Trolling the CraigsList “free” section as I do, I’ve found a handful of older, non-functional tools like tillers, lawnmowers and snowblowers. Most of them have problems with the gas motor – either they just need a cleanout or a tuneup, or they need major surgery. They’re perfect candidates for an electric conversion.
Assuming your garden is within 100′ or so of a power outlet, this tiller is going to make a perfect corded electric conversion. It’s a belt-drive tiller, so, essentially, all we need to do is to pull the old motor off, fashion a motor mount for the electric replacement, mount a v-belt pulley on it and we’re in business. With any luck, you may be able to repair and sell the gas motor, or take it to a salvage yard and get a few bucks for it.
Deciding on the specs for the electric motor is really the trick. Gas motor horsepower ratings are based on peak output, because gas motors run at their best at very narrow RPM bands. That is, a motor may have little or no power at low RPM, then gradually build up to the power band. If you rev the motor higher than the power band, the output drops off dramatically, as the mechanical reciprocating engine starts to beat itself up. Valves float, rings heat up, like that. That, by the way, is why you need a transmission in a vehicle, so you can run the motor at the optimum RPM most of the time. The best way to get a grip on the horsepower is to see what the output looks like at the power band.
An electric motor rating is a continuous output rating, so it initially looks a lot lower. It’s pretty difficult to cross-reference ratings, since the power characteristics of gas and electric are so different – electric motors will draw as much power as they need to keep from stalling, until the circuit feeding it overloads – melting internal wires – unless you build in some protection or limiting mechanism. The general rule of thumb, though, is that if you multiply the horsepower of an electric times 3 – 5, you’ll get an equivalent output to gas, assuming the load characteristics are similar. For example, if that tiller up there is running a 5hp engine, I can probably put in a general-purpose AC motor rated around 1hp to 1.5hp, and it will do just fine.
What do I mean by “load characteristics”? Simply, the type of load you’re putting on the motor. A lawnmower is a perfect application for an electric motor. Electric motors like to spin up, and hum along at a constant load, drawing more if they need it, spinning idly away if they don’t. A log splitter, on a hydraulic system is also a great application for electric – the motor is coupled to a pump, it’s job is to keep the pressure up, it gets additional load when you’re splitting a log, but it’s gradual and even.
A chipper, on the other hand, is a little more problematic. The chipper is humming away, chomping up leaves and sticks, and then it gets a nice beefy 2″ branch. Although I’ve never stalled my 10hp chipper, that’s putting a big load on a motor, and is something you’ve got to take into account when replacing that with an electric. That’s a case where the biggest motor I can find is going into the machine- maybe 2 – 5hp, with an hefty circuit breaker.
And this brings me to controls… you don’t need a motor speed control, it can simply be an on/off switch like most electric motor-driven tools. You do want to wire in some sort of circuit protection, though, so if the machine bogs down, the increased draw on the current won’t pop your house breakers, you can let it cool and reset it right at the tool. Most emergency power switches available for workshop tools will work great, and are available at homegoods stores.
All told, the electric tiller project looks like a great application for an electric conversion. Avoiding the cord with the tiller tines is a piece of cake, running a clean machine, and a quiet machine to turn your soil will keep gas, oil and emissions away from your soil and plants. Imagine, too, being able to just plug in and flip a switch to use it – no gas, no oil, no cursing and pulling ropes, no trips to the shop for tuneups on a machine you use only a few days a year…
Want to read more about electric gardening? Check out all the posts: The Electric Gardener: Part One, The Electric Gardener: Converting the Tiller, and The Electric Gardener: The Solar Charge, and The Electric Gardener- Sunday Morning Chain Saws.