Creating an Electric Weed Sprayer

We have the goal of being able to grow cherries without burning a single drop of fossil fuel however sometimes it's a bit tough to find the equipment that we need. Electrification is still in its infancy in an industry like horticulture and sometimes things just have not been created yet.

In our most recent case we could not find an easy solution for spraying the orchard's weeds. Our solution? Power an electric pump and boom off the batteries of our orchard cart.

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The cart draws power of six 8-volt lead acid batteries (the new carts have 48 lithium-ion) wired in serial to create an unorthodox 42v system, with the electric pump being a standard 12V pump that would normally be wired to a tractor or quad bike.  A simple off the shelf 15amp inverter from Mitre10, along with a trailer plug, allowed us to draw current from the cart batteries and operate the electric pump. While we were at it we added a Victron MPPT solar inverter (solar panel currently being shipped and will be apart of whole new blog post) and another 20amp inverter to operate some work lights for winter.

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Then we had to run a hose from the trailer to the boom under the cart chassis and a trailer plug wire from the battery array to the trailer to power the pump.

The hardest part of all was adapting an off-the-shelf spray boom to fit out cart and that required some careful consideration to cut the boom and re-weld parts of it to fit. We then had to mount it and that required a special bracket be devised strong enough to hold the weight of the boom and handle all the bumps out in the orchard.

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Luckly I met Eliot through the tech startup scene in Central Otago, and he now owns and operates a  water cutting operation called Wai Innovation in Wanaka. He could turn our messy white-board thoughts into a proper visual mock-up.

And the next day he cut the steel parts (40,000 psi water jet cut) with atomic accuracy so that we could mount the boom on the cart and finish our project.  

All the parts are currently off getting galvanised, and we look forward to using our new boom for the first time in May (after leaf fall) to knock these weeds back as they are getting out of control!

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It's encouraging we can check off another operational task as being fully electric with the cart being charged almost exclusively using the power generated from our solar array.

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