# Hydrostatic tractor conversion



## Woodsmith (Jun 5, 2008)

New project!
I have been asked to convert a farm tractor to electric.


The tractor is a Russell 3-D tool carrier with hydrostatic drive. It is a 1970's 'improvement' on the David Brown 2-D which is similar to the Allis Chalmers G type tractor.

This one has a dead ICE and I am yet to see it. The farming couple chose it thinking the hydrostatic drive would make it easier to convert as the motor can run continuously just pumping oil.


My thoughts are that it only needs a contactor to switch on and off as required, no speed controller and no reversing required.
I figure on it being an insulated battery box, a lead acid battery pack, an isolator switch/contactor, a fuse, a motor contactor, a motor, an adaptor plate and coupler. The charger can be kept back at base.



My initial guestimate calculations suggest that 48V, 150Ah pack will give a comfortable 7 mile range, at 10mph, in loose dirt for 50% DoD. 
Any thoughts as to a good ball park figure to include for the loss of efficiency for the hydrostatic drive?

Their calculations suggest that they only need to drive 0.7 mile per planted bed (11 tractor runs of 100 metres long per bed) and maybe only need to do up to 3 beds a day when needed. It is a small market garden farm of only a couple of rented acres all in.
That should only be 15% DoD so the batteries will have an easy life.


What we don't know is how the implement/tools would affect the range. They are only looking at using a weeding tool (as in image below) for the time being as they are able to do the rest by other means until the electric proves to be strong enough for the other jobs.









Any advice or suggestions would be most appreciated.

Thank you.


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## Jimdear2 (Oct 12, 2008)

Woody,

My take on this is you are going to need some kind of rpm control.

What happens with a ICE hydro is you would set your ground speed and then as the load comes onto the tractor the ICE governor would apply more throttle to keep the pressure (=ground speed) up in the hydro unit.

If you go without some form of DC motor controller to keep the rpm constant you will be constantly fiddling with the hydro's speed control lever.

That's just my take on it

Jim


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## Woodsmith (Jun 5, 2008)

Cheers Jim.

Hmmmm, a governor, What sort of controller set up would that require?

Or would a shunt or PM motor do the same job?

How does the pump motor on a fork lift govern itself?


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## piotrsko (Dec 9, 2007)

how about just modify some sort of idle control on the controller. That is what we use for poor man's cruise control on school bus's. You'll need some sort of device because you want more regulation than straight switching, and 6000 kwh of battery might be hard to fiddle with in a fine way.

Forklifts generally use all the fluid they pump: constant regulated pressure/volume, excess pressure bypasses back to the tank, regulation is done by the control lever. If you need more pressure/fluid quantity, more you move/open the control valve.

(joke) : Sounds like an ideal place for a used forklift pump motor.


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## Jimdear2 (Oct 12, 2008)

Woodsmith said:


> Cheers Jim.
> 
> Hmmmm, a governor, What sort of controller set up would that require?


For a series motor to work I would guess that you would need a governor that was rpm sensitive. This governor would control the resistance to the controller throttle circuit. So when the load increases and rpm drops off it would change the resistance to control the required current to overcome the load and return the rpm to the set point.



Woodsmith said:


> Or would a shunt or PM motor do the same job?


Even though the shunt and PM motors are rpm limited you would still need a controller that was rpm sensitive to over come the variable loads



Woodsmith said:


> How does the pump motor on a fork lift govern itself?


Here is my guess for a series DC pump motor. It only runs when it is needed. When the pump motor is running it already has a load on it set by the system pressure relief.

I think that the control of the pump on a series motor is built into the system design. On the other types of motors I am not qualified to even guess


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## Woodsmith (Jun 5, 2008)

We did think about a pump motor, I think that is why the chap sourced and bought a hydrostatic tractor. He thought that would make it easier, to use a fork lift pump. I have no objection to using a forklift pump motor as is if there are oil pipe connections to the trans. It would keep the conversion neat.

I will have to have a look at it to see if it works on a pressurised system, I think it might as it also runs the implement lift rams, that allows the motor to just be powered up when the hydraulic control lever is moved. That would keep it simple.

If not then it would be a shame to have to use a speed controller as he might as well sell this tractor and find a mechanical one.
However, it would be so cool to have a tractor with a Soliton Jr controlled by a pair of brass balls on a governor.









I would like to see this project work out as they also have another tractor, a bigger conventional one, that they would also like me to convert.
Then there are a load of other local organic farmers that are waiting to see how this works so they can get me to convert theirs too.

This wasn't my plan BTW, I just have a friend who took it upon himself to 'pimp' me out to his contacts!


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## jackbauer (Jan 12, 2008)

Most pump motors are compound wound. You could achieve what you need by seperating the shunt connections and using a resistor to se the shunt current to give a desired "low load" rpm. No need to worry about overspeed either.


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## Woodsmith (Jun 5, 2008)

That sounds like a good work around, jack.

I will investigate that and see.
Hopefully a forklift pump motor will be sufficiently powerful to maintain the drive pressure and flow rates required. Again I think I will need access to the vehicle to determine that.


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## mizlplix (May 1, 2011)

Woody: Nice old tractor. I am watching with interest as I am an equipment Specialist (mechanic) for the local school district.

I handle 28 mowers,12 tractors, trenchers, chippers, stump grinders (among other stuff), as part of my work load. 

Besides being an old farm boy myself....Heh

This is way cool.

Miz


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## dapug (Mar 21, 2021)

Old dead thread, these members appear to be long gone. But since this is directly applicable, I figured there is no value in starting another topic.

Is there any info about a successful hydrostatic tractor conversion? 

So far, I have only found this video, but not info on how they did it, and whether it was a good, efficient result.





I also found this thread here in this group, also a dead end, but this tractor was hydrostatic as well:
Compact tractor conversion. | DIY Electric Car Forums

Lastly, I know EV conversion for a tractor is doable for geared transmission tractors.





I'd rather convert my own than fork over huge amounts of $$ it takes so get me one of these nifty Solectrac at $45k! (evolution of the above linked video)
eUtility Electric Tractor — Solectrac

I have a hydrostatic tractor with a dead engine. Would be great to convert it rather than ditching it for a geared unit, but I could go either way. Getting a small tractor, geared, with a dead engine won't cost much.


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## JRP3 (Mar 7, 2008)

It could be a fairly easy conversion, find a motor that will turn around 3500 RPM at 24 or 48 volts and just use a heavy duty on/off switch or contactor. I've done two tractors with manual transmissions using 24V motors and a marine battery on/off switch and they work well. Hydrostatic will be less efficient of course. I have a hydrostatic Cub Cadet with a blown motor that I want to try at some point.


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