LiPoing a Ryobi 48v SLA lawnmower-- any advice welcome

[Jason Watkins]

Hi all,
I recently bought a used Ryobi 48v self-propelled lawnmower. The seller used it for about a year, then had to stop cutting his own grass due to an unrelated injury. These mowers have a notoriously awful SLA battery pack, and leaving it uncharged or half charged for several months probably didn't do it any good. I bought it with the intention of replacing the SLA batteries with lithium in the very near future, and the the time has come. The OEM replacement is over $140 after shipping and tax, and that's for a unit that won't last more than a couple of seasons.

I have no idea what power the motor is rated at, or how many whs the two 24v SLAs should have had. Can't find it anywhere online. But I figure at around 30wh per kg, 12.7 kg for the whole pack, they may have been around 381 wh brand new. I don't think they were anywhere near that by the time I got it, but it had enough power to barely manage on my >1/4 acre lawn.

I think ideally I would go with 2 or 4 packs of 7s1p 5000 mAh Zippy or Turnigy to get 51.8v, 250 or 500 wh. But the packs and a charger capable of more than 6s (not many to choose from) are out of my current budget. A123s would be even better but also more than I want to spend right now. Maybe in a couple of years.

So what I'm thinking about ordering now is two Turnigy 6s 20c 5000mAh packs ($43 ea) and a Turnigy Smart6 ($47) at HK. That's 222 wh for $166 (batteries, charger, ps), I lighten the mower by around 26 lbs, and I can go up to 4 packs later if I need. But I don't know how much my blade speed might suffer from being undervolted by 3.6v. :?

I know I'll have to buy a bunch of accessories too-- a couple of battery monitors, series harness, etc.-- but I've been wanting to get into LiPo technology for a while now anyway. Next up will be hacking my cordless tools' packs to ditch Nicad.

So I guess I'm looking for input on the undervolting problem and any tips for a LiPo newbie or any other solution I might have missed. Thanks!

 

[Hillhater]

dont worry about the "undervolt" issue,.. those lipos will be over 50v when fully charged and when under load will "sag" a lot less than the SLA's did.
So your mower will always have more volts available using the lipo than the old sla's.

PS:- i personally think you are very EV committed to be useing a cordless self propelled mower for a 1/4 acre grass ! :lol:

 

[Jason Watkins]

Thanks Hillhater. I've read a little about the sag difference between SLA and LiPo but I didn't know if it was of a magnitude to help me out.

"i personally think you are very EV committed to be useing a cordless self propelled mower for a 1/4 acre grass ! :lol: "

Thanks! :lol: I nursed a 20 year old Craftsman lawn mower my dad gave me for the last 12 years-- rebuilding carb, replacing fuel lines, tires, muffler, etc. When it finally lost enough compression to make it useless I checked Craigslist just thinking I'd get another gas guzzler. I've been an EV wannabe for a decade now so when I saw this mower I was hooked. Our yard is underlain by South Mississippi "Gumbo"-- nearly 100% silt that turns into goop every time it rains hard. So the lawn is so rutted and lumpy that it's 5x harder to mow with a push mower than our last house with 3x the lawn area in the Georgia clay. That self-propelled function is really nice to have.

The other thing I was thinking was that since it's so quiet I could put headlights on it and run it at night when the daytime temp here gets up around 100 F and 90% humidity. The last time I ran it my neighbor asked me what I was putting on the yard-- he thought it was a fertilizer spreader!

 

[dogman dan]

I say go for it with 12s too. I have a 24v electric mower I run on 6s lipo. Like you, 7s would be a bit nicer, but it works fine on 6s, even when the grass gets pretty thick. I have 1/3 acre, but only about 1/4 worth of lawn. I like to use at least 10ah pack so I keep the voltage up a bit, and don't get slow at the end of the mow. Later on last summer I went to 15 ah, and really eliminated sag on the thick parts of the lawn.

The B&D mower is so light, I feel like I'm pushing a baby buggy around the yard. So much better than a gas mower or sla mower!
So quiet, I can mow at 6 am with no problems with neighbors hearing it.

Get two 6s packs to try it out. If it's really too slow for the blade speed, you can still switch plans and go with 14s with some combination of 6s +2s or whatever. 6s runs the B&D 24v string trimmer really nice too.

Chances are, you will want at least 4 6s packs in the end. But you can definitely experiment with 5 ah first.

 

[Jason Watkins]

Packs, charger, etc are on their way. Hopefully these will do until I can add more cells. Another option for the future: the self-propelled feature seems to be driven off the main motor and it decreased blade speed quite a bit to engage it when the SLA were in there. I may try using a 12v car window motor or windshield wiper motor for driving the wheels and have it on a separate, 4s pack.

Dogman yours and others' comments in that 24v mower thread really helped when I was trying to size my system-- I stumbled across this site via Google bringing up that thread. Thanks!

Edit to add: Here's the link to that thread for anyone else who comes across my thread: http://endless-sphere.com/forums/viewtopic.php?f=1&t=27891&hilit=24v+lawn+mower

 

[wynchmprf]

HiJason,

How did this transformation work? Can you let me know some detail on how you did this-

thanks

wayne

 

[uaflyer]

I too am interested as to the result.

I am eye balling a Ryobi mower with a dead lead acid battery as well !
Does anyone know the MAH of the original Battery ?

I plan to mod it so it can use a cord or run on batteries as I had seen a model (forget which) that could do that.

 

[veloman]

I have this mower (dead lead acid) and run it on 13s 5ah lipo. Gives about 15-20min run time in average grass. Love the lightweight!

Btw I dragged this mower 20miles home, from a free Craigslist posting one night. That was an adventure with the ebike!

 

[mattdcox]

I know this tread is super old, wondering if was worth LiPoing the Ryobi, or if I should not bother?

Thanks.
Matt

 

[dogman dan]

Absolutely worth it. I'm still using my older, worn out lipo packs to run my 24v mower. I've gone to 7s at all times now, and still run a 10 ah pack so I have good voltage the whole mow, and don't run out too quick.

Similar run time, to the newer lithium mowers, that have 48v 4ah batteries. On paper my battery is more wh, but since they are old, I likely have less than 100 watt hours.

 

[Onecaribou]

I'm running the same mower with 2x6s 5Ah packs and I'm very happy with it. Perfect for my smaller yard.

My thread:
http://endless-sphere.com/forums/viewtopic.php?f=1&t=68788

Thanks for the inspiration dogman dan!

 

[dmwahl]

I know it's an old thread, but I put together a 20Ah 24V LiFePO4 pack from some old and abused headway cells and it runs my 24V Black and Decker (CMM1200) mower like it's new. Much better power and range than the lead pack and I can even use the original charger to get it almost fully charged (to about 3.45V/cell). I mow a 1/4 acre lot and use about 13Ah.

 

[wineboyrider]

Dogman wrote:Similar run time, to the newer lithium mowers, that have 48v 4ah batteries. On paper my battery is more wh, but since they are old, I likely have less than 100 watt hours.

I get a solid 40 min run time if the grass isn't thick and I suspect it's because my Greenworks 40v is a bldc motor and it has a controller and only revs up when it feels a need to. I cut my entire .5 acre yard with 2 batteries no problem and I swap the batteries in my trimmer for gas free yard work.

 

[Sage222]

Anyone looked at lipo for the 48v Ride On Ryobi??

 

[Ryobi Rob]

"Anyone looked at lipo for the 48v Ride On Ryobi??"

I am very interested in converting a 3 year old Ryobi ztr480ex. I love the mower, really dislike the sla batteries. The sla batteries are now only lasting about 20 mins. before shutting down the blades. We have meticulously recharged the batteries after 50% draw down and always kept the unit on the charger at all times... still only about 3 years of battery life.

I am wondering if I could simply just replace the current 48 volt 100 ah batteries with the same form factor in lfp's?? Would the current controller in the mower recognize the lfp batteries and run? Not really familiar with the electrical system on this mower, specifically related to swapping out sla's with lfp's. I know the charge limits (high/low/temperature constraints) are different, so would likely have to get a 48v lfp dedicated charger. Just not sure if the mower will run if I simply replace with the lip's. Anyone have any recommendations or experience in attempting this swap?

 

[wineboyrider]

"Anyone looked at lipo for the 48v Ride On Ryobi??"

I am very interested in converting a 3 year old Ryobi ztr480ex. I love the mower, really dislike the sla batteries. The sla batteries are now only lasting about 20 mins. before shutting down the blades. We have meticulously recharged the batteries after 50% draw down and always kept the unit on the charger at all times... still only about 3 years of battery life.

I am wondering if I could simply just replace the current 48 volt 100 ah batteries with the same form factor in lfp's?? Would the current controller in the mower recognize the lfp batteries and run? Not really familiar with the electrical system on this mower, specifically related to swapping out sla's with lfp's. I know the charge limits (high/low/temperature constraints) are different, so would likely have to get a 48v lfp dedicated charger. Just not sure if the mower will run if I simply replace with the lip's. Anyone have any recommendations or experience in attempting this swap?

Lifepo4 is closest to SLA voltages.
Check for type of motor (brushless or brushed)
New Charger for lithium.
Battery meter?
Probably would be easy to do.