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Ryobi Zero-Turn Mower SLA to LiFePo4 Conversion - (Updated - Build Complete With Pics!)

Hi @UltrasoundJelly, that's awesome to hear there's more of us out there! Just to be clear, @AMDPower deserves all the credit here!

If you go with the single 48V battery, I bet you can just tie it down using a couple straps, and forget about the bolt. I think having it secured is a good idea. I know these batteries are shock tested but it seems prudent to prevent it from bouncing around.

Also, let me suggest another alternative to your overall plan: You could go with 4 12V series batteries and charge them using a 4-bank charger such as this one: https://lithiumhub.com/product/ionic-four-bank-charger/. You would loose the convenience of rigging the existing plug, but I bet you could come up with a relatively convenient way of charging, even if it means having to pop up the seat. Then again, that EG4 battery does seem very appealing.

Good luck and keep us posted!
 
Hi @UltrasoundJelly. Good luck with the conversion! I'm sure you will get MUCH better performance out of your LifePo4's. Check the specs on your "drop-in" batteries and make sure they support series to 48V. If they do, they normally recommend you parallel them for a certain period of time to balance before putting them into service. After which, charging with 48V will be fine. But do make sure their batteries support a 4-bank setup as I said. Also, I don't see why you can't still use the upper bracket assembly to hold them down. At worst, you might be able to put a couple plates or plywood in there if it doesn't grab in the right locations. You definitely need something to secure them from the top in my opinion or using another method to secure them somehow.
 
Oh... My bad. I just noticed those were 48V! I thought you were doing 4 12V batteries. I'm sure you can find another method of securing it.
 
How would a "hybrid" work out, a portable generator coming along for the ride?
Surely if a battery powered mower can't do the job then you'd just use a regular internal combustion motor mower? The energy losses of each step going from fuel to AC output to DC charge battery to drive motors...
 
Hi @UltrasoundJelly, that's awesome to hear there's more of us out there! Just to be clear, @AMDPower deserves all the credit here!

If you go with the single 48V battery, I bet you can just tie it down using a couple straps, and forget about the bolt. I think having it secured is a good idea. I know these batteries are shock tested but it seems prudent to prevent it from bouncing around.

Also, let me suggest another alternative to your overall plan: You could go with 4 12V series batteries and charge them using a 4-bank charger such as this one: https://lithiumhub.com/product/ionic-four-bank-charger/. You would loose the convenience of rigging the existing plug, but I bet you could come up with a relatively convenient way of charging, even if it means having to pop up the seat. Then again, that EG4 battery does seem very appealing.

Good luck and keep us posted!
@rio Thanks. Yes, I think I stumbled upon @Will Prowse 's infectious youtube channel a few years ago and really got excited about building a battery but I'm nervous about warranty and encasement issues. I'd considered 12v batteries with a x4 charger but couldn't find info on whether it's kosher to leave the batteries in series while being charged individually. (It would be obviously cumbersome to disconnect every battery once a week). Dakota Lithium customer service tells me to use 4 of their 12v batteries in series and charge them in series with their 48v charger, but that just doesn't seem correct. The weakest battery that disconnects first would limit the top charge voltage. Don't get me wrong, I think it's a great option given all the $360 drop in options available. Would be nice to not have to worry about mounting, as the size is exactly the same as the SLAs, but if I get 4 of those with your suggested charger I'm looking at $1800 right there. Getting mighty close to a single 48v 16s 100 Ah solution in price. And I think I trust the warranties on these 48v batteries much more than all the CHINS knockoffs. And the single plug receptacle is nice.

Re: warranties on these batteries I emailed Signature Solar to get more details re: if they would honor a warranty on a battery used in a mower, and if they paid for RMA shipping. The 11 year warranty on the Dakota seems to be industry best but you certainly pay for it, sheesh. They are might proud of their batteries. If I could just get one of their cases and build my own... I'm keeping an eye out for Black Friday deals.

@AMDPower Yeah, these are the 48v behemoths. I'm not 100% certain either of these batteries were available until maybe just this year. My wife has given me grief re: the pricing here, but she'd rather not pay $800 every 2 years for environmentally unfriendly lead boxes either.

I don't know, if you guys can help me find a suitable box that'll fit in this space maybe I'll go DIY...
 
@rio Thanks. Yes, I think I stumbled upon @Will Prowse 's infectious youtube channel a few years ago and really got excited about building a battery but I'm nervous about warranty and encasement issues. I'd considered 12v batteries with a x4 charger but couldn't find info on whether it's kosher to leave the batteries in series while being charged individually. (It would be obviously cumbersome to disconnect every battery once a week). Dakota Lithium customer service tells me to use 4 of their 12v batteries in series and charge them in series with their 48v charger, but that just doesn't seem correct. The weakest battery that disconnects first would limit the top charge voltage. Don't get me wrong, I think it's a great option given all the $360 drop in options available. Would be nice to not have to worry about mounting, as the size is exactly the same as the SLAs, but if I get 4 of those with your suggested charger I'm looking at $1800 right there. Getting mighty close to a single 48v 16s 100 Ah solution in price. And I think I trust the warranties on these 48v batteries much more than all the CHINS knockoffs. And the single plug receptacle is nice.

Re: warranties on these batteries I emailed Signature Solar to get more details re: if they would honor a warranty on a battery used in a mower, and if they paid for RMA shipping. The 11 year warranty on the Dakota seems to be industry best but you certainly pay for it, sheesh. They are might proud of their batteries. If I could just get one of their cases and build my own... I'm keeping an eye out for Black Friday deals.

@AMDPower Yeah, these are the 48v behemoths. I'm not 100% certain either of these batteries were available until maybe just this year. My wife has given me grief re: the pricing here, but she'd rather not pay $800 every 2 years for environmentally unfriendly lead boxes either.

I don't know, if you guys can help me find a suitable box that'll fit in this space maybe I'll go DIY...
My wife was not happy either! I was really worried about DIY but really glad I did in the end. I was able to do it for just over $1000 and with very good components. Not much more than lead-acid. If you don't want to use wood, you could use a plastic with L-brackets for the frame maybe. I'm pretty sure the plywood I used will last quite a while. Not like a cut grass in the rain or anything and it's stored in the shed.
 
OK, I've been in google hell trying to find boxes that'll work. If I can find a box I'll build a battery. I'm not quite sure why but I'm adversed to a wood box....

Is there room for 10.57" height?

Also found this case:
Main problem here is the 6.5" of inner height clearance. Might be tough to find cells that fit that.

Here's another one with 9.8" height:
 
My wife was not happy either!

I've read that older customers of classic-car restoration shops have multiple checking accounts ...

FINCEN said (of "Client #9") that structuring financial transactions to conceal them from your spouse is not a crime.
 
From the measurements I took the vertical clearance is just under 9". The inside of the tray footprint is 13 3/4 x 26 3/4.
I considered building the box out of 1/4" acrylic or polycarb instead of wood which would have been a bit pricier, but just as easy to make.
If you have access to a welder you could also build a box with sheet metal.
I briefly looked at pre made plastic boxes but gave up quickly. It seemed unlikely to find something that would satisfy all the constraints, especially the tray width.
 
From the measurements I took the vertical clearance is just under 9". The inside of the tray footprint is 13 3/4 x 26 3/4.
I considered building the box out of 1/4" acrylic or polycarb instead of wood which would have been a bit pricier, but just as easy to make.
If you have access to a welder you could also build a box with sheet metal.
I briefly looked at pre made plastic boxes but gave up quickly. It seemed unlikely to find something that would satisfy all the constraints, especially the tray width.
Ah yes, I kinda forgot about acrylic. I do have a laser cutter that can handle that size. Maybe that’s the way to go for a box.
 
My mower also had been losing mowing time for the past year. I found this thread and it inspired me to go ahead with putting a battery pack together with 16x 100 Ah cells and the overkill bms. I got the batteries from a us stocking warehouse, and the delivery and quality were excellent. The cells matched and top balanced perfectly. The battery cells are joined with foam tape, and the pack is held together with a frame of 13/16" steel strut. I used 1/2" plywood for the box, which, with 2 rows of 160mm cells, fits the width of the tray perfectly. Unfortunately, my mower crapped out before I could wring out the battery, and it's being repaired. Maybe next season.BatteryPackOpaque.pngBatteryPack.png
 
Nice, Jack. That looks great! Those are some serious drawings. I love the power distribution block coming through the box and how you are including the original tie-down clamp.

What happened to your mower?
 
My mower also had been losing mowing time for the past year. I found this thread and it inspired me to go ahead with putting a battery pack together with 16x 100 Ah cells and the overkill bms. I got the batteries from a us stocking warehouse, and the delivery and quality were excellent. The cells matched and top balanced perfectly. The battery cells are joined with foam tape, and the pack is held together with a frame of 13/16" steel strut. I used 1/2" plywood for the box, which, with 2 rows of 160mm cells, fits the width of the tray perfectly. Unfortunately, my mower crapped out before I could wring out the battery, and it's being repaired. Maybe next season.View attachment 73001View attachment 73002
Always amazes me at how talented people are. Are you a design engineer?
 
Nice, Jack. That looks great! Those are some serious drawings. I love the power distribution block coming through the box and how you are including the original tie-down clamp.

What happened to your mower?
The blade controllers, blade motors and the keyswitch all failed. Parts are backordered and are not expected until next year.
 
My mower also had been losing mowing time for the past year. I found this thread and it inspired me to go ahead with putting a battery pack together with 16x 100 Ah cells and the overkill bms. I got the batteries from a us stocking warehouse, and the delivery and quality were excellent. The cells matched and top balanced perfectly. The battery cells are joined with foam tape, and the pack is held together with a frame of 13/16" steel strut. I used 1/2" plywood for the box, which, with 2 rows of 160mm cells, fits the width of the tray perfectly. Unfortunately, my mower crapped out before I could wring out the battery, and it's being repaired. Maybe next season.

Hey @Jack Potredi Great design! Thinking about how I could replicate your build, I have a couple quick questions for you:
  • Is the strut steel secured to the box in any way?
  • Do the strut rods hold the batteries down?
  • Where did you source the strut/rods and hardware?
  • Is the battery box only being held on with the long middle bolt and frame sandwich, or are the struts secured to the bottom frame somehow?
 
Hey @Jack Potredi Great design! Thinking about how I could replicate your build, I have a couple quick questions for you:
  • Is the strut steel secured to the box in any way?
  • Do the strut rods hold the batteries down?
  • Where did you source the strut/rods and hardware?
  • Is the battery box only being held on with the long middle bolt and frame sandwich, or are the struts secured to the bottom frame somehow?

The frame is a stand alone support for the cells, separate from the box. The long rails are secured by the battery tray end clamps. The ends of the plywood box have cutouts to fit around the struts, and the box is just slightly shorter than the struts, so the clamping force from the tray goes only into the struts. The lid has a slot in it to accept the H bracket, which holds everything down.
When I assembled the battery pack, I taped together groups of 4 cells with foam tape. Then I taped groups of 2 together end to end. The cell groups were put on the frame, (after cutting grooves in the center plywood board to accept the thermistors from the bms.) I then clamped the cells firmly together and tightened the frame bolts and threaded rods. The cells are not really being held down by anything other than the foam tape and the compression.
Home depot sells the strut and threaded rod and nuts. A 10 foot section of each is enough for this build.
I got the bms with 24 inch leads, which allows the bms to be at the opposite end from the final battery connections.
 
Hello. New to the forum here and found this thread. 3 summers for my 480e has seen huge losses. I’m going to try the individual agm charging first but definitely have some money to burn on a lithium upgrade. I’m wondering, for those that have working models now, could you all post your BOMs? Several posts seems to indicate you might have tried this or that and it would be helpful to know exactly what parts you ended up putting into your machines. Part number or description or links to exact purchase would be awesome. Thanks for all of your work in this thread
 
So the charger does seem to work and I've added a wifi switch. However, I still disconnect it because the batteries seem to keep the charger powered up. There is also arcing that occurs when connecting the charger... not cool.

I found a better charger from AIMS, but it's pricey at $275-$300 so I haven't purchased it yet. Here's a spec sheet: https://www.aimscorp.net/documents/CON120AC3648VDC.pdf

Out of the box it seems to have the voltages that I would like with proper lower voltage float so this could remain connected 24/7 as long as your BMS has low temp cutoff(which mine does not have).

Current connected sell them here: https://www.currentconnected.com/product/aims-con/
@rio Did anyone go for this charger? Looking at the manual it does have a current adjustment knob 20-100% to avoid overloading the 14 AWG wiring.

I've been trying to figure out the best way to charge this guy for longevity. I just ordered 16 of the CALB 100 Ah cells. Planning to use the Overkill BMS to build this battery and to install a shunt monitor as well. I'd prefer to keep charger costs low, but I'm willing to spend maybe $300 to protect the investment if it is foolproof. Since I'm a novice when it comes to battery charging I'll summarize my thoughts and see if you guys find any flawed logic.
  • I will be using it weekly during the mowing season, then none at all for 4-5 months. I expect to use maybe 40-50% of the battery DOD on a single mow of my 1 acre very hilly lot. It will be kept in a heated shed over the winter.
  • It would be ideal to have a plug-it-in-and-forget-about-it setup, at least during the mowing season, and I don't mind some special winterization method once a year.
  • Leaving this battery at 100% will effect longevity, especially if left on a float charger that keeps it that way for long periods of time.
  • These batteries tend to lose charge unplugged over time, 3-10%/month would be expected. Does the shunt monitor trickle much charge?
  • Compared to AGM batteries, voltage does not correlate well to SOC because of LiFePo4's much flatter voltage profile.
  • It would be ideal to have a charger that has parameters to allow the battery to be charged to no higher than 80%, so my cycle would be 80→40→80→40 rather than 100→60→100→60.
I read that some plan to program their BMS to stop accepting charge at a certain voltage to attain a lower top-end charge but this isn't considered the ideal approach from the BMS manufacturer. Even given the flat voltage curve of these batteries, would a lower charge and float voltage from the charger itself allow this lower top-end SOC? Given that it's not great to keep the battery at a high SOC I'd considered using a simple outlet timer to prevent overcharging, but this introduces too many variables to be reliable (what if I don't mow the entire yard, how will ambient temp effect charge rate etc).

I do understand that most would just buy the lithium charger with the appropriate voltage and just leave it plugged in, but everyone here modding their mowers has already been burned at least once with failing batteries and promises unkept. I'm using up my spouse points to resuscitate this mower, and I want to do it right. Is there a simple solution to maximize battery life?
 
you have a week to recharge, and use it in the summer. How about PV panel(s) and an SCC? Set voltage high enough for BMS balancer to work, low enough to not charge battery too high.
 
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