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

Hedges · Oct 23, 2021

Amazing!
They actually market it as "PWM"?
Usually we see that exact model sold under "MPPT" brand.

Cheap PWM charge controller. If you don't care about harvesting maximum power, it could work.
If it fails (not too badly, not excessive voltage), your BMS will protect the batteries.
There is a thread about what happens when SCC fails with FETs shorted so PV voltage is applied to BMS. More of a problem with high voltage string of MPPT.
I would say use this SCC only if maximum PV Voc on a cold day is within the voltage BMS can hold off in the event it disconnects.

Better to buy a higher quality PWM. Midnight carries the "BRAT", for instance.
Or a quality MPPT.

Look for one you can program to desired charge current. Then you can over-panel, limit current to what LiFePO4 can accept at whatever temperature BMS is set at for low-temperature disconnect. Repurpose the SCC or another application in the future.

AMDPower · Oct 23, 2021

Hmm.. How about this one? Also, would I need to have 48V wired in series for the panels? Could the panel voltage be less and then the MPPT would boost for charging? I'm not 100% sure how this all works and am just putting together information. I plan on putting up to 4 panels on the roof of the shed, running a ground rod behind the shed for all the panels and charge controller. But them I'm confused on what I should use for breaker, disconnect, etc. Do I need that? Just want to make sure it is safe and works well. Thanks.

Amazon.com

Hedges · Oct 23, 2021

Could be good, not familiar with the model.
Can you find the data sheet or manual? PV array has to be designed to fit within its limits.

Only a few SCC are "Boost" or "Buck-Boost" converters. Most are only "Buck", PV Vmp should be higher than max battery charge voltage. Some only need 2V headroom, some need 5V.

SanTan has several.

From what I've read, Victron is good. Epever is cheap, sometimes have functional issues and need to be reset. Fangpuson I think was a knock-off brand that copies appearance (and maybe more) of name brands.

Charge Controllers | SanTan Solar

store.santansolar.com

Midnight is highly regarded.
They have four series - Classic, Brat, DIY, KID
The DIY is a rebranded + customized Chinese brand. Midnight says they've tested and done a lot to ensure it is the quality they want to deliver. But at least one forum member reported a failure and returned, gave up on it.

Category Products - MidNite Solar's

MidNite Solar Category Products.

www.midnitesolar.com

Something I like about Victron is it can use a battery shunt and monitor to regulate battery current, while delivering additional current if consumed by other loads.
Midnight I think has indicated the Classic together with Wiz Bang Jr. can do the same (but I couldn't find manual references to battery current being used for anything other than reporting status.)

Of course, price point of those features may not match what you want today. So maybe a smaller reliable SCC is good enough.

Buff · Oct 24, 2021

Hi! I've been following this thread for a while now because I have wanted to convert my Ryobi non-zero turn riding mower to LiFePO4 and this is the best information I have found on doing that. Thanks @AMDPower! I am still on the original AGM batteries but only have about 40 hours on the mower because my yard is not huge. The batteries seem to be holding up fine even after 4 seasons so it is hard to make the switch.

I switched to charging them with solar this year and it feels like it has given the old AGMs even more life! I think the charger that comes with the mower is garbage. I have four 50 watt Renogy panels wired in series into a Victron SmartSolar 100/20 48V charge controller and it works great. I bought an EZGO charger plug that I plug in the mower to charge, just had to modify it a bit. You could very well re-use the one on the stock charger.

The Victron charge controller has capacitors so I was getting an arc when I plugged it in. To suppress this, I wired in a resistor on a dual source battery disconnect switch. So 1 is through the resistor, 2 is the mower/battery. I used a write up on here from FilterGuy I believe for the info.

The Victron MPPT requires Vbat + 5V for the controller to start so you need 3-4 panels unless you go with a boost controller from another brand. I think Renogy has one but I wanted a Victron because of their reputation.

Here are some pics of my setup. I also did the battery gauge upgrade from previous posts. So much better but I did a terrible job making the hole bigger. Oh well...

AMDPower · Oct 24, 2021

Thanks for that info! I think I’m gonna get 4 100W HQST panels and do the same thing. Is that DC isolator just a disconnect? Do you find the 50W panels are enough? I already have my old cable in an electrical box so it should be a clean swap of the solar controller for the charger. Also, is that Tesla charger in your shed or is that a garage?! Have a M3 myself and love it.

Buff · Oct 24, 2021

No problem! Yes, it is supposed to be a quick switching action as to suppress the arc from the solar panels when switched on/off. I use it to turn off the solar before I disconnect the SCC from the mower because your not supposed to have solar coming in to the SCC when it's disconnected from the battery. Here is the link to the one I got https://www.factorymation.com/SI16-PEL64R-2.

The 50W panels are enough for me as I only have about 1/3 of an acre to mow. Push mowing was just taking too much time. I calculated I use about 550-600 wh to mow the whole yard so I didn't need a bunch of solar and I wanted to keep the array as small as possible. I can charge it to float in about 4 hours if I have the panels in full sun. Worst case it would take 3ish days to fully charge and I don't mow that often.

This is all in my garage along with my M3. I love the car also. Right now I just have my panels set up on my patio. I need to find a good place to put them but my yard is pretty shaded and I am still hesitant to put them on the garage roof where there is more sun.

I was looking at HQST and almost went with them but Renogy ran a sale on ebay and their 50W panel was a bit smaller than the HQSTs. Both are good panels from what I have read.

AMDPower · Oct 24, 2021

Yeah, I’ve got the same problem with shade where my shed is. It’s a flat-ish pitch and peaks west-east. I figure with 2 panels on each side at 100w I should be able to get a full charge in a week. I figured around 1500 Wh myself with 1.25 acres. Think I’m gonna actually do this now but not sure if I’ll do it before winter. Will be fun!

rio · Oct 26, 2021

Just finished my conversion! Everything seems to be working fine, but it's raining a lot here in the NE so I haven't actually mowed yet. But I tested it in the garage briefly. I installed the battery monitor and connected its power wire to the switched terminal in the ignition switch, so that the monitor turns on only when the key is on (little red wire coming out of the box). Everything works as it should and it's really cool to see the current on the meter in real time!

I assembled the pack with 1/8" foam sheets in between cells. After the 6th row I added a 5/8" spacer made out of square dowels with a tube in the center which leads directly to the main tray thread, to act as a guide and guard to the long bolt (I had to purchase a shorter one since the box is shorter than the original battery frame). Then at the very front put in a square frame made from 2x2 squeezed in by a couple short 2x4 pieces... this provides very light pressure against the whole pack mostly just so it doesn't shift around. Also added 2 rails of 2x2 to the inside of the lid to act as a clamp down. I meant to line them with foam sheets but forgot... I'll get back in there after a couple mows.

Not super proud of the rats nest near the BMS... I kept the original wire lengths for all the cell monitors and managing the wires in there was a bit more annoying than I thought. I'll clean that up in the future by cutting each cell monitor wire to length and re-crimping ring terminals.

@AMDPower, thanks again for lighting this fire! You're my hero :D. Any thoughts and suggestions are much welcome.

I still don't have a new charger. I'm tempted to just keep using the Delta-Q TBH. It will never go above 58.4V and I feel good about relying on the BMS to cut the charging at the cell and pack voltage of my choosing. Especially with the low number of charge cycles per year, I can't imagine this being such a bad option. But maybe I'm way wrong.

AMDPower · Oct 27, 2021

@rio Nice man! I really like how you segmented that box and used a guide for the center bolt. Does the shunt setup maintain it's settings/readings when you completely cut power with the key switch? If so, I might have to do the same. Let us know how the mow goes!

rio · Oct 27, 2021

Thanks. Yes, it maintains the settings and remembers the remaining capacity. One thing I just realized though is that without power, it will not monitor the current when the batteries are charging. So I will have to remember to turn the key to the 'on' position when charging. So maybe you should hold off until I go through a full charge/discharge cycle and I'll let you know if this was worth doing. I was also just reading the manual for the shunt and it says that if it's on and idling it should go to sleep on its own... have you found this to be the case? If so, then switching it on/off with the key is probably not necessary. I was turned off by the ~400 mA draw from it just being on.

AMDPower · Oct 27, 2021

I read that too but I think the BMS might keep it alive or something. The display is always on for me.

rio · Oct 28, 2021

Successful 1st Mow! Only took about 35 Ah total, so plenty left. My yard size is a bit over an acre, with some steep hills. Suck it, Ryobi!

Opened the box back up right after and touched everything (lugs, bus bars, BMS) and it's all cool to the touch. This is amazing.

icenov · Oct 28, 2021

ascottdude said:
Any updates on how everything worked out? Is the BMS sized big enough to get up the hill with blades spinning? I need to get new batteries and want to upgrade. I cut 12 or so lawns a week so I'd be interested in the 280ah if they fit.

I'm interested in the larger capacity batteries as well - but 200 Ah is enough for me. Did you decide if there is enough space for 280 Ah? I've got my eyes on the Ganfeng cell which is 6.8 x 2 x 7.9 in. so theoretically will fit in the box size mentioned above.

UltrasoundJelly · Nov 16, 2021

@AMDPower and @rio Thanks so much for this thread. First time caller, long time listener. I have been planning a LifePo4 conversion of my Ryobi RY48ZTR75 since I bought it. Mowing my 1 acre yard on a significant slope has brought my AGM batteries to their knees over two seasons of mowing. My last mow took me 3 charges, so it is time.

I've been following your builds closely, and I think I am going to go with a drop-in solution for time, reliability and warranty. I has originally just planned on getting drop-in replacement 12V 100 Ah LiFePo4, but I've been reading online that charging them in series can be problematic (once one tops off, the other BMS units will see over-voltage and stop charging, limiting the total capacity).

I was able to find two batteries that seem to fit the battery bay that are ~48v 100Ah:

Dakota Lithium 48V 96Ah Golf Cart Battery

Buy Dakota Lithium 48v 96Ah Golf Cart Battery. No maintenance with easy installation. Free 48V 8A amp LiFePO4 charger. Lasts 8x longer and 11-year warranty.

dakotalithium.com

48V 100AH Water-Proof Bluetooth Battery by EG4

ADD-ON CHARGER DEAL Get the EG4 LiFePo4 Battery Charger for 33% off in cart DESCRIPTION SPECS & MANUAL VIDEOS SHIPPING 48V 100Ah EG4-WP Waterproof LiFePo4 5.12kWh Lithium Battery with Bluetooth Monitoring and Built-In BMS 20.5L x 10.5W x 9.125H This battery is the ULTIMATE upgrade to any...

shop.signaturesolar.us

Each company offers a 48v charger, so I'll source it from them. I will disconnect the thermistor (3rd pin) on the charger plug as it will be useless. I will probably add the shunt you guys have suggested to monitor usage, at least for the Dakota Lithium - the EG4 has bluetooth.

So the hardest part of this conversion will be securing the battery. It looks like the Dakota battery is 3-4" narrower and shorter than the tray, but the height is the same. I wont be able to use the center screw to hold the battery down. Do you guys feel that the upper rack is needed to keep the battery from clunking against the upper bay? Any recommendations on securing this guy?

Thanks in advance.

Hedges · Nov 16, 2021

$2700, $1650. 4kWh or 5kWh.
Building 48V battery with DIY with 280 Ah LiFePO4 (14 kWh) probably costs around $2000.

With lithium you might get 3000 cycles, 30 years mowing twice a week or 60 years one a week (i.e. it will age out or something else will fail first.)

On the original AGM, maybe you only got 100 or 200 cycles. Fully discharged reduces their Ah life compared to 80% cycle.
Mowing half the yard at a time from the beginning might have given longer life. But probably wears out after 3 years not two.
Premium AGM batteries (I use SunXtender) might double that, would cost $1400. So almost as much as the lithium you're looking at.

How would a "hybrid" work out, a portable generator coming along for the ride?
How many hours does it take to mow 1 acre?
Imagine a 2kW generator and 25A charger. Or whatever generator would supports existing charger. Have anything on hand you could try, if only for the experiment?

rio · Nov 16, 2021

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!

AMDPower · Nov 16, 2021

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.

AMDPower · Nov 16, 2021

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.

wattmatters · Nov 16, 2021

Hedges said:
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...

UltrasoundJelly · Nov 16, 2021

rio said:
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...

AMDPower · Nov 16, 2021

UltrasoundJelly said:
@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.

UltrasoundJelly · Nov 16, 2021

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....

Pelican 1556 Wheeled Air Case

Grab yourself a Pelican 1556 Wheeled Air Case for easy transferring of gear and other vital equipment from place to place. Available now.

www.batteryjunction.com

Is there room for 10.57" height?

Also found this case:

https://www.monoprice.com/product?p_id=39020

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:

https://www.monoprice.com/product?p_id=12139

Hedges · Nov 16, 2021

AMDPower said:
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.

rio · Nov 16, 2021

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.

UltrasoundJelly · Nov 17, 2021

rio said:
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.

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

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