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

[Hedges]

Best way to hit 80% SoC is charge into knee of the curve, then discharge 20 Ah.

If you measure how many Ah consumed running the mower, you know SoC. Then recharge with a CV/CC charger on a timer to reach the SoC you want.

 

[UltrasoundJelly]

Best way to hit 80% SoC is charge into knee of the curve, then discharge 20 Ah.

If you measure how many Ah consumed running the mower, you know SoC. Then recharge with a CV/CC charger on a timer to reach the SoC you want.

This is what I do. Charging at about 12 amps for 3 hours using the AIMS charger I get 50%->80% (30% change) SOC on my shunt monitor. I use a cheap mechanical timer and it works well. If you get smart timer you could trigger it remotely and have it charge the night before you mow when the battery temp is in the ideal range. (in the SE USA night would be coolest 65-70F).

Thought about rigging up an Arduino using the Overkill library so I could turn off the MOSFET charging controller at a certain SOC, but the Overkill reported SOC isn't reliable as far as I can tell (within 5-6 charges it disagrees with the shunt by 20% or more). Would be nice if there were a shunt that came paired with a lithium charger, so the charger always knew the current SOC and could be set to a certain range.

 

[Hedges]

Counting coulombs will always accumulate error.
Some equipment could be adjusted to reduce that. Zero-offset, slope. But there are likely differences from waveforms charging vs. discharging.
So it is going to drift. Periodically hitting the knee approaching 100% or 0% should reset, depending on which is implemented.

If you're remaining between 50% and 80%, how well is cell balancing maintained? Which you can only determine at the knees, and rebalancing only happens there.

 

[Lebnjay]

Another RM480e conversion thanks to the pioneering work of so many of you.
New EVE 105ah cells from 18650batterystore.com, delivered quickly and were packaged well. All 16 arrived at exactly the same voltage, delta of .001.
Overkill BMS
Cheap 12a Lifepo4 charger from eBay.
Put the charger in the battery box I built, not using the built in charging port. Didn’t mess with the gauge as it never worked anyways and I just monitor the battery from my phone now.
Runs great, can easily do our whole property where the agm’s could only do a quarter at a time.

 

[AMDPower]

Nice job! Surprised you had enough room to even put the charger in there! That's great.

 

[eleven_brews]

Another RM480e conversion thanks to the pioneering work of so many of you.
New EVE 105ah cells from 18650batterystore.com, delivered quickly and were packaged well. All 16 arrived at exactly the same voltage, delta of .001.
Overkill BMS
Cheap 12a Lifepo4 charger from eBay.
Put the charger in the battery box I built, not using the built in charging port. Didn’t mess with the gauge as it never worked anyways and I just monitor the battery from my phone now.
Runs great, can easily do our whole property where the agm’s could only do a quarter at a time.

Looks great! The cable management is way better than how mine turned out.

How did you manage to find 4awg battery lugs that fit the m4 bolts? I ended up having to use dual 8awg between the groups of cells, just like the overkill BMS ships with.

 

[Rapscallion77]

I joined this forum just for this thread, I bought my ryobi 2 years ago and the batteries are shot, can barely mow for 5 min and it stops cutting now.
I need to get it working ASAP. My plan is to get drop in replacements but i am new to all this, and ive read and reread through this and am very nervous about trying to do this myself. These are the batteries i am looking at (https://www.amazon.com/gp/product/B099FB9PQ4/ref=ox_sc_act_title_2?smid=A138YWHSOUG8CW&th=1)
I think they are just about the same size as the oem batteries. What else will i need to get my mower running again any help will be greatly appreciated

 

[LittleLebowski]

Another RM480e conversion thanks to the pioneering work of so many of you.
New EVE 105ah cells from 18650batterystore.com, delivered quickly and were packaged well. All 16 arrived at exactly the same voltage, delta of .001.
Overkill BMS
Cheap 12a Lifepo4 charger from eBay.
Put the charger in the battery box I built, not using the built in charging port. Didn’t mess with the gauge as it never worked anyways and I just monitor the battery from my phone now.
Runs great, can easily do our whole property where the agm’s could only do a quarter at a time.

Well done.

 

[rio]

I joined this forum just for this thread, I bought my ryobi 2 years ago and the batteries are shot, can barely mow for 5 min and it stops cutting now.
I need to get it working ASAP. My plan is to get drop in replacements but i am new to all this, and ive read and reread through this and am very nervous about trying to do this myself. These are the batteries i am looking at (https://www.amazon.com/gp/product/B099FB9PQ4/ref=ox_sc_act_title_2?smid=A138YWHSOUG8CW&th=1)
I think they are just about the same size as the oem batteries. What else will i need to get my mower running again any help will be greatly appreciated

I think most of us joined just for this thread also!
Double-check that these batteries will fit (they should). You might need new connecting cables for the battery terminals and series connections if the Ryobi ones don't work with the terminal post geometry of the new batteries. Hopefully that's not the case.
Also for that setup you may want to look into a LiFePO4-specific charger that will not over-voltage the cells. Ideally you might want a 4-bank charger so that you can charge each battery independently, but that adds an extra burden in charge logistics. The whole charging thing seems to be that most uncertain aspect of these conversions. That said, as long as the BMS in the batteries can be trusted, I think it's unlikely that you can cause harm, in my opinion.

 

[rio]

My 2 cents on the whole charging thing. I've continued to use the original Delta-Q charger with my converted system and at this point I see no reason to get a different charger. Given that cutting my entire 1 acre lawn uses only about 35Ah, I can easily maintain my SoC very comfortably between 20% and 80%. Knowing that the Delta-Q charges at 14 A, I can just set a timer when I'm charging and unplug. To account for drift in the Ah measurements (both in the shunt and in the Overkill BMS), I "top it off" once every month or two: let it charge to about 3.5V (above the knee for my cells) and reset the Ah counter to 100%. When I do this I keep a close eye on the app, and the Overkill always cuts charging the instant one cell hits 3.5V. I feel very comfortable with this process, and find it very convenient. By now I probably have about 15 charge cycles on it; it's been reliable so far and my cells remain very well balanced. For this application (35% of charge used once weekly for ~20 weeks out of the year), I feel comfortable with this approach, especially because I trust the quality of the Overkill BMS. With a drop-in replacement 12V battery setup, then I might feel differently.

 

[Hedges]

These are the batteries i am looking at (https://www.amazon.com/gp/product/B099FB9PQ4/ref=ox_sc_act_title_2?smid=A138YWHSOUG8CW&th=1)

"Allow to be extended up to 4 in series and 2 in parallel (Max 4S2P) to get more capacity (Max. 12Ah) and higher voltage (12V, 24V, 36V, 48V)."

Good, that is a key requirement, that BMS can handle 48V. Not all brands can connect in series.

Ideally you might want a 4-bank charger so that you can charge each battery independently, but that adds an extra burden in charge logistics.

I would think 48V charger takes care of most charging, and a small 12V could be used occasionally to "top balance" the four batteries with respect to each other.

I can easily maintain my SoC very comfortably between 20% and 80%. Knowing that the Delta-Q charges at 14 A, I can just set a timer when I'm charging and unplug. To account for drift in the Ah measurements (both in the shunt and in the Overkill BMS), I "top it off" once every month or two: let it charge to about 3.5V (above the knee for my cells) and reset the Ah counter to 100%. When I do this I keep a close eye on the app, and the Overkill always cuts charging the instant one cell hits 3.5V.

If 48V charger is relatively high rate, and aiming for a high enough voltage that BMS disconnects first cell at 3.5V, probably doesn't allow much time for rebalancing.

Your cells will of course look balanced after they settle just below the knee. At the moment of disconnect, do you know what the spread is?

I'm thinking, for those who use 4x 12V batteries rather than 16 cell DIY pack, a low-current 12V charger would give BMS more time to balance.
For those with 16 cell BMS and non-lithium charger, a series resistor (e.g. light bulb) would let charger hold its target higher voltage while battery receives low enough current that passive balancer can do its job.

 

[Skabam287]

Like others, I joined the thread specifically for this and don’t have experience so am looking to use four 12v drop ins (ampere time). I’m too worried about screwing something up in a battery build and blowing everything up haha. I’d love to get away with the oem delta-q charger, but also share the concerns there, especially after some of these latest comments since idk if I can trust the bms in those batteries, and wouldn’t have any app that could help me keep on top of things.

Would anyone know if it’s possible/ how to splice/connect the triangle shaped plug from the delta q charger to a 48v lifepo4 charger (aims or other via Amazon)? I think dochoot went this route but i don’t think he’s said how it’s been working out. How many amps should I look for in a charger? I know rio said earlier no more than 15a, others had issues with lower amp chargers. Any other recommendations there would be super helpful. I don’t want to completely ruin the lifepo4’s with bad charging practices. Thanks to all on this amazing thread!!

 

[gwang_hoops]

Like others, I joined the thread specifically for this and don’t have experience so am looking to use four 12v drop ins (ampere time). I’m too worried about screwing something up in a battery build and blowing everything up haha. I’d love to get away with the oem delta-q charger, but also share the concerns there, especially after some of these latest comments since idk if I can trust the bms in those batteries, and wouldn’t have any app that could help me keep on top of things.

Would anyone know if it’s possible/ how to splice/connect the triangle shaped plug from the delta q charger to a 48v lifepo4 charger (aims or other via Amazon)? I think dochoot went this route but i don’t think he’s said how it’s been working out. How many amps should I look for in a charger? I know rio said earlier no more than 15a, others had issues with lower amp chargers. Any other recommendations there would be super helpful. I don’t want to completely ruin the lifepo4’s with bad charging practices. Thanks to all on this amazing thread!!

when viewing the plug bottom side down during insertion with mower: LEFT = - RIGHT = + TOP = N/C (it's probably easier just to buzz it out before connecting wires since the mower side is connected to the battery 24/7).

use up to 14A (?) per previous AGM chargery limited by the mower power connector cabling. I don't think the current really matters unless you really want to recharge it faster than overnight. Went with 8A 16S LiFePO4 charger because of cost. You can keep using the original AGM battery charger if you put it on a timer assuming you can roughly guess current and desired SOC or have a AC switch with some CPU measuring current. Others recommend adjust down the 16S max voltage such as buying a 15S charger to avoid 100% SOC / max voltage problems if cells/batteries are out of balance.

All kinds of methods to charge LiFePO4 batteries. No perfect answer for everyone. Read through this thread and you'll see a variety of answers for different situations / desired goals.

 

[bcb7514]

Glad I ran across this thread and enjoy seeing all of the conversions.

Looking at possibly going with the plug in play option of the LiFePO4 12v 100Ah batteries to save some time and also because I’m not super trusting of myself to not screw up something by building a custom setup.

Ampere Time LiFePO4 Deep Cycle Battery 12V 100Ah with Built-in BMS, Perfect for Replace Most of Backup Power and Off Grid Applications... https://a.co/d/7lj6J1N

Is there anything else specific I would need or need to do besides simply pulling out the OEM batteries and putting these in?

I’ve seen others mention being able to use the original charger, but also mention setting a timer to unplug to be safe. Normally I leave the original batteries on the chargers all the time. This just a best safety practice? Cause any issues should I forget to unplug after swapping to the LiFePO batteries?

I feel like I know just enough to be dangerous at the moment.

Thanks!

 

[Jakeman]

Finally made the change! Yesterday I finished swapping the original batteries to this:

https://www.amazon.com/dp/B08G7YMWND?psc=1&ref=ppx_yo2ov_dt_b_product_details.

Also replaced the charge indicator:

https://www.amazon.com/dp/B08HWFPGL5?psc=1&ref=ppx_yo2ov_dt_b_product_details

Entertained the idea to build a 150 ah battery but the snow would be flying before I'd have it finished.

Wasn't exactly plug and play as the new battery needs to be secured differently. Got it finished yesterday afternoon, held my breath, and plugged the Ryobi charger in. No problems. New battery monitor showed a charge rate of 14.4 amps, which settled in at 13.5 after a short while. The monitor showed the battery as being pretty low in charge, 2 or 3 bars. Kept an eye on it for about 8 hrs until it reached 9 bars. Shortly after that the monitor started fluctuating a lot, I immediately unplugged the charger. The monitor read 90.1 amp hrs. and 90% charge. I have not calibrated the monitor so I know these numbers may not be accurate, but this was good enough for me.

Tried it out today. Mower worked fine, ran it for about 1 1/2 hrs. Monitor showed 53% remaining. I'm very happy with that! Original batteries would've been dead long before that.

The only thing I'm not sure about is, do I continue to use the Ryobi charger? I don' know anything about the BMS in the new battery, just that it claims to protect from overcharge, etc. I babysat it to hopefully avoid the problem AMDPower originally had with his.

I want to thank everyone here for their help and the information they shared.

 

[rio]

@Jakeman that's great! Got pictures?

I'm a bit confused about the monitor initially showing low charge. This monitor has no way to know state of charge if it's not calibrated. Usually you would have to fully charge the batteries first, then set the monitor to 100%. Then after that the monitor would estimate state of charge based on measured current (discharge / charge) over time. Charging for 8 hours at 13.5A would have supplied over 100Ah - so probably overcharge protection in BMS tripped (not a bad thing). If I were you I would call that 100% and then only charge to about 90% from then on.

I would say you're probably fine with the Ryobi charger, especially if you time the charge cycles properly to stay below 90% or 85% SoC.. You can do that easily by taking note of the total Ahs used during mowing. That said, without being able to monitor the BMS you may want the piece of mind to protect your investment with a lower-voltage LiFePO charger.

 

[gwang_hoops]

AFAIK, errors accumulate via coulomb counting via self discharge and accuracy of the measurement device. If you coulomb count only, it needs to be "reset" with some kind of "full charge" occasionally or you may run out of juice prematurely depending upon your usage / low Ah number to charge, and guarantee BMS re-balancing (am I right? depends upon the BMS implementation?).

Went with a LiFePO4 48V 16S charger to bypass the timing thing, but in retrospect should have gone with a slightly lower voltage charger but that's minor. I'll probably do a full charge maybe every 3-4 mowings and top balance the 12V batteries once a year. These batteries aren't being asked to do a lot. Was going to throw in some diodes in the 16S charger, but didn't care enough...

 

[Jakeman]

@Jakeman that's great! Got pictures?

I'm a bit confused about the monitor initially showing low charge. This monitor has no way to know state of charge if it's not calibrated. Usually you would have to fully charge the batteries first, then set the monitor to 100%. Then after that the monitor would estimate state of charge based on measured current (discharge / charge) over time. Charging for 8 hours at 13.5A would have supplied over 100Ah - so probably overcharge protection in BMS tripped (not a bad thing). If I were you I would call that 100% and then only charge to about 90% from then on.

I would say you're probably fine with the Ryobi charger, especially if you time the charge cycles properly to stay below 90% or 85% SoC.. You can do that easily by taking note of the total Ahs used during mowing. That said, without being able to monitor the BMS you may want the piece of mind to protect your investment with a lower-voltage LiFePO charger.

Can take some pics if anyone's interested in anything specific. Figured there's plenty of pics of most of the steps I took, exception being how I secured the battery.

I was confused about the monitor as well, but it seemed pretty accurate? The manual confused me by stating that the battery should be fully discharged, enter a larger value, then re-charge and re-enter the capacity. I didn't want to fully discharge the battery, so I didn't follow that step. I did initially enter the 100ah capacity of the battery. I will set it to 100% and see how it goes.

The 8 hrs. of charge is an estimate, should've been close to that. If the BMS tripped, it didn't have the result that AMDPower had, which faulted his Ryobi charger. I charged it again today and it acted exactly like the first charge. Almost forgot about it charging but luckily caught it right before 90% and, like the first charge, the monitor showed some very low, fluctuating amp readings and I disconnected it. I may get tired of monitoring the Ryobi charger and get the proper charger.

 

[Jakeman]

AFAIK, errors accumulate via coulomb counting via self discharge and accuracy of the measurement device. If you coulomb count only, it needs to be "reset" with some kind of "full charge" occasionally or you may run out of juice prematurely depending upon your usage / low Ah number to charge, and guarantee BMS re-balancing (am I right? depends upon the BMS implementation?).

Went with a LiFePO4 48V 16S charger to bypass the timing thing, but in retrospect should have gone with a slightly lower voltage charger but that's minor. I'll probably do a full charge maybe every 3-4 mowings and top balance the 12V batteries once a year. These batteries aren't being asked to do a lot. Was going to throw in some diodes in the 16S charger, but didn't care enough...

You mention going with a lower voltage charger, I see that many are 58.4v and a few are 54.6v. Do you think 58.4 is too high?

 

[wattmatters]

Do you think 58.4 is too high?

That's right at the upper end of a safe LiFePO4 voltage at 3.65 V/cell (assuming the battery is a 16S configuration).

Personally I'd be wanting to drop that charging voltage down to around 56.0 V - 56.4 V range. But check the battery's charge specifications.