Electric Riding Mower Conversion

Due to the job I picked up after starting this project and the safety concerns I have with completing it for the location it would be used at (near a pond or other body of water).  I am (at least until things settle down) putting this project on hold.

Good news for me: Briggs and Stratton will provide torque curves and related data if you ask them.
So for the 40H777-0241-E1 engine used on the GT2254 riding mower from 2005, I received the following table:

Husqvarna also responded for a request regarding the load ratings of the lawn mower in question, stating that it was rated for 846 lbs of No Load Weight.  This seems illogical to me, as I highly doubt the mower weighs this much, even with the deck installed, and somebody much heavier than myself riding on it.  Full Load data was not provided, and when asked for clarification, I was told that the 846 lbs load was specifically No-Load.

HP of a motor is measured at full RPM, but Torque ratings are taken at 3060 RPM according to a gross power chart that came with the table above.  And do not include losses from installing the air cleaner or exhaust systems.  This makes things slightly trickier, but I'll worry about that loss later.

Horsepower = Torque * RPM / 5252

(Source page 1, column 2) 

This source also gives Mechanical HP = 746 W = Electric HP. 

Torque is defined by science as kg * m^2 / s^2 in units.  Or mass * distance^2 / time^2.

The ratio between the drive shaft torque and the flywheel torque is simple to calculate if I treat the flywheel and shaft as one assembly.  This causes the mass parts of the Torque definition to cancel itself out, and since they're both acting within the same timespan, the time variables cancel out.  Leaving a ratio of two circumferences.  The diameter of the shaft is listed at 1.125 inches and measures within tolerance of that value.  The diameter of the flywheel, I am taking from measurements as well, and comes out to 9.5 inches (approx.).  Thus:

T_flywheel / T_shaft = ( pi() * 9.5 )^2 / ( pi() * 1.125 )^2 = C_flywheel^2 / C_shaft^2

 ~Remember, diameter is 2x radius, and circumference (C) is 2 * pi * r .~

or T_flywheel / T_shaft = 890.732 / 49.965 (within about a significant figure of tolerance)

Thus:  T_flywheel / T_shaft = 176.0 Nm / T_shaft = 890.732 / 49.965

T_flywheel * C_shaft^2 = T_shaft * C_flywheel^2

T_flywheel * C_shaft^2 / C_flywheel^2 = T_shaft

176.0 * 49.965 / 890.732 = T_shaft

8793.8 / 890.7 = 9.9 Nm within one sig fig of tolerance.  (slightly less if ignoring significant figure truncations)

This is what I have for today's update.  I need to do some research into the motors and such before I continue further.

So this update is specific to the lawn mower in question.  Exact details will vary with mower system and is mostly so I can collect the data in an organized fashion in one place.

1.) Make and Model:  Husqvarna GT2254, 2005, with 54" deck.  Electrolux 96025000201 model.  Catalog No. L0GT2254

2.) Weight values: Not specified in any manual or advertising.

3.) Drive wheel diameter and location: Rear wheel drive, 23" diameter. Double-wall 10 PSI, 23 x 10.50 - 12.  Estimated 880 lb load

4.) Non-drive wheel radius and location (Radius used by DD Motor Systems in their online form for quotes): Front tires/steering, 8" radius.  Double-wall, 10 PSI,  16 x 6.50 - 8. Max 415 lb load.

5.) Engine: Briggs and Stratton, 22 HP ELS656.  Model number (as listed on engine) is 40H777-0241-E1.

6.) Mechanical drive train:  Pulleys to integrated trans-axle.

7.) Motor shaft: 1 1/8 diameter, 4 5/16" long, with a 7/16 x 20 bolt threaded into the shaft to hold on the clutch.  And a 1/4" key slot about 4" long (yep, even into the curve of the shaft up to the motor)

8.) Drive train pulley: 4" idler pulley, v-groove, metal, with no key slot, rather the inner wall of the pulley is punched to make a pseudo-key.  (Imaginative, if garbage design).

9.) Trans-axle Pulley: 8.5" diameter, metal, v-groove.  (The Trans-axle does all the gearing changes for the forward and reverse and speed of the mower.)

10.) Electric Clutch for mower deck: Fully functional, I'd like to avoid changing this if at all possible, and am leaving it out of the equations, on the assumption that I won't need to at this point.

11.) Drive train to trans-axle gives a pulley ratio of 4:8.5, or just a bit more than 1:2.

12.) Maximum no-load speed (assumed to be max forward velocity as per manual): 5.4 MPH

13.) Minimum no-load speed (assumed to be maximum speed as listed for lowest gear in the manual): 0.7 MPH

14.) No maximum load given, nor max load speed.  I expect the velocity should be equal to unloaded speed.

15.) Velocity on any given grade aside from 0% is unlisted.  I would assume 5% grade would not alter maximum or minimum velocities. (this may be ignorance)

16.) Engine RPM: Briggs and Stratton does NOT list this, nor does it show on any of the engine's markings.  I can therefore only estimate based on other engine RPMs of similar type.  This puts RPM in the 3100 to 3600 RPM range, and I will guestimate at the higher end, for the purposes of this project.

17.) Range: I would like the mower to run for about 1 hour on a charge, if possible.

18.) Battery voltage: 48VDC ideal.  (NEC does not provide guidance on this, at least as of 2008.  This has hopefully changed with the re-introduction of electric vehicles.)

19.) Battery Type: Lead-acid deep discharge/cycle type.  Short overall life, heavy, and bulky, but cheap to procure and replace if something happens.  

20.) Expected load current, based on readings listed in my description of this project, come out at 120A max, with some safety built in.

21.) Thus ampere-hours of the battery pack should come in around 100Ah to 120Ah.

22.) Duty Cycle: 30 minutes to 1 hour of operation on a charge. So 50 to 100% of capacity.

Most of what I've listed here are based on the estimate form given by D&D Motor Systems on their website.  And may need expansion or alteration to fully describe what I  need later.

06/16/2020 FrictorOTS