Re: (ET) Converting a gasoline lawnmower

["John R Guetter, PhD" <jguetter paonline com>]

John:  I did a conversion on a 26" Snapper mower with an 8 hp gas motor.  
My
first attempt was to mount a 1.5 hp series wound 36 v motor in the 
location the
gas motor was; it worked, but was under powered.  A 2.0 hp series wound 
motor
did a better job.  The electrical engineers I talked to suggested a 4:1
conversion factor (4 gas hp = 1 dc hp) which seemed about right to me.  The
biggest problem was figuring out a good way to position the 3 12 v marine
batteries on the chassis.  I got mowing run times of about 45 minutes; 6 6v
batteries with higher amp hr ratings would extend that, of course.

I decided for this experiment that I'd run the motor full speed and manage
ground speed through the existing transmission (Snapper's transmission is a
piece of engineering elegance!).  Worked fine for me.  Cost of motor 
controllers
far outweighed the slight loss of run time I suffered by full speed mowing.
Mounting and powering one motor was simpler than two, and I didn't see a 
real
advantage to the two motor system for my application.  For a riding mower,
rather than a general purpose tractor, the mower is usually in use so the 
motor
usually runs at full speed anyway.  Most of the work the motor has to do 
is spin
the mower blades; propulsion takes less work (mower engineers told me they
estimate that 2/3 of engine power goes to mower; 1/3 to moving the 
machine).
Good luck on your project!

JRG

John de Rivaz wrote:

> Anyone any suggestions on converting a gasoline lawnmower to electric
> battery operation?
>
> It is a 36" ride on and has a single engine driving a single blade and 
> the
> wheels through a simple forward and reverse gearbox.
>
> Options are:
>
> 1. replace engine with a large electric motor
>
> advantages: little mechanical change
> disadvantages: more mechanical parts left to go wrong.
>
> 2. replace engine with two motors: one for forward/reverse movement, and 
> one
> or three for blades. (if three replace blades with smaller ones, of 
> course).
>
> Advantages: machine more reliable with less mechanics, could get low 
> speed
> DC motor for traction and remove gearbox or even put one motor on each of
> the rear wheels and remove differential as well. Can control forward 
> speed
> independently so as to reduce cutting load for heavy work.
>
> Disadvantages - much more work to install
>
> Choice of motors.
>
> DC motors -  good torque/speed characteristics from series motors for the
> work, but expensive and difficult to get.
>
> Auto alternators modified to work as motors (remove rectifier etc and 
> drive
> from 3 phase inverter). Negligible cost (from scrap yard) in comparison, 
> but
> efficacy of torque unknown.
>
> 100v AC 3 phase induction motors driven from inverter. Low cost, no
> brushes/slip rings, but less efficient than synchronous motors (as above)
>
> General comments/queries:
>
> Anyone tried such conversion using sources of electric power other than
> series DC brush type motors as discussed above, and did you meet with
> success or failure?
>
> The gasoline engines on these machines have ratings of several 
> horsepower,
> ie 7/10 kW in electric motor terms. Yet when running they spend most of 
> the
> time without giving full output. An electric motor rated at say 750 
> watts in
> something like a drill is often called upon to give far more power in 
> short
> bursts. The motors discussed here for Elec-Traks seem relatively small in
> comparison to gasoline engines - anyone know what is their rated power
> continuous and peak?
>
> --
> Sincerely, John de Rivaz:      http://www.deRivaz.com :
> http://www.AlecHarleyReeves.com
> http://www.longevity-report.com : http://www.autopsychoice.com :
> http://www.cryonics-europe.org
> http://www.porthtowan.com

--
John R. Guetter
Lancaster County, PA