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

SparkyJJO

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I might recommend PVC tubing for insulation properties. Less "stuff" in it than heater hose, and cheap.

If we end up buying a property big enough for something more than my push mower this may be the way to go. If gas becomes hard or hugely expensive to get it would be nice to still be able to mow the lawn :LOL:
 

Sracer42

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Aug 20, 2022
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It may depend on the BMS in those batteries. It may reset or it might take a small charge to reset it. The BMS protected the batteries so no worries on damage.

I think that is exactly what you are seeing. If you can reduce the inrush by using a resistor as a prestart circuit that might do the trick. It is probably the capacitors in the motor controller if you have one. Otherwise the start up current for the motor if it has no motor controller. I had a similar problem with a chipper shredder. Thanks to advice I got here, I just reduced the voltage from 60 volts to 30 volts and it did not trip my 200 Amp BMS. I was reminded by a user here that a motor presents to the battery like a big resistor and the higher the voltage, the more current will flow in the circut.

No, I think it is recoverable in a number of ways. It depends on whether it has a motor controller of is a direct connection. keep us informed on your progress.
OK - so thanks to those on this thread I have my Ryobi 54" ZT mower up and running on 4 Chins 100Ah LiFePo batteries.
The biggest challenge was figuring out that I needed a precharge resistor to keep the battery's BMS from cutting out on the initial surge when the key was turned on. Solved that with a toggle switch and a 200 ohm power resistor.
Mowed the entire lawn today (about 2.5 acres) that was pretty overgrown and the batteries went from about 90% to 30%. That would not have worked with the original AGMs.

Plus side it is peppier due to lower weight.
Minus side it has lost some traction due to lower weight.
Big plus side I shouldn't ever have to replace these batteries in my lifetime, plus it was an interesting project, if a little nerve racking.


I can post more details if anyone is interested.
 

Xebec

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May 21, 2022
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I wish to say thanks to everyone in this forum, my 54" is so much better after the upgrade and I dont know if I would have been able to do it without the help here. I went a little overboard as I did not know how much more power my 54 in would draw compared to the others that were completed here

230 Ah (16S EVE cells)
200A Daly BMS
350A Shunt with monitor
Compression with aluminum angle iron and HDPE ends, threaded rod and PEX to keep the cells from the threads
Aims charger with 20 ft charging cord (I hated how short the stock one was)

It runs so much better and I can now mow for 5 hours. It maintains power and I almost never hear it get bogged down.

Thanks Again
Zach

Very nice and impressive! A few basic questions (I also have the 115Ah 54”):

Do those painted frame pieces on top of the battery use dead end at the back or did you cut them off?

With 16 cells in series - is there a chance for cell 1 and cell 16 to drift significantly in voltage over time? Or does the BMS take care of this during charging? (Long slow charge at end?)

I really like that box you built - I assume HDPE is the thick plastic that you have ‘compressing’ the cells together? And how does this box bolt or stay affixed to the painted metal tray inside the mower?

(I’m a year or two away from wanting to do this upgrade - I’m learning.. but have almost 3 acres of grass..)

Thanks!
 

SolarDaveCLE

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Sep 5, 2022
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I found my way to this forum while searching for Ryobi SLA battery replacement. After much reading, I decided to jump in with both feet and order some off-the-shelf LiFePO4 batteries on Amazon. Thanks to AMDPower for starting this exchange of information and help, and to the many others who have contributed as well.

I bought four Eco-Worthy 12V 100Ah LiFePO4 batteries, same size as the 75Ah Leoch SLA batteries that were being replaced after one year, and a Qwork shunt-based battery meter. Charged the new batteries on the ground, all looked good, installed them and the new meter. Mower starts - Yay! I mowed for a few hours, impressed with how slowly the battery SOC was decreasing. So now it's time to charge with the batteries installed. I cut the 3-pin charging cable off the old Ryobi charger and wired to the replacement Waouks 10A charger (Amazon as well). Here is where I decided to get clever, and it back-fired. I wanted to retain the charger interlock feature and used the diagnostic diagrams from the Troubleshooting and Testing guide posted here. I decided that the upper pin should be tied to (+) based on the diagram on page 41 to tell the mower that a charger is connected. Well, it worked great for about 3-5 seconds, then the green LED on the charging port started to flicker, and the magic blue smoke was released from whatever components are potted inside the charge connector.

After some tinkering, I am guessing that the single blue wire that connects to a black molded plastic component with "TJ918-1" on it tells the main relay that it's OK to start. Can anyone tell me what voltage on this blue wire means "go"? Alternately, can I short two wires together somewhere else to bypass the over-temp and charger interlock features? There is a 3-wire cable leaving the black box (red, yellow, black) which has battery voltage across red and black. I am guessing that the yellow wire controls something downstream, but I'm a little nervous to randomly short it to things after what happened! {hangs head low}.

I am more than happy to post pics of the re-build and share any knowledge I have gained along the way. I was so close to a hassle-free experience.

Thanks everyone!
Dave in Cleveland
 

Hedges

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I decided that the upper pin should be tied to (+) based on the diagram on page 41 to tell the mower that a charger is connected. Well, it worked great for about 3-5 seconds, then the green LED on the charging port started to flicker, and the magic blue smoke was released from whatever components are potted inside the charge connector.

"Inside the charge connector"

If in the connector, it may be a resistor, part of a precharge circuit.
Just guessing, because I haven't seen or touched these.
Applying a relatively high impedance load and recording voltage/current could serve to distinguish circuits behind pins. (Thevenin equivalent.)

Rather than "shorting", I would suggest resistor or light bulb. That provides some power with current limiting.
 

Kavalliero

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Aug 18, 2022
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Here is where I decided to get clever, and it back-fired. I wanted to retain the charger interlock feature and used the diagnostic diagrams from the Troubleshooting and Testing guide posted here. I decided that the upper pin should be tied to (+) based on the diagram on page 41 to tell the mower that a charger is connected. Well, it worked great for about 3-5 seconds, then the green LED on the charging port started to flicker, and the magic blue smoke was released from whatever components are potted inside the charge connector.
I totally feel your pain. I tried to temporarily "restore" the AGM pack on mine by hooking up a different charger with a EZGO plug to the existing charge port vs pulling the batteries before attempting this conversion project. Unfortunately the pos and neg wires were reversed on the EZGO plug I bought which nuked my charging port. Not sure if anything downstream got nuked but so far it seems from the components I tested it seems isolated to the charge port and possibly related sensors. I was able to get Ryobi support to directly ship me both a new port and charger since my mower has about 6 months left on the warranty. Unfortunately both parts are still on backorder with an unknown ship date. So now I'm trying to figure out whether I wait for those official parts to come in, try to figure out how to bypass, or try picking up a golf cart EZGO charge port to see if that will work instead. It totally sucks.

It is always interesting to see what people have experienced with building their own battery packs vs the different LiFePo4 "drop in" options. I was still leaning more towards the AmpereTime 100Ah with an alternative being the CHINS 100Ah. Having the bluetooth app on the BMS would be nice and CHINS does make a 100Ah now that has bluetooth, but not sure if anyone has tried that particular battery. It would be good to hear if anyone has had any challenges with the AmpereTime 100Ah packs.

Regardless, I'm looking to get my mower back to a known operational state before moving forward with the conversion just in case I need to haul the mower to a service center. The new lithium Ryobi mowers seem interesting, but if they build their proprietary packs the same way they build their smaller cordless tool lithium packs I would be really suspicious on battery longevity!
 

SolarDaveCLE

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Sep 5, 2022
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I totally feel your pain.
Thanks, Kavalliero. I hope by sharing my experience I can save someone else the frustration.

I've decided that I am content with not having any sort of charging interlock (leave the charger on the seat), and the temp sensor for the battery is moot now since the new batteries have built-in BMS with thermal protection.

ChargerPort.jpg
Here is my charge port. Black and red wires get battery directly from Anderson connector (not switched), white 2-pin connector picks up thermistor that is bolted to a batter terminal for battery temp monitoring, blue single wire with large 1-pin Delphi connector sends "all good" signal to the Charge Relay (another black potted plastic device screwed to the frame under the seat). I was ready to pay for a new one, but my research led me to believe that it may have been discontinued by Ryobi. Part number HM-996515001. If anyone has a lead on available stock, please let me know.

ChargeRelay.jpg
This is what I'm calling the charge relay. Thanks to Hedges for cautioning me on shorting things together :) I pulled out a couple of variable DC supplies and a couple of meters to delicately learn how this thing works. Red and black on the 3-pin connector are battery, which is switched by the main key, so I connected them to 48V. I then turned the current limit way down and started applying a given voltage and measuring the current into the blue wire. Around 6V I heard a relay click inside the black box, and now 48V is present on the yellow wire. Turn the voltage down on blue, the relay opens and yellow goes open. I can't know for sure, but based on the numbers, I think the blue wire feeds into a 25 kohm resistor in series with a PN junction (base of a BJT I'm guessing). Current maxes out at 2 mA when voltage on blue pin is 56V (I ramped up battery voltage as well to 56V).

My solution is to tie the blue wire to the red battery+ wire through an additional 10 kohm resistor to keep the current around 1.5 mA. I installed the modified charger relay, and... the main relay clicks on when the key is turned, and the mower works again!

If anyone else has fried their charging port, this could be a way around the problem.
Enjoy!
 

Kavalliero

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Aug 18, 2022
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Thanks, Kavalliero. I hope by sharing my experience I can save someone else the frustration.

I was ready to pay for a new one, but my research led me to believe that it may have been discontinued by Ryobi. Part number HM-996515001. If anyone has a lead on available stock, please let me know.

View attachment 110972
My solution is to tie the blue wire to the red battery+ wire through an additional 10 kohm resistor to keep the current around 1.5 mA. I installed the modified charger relay, and... the main relay clicks on when the key is turned, and the mower works again!

If anyone else has fried their charging port, this could be a way around the problem.
Enjoy!
SolarDaveCLE, Thanks for the the additional information and pictures of the parts. As I read through the forum I found several references to folks that had removed the temp sensor and bypassed the lockout relay, but I haven't seen any clear pictures of the final solution. There are a lot of red and black power lines that feed through different connectors all back to the battery in some way. So it would be really nice if there was just a couple of clear shots of the final working solution just to have the proper visual reference.

When you came up with your solution did you crack open that black charger relay box and change the wiring inside or did you just make your modifications another way? It would be great if there was a final picture of the actual modified charger relay before it was installed and another post install picture to use as a reference. Of course I totally understand the hassle if things are all back together and working again.

What you found on the charger port part HM-996515001 reflects my experience as well showing either "Discontinued" or "Currently not available" when looking at part suppliers online. It also looks like the SC-48 charger has been replaced with a different type from what I saw elsewhere. It seems like Ryobi has decided to phase out the earlier generation of riding mowers we are all working on in favor of their new 80v lithium solution. However, there are still a lot of people that purchased these mowers that have active warranties on them. So it would be odd that they would totally discontinue an actively supported product until everything was out of rotation. I'm more inclined to believe they ran into COVID logistics issues in the manufacturing chain and maybe that is compounded by any lack of urgency to resolve the issue. So it would be great to have a clear picture of a working bypass solution as a fallback approach.

All of these components seem to be basically the same as an EZGO golf/club cart charging solution. Ryobi just had companies like Delta make some special modifications to the port and charge plug moulding to make it proprietary. Same thing goes for the for the power coming off the port to the battery which uses the blue Anen SA2-30 connector whereas a standard EZGO golf/club cart charger port has the same wires but terminated with ring connectors. Simple enough to replace inline the connector, and the same would be true to wire up a standard RXV charge handle versus Ryobi's custom shape.

It is just a hassle. In the meantime I'm back to using a self-propel walk behind mower...not so much fun in the Florida summers!

Thanks for your contributions.

Once I get through all of this I would like to consolidate the lessons learned in this forum into a just a PDF file that shows a build of materials and step by step.
 

SolarDaveCLE

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So it would be really nice if there was just a couple of clear shots of the final working solution just to have the proper visual reference.
Here you go, Kavalliero.
ChargeRelayDetail.jpg

This image shows how I modified the charge relay. I "borrowed" the 1-pin connector and blue wire from the charge port and soldered the end of the wire to a 10k resistor. Then I coaxed the red pin out of the 3-pin connector shell by pressing a thin tweezer against the barb on the contact and soldered the other end of the resistor to the contact. Slide heat-shrink down over resistor and shrink, then re-insert the red contact into the connector shell. There is no way that I know of to break into the hard potting material without damaging the encapsulated components, so the resistor was added externally. I don't know if the resistor was really needed, but my gut told me that I wanted to limit the current going into that pin.

ChargeRelayConnected.jpg
Here is the modified charge relay connected to its respective cable on the mower, laying on top of the battery area under the seat. I suspect another solution would have been to simply short the yellow wire to the red wire and remove the relay altogether, but I was hesitant to be heavy-handed again.

ChargRelayInstalled.jpg
And here is the final assembled view, top-down under the seat.

The mower is currently charging in the garage, everything seems to working fine, the battery meter is showing a current flow into the battery, and I can see the Ah value increasing. Needless to say, the green LED on the charge port is no longer working.
 

Hedges

I See Electromagnetic Fields!
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Mar 28, 2020
Messages
12,121
When a thru-hole resistor has its leads bent (e.g. to fit holes in PCB), proper technique is to grip the wire, not the body, while bending. That is to avoid breaking off.

The resistor used as shown is subject to stress. I suggest having a length of wire coming from connector, and mount the resistor somehow protected against bending. Maybe with wires cable tied to a stick, or better yet to ends of a tube, with resistor inside.

Resistors are either mounted horizontally or vertically on a PCB. For an alternate assembly idea, you could bend one lead 180 degrees so both wires exit in same direction. Heatshrink to insulate them apart, heat shrink the entire assembly, cable tie the two wires together. That way, wires don't put stress on resistor, and it is just a stub about 3/4" long.
 

Kavalliero

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Here you go, Kavalliero.
Thanks SolarDaveCLE! You rock for posting the pictures with the details. Also thanks to Hedges for pointing out ways to further improve the resiliancy! You're both great contributors.

I'm certainly going to keep that solution ready in case I need it.

As far as the earlier comments on OEM part replacements and the "discountinued"/backordered charging receptacle part (HM, 996515001) for the RY48ZTR100. While I am waiting to see if Ryobi does eventually ship me that particular part and new charger once they comes in, it seemed strange that the receptacle part wouldn't be available given the number of different 48v riding mower models Ryobi produced. I decided to check the part assemblies for their older steering wheel 48v 100Ah 38" mower (RY48111) and their newer 54" 115Ah ZTR (RY48140) that also used the AGM batteries. With all of these models operating at 48v with AGM batteries and the SC-48 charger it seemed to reason that all of these mowers would be using the same lockout circuit and charger receptacle. When I checked the older 38" and newer 54" ZTR both use the same charger receptacle part of HM-996207001 which is in stock through both Ryobi's on replacement parts site (https://ryobipower.ordertree.com/) and PartsWarehouse (https://www.partswarehouse.com/Ryobi-RY48111-48-Volt-38-inch-Riding-Lawn-Mower-s/554796.htm). It is really strange that those models have the same part number but a different part number is listed for the RY48ZTR models. Unless they have done something really funky that was specific to the RY48ZTR that they didn't put into their other 48v mowers it should be compatible. I figured I would give it a whirl to see if it works without the bypass modifications. At least I have a spare parts if I mess something up later.
 

SolarDaveCLE

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... it seemed to reason that all of these mowers would be using the same lockout circuit and charger receptacle. When I checked the older 38" and newer 54" ZTR both use the same charger receptacle part of HM-996207001 which is in stock through both Ryobi's on replacement parts site (https://ryobipower.ordertree.com/) and PartsWarehouse (https://www.partswarehouse.com/Ryobi-RY48111-48-Volt-38-inch-Riding-Lawn-Mower-s/554796.htm). It is really strange that those models have the same part number but a different part number is listed for the RY48ZTR models.
Thanks for the lead on the alternate charge port part number. I guess there is no way to know for sure if it is compatible with the 48ZTR until someone tries it. Does it also have two mechanical variants like the original part (from ordering instructions somewhere, Ryobi asks for a picture of the charging cable to make sure they send the correct port)? $135 seems awfully steep for what it is, but if you're stuck, it's a great price! ;-)
 

Yoe777

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Aug 14, 2022
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I recently converted my Ryobi Zero Turn RY48ZTR over to lithium. Resting voltage is 54.4v area. I tested first full 2 acre mow flawlessly. I went to play around later the next day to do some testing and my DECK MOTOR CTRL SLAVE ZTR part #12 on the parts list blew a cap. I wasn't even using the mower deck at the time. Is this purely coincidence or could the slightly higher Lifepo4 voltage compared to Lead Acid have anything to do with it? Is anyone using a DC-DC converter to step the voltage down a few volts?

Thanks.
 

Sracer42

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Aug 20, 2022
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I recently converted my Ryobi Zero Turn RY48ZTR over to lithium. Resting voltage is 54.4v area. I tested first full 2 acre mow flawlessly. I went to play around later the next day to do some testing and my DECK MOTOR CTRL SLAVE ZTR part #12 on the parts list blew a cap. I wasn't even using the mower deck at the time. Is this purely coincidence or could the slightly higher Lifepo4 voltage compared to Lead Acid have anything to do with it? Is anyone using a DC-DC converter to step the voltage down a few volts?

Thanks.
Ouch. I sure hope it isn't the higher voltage as I just converted my 54" Ryobi ZT.
 

icenov

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I'm sure it's not the LiFePO4 battery pack voltage. A fully charged lead-acid 48 V pack can sit at 56 V and even the DeltaQ charger that Ryobi supply with the 48ZTR will charge over 56 V when connected to the lead-acid pack. Even Ryobi wouldn't risk under-rating their caps by such an amount just to save a few cents. I've run my 48ZTR with a LiFePO4 battery pack for over 20 hours so far and had no issues. I suspect it was an unrelated failure.
 

Hedges

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Capacitor inrush current when lithium battery connected? That could be several times higher than with AGM.
Maybe a precharge circuit is indicated.

Ever connected reverse polarity? That would eat away dielectric.
 

Vigo

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If that piece is open circuit to the battery pack when the deck motors are not engaged, then by extension it will be experiencing full 'inrush' every time the deck is activated, which will eventually blow up the caps.

Unfortunately it's something you probably can't diagnose any further without buying one that's not broken (or repairing yours) and then proceeding VERY carefully.
 

Sracer42

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If that piece is open circuit to the battery pack when the deck motors are not engaged, then by extension it will be experiencing full 'inrush' every time the deck is activated, which will eventually blow up the caps.

Unfortunately it's something you probably can't diagnose any further without buying one that's not broken (or repairing yours) and then proceeding VERY carefully.
IIRC from a circuit diagram of the mower - the motor controllers are energized when the main contactor is energized by the "ignition" switch. There is a separate low current control circuit to each controller for traction and mower controllers.
On my 54", a precharge resistor circuit energized before turning the ignition switch solved my inrush problem.
 

chazman113

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I just snagged a ZT480ex from a local outlet store, factory reconditioned, for $2k. Had 8 hours on it, comes with a 1 year warranty and 30 day return policy, I think it was a pretty decent deal. I know a little about LFP batteries from a small solar setup I built. Immediately thought I could shove one in this thing when the SLA batteries die. Going to bookmark this thread, I'm almost excited for them to die to try and retro fit it! Anyone have any experience how long the stock batteries last? Guessing 2-3 years before it gets noticeable? I'm mowing a little less than 2 acres, probably around 20 times a year. I was reluctant to get it with lead acid batteries and some unfavorable reviews regarding it's longevity, but figured I would give it a shot. I'm already exhausted dealing with my old Cub Cadet's deck problems, worst case I have 2 half working mowers in a few years.
 
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