# Mower Conversion Question



## PhantomPholly (Aug 20, 2008)

When comparing gasoline operations to electric, a simplistic rough rule of thumb which includes an overhead to assume never running the batteries down more than 80% is to calculate 8Kwh of battery power = 1 gallon of gas.

I sincerely doubt 4 deep cycle batteries would provide even as much power as 1/4 gallon of gas, so you may want to re-think your batteries.

Recommend you read through the info on the wiki and / or the EV Information section as a starting point.

Good luck!


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## HillbillyHubble (Sep 11, 2015)

Thankfully I am in the very fortunate position of getting some free/very cheap batteries from a coworker, so power isn't so much of my problem from a cost stand point, but more from a space issue.

That said, after running the napkin math gives me just over 10HP at 200A and 32HP at 500A. After looking around a bit at other conversions I've seen most recommend 1KWh batteries (small mowers with manual trans and small yards) to 8000KWh (more along the lines that I'd need, big mower with a hydro trans). Again, running the napkin math I would need 8 25Ah deep cycles, which actually gets me up to a 9.6 KWh battery so I shouldn't ever run it flat.

I think even that may be overkill since that math was pulled from a yard that takes an hour to mow, and mine only takes a half an hour. Which would hopefully be even less since I wont need to baby the half dead engine when it bogs.

So how far off is my math? It obviously ignores inefficiencies but I would think the buffer should help that out.


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## samwichse (Jan 28, 2012)

8 25 ah (12v) deep cycle batteries is 2.4 kwh.

10 hp is 7.5 kw, which draws 78 amps @ 96v. That means in a theoretically perfect world, your battery pack would last about 20 minutes @ 100% depth of discharge... which would insta-kill your lead pack. With voltage sag and a reasonable DOD (50%), you're looking at maybe 8 minutes.


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## PhantomPholly (Aug 20, 2008)

There are now a number of LiIon batteries on the market (Google "LiIon Starter Batteries") which can help you increase your pack Amp hours in the same amount of space. They are essentially drop-in replacements for Car / Deep Cycle batteries so should not require as much special TLC as building your own pack, but that is also an option.

Edit: I posted these in another thread, there are doubtless others:
Deltran
SmartBattery (built in protections, but at a premium price)


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## major (Apr 4, 2008)

PhantomPholly said:


> There are now a number of LiIon batteries on the market (Google "LiIon Starter Batteries") which can help you increase your pack Amp hours in the same amount of space. They are essentially drop-in replacements for Car / Deep Cycle batteries so should not require as much special TLC as building your own pack, but that is also an option.
> 
> Edit: I posted these in another thread, there are doubtless others:
> Deltran
> SmartBattery (built in protections, but at a premium price)


Watch out for these. That first link uses PbEQ Ah, so it is a fake rated capacity of likely three or four fold.

The second link may be real Ah, but the price per Wh is 3 to 4 times what you'd pay for Lithium cells.

Beware and know what you're buying.


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## major (Apr 4, 2008)

HillbillyHubble said:


> So the big question: will a Motenergy ME-1004 motor have enough power to run the hydrostat and the three blades? My plan was to use 4 12V deep cycle batteries to run the motor at the full 48V.
> 
> Follow up question: About half of my yard is infested with 'water grass' which is thicker and grows faster than regular 'yard' grass. Those areas already bog down the limping Kohler motor and I have to mow at a crawl (I would be extremely impressed if I am pulling even 10 HP out of this near-dead engine). Will those areas draw enough of a current to need to worry about getting heat away from the batteries?


Propulsion of the mower is easy. Cutting tough grass is a bitch. That is a brushed PM motor and not the most durable type. That is where you may have thermal issues.


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## HillbillyHubble (Sep 11, 2015)

hmm.... So from the replies I'm getting it seems to be a pretty resounding 'no' to this conversion. Would perhaps a 120V AC plug in option be more doable (I dont see how without blowing my 20/30 amp breakers)? Or should i just admit that this mower isn't getting converted to electric and start sourcing a replacement ICE engine?


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## major (Apr 4, 2008)

HillbillyHubble said:


> hmm.... So from the replies I'm getting it seems to be a pretty resounding 'no' to this conversion. Would perhaps a 120V AC plug in option be more doable (I dont see how without blowing my 20/30 amp breakers)? Or should i just admit that this mower isn't getting converted to electric and start sourcing a replacement ICE engine?


It is doable with batteries. Just get a hefty motor and don't expect long cutting sessions using PbAcid. Just trying to help you avoid smokin' a motor. Look into a used forklift or floor sweeper or utility vehicle motor.

I've seen guys succeed with those PM motors on smaller decks and wimpy grass. 3 blades and bitchin' grass; you need a stout wound field motor.


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## ken will (Dec 19, 2009)

You could use the small motor if you:

A) drive slow and listen for the motor straining, which means drive even slower.
Or
B) take off one or two of the 3 blades (if you can't stand driving slow)

And in either case.... keep the blades really really sharp!


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## dcb (Dec 5, 2009)

fwiw for comparison, I wound up using 15 leaf modules in my electrak e10m, it does a fairly tall 1/3 acre about 4 or 5 times before I worry about recharging. And it makes very quick work of it.

http://www.diyelectriccar.com/forums/showthread.php/dcbs-ge-e10m-leaf-battery-upgrade-159010.html

I tried mulching blades but it trips the overheat a lot quicker. The motors could use rebuilding too. I just run on half a deck till it kicks back in for now.

It is a 36 volt system and has a 25-35 amp shunt motor for drive (w/gears and reverse) and 2 15 amp PM deck motors with built in thermal cutout. 

my push mower is corded, really easy to manage, but I don't know about a cord on a tractor. Would be nice to sort out, batteries aint cheap and often more hassle (even my goto drill is corded). The kw demands at 240vac would only be about 10 amps in my case (ignoring power factor). But I also use it with a wagon sometimes and shuttling stuff from front to back could be a hassle. the 100 foot pusher cord is only good for doing 1/2 the lot at a time with a house in the middle.


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## HillbillyHubble (Sep 11, 2015)

major said:


> It is doable with batteries. Just get a hefty motor and don't expect long cutting sessions using PbAcid. Just trying to help you avoid smokin' a motor. Look into a used forklift or floor sweeper or utility vehicle motor.
> 
> I've seen guys succeed with those PM motors on smaller decks and wimpy grass. 3 blades and bitchin' grass; you need a stout wound field motor.


bah, I was really hoping to stay away from needing a controller. But if that little motor isn't up to the task I'll be on the lookout for a stronger motor.


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## Sunking (Aug 10, 2009)

samwichse said:


> With voltage sag and a reasonable DOD (50%), you're looking at maybe 8 minutes.


You forgot Peukert Taxes, 3 to 4 minutes max until dead.


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## major (Apr 4, 2008)

HillbillyHubble said:


> bah, I was really hoping to stay away from needing a controller. But if that little motor isn't up to the task I'll be on the lookout for a stronger motor.


You'd need a controller on a series wound motor, but not if you use a compound, shunt or Sep Ex.


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## storx (Nov 24, 2013)

I have actually thought about doing a electric lawnmower myself before, but i am working research on an electric motorcycle build instead now.. take a stroll down to your local hardware store.. I was looking over my neighbors gas generator that has 240v 30amp outlet and noticed that it was brushed, so i looked for a plate on the electric portion and noticed that its generating 48VDC and then converting that to to 120v and 240v..

I am not sure how you would test the output, but i have been contemplating bypassing the inverter circuit and see what type of output the DC can output, i found no motor tag with part number to look up the actual motor specs...


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## dcb (Dec 5, 2009)

It sounds like you are describing and electric transmission, in essentially a gas powered vehicle. Not an electric vehicle.

It wouldn't make any sense at all to avoid rebuilding the 25hp engine, only to replace it with a generator set and drive/deck motors. It would probably be a lot more inefficient and expensive.


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## HillbillyHubble (Sep 11, 2015)

Splitting up the motors would be really interesting, but I think that project would quickly become more expensive than i am comfortable with. 

I do have another mower that might just be a whole lot better suited for this conversion. its a 12.5 HP ICE with a 2 blade 36" deck and a manual trans. It seems that the PM motor should be able to handle that much better. Unfortunately it has a good ICE but a busted deck and a crappy system for disengaging/engaging the deck which means it pretty much runs the deck constantly (yes, it's both infuriating and terrifying).

Decisions, decisions. At any rate, thanks so much for all of the advice. I'm definitely going to catch that coworker and ask how many batteries he has access to.


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## dcb (Dec 5, 2009)

fyi, that "little" e10m of mine was designed for 6x6v batteries, t105 sized. maybe $80 apiece (if you have a core) for house (sams/costco) brand, 65lbs apiece, so like $500 and 400lbs, and most folks only seemed to get about 3 seasons out of them (though I imagine some folks here know how to take care of them better)

the 15 leaf modules are about 125 lbs, and last a long time. but are about ~$120 apiece (without scrapping a leaf yourself) so $1800. 

Batteries are the suckiest part for an economy build, and leaf cells are pretty low on the cost per kwh scale. I borrowed them from another project, is the only reason I went with them. But you might just want to look for an old elec-trak in your area, frequently they are just a few hundred bucks, but a "proven" design, and the purchase price will probably be dwarfed by the cost of batteries. The thing is literally a battery box on wheels, would save a lot of effort and component costs in a conversion.


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## HillbillyHubble (Sep 11, 2015)

What motors are driving the blades on your Elec Trak? Voltage/Amps per motor? I searched pretty hard for one, but the only one i could find in 500+ miles didnt come with deck.

That may actually be a somewhat reasonable solution.


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## dcb (Dec 5, 2009)

it is a 36v system and the two deck motors are listed as 15 amp permanent magnet motors. I also use the built-in charger fwiw.

To majors earlier point though, my 120v pusher seems a lot better suited to the task. It is basically a series wound "universal" motor, no controller so it must be rpm limited by the blade drag (mulching blade typically). But when it hits thicker grass, it just slows down a little and torques up, really powers through stuff that my gasser would bog down on (and it is a ridiculously simple looking open frame affair). the PM's are a lot wimpier when loaded, though they aren't drawing as much power individually, and they get the job done.


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## HillbillyHubble (Sep 11, 2015)

So I had some time to look over the mower and it seems like i could definitely split the motors. My push mower has a little 140cc ICE that from what I can find runs 4-5 HP. With a 3 blade deck lets say it takes 15HP to run those three blades. So if I ran that Motenergy ME-1004 on the blades and separate, less powerful continuous motor for the hydrostat.

Obviously this isnt gonna be much of a budget bill anymore, but if i can keep it under the cost of a new electric mower it seems worth it to me. (and justifiable to the wife). So, now onto the battery pack, which i still cant quite figure out what Kwh i should be looking for? Would it be better to split the batteries up or run both on one pack?

Thanks again everyone, you guys are awesome.


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## PStechPaul (May 1, 2012)

I came late to the party but I am also in the process of trying to build an electric mower or lawn tractor. I plan to use three phase motors and VFD control, but just to "git 'er done" a simpler DC motor and controller is easier and more practical.

I have also done some work on a battery-powered push string trimmer mower using two high speed brushed DC motors and two trimmer heads for a 24" swath. I also have a pair of heads with stiff plastic blades that may work for heavier brush. You might be able to find some battery powered electric drills and use the motors without the reduction drive. String trimmers use something like 5000-10,000 RPM.

You may also find 120 VAC electric trimmers for cheap and you might be able to drive the motors using automotive inverters. Maybe even adapt a hedge trimmer for really tough grass.


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## dcb (Dec 5, 2009)

PStechPaul said:


> I
> You may also find 120 VAC electric trimmers for cheap and you might be able to drive the motors using automotive inverters.


fwiw, most of the plug in trimmers and mowers I've seen look like universals, i.e. 96vdc+ would probably work without an inverter.

edit: it may possibly already be running in DC: http://www.st.com/st-web-ui/static/...ical/document/application_note/CD00003829.pdf


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