Electric Lawn Tractor

[halfcrazy]

Ok i am going to try to build a electric lawn tractor and i have a 5 hp baldor series wound dc motor 48 volt. My question is though i was told i need a controller for the motor so it doesnt over rev? my thoughts where this tractor has a hydrostatic drive so i was going to put a neutral switch on it to kill motor when in neutral and also switches like seat switch so it saves power when you get off the machine. i will post pictures and info as i progress with this project i plan on charging it with 2 90 watt sunwize panels and a small charge controller.

[Nando]

If the hydrostatic drive can be set to Zero power transfer you may not need motor RPM control, otherwise you will need control.

Do you know how to calculate the battery size and energy needed to operate the tractor for certain period of time, knowing the motor current usage ?.

Nando

[nanotech]

Heh, hope you only need to mow once a month!!  

At 90W for 8-10 hours a day, gonna take a while to put back in what a 5HP 48V motor's going to use!!

It's a good idea converting it to electric, just your charging method I'm wondering about.  

When you consider my 42" mower uses a 1/2 gallon mowing my yard, I forget how much wattage of power a gallon holds, but it's a LOT!!

[nanotech]

Oh, and a controller for it would be relatively cheap if you can find someone who rebuilds golf carts or fork lifts.

[richhagen]

I was also thinking that a used curtis golf cart controller might be very useful here (make sure it is for a series wound motor) and not that expensive.  

The following are just ball park estimates.  (and they could end up being out of the park)  For power, my small electric car uses about 10KWH per hour.  It has an 11 or 12 HP engine which revs up and down as you drive and switch gears and such.  Now, if your mower were proportionate usage based upon motor size, that would be about 4.55 Kwh/hour of mowing.  This is about 16,380,000 Joules of energy.  Now if you only wanted to discharge your battery pack about 30% then you would need a bank capacity of 54.6 Mj.  At 48 volts that would work out to about 316 amp hours.  That is a whole lot of battery weight to be dragging around.  If you could mow at 1/2 hour stretches and recharge, then you could half the battery bank size, in which case a string of golf cart 225AH batteries should be more than sufficient.  You will also need large cabling (I now use 4/0 on my car) and very good connections as you will have huge current draws when you start up, similar to what I have on my electric car at 72V.  An ohm at 500 amps will result in a melted battery terminal. (which if that happens I now have a little experience at repairing) Rich  

[halfcrazy]

thanks for the advice and info the motor uses 96 amps at full load i am pretty shure i will never see full load maybe 50-75%. it takes me about 30 minutes to mow the lawn i have a cordless pushmore to do the small work so i figured worst case senario i will need about 1 hr a week. my real question is can i run this motor at 24 volt? it is a 2800 rpm 48 volt 5 hp i would have liked to get something like a 24 volt 3-4 hp. A friend had mentioned with a series wound motor will take lower voltage just not produce as much hp and will run a slight bit slower? If this was the case i can gear it up in the drive pulleys and will derate the hp for me a little. make any sense so far? if i need to stay 48 volt i will use 4 12 volt 100ah batteries if i can stay 24 volt i have 4 golf cart batteries i can use that would be my preffered method as i own them. and yes the hydrostatic has a neutral position that is zero power to weels and is variable from there the more you push the lever the faster you go.thanks again for the info and the future help

[nanotech]

Just some more info here....

Your original Briggs & Stratton or Tecumseh engine will have been governed to about 3500 - 4000 RPM at full throttle.  The rest of your mower was designed to operate around this RPM, everything from the traction drive to the blades.  The blades are the important part in this, as they have to be spinning fast enough to throw the clippings out of the way, but not so fast that you're ripping your blade bearings and drive belts apart.

Your motor is rated at 2800 RPM at 48V.  If you run it on 24V, you cna more than half that to about 1500 RPM.  Load it up with the traction drive losses and the blades chewing through 2 weeks worth of grass (heh, you went on vacation), and I can see that motor coming down to about 900 RPM.  So you'll need to multiply that RPM by a factor of 4.

Now, considering most drive pulleys are 6" - 8" in diameter, you're going to need a jackshaft.  Spinning up a 24" - 32" drive pulley just isn't practical.  So you're going to have to figure some way of doing multiple pulley amplifiers to get the correct RPMs.  A double jackshaft is your only real way.  But please remember it's going to have to be a hefty one, and the full torque of that motor will be going through it.  And don't forget that just because the motor says it only has 5hp, it's going to have about 2-3 times the torque of the original gasoline engine......

[halfcrazy]

the drive pulley now is 5 inch for both drive and blades i can go 48 volt if needed i am just set up better to charge 24 volt but that is workable i have no idea ratios but i guess i was figuring like a 15" drive pulley for starters but i will look at all info before making any decisions and really apreciate the info on the dc motor being strong my first concern on this project is safety then second is longivitey that said i dont mind haveing to do some experimentation. i had someone tell me the electric tractors they had seen used a seperate motor for the blades would this be advisable and try to sell the 5hp and get like a 2 or 3hp for the traction motor? if so what hp would you think for a 34" 2 blade deck?

[nanotech]

A 2HP for a traction motor would be a little overboard.

The 2HP (or maybe even less) would be good for the blades, as they are what take over 90% of the power in a riding lawn mower.

The advantage of going twin motors is that you wouldn't necessarily need a speed controller then.  A simple on-off switch connected to the "go" pedal for the traction would be fine as the existing system is set up to run at a constant supply RPM anyways.  And the blades could be rigged for constant connection to the blade motor and they run at one speed also.  On-off relay connected to the existing blade safety switch could engage the blade motor.

This is a way you could go 24V as neither motor would need to be near as strong as a single motor system.

I would say a maximum of 1HP for the traction motor (and that's if you plan on using the rig as a tractor as well when it comes time to rake up the leaves).  If it's only for moving the mower deck around the yard, I would think you could go as low as 1/4HP because of the gear reduction in the transaxle.  It just really doesn't take much to move one of those mowers around.  I can have my mower at idle and "drop the clutch" on it in high gear and it really doesn't kick the governer up at all.  And mine's a heavy SOB.  But engage the blades even at a standstill?  That engine's gonna stall every time at idle.  Needs at least half throttle.  Mind you, mine's a 42" deck.  Pretty hefty blades to get moving there.  And for some reason mine spin at a REALLY high RPM.

Depending on where you're at, I have a 24" snowblower head that you could rig up as well with a seperate motor!!  Free for the taking!!  

You know, if my riding mower wasn't only 2 years old, you'd have me thinking of doing an electric conversion on it!!    You've got me thinking what all I could convert now......

[halfcrazy]

nanotech my rider is 8 months old but i have such a excess amount of pvpower in the summer as the boiler isnt going roughly 2-2.5 kw hours a day on good sunny days seems a good move for me so i will look at going the 2 motor route i may play with the 5hp as i have it but i can sell it i am shure for enough to get the 2 dc motors or close

[nanotech]

When I lived in Oregon there was a place the made motorised wheel chairs.  One of those motors would be good as a traction motor.  Might have to play with the reduction ratios a bit.

For the blade motor, a golf cart traction motor would probably be sufficient.

Just a couple of suggestions.  Other people might have better ones, though.

[pyrocasto]

I think you may be better off in this situation to run some power cables from your house to you mower.

I would do either a small diesel, or leave it as gas. They dont use much.

[nothing to lose]

"power cables"

Ya, I love running over those too

Makes 4th of July come more often with all those nice fire works

Actually I always found cables to be too much of a pain for mowing, why I never went electric! Always wrapped around something or in the way. Not long enough, etc..

[nothing to lose]

OK, I put alot of thought into things I will probably never get around to building

Just too many things not enough time.

I do have alot of broken junk riding and push mowers, thanks for getting me started on somethng new guys! Currantly I do not have ANY working mower, cost to much for parts to fix the broke ones and they are not worth it, but they do have good 8-15 hp gas engines.

I have 12 acres of brushed up woods, large yard I let grow, small area at house I weed wack once a week or 2, mostly rocks dirt and weeds, not real grass. Still a pain to do anyway.

First thing I think I will do is take a working AC motor and mount on a push mower, use a cord for that. Those little gas motors are junk and don't run. This will be good for where I normally weed wack and a rider is not good anyway. I may do this tommorow.

For the rider I have been thinking 2 things so far, not done either yet though.

1. , Take the best tractor, deck is shot, use that for the tractor on gas. Take a good deck off one with shot wheels and bearings etc.. Make a trailer and  mount  deck under it. Run deck with AC motor, put batteries on trailer and my 5K inverter. Run wires up to a switch on the tractor. Now I drive to where I want to cut, flip switch and turn on motor and mow. Under the tractor where the old deck used to be I could install a alternator also if wanted. None of these parts interchange, not enough room under there to mount motors either so this would be a fast easy way to do it. Also I like trailers.
   
2. cnd, I thought about taking the engine off a tractor that is pretty good for the above use. On this one I put an AC motor to run it, use the inverter on the trailer for this one also. Simple on/off switch, like someone said the engines on these normally run a constant speed any way, I still have my clutch and gears etc.. as normal.
   
   

Now if I build both, Gas tractor, Electric tractor, and mower deck trailer, I can mow with all electric, if the gas tractor has an alternator then I can switch to it if the batteries start to go low, mow and charge at same time, if I top of the batteries I can take a break and switch to the electric tractor again.

Also all mowing at the house could be with the electric tractor, then swap to the gas one for further out like near the pond where I would not want to get stuck with dead batteries!

As for using the inverter and AC motors there are 2 reasons. I get AC motors dirt cheap from a salvage yard, I can't find decent cheap DC motors. Also the 2 DC motors I do have are around 180 Volts 2 HP, one is a rinky tread mill motor the other a 75LB Dayton. Using the inverter I have 120Vac, convert to 120Vdc at the motor and I got those covered somewhat if I use them for anything.

Now I said I was planning to build an electric bicycle trailer also recently. Using the above ideas, I build one really heavy duty but light wieght 2 wheeled trailer for hauling batteries around that is self propelled on the road, install deck mounts under that, one set of batteries will run my electric bike down the road or mow my yard

I just have to connect the trailer hitch and connect the wires. One set of batteries used for several uses during the week.

 Also I just realized the other day for DC relay, high amps, low cost, Fords have that nice neat 12V starter relay on the fender under the hood. Connects pretty high amps to that starter, uses 1 small wire to turn it on

 I have gotton starters very hot, very got one of those relays hot. I wonder how many amps and volts they are actaully good for?

[Norm]

   Just to get you thinking how easy and efficiently

you can mow a lawn......

   



this is a blower motor if you make a special blade

where just the 2 inches of the tips are dropped

down and sharpened ...it will cut a 10-12inch

diameter swath with ease!

                  ( :> ) Norm.

Now back to the real world where most people

mow weeds with blades as sharp as a 2x4 with a

gas guzzling full power 17.5 dyna-balanced hp

engine.! LOL!

[kitno455]

i was thinking about all this myself sunday, ran over a piece of buried chickenwire with my rider. oh well, good excuse to take the deck off, clean and paint it, and sharpen the blades. (50 inch cut, its got alot of blade)

this deck might only have a couple more years before it rusts thru, so i was looking at replacements. very expensive. other brands mounting holes dont quite line up, and this thing is belt drive, no pto. my land is also a little lumpy, so the wide deck scalps some spots, and leaves others long.

so what about replace the deck with an ac generator, and get three push mowers to pull behind, each with an ac motor. the 'jointed' deck will follow the land better, and i can use it as a generator in a pinch...

allan

[nothing to lose]

Kinda my thought exept I have trees, cars, other things in the way and will stay with a single smaller deck maybe 42"

If your using 3 motors, then each could be smaller than you would have to have if only using one I think. So 3 1hp motors might be better than 1 5hp motor, and you won't have the belt/pully losses.

If your deck just rusts out, would could just make a new deck with the old parts, spindles/pullies and set it up for one motor to drive that. If you wanted it jointed to flex then use idle pullies on springs to set tension and keep belts tight all the time.

 If you make it a pull behind trailer type you'll have to support the center section on wheels I think so that the outer sections can rise and lower as needed (I think).

"so what about replace the deck with an ac generator, and get three push mowers to pull behind, each with an ac motor."

That may work but don't forget the blades have to over lap somehow or you will be leaving 2 strips of uncut grass each path. Also you need the gennie to run those motors if you don't have batteries and inverter so your not gaining much if anything here.

 If you can power the motors from batteries and build it as a trailer unit you can charge off a wind genie/solar all week free or grid over night cheap, save some fuel. Gennie on tractor keeps it going  as needed then for extended run times if need be.

Mow when you have plenty of power

 Use the trailer mower batteries as an extension of the house battery bank when not in use? Make a plug to easily connect or remove it as needed. SO if you don't have wind a few days, wait to mow and use those batteries on the house, when everything is charged and you have plenty of wind to keep the house going, then go mow and not miss those batteries at the house

I wonder how many HP it actually takes for one of those 12"-16" daul rotor gennies to run off a gas engine that way geared down to say a constant of 600rpm ?

[davharv]

Look at G.E. Elec-Traks or (electric tractor.com).Hydrostatic will turn battery power into heat:bad.

[nothing to lose]

Nice vehicles.

" The secret is in our patented electric drive system. Using an individual motor/gearbox on each drive wheel and an electronic differential, the"

Well that's no secret, I been thinkng about the same thing for along time. 4wheel drive electric

I'll never build it probably, but I keep falling back to the thought of each wheel having it's own motor. Under heavy load all 4 run, for crusing the highway at steady speed then only 2 run. Regenantive braking off all four maybe, provided not enough resistance to cause a skid in bad weather, or seperate switch to engage when wanted.

If I could just find 4 4-5hp dc motors for $75 I would build it!

Just can't afford the motors.

Where can I get decent motors at a decent cost? Can't afford several hundred per motor here.

[nanotech]

Um, seperate motors on the drive wheels on a lawn tractor = good idea.  Makes for an electric ZTR.

Seperate motors on the drive wheels on a highway (read road use) car = bad idea.  Makes for obscene (read dangerous) handling issues.

The GM EV-1 was originally designed to have twin drive motors, one for each front wheel.  But with all the computing power available to them (even external) they couldn't counter the dangerous (often lethal) side effects.  Even two perfectly matched motors are going to have miniscule differences in the way they transmit the power.  These differences make for VERY ugly handling.  Especially in front wheel drive.

[nothing to lose]

You could be correct about street use 4 wheel electric drive, but I think it could be made to work well easily. When you look at the big auto makers look at all the problems they have too. Heck I can paint a car, none of my paint ever fell back off. I have 5 vehicles in the yard that the factory paint has truely just fell off of in patches, see others on the road every where! Hmm, what else can I do better than the big auto makers?? I never built an engine the blew up in less than 20,000 miles either, I know people that had that happen on new vehicles, replaced under warauntee.

But anyway, rear wheel drive cars were often 1 wheel drive somewhat. Limited slip, positraction, etc..  Not equal power to the wheels at all. Many of the 4 wheel drives were only really 2 wheel drives. 1 rear wheel, opposite front wheel. If the drive wheel started to spin the other wheel same axle was supposed to grab in and pull. Never checked but I would not be surprised if most front wheel drives don't work the same way.

I know it's not equal power to the wheels, 1 wheel spins on ice but you just sit there and the other wheel is not turning at all. If it were equal power to the wheels then the wheel with traction would move you forward even if the other was spinning a bit.

If the gas/desiel vehicles can work without equal power to the wheels then a minor difference in electric motors should not make that much differince either.

[dmendozadmd]

Hi,

This subject is 2 years old; I just found it because I am searching for info on how to build or convert a gas powered riding lawn tractor/mower to electric. I am just curious to know how yours turned out?

Thank you.

dmendozadmd