A yard-sale mower converted to battery-electric and charged from an 11 W panel.
Solar-Charged Lawnmower by Open-Source-Imports
https://thediyjunky.com/@open-source-imports/solar-charged-lawnmower
Licence: CC-BY-SA-3.0
Adapted from: https://www.appropedia.org/Solar-charged_lawnmower
Original author: Jeremy James (User:Anonymous1), Cal Poly Humboldt
Original licence: CC-BY-SA-3.0
| Spec | Value |
|---|---|
| Motor | Dayton 3/4 HP, 12 VDC |
| Battery | Sun Xtender 40 Ah deep-cycle |
| Solar panel | 11 W, 16.5 V operating, 0.62 A in full sun |
| Charge controller | Morningstar SunGuard 4.5 A, 12 V |
| Switch | 70 A |
| Deck patch material | stainless steel, about 1/16 in thick |
| Total as built | $699.00 |
A $5 yard-sale lawnmower stripped of its internal combustion engine and rebuilt around a 3/4 HP 12 VDC motor and a 40 Ah deep-cycle battery, charged between mows by an 11 W solar panel.
| Part | Size / spec | Qty | Unit cost |
|---|---|---|---|
| Used lawnmower | 1 mower | $5.00 | |
| Electric motor | Dayton 3/4HP, 12VDC, part #6ML04 | 1 motor | $312.00 ^[Motors of similar specs can be found around $60, bringing the final price to $447] |
| Solar panel | UniSolar 11 Watt | 1 panel | $120.00 |
| Charge controller | Morningstar SunGuard 4.5A, 12V | 1 controller | $39.00 |
| Voltmeter | 1 meter | $22.00 | |
| Ammeter | 1 meter | $16.00 | |
| Battery | Sun Xtender 40 AH | 1 battery | $90.00 |
| Misc. electrical | Wire, etc. | 1 set | $25.00 |
| Misc. hardware | Nuts & bolts | 1 set | $20.00 |
| Switch | 70A | 1 switch | $50.00 |
Required total: $699.00
With substitutions: $447.00
The donor mower before stripping
After searching various yard sales I found and bought this old lawnmower for $5.00. I was hoping to remove the internal combustion engine by loosening the bolts that attached it to the mower deck. No such luck. They were rusted to the deck so I spent a large amount of time cutting the deck with a rotary tool to allow the engine to be removed. I used some spray on paint remover to remove a majority of the red paint. Then I used a wire brush to remove all the rust. After that I sprayed the rust spots with a rust retardant to stop the rust from spreading.
What went wrong: The engine bolts were rusted solid to the deck, so removing the engine meant cutting the deck apart with a rotary tool — and then fabricating a patch for the hole it left.
Patching the deck
After stripping the mower and removing the engine I was left with a mower deck with a huge hole in it. I went to a local scrap yard and found a couple of small sheets of stainless steel about 1/16" thick. I then cut the steel to the proper size to cover the hole in the deck.
The motor before mounting
When mounting the motor to the mower deck the most important thing was to make sure it was centered and properly secured. I made sure it was centered by measuring an equal distance from the sides of the motor to the outside diameter of the mower. I secured the motor to the deck with four 3/8" bolts.
The fabricated blade mount
Unfortunately, when removing the old blade from the old mower I was unable to salvage the piece that attached the engine shaft to the mower blade. This meant that it was necessary to fabricate my own blade mount. I found a piece of metal rod about 3/4" in diameter in the scrap pile in the HSU metals lab.
What went wrong: The original blade-to-shaft coupler could not be salvaged, so the blade mount had to be machined from scrap rod.
Finished battery mount
Once the motor was mounted I needed to find a place for the battery to sit. The base of the motor was facing the rear of the mower and would provide a solid mounting surface for the battery mount.
Mower wiring diagram
The electrical was one of the more complicated parts of this project. I had originally thought it would be rather simple, just run some wires from the battery to the motor, add a switch and that would take care of it.
Background: I had originally thought the electrical would be rather simple — battery, motor, switch, done. It turned out to be one of the more complicated parts of the project.
Solar charging station
After the mower was assembled and ready to go I needed a way to charge it. I used an 11 Watt Uni-solar panel that plugs into the mower when not in use. This panel is made to charge a 12V battery at 0.62 amps in full sun. I screwed a couple 4' long 2x4s to three cross supports to serve as a mount for the panel.
| Measure | Value |
|---|---|
| Reserve capacity test | Run per manufacturer recommendation after the battery had gone unused for over 6 months |
| Fifteen minute mow test | Battery measured 12.5 V (about 90% capacity) prior to mowing, in wet grass |
| Charging station test | Rain prevented ideal conditions; a 2 amp battery charger was used instead |
Over all I really enjoyed completing this project. It was a lot of hard work but most things worth doing are. In retrospect there are only a few things I would change. First, I would find a mower that could be easily disassembled or at least able to be disassembled. This would save time and labor.