You might want to check my other related thread on this. I made a real simple circuit to do the job. Main benefit is isolation meaning it eliminates ground loops and if the FC develops an electrical fault it won’t take your expensive mower drive module with it.
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I had an interesting experience with the Ryobi yesterday. I converted it to Lifepo4 and was using it to cut the grass in manual mode. After a while of cutting I noticed the blades wouldn’t stay running; they’d just start and stop a couple seconds later.
Batteries dead already? No, voltmeter says 53 volts.
I’ll spare you the long sorted troubleshooting details mainly because I’m too lazy to type them but the issue ended up being one of the motor phase wires developed a bad connection inside the molded connector! Very surprising. I was able to cut it open with a bandsaw and resolder it. It’s back to working fine again.
I am curious about the conversion over to Lifepo4 batteries. Wasn’t the original mower 56v? what combination of Lifepo4 batteries does it take? How much run time do you think you will get? The advantages of an electric mower are real, depending on your circumstances. You just have to mow more often and hopefully it’s more automated so it doesn’t take your time. I don’t have a Ryobi zero-turn, but I assume the original battery plugged in a battery socket. The new batteries must be connected differently?
The original mower was 48v. It’s a discontinued model. The lifepo4 batteries were simple replacements for the 4 12v original lead acid batteries. Pretty much plug and play, just standard screw terminals. The old charger won’t work though but no matter to me; I’m planning on connecting to a solar MPPT charge controller.
They weigh half as much and at 7.68kwh I can run a thousand watts for 7.5 hours. That’s a lot of mowing. Plus when automated it won’t be toting me around thus saving even more. I have noticed with even my gas mowers I use about half the gas due to less mower weight and more efficient cutting pattern.
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Do you know how many watts you’re drawing when mowing?
I have a 42" ride-on mower I converted to electric and the 2kwh battery gets me 20 minutes of mowing by my recollection. At times, the 48V motor draws 400A when you’re going through something tall (but it doesn’t slow down!)
For comparison, in my case, your 7kwh of battery is about an hour of my usage.
48v motor pulls 400a? That’s almost 20kw or about 25hp. Sure seems like a lot!
I think this ryobi has maybe 1kw motors a side at most. I do however plan on putting a power monitor on it to get real numbers .
My grass usually doesn’t get all that thick so hopefully won’t see numbers anywhere what you are seeing. Plus it won’t be toting me around which as I mentioned saves about half the power.
I believe the motor is officially rated 13hp, but can and will surge at times to much more.
What I found interesting - and why I bring it up - is that the amount of power I use to MOVE the tractor, is a rather small fraction of what the spinning blades of death draw.
For instance, I can plow snow for a week on one charge. Or drive all over creation. But once I engage the mower blades, run time is minutes and not hours.
Likewise my ardu-mower run time is substantially less once I hook my reel-mower up behind it.
Most of the people building mowers are converting their gas mowers - and even those adding electric propulsion are using gas powered mowing blades.
I would love to see 7hr run time for you, but I don’t think there’s a lot of collective information on just how much power those spinning blades chopping air and grass actually consume.
It is surprising.
I think you’ll still meet with good results, but I look forward to any good numbers you gather.
Thanks. As my mower has a 125a fuse from the factory they never anticipated it drawing close to that. That would correspond to at least 1.5 hrs of mowing time which I would find just great. I could parcel out the parcel into a few day’s missions. Frankly I don’t want to have to spend several hours at once watching it anyway.
The proof will be in the pudding as they say. I almost have the conversion done and will likely be testing it next week.
So I got it working today. I borrowed the unit I put together for my Ferris mower and did a little servo adjusting and hit GO. Here is a video of the first test:
I’m still awaiting the proper op amps which should clean up the controls quite a bit. This test used the knockoff MCP602 op amps Amazon sent. I could probably compensate for their non linearity via tuning but would prefer accurate control.
One thing I did is add an 8 channel relay board which allows me to completely enable or bypass the autopilot with one switch on the RC remote. This means when that switch is off - or the AP is not powered - the mower is operationally back to original. That’s super nice as I should be able to run a mowing mission then just flip the switch and do the trimming manually. And the electric mower is so much nicer to run then the gassers. Quieter, smoother, no stench and the controls are excellent.
Next stop is tuning and solar charging.
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Nice work. Good to see it in action.
Very much a matter of opinion 
Ha yes that it is.
I have an uncanny knack that, no matter how much I try, I get gasoline on myself whenever I refill a gas powered device. Every time!
Also I’m a southerner who is at risk of getting their card pulled as I am currently between pickup trucks and therefore have to transport gas cans in the back of the suv. That can get woozy too.
What part of the South? Alabama here.
Ocala Florida. Horse country with lots of huge grassy meadows.
no grassy meadows, but father has a sod farm…