heavy torque load rather well. That is the advantage of an electric motor. In the same situation, a gas motor would have to be oversized in order to respond as well. So in applications like a log splitter, the rule of thumb applies. For a constant load at rated speed, one is concerned with HP and you need the same size motors (or so I would believe).

Ken

 

[MossRoad]

Yep. That's the way I understand it, too.

 

[JD-Beach]

Thanks for all the responses, ideas, and links.

Yes, Moss, I'm the one who had Tazewell install the bigger wheels. I've been out of touch for a while running a business, marrying off children and enjoying grandchildren. I used my PT-425 to move migrating sand off of the beach every spring but then we had a seawall installed, so my tractor use decreased. I ended up selling my PT to my business partner with the condition that I could borrow it any time I wanted. Kinda like owning a machine without the maintenance or storage issues.

I've been thinking about buying a used machine for this project. … perhaps a ground-up restoration of a used machine.

I'll continue the research and report the progress.

JD

 

[JD-Beach]

Yes, current as in time. :laughing:

One thing I was thinking about. Since the PT425 is all hydraulic, and the gas motor only turns one-way, all you'd need is an electric drive motor and an on-off switch. No reversing circuit would be needed and no speed control would be needed. You could put in speed control for the electric motor, but would it really help anything? You need full flow to create enough pressure to do the steering/FEL functions well. The AUX PTO wouldn't need full pressure, but since it's fed from the same valve bank as the FEL, which is fed from the power beyond on the steering valve, it's gonna get the same pressure anyway.

I suppose you could put in some sort of sensors to only apply the motor when the forward are reverse pedals are pushed, but I think response would be awful. And then you'd have to figure out circuitry to do the same for the FEL and steering. That's why I'd think you always want the electric motor on at speed all the time.

Just some thoughts.

Moss, my thoughts exactly.... I understand that converting electrical energy to rotational to hydraulics back to rotational is not very efficient, however, replacing the wheel motors with electric motors introduces a whole new level of complexity. This would require speed and direction control and you would still need to run a pump for the steering and FEL. Plus consider a tight turn where the outside wheels turn faster than the inside wheels. The present hydraulic system has this all under control.

 

[JD-Beach]

There is a company in Ohio, “Mean Green Mowers”, that use small electric wheel motors on a zero-turn-mower. I called them to discuss this project. In short it appears that it would be much easier to use electric drive motors in a skid steer version of the project. Each wheel motor could be quite small and each side would require an independent controller. The articulated steering aspect and four-wheel drive of our PT’s adds much complexity to an electric drive motor conversion. For this reason, I should like to keep all of the hydraulics in place and overcome the resulting inefficiencies with more battery.

My thoughts are to focus on the single engine to motor conversion with an arrangement of batteries located around the motor. … and leave the remainder of the tractor intact. I understand that the PT tub will need modification. I’m prepared to hire out a welding shop to handle those mods.