Electric Drive Motor Retrofit

[JD-Beach]

I have begun the research to replace a Robin 25 HP gas engine in a PT-425 with an electric motor and battery system. I remember that this was discussed many years ago in this forum. Has anyone done this?

I知 interested in this project for a few reasons. ...

1. Battery technology has improved greatly in recent years.
2. The old Gas engine is sometimes hard to start.
3. My use is intermittent, perhaps 4 hours per month with sometimes 2 or 3 months between projects.
4. I知 recently retired from a career in electrical engineering and have a bit more time for fun projects.

All ideas, suggestions and guidance are welcomed.

I致e seen the 溺ean Green zero turn mowers use electric drives very successfully. I致e also enjoyed driving a GEM electric vehicle through the streets of Key West for a 4-hour afternoon with plenty of capacity left. And I owned an SUV hybrid for 4 years and loved the quiet, smooth operation.

 

[MossRoad]

Long time no hear. You have the big wheel machine, correct? :laughing:

Sounds like an interesting project. Maybe look at golf cart batteries and charging systems and see what kind of power they put out? :confused3:

Or if you want to go high tech, start looking at crashed Prius for motors and figure out how to get a battery pack adapted to fit in your available space.

I guess you'd have to look at how much torque and HP the current gas engine puts out and try and duplicate that with an electric motor. It's going to have to get to about 3600RPMs while supplying the power to all three pumps.

Just some thoughts....

 

[MossRoad]

The one thing about the current design, though, is it's stupidly simple.

 

[hiddentacocatneddih]

Unless you score a motor cheap, it's not going to be cheap. Also studied EE and have looked at doing an electric mini truck. To find a motor with 40 or so HP but also light enough was a a couple grand alone

Batteries are cheap. Get old 18650 cells and build a pack

There are lots of cheap 3 phase squirrel cage motors but 2 disadvantages. Weight and efficiency but you can wire some VFD's to be fed straight D.C.

 

[MossRoad]

Golf cart is probably out.... not nearly enough power.
Golf Cart Links and Resources - Diversified Golf Cars, Inc. - Orlando, Florida

 

[MossRoad]

What about electric forklifts?

 

[MossRoad]

Electric Forklift Motor | eBay

 

[cqaigy2]

You might want to check out Rich Rebuilds on youtube. He finds broken tesla's and works on them.

 

[hiddentacocatneddih]

I skimmed thru and the biggest I saw was 5.6KW. About 7.5 HP. They are traction motors so they do have some torque. If you could run a single motor for each wheel and maybe single reduction gear it would be so able.

Rich rebuilds is awesome but he is in the big boy budget buying salvages for 10s of thousands

 

[CobyRupert]

The one thing about the current design, though, is it's stupidly simple.

As in today's "present" designs, or in a design for an "ampacity"?

As an EE, one thing I learned was not to use the word current to mean "presently".
Granted, in your sentence it's easy to figure out from the context, but not always.

E.G. "Why did you spend $2000 on CT's, and transducers to install an amp meter on the control panel?" "You said you needed to know the current status of the motor" "All I wanted was an ON/OFF light!!"

 

[MossRoad]

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.

 

[MossRoad]

Also, do you have any powered implements, like a mower, broom, etc... that run of the main PTO?

 

[MossRoad]

Just to shed some light on how the PT425 is set up....

There's a gas engine that turns 3 hydraulic pumps.

Pump 1 is the tram pump, a variable volume pump that supplies the forward and reverse power to the 4 hydraulic wheel motors, one at each wheel. Direction is controlled by a center treadle, right foot forward, left foot reverse, self centering setup.

Pump 2 is the steering/FEL/AUX PTO pump, which supplies power to the steering valve, out a power beyond port to a 3 valve bank that has the FEL lift/lower, dump/curl, and AUX PTO functions. The AUX PTO provides hydraulic power to the quick attach mechanism, or to things like a grapple, power angle snow blade, etc...

Pump 3 is the MAIN PTO, which provides 8GPM @2500psi to a circuit on the FEL arms that can provide power to things such as mowers, tillers, trenchers, stump grinders, etc....

 

[BobRip]

One of my concerns is drain on the battery when doing very little activity. Except for the tram pump the others are flowing oil all the time. If you could slow the motor down you could save some energy. If you could have three electric motors and run only when you need it that would help. It would be nice to know what the no activity energy consumption is. Then you could see if this is really an issue. Just from listening to an electric fork lift I think they shut off the pumps when you are not using them. I am an electrical engineer, but have never worked on this type of project before.

 

[MossRoad]

Yes, the electric forklifts only activate the pump motor for the lift mast when you move the control lever. And it only activates the drive motor when you step on the forward or reverse lever.

 

[MossRoad]

Since gas and electric HP is hard to compare, how would one go about finding a suitable electric motor to provide the same power as a gas engine?

For example, gas engine is rated at 25HP at 3600rpm. Gas engine HP and Torque decrease as a load is applied, while (if I got this right) an electric motor's torque will increase as a load is applied. How do you size an electric motor to provide similar power as the gas engine it's replacing?

 

[cqaigy2]

I could see the motor turning on and off on flat ground, but you might need it to stay running if on a hill, to keep you at the same elevation.

 

[CADplans]

A hydraulic drive machine has to be the worst application for an electric motor,,, WAY TOO much energy is lost,,

The machine needs to be gear drive first, and foremost,, because you have so little stored energy to start with,,,

Intermittent operation of the hydraulics will be marginal,, current electric/hydraulic power sources have VERY low duty cycles,,

The Power Trac is truly a design that needs LOTS of energy,,,

Of course, you could go back to the roots of the design of the Power Trac,, and pull a 6KV power cord,,

If I wanted an electric one, I would drive to the town Power Trac is located in,,
and,, buy a used battery powered one for a few thousand dollars,, it might need new batteries,,,

Of course,, it might be a little low to the ground,,

This one says it is battery powered,, but, that looks like an engine on the back ??

 

[radios1]

Since gas and electric HP is hard to compare, how would one go about finding a suitable electric motor to provide the same power as a gas engine?

For example, gas engine is rated at 25HP at 3600rpm. Gas engine HP and Torque decrease as a load is applied, while (if I got this right) an electric motor's torque will increase as a load is applied. How do you size an electric motor to provide similar power as the gas engine it's replacing?

If you can get your hands on a Baldor motor book, you will see that the torque increased as more load is applied. The torque can increase to 2 to 3 timeç—´ more than running torque. Baldor shows what they call "break-down torque". The torque can increase to 3 times or more than running torque. A motor produces it maximum torque at stall speed, and this is called "locked rotor torque". The motor torque does not fall off as the load increases. This is very simple. Gas engines only produce power every other revolution of the crankshaft. DC brushed Electric motors produce power every single revolution. That is why a 10 hp electric is same as the 20 hp gas this being said, a 20 HP electric motor will need some VERY high capacity batteries, and be VERY expensive to buy, then there's the recurring replacement cost.. think LARGE rechargeable lithium batteries!..

 

[4570Man]

A hydraulic drive machine has to be the worst application for an electric motor,,, WAY TOO much energy is lost,,

The machine needs to be gear drive first, and foremost,, because you have so little stored energy to start with,,,

Intermittent operation of the hydraulics will be marginal,, current electric/hydraulic power sources have VERY low duty cycles,,

The Power Trac is truly a design that needs LOTS of energy,,,

Of course, you could go back to the roots of the design of the Power Trac,, and pull a 6KV power cord,,

If I wanted an electric one, I would drive to the town Power Trac is located in,,
and,, buy a used battery powered one for a few thousand dollars,, it might need new batteries,,,

Of course,, it might be a little low to the ground,,

This one says it is battery powered,, but, that looks like an engine on the back ??

Agreed. To have any chance of working you need to throw away the hydraulic drive motors and use electric wheel motors. I don’t think this is a feasible project the way it is. I really doubt the wind and rolling resistance of electric car is as high as load on a powertrac and they have way bigger batteries than will be possible for this project. The electric forklifts use massive batteries. I had to take my backhoe to go unload a forklift battery and it weighed 50 percent more than the whole PT does. And probably doesn’t use as much energy. The electric forklifts only drive around on on flat ground which with a deep gear ratio doesn’t take much power and lift the mast. Depending on the load that could take quite a bit of power but it’s only momentary.