One Man's Adventures into Renewal Energy

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DIY Solar Powered Cordless Mower - Performance & Usage

26th July 2014


So here's the DIY Cordless Mower in action. This is the first full test of mowing both my front and back garden on a single charge.

The mower was taken out of the "Solar Shed" at around 10am in the morning. The time is significant because the battery would have been drained slightly by the previous nights use of my garden lights. And the "Solar Shed" batteries don't recover (by solar charging) from this use until early afternoon.
So I would estimate the mower had about 85% of full charge.

The total mow area is approx 80m²

The front garden posed more of a challenge for the mower because it has two weeks worth of growth and so needed about 5cm cut from its height.
The mower did bog down on a few occasions, but never stopped. I've slowed down the video at the bits where the mower struggled.
The grass was successfully mulched and close examination later revealed grass clippings around 1cm in length.

The back garden was easier for the mower as it only had a week's growth and needed about 2.5cm cutting.
The mower never bogged down.
The grass was successfully mulched.

The entire mow took about 10 minutes, which is approx twice as fast as with my plug in mower.
The battery went from 12.8 volts to 12.4 volts. Based on remaining battery capacity, I reckon I could have mowed twice the area I mowed.
The ESC and Motor were both warm after the mow. But neither would be considered hot.

2nd September 2014 - Motor Burn Out!

So I burnt out my motor!
Last week I decided to mow the lawn with my awesome cordless mower. After a perfect storm of issues, my motor got really hot and burnt out. I think I've melted the windings and/or demagnetized it.
So what actually happened?...
I could see as I was cutting the lawn that the motor was struggling. The RPMs were dropping and mower was reaching a point where it wasn't really cutting the grass. The blade was just pushing the grass downwards, but not cutting.
I could see the volts were dropping to less than 10.5 volts and the amps were reaching in the high 80s to 90s.
After mowing the front lawn, the motor was smoking, literally.
I took it off the grass and span it up, but the damage had already been done...the motor coughed, spluttered and died.

I got a little bit upset that I'd broken my mower, but decided to learn from it...read below...



DIY cordless mower brushless motor aluminium mount
First thing you'll notice is I've bought a new motor.
This is a N6364/09-KV230, for which I paid around £50.
It's slightly bigger and heavier than my old motor.
But the two critical points to note is that this motor can handle 800 watts more than my old motor, taking it near 3KW.
And it has a KV rating of 230, which means at 12volt it'll spin at approx 2760RPM, compared with my old KV200 motor that span at 2400RPM.
The extra power handling and RPMs, I hope, will make this motor more suitably matched to purpose.

You'll also notice I've replaced my old plyboard motor mount for an aluminium mount. Not only is this a lot stronger, but it'll also act as an heatsink, helping the motor stay cooler.


DIY cordless mower brushless motor heatsink
Here it is mounted up the mower.
You'll also notice I've installed an heatsink on the top of the motor. This heatsink is actually a computer processor heatsink I found in an old PC I had lying around.
The heatsink looks pretty cool, but crucially will provide significant cooling for the motor.

Initial testing of this new setup reveals some stark differences.
I've mowed both the front and the back garden and at no point did the motor get hot, in fact, it barely got above ambient temperature.
The mower, what with its faster spinning blade, now cuts the grass better.
All in all, some good improvements.







Next - Solar Lawn Mower Motor



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