# Planning a Steiner lawn tractor conversion



## Åndrew (Dec 15, 2019)

I have a 20hp Steiner 420 lawn tractor with a dying engine. I'm being quoted CAD~4k to repower it with a new gas engine and I'm thinking this is a good opportunity to convert to electric instead. I use it for mowing our lawns, which is a 2-3 hour job that can be broken up into a couple chunks. Plus light bush-hogging, towing a trailer through trails and bush, and ploughing snow in the winter. Mowing is the task that will take the most power storage.

It's a hydrostatic drive, which in my thinking is what was supposed to make this conversion easier, albeit less efficient. However, I emailed an acquaintance of mine with significant EV conversion experience and he said "it would be very expensive to go electric and with hydrostatic would not be practical". I'll call him to get a deeper opinion but of course that's not what I wanted to hear.

In trying to get a price on this job, it seems like the biggest cost is batteries. Is there a good safe place to save some money here, or do I just call a Sinopoly or equivalent reseller and order 150-200 ah of batteries @ 48 volts and pay up?

Same with motors. 20hp is about 15kW. So for sizing, do I get a motor that can hit peak of 15kw but for sustained power maybe 10kW?

I've been doing a bunch of reading, but as my engine is hours/days/weeks from likely being unable to propel my Steiner I need to do something soon. So I'm trying to move from reading/learning to planning.

Thanks for any information you can provide.


----------



## kennybobby (Aug 10, 2012)

So the gas engine is only used to turn the shaft of the hydraulic pump, and hydraulic motors spin the blades and turn the drive wheels? Does the gas engine run at a constant speed or does a throttle pedal control it?

If so, then if you can find the speed (rpm) and torque specs for the pump, or a chart known as the pump power curve, then it would be possible to determine the specs needed for an electric motor to turn the pump.

Once you know the motor parameters, then you can size the battery pack for voltage and current, and pick the cell capacity based upon how long you want to mow before recharging.


----------



## Åndrew (Dec 15, 2019)

The hydraulic motor drives the wheels and articulated steering. There is a throttle control but that's separate from the speed control. I figured as long as the electric motor is driving the pump at the right RPM, compared to the gas engine at full throttle, I'm fine. I always run the gas engine at full throttle when I'm working it. There's a separate control for motive speed - just a forward/reverse lever that controls hydraulic power to the wheels. There are also two sets of hydraulic remotes at the front that I use for the blade: up/down, left/right.

There's also a front pulley that drives the front mower deck. That comes right off the engine and would need to be looked after. I'd either use a secondary motor for that, or would possibly retrofit my mower with three small electric motors, one for each set of blades. Advantage of using a second motor on the tractor is that I can attach any implement as I keep it pretty close to stock. Advantage of modifying the mower is that I get rid of three drive belts that are prone to breaking at inopportune moments.


----------



## brian_ (Feb 7, 2017)

Generally, using an electric motor to drive a hydrostatic transmission seems like a lot of unnecessary hardware and power loss to me, but the Steiner 420 is a 4WD machine with articulated steering, so maybe it is worthwhile to retain the hydraulics to keep its capabilities. I'm guessing that the hydraulic pump(s) for the steering and blade control (it has a snow plow blade?) are integrated with the transmission; it could have separate hydraulic pump and wheel motors, but online listings show a Sunstrand 15-series transmission - that's a variable-displacement swashplate pump (with an additional charge pump which can run accessories such as the steering and those blade cylinders) plus a fixed-displacement swashplate motor.

On the other hand, the TractorData page for the Steiner 420 transmission lists "Sundstrand 15 hydrostatic with Peerless 2500 two-speed transaxles", which makes no sense, since both Sundstrand 15 and Peerless 2500 are hydrostatic transmissions, and it would make no sense to drive one with the other. It's possible that the Sundstrand drives the front axle (right under the engine) and pumps fluid to a Peerless 2500 rear axle, or that only the Sundstrand 15-series pump is used, pumping to a Peerless 2500 at each axle.

I can only guess that the 420 is very similar to the current Steiner 440.



kennybobby said:


> ... if you can find the speed (rpm) and torque specs for the pump, or a chart known as the pump power curve, then it would be possible to determine the specs needed for an electric motor to turn the pump.


I found a manual for the Sundstrand 15-series... it may or may not be the right one for this machine.

Åndrew, perhaps you can look at the configurations shown in this manual and tell us which of them - if any - correspond to what is in your tractor?



kennybobby said:


> Does the gas engine run at a constant speed or does a throttle pedal control it?





Åndrew said:


> There is a throttle control but that's separate from the speed control. I figured as long as the electric motor is driving the pump at the right RPM, compared to the gas engine at full throttle, I'm fine. I always run the gas engine at full throttle when I'm working it. There's a separate control for motive speed - just a forward/reverse lever that controls hydraulic power to the wheels.


The "throttle" for the engine isn't really a direct throttle control - it's the input to a crude governor. The engine runs at roughly constant speed (bogging down somewhat under load), with the governor varying the throttle (or fuel pump rack, in the case of the diesel engine) to maintain that speed. This is normal for hydrostatically driven equipment like this.

The control of an electric motor replacing the engine would then need to be speed-based, not the usual (for a car) torque-based.


----------



## Grandoll (May 18, 2020)

I was looking recently for equipment here, and read about ikra tools with 40V batteries for everything^ hedge trimmers, lawnmowers, etc. Did not get actually why is that electric motor and hydrostatic transmission do not work together.


----------



## brian_ (Feb 7, 2017)

Grandoll said:


> Did not get actually why is that electric motor and hydrostatic transmission do not work together.


They can work together, but there's just not much point. A transmission exists to match a source of drive (an engine) to a load. A hydrostatic transmission allows a continuously variable range of speed ratios, so the engine can run at a constant speed and the driven thing (the wheels) can run at the desired speed... but an electric motor can run at whatever speed you want, so there's no need for the hydrostatic transmission.


----------



## Rbertalotto (May 26, 2020)

I converted two tractors to electric in the last 60 days. Read the article I wrote on my web site it lists all the details.

Loads of folks have converted hydrostatic tractors to electric with excellent results. You need a motor that runs at 3300-3600 RPM for a gas motor / hydro replacement. The motor I used was bought from AMAZON and is working fantastic.....This is actually a relatively easy conversion. You will love the results as long as the run time of about an hour while cutting cutting or three hours of yard work is enough. This would be with conventional AGM or Golf Cart deep cycle type batteries.But if you go Lithium batteries you can double or triple this time of operation. But the cost also doubles or triples.......Good luck....Keep us informed!

www.rvbprecision.com


----------



## catb50 (2 mo ago)

Just to clarify, the Steiner has 2 sundstrand 15 motors paired to a front peerless 2500 transaxle and a rear one. So the unit consists of a sundstrand pump that connects to two sundstrand motors which couples to the axles. Since the Steiner is built around the axles for strength and structure I'd keep the axles and look into smaller electric motors for each axle. With the option to turn one or the other off to save power in cruising situations.

As for the hydraulic accessories, since it is low pressure around 900psi for the hydraulics you could probably run a electric hydraulic pump that is rated for that. 

Then the next thing is the PTO shaft for the mower powering that should technically be done by another electric motor if you wanted to keep the existing PTO attachments working. Ideally you'd have a controller and motors on the mower deck directly powered on by switch.

Unfortunately just putting a electric motor in place of the gas one would be very inefficient and costly overtime with batteries getting exhausted from cycling. 

Personally I'd like to do that with my Steiner but crunching the numbers and seeing what's involved you are better starting from the ground up with individual motors for the wheels etc. Giving you better traction (kinda like a differential lock if enabled) as well as higher ground speed. You'd also free up more space for battieres or any other electrical controllers and such. 

But would be curious how it would sound with a electric motor in place of the gas one and how long you can cruise around.


----------

