CubCadetLiPo3I decide to go the electric mower route about 5 years ago.  I was hesitant as the 12V lead-acid batteries most electric mowers come with suck – and they are heavy.  At that time, the only better technology was Lithium Ion battery-based mowers, but they were very expensive.  I decided on the CubCadet CC500, which was a good balance of quality and price. It was a 48 Volt lead-acid unit.

It only took 2 years for the batteries to waste away.  I was stuck between going back to gas, or replacing batteries.  Oddly, I let myself go somewhere in between by only replacing 2 of the batteries.  That only lasted a season and I soon found myself charging the batteries twice for each mow.  To add insult to injury, our new patio further reduced the cutting area – yet I still needed 2 chargers per cut!  I needed a solution…

After getting into RC quads, I realized the solution was right there in front of me with the Lithium Polymer batteries I’m using for my quads.  They are the perfect combination of power/weight and longevity.  After doing some math, I figured I needed approx 10000 mAh of juice which would give me about 40 minutes cut time (48V @ 550 Watt motor).  LiPo batteries can be expensive, so I decided to go low risk route and start with 2 x 22.2 Volt 5200 mAh batteries ($100 each).  This gave me ~45 Volts @ 5200 mAh (series connected) – which would give me ~20 minutes cut time.  Another bonus was that LiPo’s have a nice power to weight ratio, so I gained some significant weight savings with this new set-up. The CubCadet wiring design is straight forward, and I was able to hack the LiPo’s into it quickly while also maintaining the existing circuitry (i.e. the safety switch, overload fuse etc).

CubCadetLiPo4

Results:

The results are impressive.  After being on vacation for a week-and-a-half, the grass got pretty tall.   The new set-up cut through it with ease and power – even the denser damp grass.  I’ve got to do a few more cuts over the next few weeks to get more concrete results, but I don’t think I need to add more batteries (I had originally banked on about 10000 mAh).  This mod cost about $250 CAD in parts.  For many, this could be viewed as a waste since you can get a gas mower for that much. However, I expect to get a few hundred mows out of these batteries.  To me, the cost justifies the benefits (environmentally sound, quiet, lighter (than both gas and a lead-acid set-up), long lasting, faster charging, no pollution).  I figure I will get at least 5 seasons out of this.

Update:  I just completed another cut and the system performed great.  Batteries maintained good power through the entire cut with current bursts through the heavy parts.  I was even able to take the mower into the valley and clear a path through 4 foot weeds down to our garden.  When I was done, it still had plenty of juice.

Update Aug 22:  Very happy with the results.  I am averaging about 2 cuts per charge on the 5200 mAh set-up, so I don’t expect to be adding batteries as this works for me.

 

 

Sound Byte:

Some folks have asked for a video of the sound of the mower.   Given it was an electric mower when I started the mod, there is no real difference in switching over to LiPo’s.  Electric mowers are pretty quiet to start.  I can mow and have a conversation with someone no problem.   That said, here’s a video clip of the sound with some SPL numbers.  In short, it registered @ 120dB.  That’s pretty significant, but keep in mind the tablet was 1 ft way from the motor/blade.

Next step – Charge / Power Switching:

One of the challenges I knew would be a pain was charging the batteries.  I didn’t want to connect/disconnect the batteries each time I wanted to charge them.  The set-up is further complicated because in “power” mode, the batteries are in series.  In “charge” mode, they need to be in parallel.  I wanted a means where I didn’t have to remove any connections. Instead, I came up with the below switching circuit using a switch.    This would allow me to switch it between power and charging modes with ease.

The concept is pretty straight forward.  A DTDP switch is used to flip between charge and power (mowing) modes.  I also checked the circuit for potential shorts or fails should things be hooked up wrong (i.e. switch in power mode with charger plugged in) and it’s all good.

CubCadetLipoSchematic CubCadetLiPo_pcb CubCadetPowerChargeCircuit

Hardware:

22.2 Volt LiPo Battery 5000 mAh 30C   (You will need 2 batteries in series = 44.4 Volts)  (other options)

XT60 Series Battery Connection Cable

Tarot Para Board TL2716 Lipo Parallel Charger Board

6s Extension Cables

Double Pole Double Throw Switch

12 Gauge Wire

Various XT60 M/F connectors

Turnigy Mega 400W Charger

HobbyKing 350W Power Supply

You will also need a charger and charge power supply.  Something capable of pushing a lot of Amps.   For my set-up, I’m parallel charging at 10.4 Amps using the Parot parallel charging board.  You can look here, or check Hobbyking for their selection.

HKPwrSupply TurnigyCharger CubCadetLipoBattery CubCadetLipoChargingBoard

 

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