# Solar lawn mower

this Instructable will show you how to mow you're grass using solar power to charge the mowers batteries

## Step 1: What you'll need

-battery operated lawn mower
-12 volt solar cell
-wire (red and black)
-multi meter
-multi tool (I used my leatherman)
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drumdude4 years ago
dang, when I saw the picture I thought it was a TV on the lawnmower! haha
4 years ago
Im glad im not the only one!
INDUCTION_MIND7 years ago
Great Instructable!!!! I do have a few questions, hopfully it is not in the comments below but; how long does the battery supposing it is fully charged support mowing? How long can a fully charged battery by any means cut what square meter or square foot of grass, how high, and how long? My family has many acres, my parents have about 4 acres(my father cuts). It would be interesting to mount more batteries on this unit, how many can it support? I wonder how much for a riding mower, and how much energy it would require? since the mower is moving at low speed I suppose weight does not have much of an effect. what horsepower is the lawn mower you are using? Again great job -Inductionmind
5 years ago
NOTE your questions do not really apply to his instructable. assume you ALREADY have an electric battery mower. Does it work for you now? this does not change that. It just changes WHAT charges the batteries. I have a battery electric mower. IT DOES have enough charge to cut my lawn. (unless its wet then it will only do about 75% of the yard :-) with that established all this does it use a solar panel to recharge instead of my wall outlet. SO determine if a battery electric mower WILL work for you IF YES then you can do this mod. if not then its not relevant since you won't be using a batteriy powered mower anyway.
4 years ago
Wow... sure my questions apply, it is simple mathematics.
Using push mower with a dc motor of (T)hp, a blade length of (U) a battery with (W) amount of joules is able to cut X meters of grass of w\ length by Y density =Y. all that has to be entered is the variables, and we can make good predictions of the area that could be mowed assuming the batteries are fully charged and the grass is as wet as the control condition, lets assume dry.
somebullcrap (author)  INDUCTION_MIND7 years ago
as it is now it will cut grass a thats about 4-5 inches tall on the muclh setting for about 30 minutes .in about a 20 by 30 foot lawn (my front yard) .and as for mounting more batteries on it .I'd not do that unless you were going to go the riding mower route .as is stands now it weighs more then a regular gas powered push mower and isn't to easy to push .especially in the higher grass
5 years ago
Hmmm,,, Electric Solar Powered Riding Mower,,, Bigger, multiple motors,  More batteries, larger solar panel.... Interesting....
wogga4 years ago
@sbc (author):
You do know the amperage of a solar panel if you know the wattage and what kind of battery it was designed to charge. A 12v panel in the full sun will probably charge at about 16 volts. WATTS = VOLTS x AMPS, so 5watts = 16volts x AMPS. Solving for AMPS, you get about .3 or .35 amps from a 5 watt solar panel.

I'd recommend DIYers look at the voltage that goes into their mower from the wall AC adapter. If the adapter says DC out - something like 26 or up to 30v DC out, then you can simply put 2 '12v' solar panels together in series to double their voltage. (Think of how you put two AA batteries together to get 3 volts.) Then find the adapter plug that is identifcal to the one on your AC adapter and attach that to your solar panels. The molex.com website is very helpful in tracking down the odd adapter plugs used by Black and Decker and will let you order one free!

I'd also recommend when shopping for a used mower to start this project that you choose a single battery (12v) model. It removes the need to put the panels in series. I have a black and decker single battery model and have had a 5 watt panel (now 10w by connecting 2 identical panels in parallel to increase the wattage without changing the voltage) charging my mower for 3 years winter and summer. After buying the molex connector, I just plug the panels into the female receptacle in the exterior of the Black and Decker mower. It handles the power maintenance, though my panels both DO have blocking diodes to prevent power going the wrong way - if the mower doesn't do that itself.

In my case I was lucky. The battery is a 26amp hour battery and will run for about 50 minutes and was in great shape 3 years ago - and is still in 'okay' shape now. You should keep your lead acid based batteries on trickle/solar charge all the time, rather than charging them up and storing them till use. Also, try not to use up all of the charge ever - the battery will last a bit longer. Any body have any good 'This mower runs on SOLAR" stickers?!
cobaltxxxfusion7 years ago
I think most the comments were very constructive regarding this instructable. We need more of such maturity on this website. I was once told, "Those who do not fail are not trying hard enough". This by no means is a failure, I think it is great. It is great when someone has the courage to make an Instructable and others are helpful with suggestions and it continues to be "tuned". I will throw my two cents in as a trained horticulturist. As far as mowing, the average homeowner mows once a week, perhaps twice during peak growth, dependent on irrigation and season. (Allow the ignorant to dream) What if this idea could be combined with some others such as low power/high torque motors for propelling the mower? Removal of the solar panel(s) making a charging station. Combine that with the tech used in such as the "robot vacuums" or "invisible fence". I dream more, when the electric power reaches a near depleted level the "mowing unit" if you will, returns to the charging station until recharged yet only mows during a set time period. Finally, what if the charging station had a rain sensor as well as the mower. If it is raining it does not mow during the set times or if it starts it goes back to the station. IF these techs could be combined in one unit you would have a "robotic mower". I do not have the skill nor tech knowledge. I am just casting out an idea. Please be kind in your comments.
7 years ago
I'm dreaming of this too. I hate mowing my lawn!!

I've been tinkering for a while with the Arduino microcontrollers which will serve nicely as a 'brain'. I've also just started out with stepper motors coupled via an EasyDriver stepper driver, which as the name suggests, is VERY easy to hook up.

It'll likely be less of a mower, more of a 'grazer' I think. ;)
[m]
7 years ago
Beardy, Exactly, "Grazer" is the concept I was trying to explain. A solar powered robotic mwer that does not mow the whole lawn at once but continually grazes maitaining the grass continuously. The effect would be the grass never grow over the set mowing height, never giving that "needs to be mowed" look. I wish you luck and would love to hear about your progress.
5 years ago
I want to make something like this sooo badly but it would be stolen in days around here :-(
4 years ago
5 years ago
hey cobaltxxxfusion! It's been a while and the desire to build a lawn grazer hasn't gone away. Happily, I recently started teach electronics to a couple of teen boys at a local private school. They've really grabbed hold of my suggestion to build a robo-mower ;) so we're on our way. There's nothing to show for it yet - we're still exploring the design considerations - but I'll post something somewhere as we go. kr
7 years ago
yeah I think they do have them I seen it on a segment on a discovery science show can't remember the shows name but the segment was called tech toys it uses a magnetic wire to know where not to mo and has an alarm if someone tries to steal it its pretty cool Aaron
lar27 years ago
This looks like a great idea! Pretty cool for a first Instructable. Mowing later in the evening allows a full day for charging. You mentioned cutting up "the Cigarette lighter plug". It wasn't mentioned in your first step. Was it something else someone needs before this is attempted?
5 years ago
Something that was overlooked about that lighter plug was that there is a diode inside it to prevent the battery from discharging into the solar cell. When there's plenty of light out, the PV cell is making electricity and charging the battery. When it gets dark, what do you think happens? The battery has greater potential so it discharges into the solar cell. Using 2 of these (usually on sale at harbor freight for \$20), one for each battery and with diodes installed to isolate the batteries from each other should make it so you just store the thing in the sun and it's ready to use any time you need it.
somebullcrap (author)  lar27 years ago
no .just how it came from the factory
I was thinking about doing something similar to this with my mower, but it seems someone beat me to it.
5 years ago
Don't let that stop you!
saites20017 years ago
This could stand to get a few more details, but it's a very cool project. I wish someone would post a guide on converting a gas mower to an electric solar powered mower. Nice project, man.
5 years ago
you don't you buy an electric mower and go from their :-) it would be crazy costly to "convert" a gas mower to gas. in fact you can't you would have to remove the gas engine and simple use the mower deck to MOUNT your electric motor and batteries too. I guess if you already have all the bits this makes sense but for those who don't just hit craigslist and get a cordless mower.
7 years ago
do you know that you can convert a car that runs on gasoline to run on natural gas? maybe someone comes up with a mower that runs on natural gas. it will only bee convenient if natural gas is cheaper that gasoline and you will get about the same horse power as gasoline. to fill the natural gas tank from the mover you can make a device to hook up to your gas outlet from behind the stove and on to your natural gas tank.
7 years ago
I just came back from Brazil where everyone is outfitting their cars with Natural Gas kits and just about every gas station has a natural gas pump as well. It's entirely possible... Brazil's ahead of the curve.
Mr. Rig It7 years ago
This could use more information in it. Like, how long will it run for? How long does it take to charge? What keeps it from over charging? How thick of grass will it cut? etc You are on the right track though, keep going.
5 years ago
Answers - Run time irrelevant determined by what mower you buy (he did not make a solar battery powered motor he bought a STOCK battery electric motor with its specifications from the manufacturer and ADDED what is simply a solar charger.

Time to charge depends on size of panel size of battery depth of discharge and available sunlight. HE is in texas he gets a lot more sun than for example ME in pennsylvania.

Assuming FULL depletion 3 weeks to recharge the batteries in PA 1 week in Texas. I assume he does NOT use 100% of the batt cap to cut his grass so probably 4-6 days to recharge which is fine since I assume he does it once a week.

Overcharging. he is only putting in 2.5 watts AT PEAK (sun directly overhead) at that charge rate its a virtual FLOAT charge and he has almost zero need to be concerned about over charging.

ask the manufacturer about how thick the grass it will cut he did not design or build the mower :-)

IF you can find a battery electric mower that WILL meet your demands what you do is GET that mower and then use his instructable to convert to solar charging.
willyb217 years ago
Anyone have a DIY to change a Corded Mower to Battery or Solar? Thanks
5 years ago
yeah hit craigslist and get a cordless mower. Worst case you get a dead one cheap and put 2 car batteries in it.
7 years ago
Besides the obvious method? That would be mounting a battery and an inverter (properly sized) to the mower base and plugging the mower into the inverter, then it's just mounting a 12V panel on top that's wired to the battery connections, with charge regulation as needed. For a fan cooled inverter you'd need filtering over the air intake. I'd go Project 2 route, make a portable panel/battery/inverter unit for go-anywhere power (battery in battery box with the rest mounted to the box), and construct a parking place for it on the mower, strap down, plug in, attack weeds. Otherwise, you'd be talking about needing a different motor, one working at battery voltage, and figure in cost, hassle, mechanical and maybe metal fabrication skills needed for the changeover... Plus minor safety concerns with spinning large chunks of sharp edged steel... Hey, that portable solar power station sure seems a good place to start!
7 years ago
Cool thanks I just bought the mower and this was just to get a rough idea on the difficulty in changing over. I will be waiting a while but will continue to research. thanks again forgesmith.
portablestew7 years ago
as the batteries begin to grow old, that charging method might drastically reduce their life. even though the batteries are of the same type, they are not EXACTLY alike. the difference in their capacity usually grows more pronounced with age. so because they are normally in series, their discharge rate might be slightly different ... and when you connect them in parallel, the batteries might rapidly charge/discharge one another for a moment. gel cells dont really like that. that said, the extra wear is overall probably not a big deal, but it is something for you to consider. personally i would have gotten 2 smaller solar panels to put in series so that both batteries can always be trickle charging safely.
5 years ago
at the 2.5 watts he is charging at he will not harm them even as they get older. INFACT his very very slow charge rate and LOW usage (30 minutes means he is likely only using maybe half the battery capacity) should greatly extend the life of the batteries.

Deep Discharging and Fast Recharging are what kills leads.
7 years ago
gel cells are nothing more than lead acid batteries with a gel electrolyte instead of a liquid. In my experience they are very robust and take a real beating and keep going. What is being done with the charge circuit is probably not going to cause a problem.
marjorieallea6 years ago
Where did you get that cute pink lawnmower from anyway?
somebullcrap (author)  marjorieallea6 years ago
well it started off red but was faded by the brutal texas summer sun .and my dad got on on sale at one of the home improvement stores
5 years ago
ahhhhh texas. THAT is why that 5 watt panel works so well for you.

up here in PA even 4 of those might not recharge me in a week :-) hehe

No theft issues? I can't leave mine out it would be stolen inside a few days. hence I will mount my panels on the garage roof and wire inside to charge the mower.

Great job on the instructable I hope to see more from you!
HarveyH446 years ago
I'm in need of a new mower, and have been considering a battery powered one. Not much grass, usually mostly weeds. :) They are kind of expensive, and not real thrilled with the reviews. Will probably take the plunge sometime this month. Most seem to be 24 volts, so will use 2 solar panels in series. Will also use a charge controller, as batteries are expensive to replace. With the charge controller, you can leave the panels hooked up between mowings (week/months), and the batteries won't overcharge. Pretty easy to do in Florida. A robot mower would be awesome, but would still think it necessary to supervise, might get stuck, fallen tree limb, beer bottle over the fence, neighbor's cat... Also, if you don't have a fenced in yard, it's bound to attract attention and admirers. Would think it kind of dangerous for toddlers, and old men...
5 years ago
at the 5 watts he is charging at (2.5 watts since he is charging TWO batteries) he does not need a charge controller. its virtually a float charger.

if you use more panels say 15 watt panel per battery then a charge controller would be advised.

DO NOT buy new. Get a used one for a fraction of the new cost. Your recycling and lose less if you don't like it or it does not work out well for you.

BE WARNED batteries for these things are NOT CHEAP and every 2-5 years depending on your usage and care you will be replacing them.
rcmaniac107 years ago
you should add a switch to switch between charging mode and cutting mode. you wont have to re wire every thing every time. Ill make a schematic and post the image here... right now I can't because this computer has no photoshop. Another thing you can do is throw out the 2 batteries get another 12 volt solar cell put the 2 12 volt solar cells in series to get 24 volts and cut the grass on a sunny day without waiting for the batteries to charge.
7 years ago
Wait a minute is the motor ac or dc? if its ac you can't put the 2 solar panels in series because they give of energy in dc unless you get a circuit to change 12 volts dc to 12 volts ac.
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