# Suggestions for a deck motor for a riding lawn mower?



## Batterypoweredtoad (Feb 5, 2008)

I have decided to convert my riding mower to electric. The plan is to use a 6.7" series motor I already have, and a small controller for propulsion with separate motor/s for the blades. I am thinking PM motor/s would be best for the deck motor. Any suggestions for cheap sources for one that could drive all 3 blades or 3 smaller ones to drive each blade?


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## Tesseract (Sep 27, 2008)

Hey BPT... A shunt motor seems like it would work best for this application and a good source might be battery-powered floor scrubbers. You know, the kind that are always trolling up and down the aisles of Home Despot, leaving a wet and muddy trail in their wake?


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## pariah (Oct 10, 2008)

I know that this flies in the face of electric powered vehicles but why don't you consider a two or three gang non-powered reel type mowers like those used at golf courses? It would eliminate the hassle of motor connections and perhaps not add much to the power needed to drive the tractor.


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## esoneson (Sep 1, 2008)

You have obviously never tried to use a push mower on your lawn.
It requires a significant increase in the amount of energy.


Eric




pariah said:


> I know that this flies in the face of electric powered vehicles but why don't you consider a two or three gang non-powered reel type mowers like those used at golf courses? It would eliminate the hassle of motor connections and perhaps not add much to the power needed to drive the tractor.


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## Tesseract (Sep 27, 2008)

esoneson said:


> You have obviously never tried to use a push mower on your lawn.
> It requires a significant increase in the amount of energy.


Oh, man - you aren't kidding! I bought one of those after my gas mower died... only used it twice because it was so hard to push (and in between the first and second use I had it sharpened - made it better, but it was still a bear).


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## ngrimm (Oct 19, 2007)

I'm not sure rotary mower would work too well either if the blade was just driven by the wheels.


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## major (Apr 4, 2008)

Batterypoweredtoad said:


> I have decided to convert my riding mower to electric. The plan is to use a 6.7" series motor I already have, and a small controller for propulsion with separate motor/s for the blades. I am thinking PM motor/s would be best for the deck motor. Any suggestions for cheap sources for one that could drive all 3 blades or 3 smaller ones to drive each blade?


Hi toad,

Here is a deck I did with a 7.2 inch motor. It is a Kuntz C60K. Usually has an 18hp Kohler ICE. Three 20 inch blades. 60 inch cut. Works great. 

Regards,

major


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## OBeer-WAN-Kenobi (May 28, 2010)

I'm also interested in having a seperate motor for each blade. My build thread is here: http://www.diyelectriccar.com/forums/showthread.php?p=183934#post183934

My first inclination was to do what major posted, but I've been thinking about the horrible inefficeincy of V-Belts and looking on the net; the two commercially availlable e-mowers use seperate motors.

The only problem I could see is that you'd need some sort of clutch between the motors and the blades in case you hit something. You would't have any belts to slip.


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## major (Apr 4, 2008)

OBeer-WAN-Kenobi said:


> My first inclination was to do what major posted, but I've been thinking about the horrible inefficeincy of V-Belts ....


I see you found it 

I don't think belts are bad at all, efficiency wise. Even with a tensioner, these don't get hot and have lasted 5 years, I think.


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## OBeer-WAN-Kenobi (May 28, 2010)

major said:


> I see you found it
> 
> I don't think belts are bad at all, efficiency wise. Even with a tensioner, these don't get hot and have lasted 5 years, I think.


Yeah, I found it, then I found your post to say to look at it. 

I've been doing a little research and maybe you're right. I looked in some of my books and they are a lot more effcient than I thought. Still, there must be some reason that the commercially availlable mowers are using seperate motors. You get to get rid of a bearing, so that would help. It's nice to not need to worry about belts or pullys wearing out and getting dirty.

Would 3 small motors draw less current than one large one that was working harder? Once again, I'm not up on my electrical stuff at all.


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## major (Apr 4, 2008)

OBeer-WAN-Kenobi said:


> Would 3 small motors draw less current than one large one that was working harder?


Theory says if the each of the 3 small motors was 80% efficient and the single large motor was 80% efficient, current draw for the two systems would be equal. However, typically one large motor rated at three times the power compared to 3 smaller one third power rated motors will be more efficient. Therefore, a single motor would draw less current for the same total power.

Yes, commercial decks typically use a motor for each blade. In volume production, this has cost advantage, not efficiency. And typically, as far as I know, they do not have a breakaway clutch. They are designed and tested to withstand the "stake test". Where at full speed, a steel stake is thrust into the blade path. The motor is allowed to fail, must not produce any projectiles. In other words, it can bend, but not break off.

The old GE Electracs (or Electrak) used this multiple motor blade system on 2 and 3 blade decks. The picture of the deck in post #7 replaced such a 3 motor deck. The user (a friend of mine) likes this system much, much better.

major


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## OBeer-WAN-Kenobi (May 28, 2010)

Major,
If using a series wound motor I understand from reading that a broken belt could cause a really bad failure. How do you go about protecting the motor and yourself from that? Will a controller stop it from happening? Is there other ways to stop it from happening without a controller?

Thanks!


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## major (Apr 4, 2008)

OBeer-WAN-Kenobi said:


> If using a series wound motor I understand from reading that a broken belt could cause a really bad failure. How do you go about protecting the motor and yourself from that? Will a controller stop it from happening? Is there other ways to stop it from happening without a controller?


Yeah, bad news for series motors when you lose the load. On my deck, and other belt drives, I use compound motors which have a defined no load speed. And your typical series motor controller will not protect against it.

You need to use an overspeed protection circuit which will shut down the controller or open the contactor when a set speed is sensed. This typically involves speed sensing, a tach or encoder mounted on the motor shaft. I use this on a chain drive go kart. Has a comparator circuit, feedback from a shaft sensor and shut off to the controller. Others have proposed a microswitch on a belt tensioner spring arm. I'm not too sure how safe that would be, but might work. Other things like a calibrated centrifugal switch might be made to work.

Regards,

major


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## Weisheimer (May 11, 2009)

OBeer-WAN-Kenobi said:


> I'm also interested in having a seperate motor for each blade. My build thread is here: http://www.diyelectriccar.com/forums/showthread.php?p=183934#post183934
> 
> My first inclination was to do what major posted, but I've been thinking about the horrible inefficeincy of V-Belts and looking on the net; the two commercially availlable e-mowers use seperate motors.
> 
> The only problem I could see is that you'd need some sort of clutch between the motors and the blades in case you hit something. You would't have any belts to slip.


I converted a 20" push mower to electric about 5 years ago. I used a PM 24V 3/4 hp motor by Imperial. It worked great until I hit a metal flashlight that someone left in the high grass. That bent the motor shaft and the blade. I had another identical motor, so I replaced the parts. Last year I hit a tree stump (I get tired and in a hurry. It's an acre on a hillside with a push mower that weights about 100#) and bent that motor shaft too. I have gone back to the gas mower for now, and I'm in the process of converting a 42" deck to electric using both of the motors after I straightened the shafts. I know there are better motor choices, but I already have these in hand. When I ran a single 20" blade direct with this motor it drew 44 amps. When I used 2 of these motors to belt drive a 42" deck with 2 21" blades each motor drew 44 amps. So it seems to be at least as efficient. These are 3400 rpm motors and I used 4" pulleys on the motors and drove 4" pulleys on the deck.
My point is that the direct blade drive is going to take a hardened motor shaft and that is going to further complicate your search for a motor.
Though you may be a bit brighter than I am and not hit anything!

Mark


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## Weisheimer (May 11, 2009)

major said:


> Hi toad,
> 
> Here is a deck I did with a 7.2 inch motor. It is a Kuntz C60K. Usually has an 18hp Kohler ICE. Three 20 inch blades. 60 inch cut. Works great.
> 
> ...


Major,

Can you elaborate on the motor a bit? Is it 36V like the ElecTrak? What brand, speed, HP? That is one heck of a deck to run at 36V, so now I am curious.

Mark


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## major (Apr 4, 2008)

Weisheimer said:


> Major,
> 
> Can you elaborate on the motor a bit? Is it 36V like the ElecTrak? What brand, speed, HP? That is one heck of a deck to run at 36V, so now I am curious.
> 
> Mark


Hi Mark,

I was hoping you wouldn't ask. It is an old prototype Prestolite 7.2 inch diameter compound wound motor intended for a floor sweeper back about 35 years ago. Originally for 72 volts. But on his mower, an old Electrack with an Onan generator, at somewhere about 45 volts does just great  Never put a tach on it, but I'd guess at least 3000 RPM. I'm just guessing, but I'd say maybe 6 or 7 hp under normal load. It was totally enclosed with internal fan, but he opened up the coverbands to provide some ventilation while still keeping out the bulk of sh!t which flies over the deck.

I have always hated mower blade motors. Had a bad experience with them early in my career. So I was skeptical when Tony asked me to do this . But WTF. I had this motor. He bought the deck. The rest is history. This beast sucked up small children off the lab floor during tests. It is absolutely the most monster electric deck I can imagine ever to see.

When it comes to electric mower deck motors, more power 

major


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