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battery powered electric lawnmower help?
#1
Hi, new guy here,

trying to build a solar cell to battery to electric lawn mower setup.  I have a Black & Decker MM875 19" corded electric lawnmower. Cheapo Chinese power inverter that puts out 220v and a solar controller, a travel power adapter, the Amazon "25 Watts Monocrystalline Newpowa 12v Mono Solar Panel Module 20W < 25W < 30W Rv Marine Boat Off Grid by Newpowa " and a lot of left over 18650 laptop batteries.   

My hope is to end up with a lawn mower with a solar panel attached to it that charges a battery array that power the lawnmower through the inverter so can mow the lawn for about an hour once a week. or roughly there about.  Cost: panel $40, solar controller from China $10, inverter was $30, batteries = free, and mower $25 used.  Had the power adapter from my travels abroad.

If you got time and can point me towards some good advice, besides, "use the search function" (which i'm doing on my own), I would greatly appreciate it.

It's a poor mans pipe dream i know, but hey.  even if i cut half the lawn each week, i'll just leave it where it stops until it charges up for next week.  f-it.  free power!
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#2
(10-30-2018, 02:02 AM)MikeKanterakis Wrote: Hi, new guy here,

trying to build a solar cell to battery to electric lawn mower setup.  I have a Black & Decker MM875 19" corded electric lawnmower. Cheapo Chinese power inverter that puts out 220v and a solar controller, a travel power adapter, the Amazon "25 Watts Monocrystalline Newpowa 12v Mono Solar Panel Module 20W < 25W < 30W Rv Marine Boat Off Grid by Newpowa " and a lot of left over 18650 laptop batteries.   

My hope is to end up with a lawn mower with a solar panel attached to it that charges a battery array that power the lawnmower through the inverter so can mow the lawn for about an hour once a week. or roughly there about.  Cost: panel $40, solar controller from China $10, inverter was $30, batteries = free, and mower $25 used.  Had the power adapter from my travels abroad.

If you got time and can point me towards some good advice, besides, "use the search function" (which i'm doing on my own), I would greatly appreciate it.

It's a poor mans pipe dream i know, but hey.  even if i cut half the lawn each week, i'll just leave it where it stops until it charges up for next week.  f-it.  free power!
Trust me. Buy an extension cord or buy a battery electric lawn mower used and make your own battery. That black and decker motor  is probably 16 amps at 120 volts or 1900 watts you would need a 2.5 Kwh battery to run it for an hour. It would be heavy as all Fu** and you could buy a new electric Ryobi 40 volt battery lawnmower for what the conversion would cost. I'd go with the extension cord and use your battery stuff for another project.
MikeKanterakis likes this post
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#3
I get it. but the official sold at homedepot ones aren't all that heavy. i figured i could handled the extra weight of the panel and inverter. besides i like the self-contained aspect of it all.
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#4
Check the motor. You will probably find that it's a universal motor. It'll run on DC just as well as AC. If it has brushes, you should be able to run it on DC.

However, running on DC means you need to meet the voltage requirements. So with standard lithium cells that'd that be 29s or 30s (110V @ 3.7V cell nominal). You can run it at lower voltage, but it won't have the torque.

It is doable, just not as easily as most of the projects on this forum. Also, 110VDC is no joke. It can kill just as AC can. And DC is worse as it causes your muscles to latch, not spasm. So in this case, I would not recommend it. If you do do this, make two smaller packs that are 15s and they "only" become 110V when connected at the mower. And no wires can be touched. Also, you would need to change out the switch to a DC rated switch/relay to handle the arcing that will occur at those higher voltages.

For charging the batteries from solar, you really don't need a large solar array/panel. If you only use the mower once a week, then a smaller panel should be fine as it'll charge the batteries over the course of a few days. In this case, I'd charge the packs separately, so 2 charge controllers to charge each pack individually. But then you gotta hope they will charge equally.

The project is possible, but it does come with a lot of safety issues that must be taken into consideration. The other option is to replace the motor with a lower voltage unit so you can it on 48V. It'll pull more amps, but it'll be easier to do from a DIY perspective.

Btw, even the Ryobi 96V riding mower, uses several batteries. They are not connected together until they are plugged into the housing on the mower. Also, they are not charge "in" the mower as that would add a lot of excess cost and weight to the mower.
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#5
(10-30-2018, 02:49 AM)Korishan Wrote: Check the motor. You will probably find that it's a universal motor. It'll run on DC just as well as AC. If it has brushes, you should be able to run it on DC.

However, running on DC means you need to meet the voltage requirements. So with standard lithium cells that'd that be 29s or 30s (110V @ 3.7V cell nominal). You can run it at lower voltage, but it won't have the torque.

It is doable, just not as easily as most of the projects on this forum. Also, 110VDC is no joke. It can kill just as AC can. And DC is worse as it causes your muscles to latch, not spasm. So in this case, I would not recommend it. If you do do this, make two smaller packs that are 15s and they "only" become 110V when connected at the mower. And no wires can be touched. Also,  you would need to change out the switch to a DC rated switch/relay to handle the arcing that will occur at those higher voltages.

For charging the batteries from solar, you really don't need a large solar array/panel. If you only use the mower once a week, then a smaller panel should be fine as it'll charge the batteries over the course of a few days. In this case, I'd charge the packs separately, so 2 charge controllers to charge each pack individually. But then you gotta hope they will charge equally.

The project is possible, but it does come with a lot of safety issues that must be taken into consideration. The other option is to replace the motor with a lower voltage unit so you can it on 48V. It'll pull more amps, but it'll be easier to do from a DIY perspective.

Btw, even the Ryobi 96V riding mower, uses several batteries. They are not connected together until they are plugged into the housing on the mower. Also, they are not charge "in" the mower as that would add a lot of excess cost and weight to the mower.

A 30 watt 12 volt panel would take a month to charge a 2.5kWh 18650 based battery. You would need a contactor to engage the motor. If you replaced the motor with a 48 volt motor it would be mucho expensive. I looked at buying three of them for a lawn tractor project and it was going to be about $500 with shipping. It's not geared like a electric bike motor so it takes considerable amps and lots of copper to develop the torque required.  I paid $200 buck at Home Despot on sale for a 20" 40 volt Ryobi with a charger and a 5amp/hr battery for my Mom's lawn and it cuts well and bags well. I didn't want to have to load up my lawn tractor weekly. It's quiet and clean makes pushing a lawnmower a nice walk in the yard.  If you really want to DIY it, you could try to buy a replacement motor (and blade and nut) from one of the manufacturers.
Cheers
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