Help Needed - Lifepo4 Battery Plans for Ryobi RM480e Tractor

[JimmySteel]

I found this forum by searching for others who had taken the leap and converted their Ryobi lawn tractors from SLA to Lifepo4 batteries. The detailed information posted by @AMDPower, @UltrasoundJelly and others users has been a great resource. Our 48v lawn tractor came with four LEOCH 12v 75Ah SLA batteries. After four years of use, our four original batteries are in very bad condition. These are the test results for the four batteries after a full charge:

1. 96% SOC - 38% SOH
2. 96% SOC - 31% SOH
3. 99% SOC - 29% SOH
4. 100% SOC - 26% SOH

We found what looks like a good replacement at a very reasonable price. Eco-Worthy offers 12v 50Ah Lifepo4 batteries for $199 which is less than buying replacement LEOCH 12v 75Ah batteries from Home Depot. Considering that the depth of discharge for Lifepo4 can be over 90%, compared to around 50% for SLA, it seems that we would have more available power with these than with the original batteries.

$800 to replace all four batteries with free shipping seems like a great solution. We would greatly appreciate help to confirm (or not) this from someone who has more experience or knowledge than we do.

 

[NVS]

You could probably go with these 100ah cells from Docan which seems to be one of the go to suppliers for US available cells. Buy a bms and make your own battery. The other cool thing you can do is add an inverter to it so you could power some yard tools as well.

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[gwang_hoops]

FYI There's a facebook group for the RM480e.

I just converted mine with Ampere Time 12V 100Ah LiFePO4 batteries but was seriously considering going with 50Ah ones. The issue I have is whether the 50A max continuous discharge would be an issue or not with the Ryobi RM480e. I've mowed it twice now with LiFePO4 batteries with a new battery monitor on it and the RM480e caps the current draw at 50A (you can see the current draw go up to roughly +/- 4A around 50A within a second or so). It generally mows my grass between 25 and 50A, with 50A when doing heavier stuff and 25A just moving and spinning the cutting blades. Is this going to be a problem with batteries with a max continuous discharge current of 50A? Don't know, but I wasn't going to take a chance with a BMS shutdown.

Maybe someone with knowledge of BMS max current shutdown behavior could chime in...

BTW, someone else on the facebook page just bought some 50Ah LiFePO4 batteries but hasn't finished it yet.

 

[JimmySteel]

You could probably go with these 100ah cells from Docan which seems to be one of the go to suppliers for US available cells. Buy a bms and make your own battery. The other cool thing you can do is add an inverter to it so you could power some yard tools as well.

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Thanks for your reply. We plan to buy preassembled batteries for our lawn tractor for now to have some reasonable warranty coverage and also for the build quality and weather protection. This is great information for our future projects!

 

[JimmySteel]

FYI There's a facebook group for the RM480e.

I just converted mine with Ampere Time 12V 100Ah LiFePO4 batteries but was seriously considering going with 50Ah ones. The issue I have is whether the 50A max continuous discharge would be an issue or not with the Ryobi RM480e. I've mowed it twice now with LiFePO4 batteries with a new battery monitor on it and the RM480e caps the current draw at 50A (you can see the current draw go up to roughly +/- 4A around 50A within a second or so). It generally mows my grass between 25 and 50A, with 50A when doing heavier stuff and 25A just moving and spinning the cutting blades. Is this going to be a problem with batteries with a max continuous discharge current of 50A? Don't know, but I wasn't going to take a chance with a BMS shutdown.

Maybe someone with knowledge of BMS max current shutdown behavior could chime in...

BTW, someone else on the facebook page just bought some 50Ah LiFePO4 batteries but hasn't finished it yet.

Thanks for your reply. The RM480e Facebook group is a great resource along with this forum. The FB member that did the conversion using 50Ah batteries finished the job and seems to be doing great.

"So I tried it all out, and everything seems pretty good. It can now tackle and complete my entire 1.2 acre yard with hills in 80mins of mowing with about 30-35% charge left afterwards (54V -> 52.1V) – roughly the same performance / capacity as the original 75AH SLAs when new."

We are going to order a set of batteries today and then check on the charger, plug and replacement gauge for the dashboard.

Thanks again. This is exactly the confirmation we were looking for to move ahead with our plans!

 

[JimmySteel]

FYI There's a facebook group for the RM480e.

I just converted mine with Ampere Time 12V 100Ah LiFePO4 batteries but was seriously considering going with 50Ah ones. The issue I have is whether the 50A max continuous discharge would be an issue or not with the Ryobi RM480e. I've mowed it twice now with LiFePO4 batteries with a new battery monitor on it and the RM480e caps the current draw at 50A (you can see the current draw go up to roughly +/- 4A around 50A within a second or so). It generally mows my grass between 25 and 50A, with 50A when doing heavier stuff and 25A just moving and spinning the cutting blades. Is this going to be a problem with batteries with a max continuous discharge current of 50A? Don't know, but I wasn't going to take a chance with a BMS shutdown.

Maybe someone with knowledge of BMS max current shutdown behavior could chime in...

BTW, someone else on the facebook page just bought some 50Ah LiFePO4 batteries but hasn't finished it yet.

Hi again.

Do you think a 54.6 volt 10A charger will work properly or is a 58.4 10A charger necessary?

Thanks in advance for your help and advice!

 

[gwang_hoops]

If you are talking about a Li-Ion 13S 54.6V charger running at 10A, very likely regardless of how they implement a charging algorithm because of the relatively low current it's hard to screw it up.

Personally, I'd just get a 58.4V LiFePO4 16S charger and get the last few % (?) charge and maybe a little faster.

 

[JimmySteel]

The charger that had been recommended was a 16S 58.4v model. Using a lower voltage 13S 54.6 might mean that the batteries never reach 100%.

Can we use a regular car charger to charge the four 12v batteries before wiring the 48v pack or should we buy a 12v LiFePo4 charger for that as well? Thanks!

 

[gwang_hoops]

Since you're using batteries in series for the mower, I'd want to re-balance them periodically, every 12 months (who knows?), not just at installation due to repeated high current discharge cycles. Too many unknowns and likely differences in chemistry with a "regular car charger".

Here's a link to a "use your lab bench top balance tutorial" that was interesting as an alternative to getting a 12V LiFePO4 charger if you already have a decent power supply.

Top Balance Tutorial

 

[Ampster]

I'd want to re-balance them periodically, every 12 months

I do not believe that is necessary with a BMS or balancer. I drive two EVs and as far as I can tell the BMS in those has been keeping the pack balanced. One is six years old.

 

[gwang_hoops]

I do not believe that is necessary with a BMS or balancer. I drive two EVs and as far as I can tell the BMS in those has been keeping the pack balanced. One is six years old.

True, OP could add a balancer or BMS instead.

I'm old school...I trust simple LiFePO4 charging technology (still made in China) over a $15 Chinese 4S 50/100A balancer/BMS. Simpler the better in a bouncing lawn mower.

 

[Ampster]

I am old school. I trust simple LiFePO4 charging technology (still made in China) over a $15 Chinese 4S 50/100A balancer/BMS. Simpler the better in a bouncing lawn mower.

One of my BMSs cost $600 and was designed to survive the abuse of an automotive use case. It is not the physical bouncing that is the issue, it is the drift of individual cells that causes the cells to vary in voltage. You are free to be the BMS but I would not call that charging technology. I am not old school, but I am too old to waste my time trying to do what simple electronics will do to protect my pack.

 

[gwang_hoops]

One of my BMSs cost $600 and was designed to survive the abuse of an automotive use case. It is not the physical bouncing that is the issue, it is the drift of individual cells that causes the cells to vary in voltage. You are free to be the BMS but I would not call that charging technology. I am not old school, but I am too old to waste my time trying to do what simple electronics will do to protect my pack.

sorry, I'm not arguing your use case and BMS use.

I'm saying for a Ryobi RM480e lawn mower without a suspension, throwing in a $15 BMS with balancer adds more complexity and breakage possibilities (mechanically and electrically) than just using a simple charger once a year.

Difference of opinion, but since you're the senior member here, I'll defer and keep my comments to myself while other members post.

 

[Ampster]

Difference of opinion,

I reread the post and realize you were talking about 12 volt batteries in series each of which has its own BMS. There is no device that I know of that will balance those anyway. As long as the battery manufacturer says they can be strung in series, you are probably okay. It is the excess voltage ofr a series connection that can cause problems with some devices. The other issue to be aware of is if one of the internal BMSs cuts out then the entire string will go offline. I am doing a tiller conversion and I am using individual cells with a BMS instead of putting 12 volt batteries in series.

 

[gwang_hoops]

I reread the post and realize you were talking about 12 volt batteries in parallel each of which has its own BMS. There is no device that I know of that will balance those anyway. As long as the battery manufacturer says they can be strung in parallel you are probably okay. The issue to be aware of is if one of the internal BMSs cuts out then the entire string will go offline. I am doing a tiller conversion and I am using individual cells with a BMS instead of putting 12 volt batteries in series.

I was referring to 4S 12V batteries and I have a mistrust of cheap Chinese stuff without a track record in that environment. Mounting a BMS board in that Ryobi lawn mower (and your tiller less so because the mower is really bouncy) is placing too much faith in the structural integrity of the PCB, soldering, etc. over simple charging.

I'm more likely questioning products more than the average person -- was a software engineer doing consumer electronics including charging algorithms, battery management, etc. Robustness has it's costs.

 

[Ampster]

I was referring to 4S 12V batteries

I corrected my post to read serial not parallel. Each of those 12 volt LFP batteries contains its own BMS so the cells inside each of them are protected. I think we are on the same page, except my tiller with the old gas engine was pretty bouncy and dusty too. I already have a spare BMS for that. Securing all the connections so they do not vibrate loose is important.

 

[ghostwriter66]

So out here in the middle of the 109 degree (SPRING TIME) heat in the oil fields we get pretty easily bored with things ... soooo one thing we like to do is run over to the other competitors compound and get the batteries wet-cell batteries that he is throwing away because they "no longer hold the charge they use to ... some of these are small (car battery) and some are huge (use a tractor to lift) ... BUT each one is basically the same technology ... we dump out the liquid .... rinse out the chambers with water ... then fill with a epson salt and water mixture - hit the battery with 250A of the proper voltage for that battery -- and 9 times out of 10 we can bring the battery back to almost full life ... then we just give those to the locals or whoever needs one ... yes its time consuming .. and yes you hit it for 10 minutes and rest 10 and hit 10 and rest 10 and do that until the specific gravity is right .. BUT if you can do that to your cells try it ... even the so called maintenance free cells require maintenance ...

there are many great videos on youtube that show you how to do it ...

 

[OzSolar]

You could probably go with these 100ah cells from Docan which seems to be one of the go to suppliers for US available cells. Buy a bms and make your own battery. The other cool thing you can do is add an inverter to it so you could power some yard tools as well.

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Just an FYI: I followed that link and my antivirus warned me I was in unsafe territory.

 

[Ampster]

Just an FYI: I followed that link and my antivirus warned me I was in unsafe territory.

My McAfee antivirus had not issue with it.

 

[JimmySteel]

FYI There's a facebook group for the RM480e.

I just converted mine with Ampere Time 12V 100Ah LiFePO4 batteries but was seriously considering going with 50Ah ones. The issue I have is whether the 50A max continuous discharge would be an issue or not with the Ryobi RM480e. I've mowed it twice now with LiFePO4 batteries with a new battery monitor on it and the RM480e caps the current draw at 50A (you can see the current draw go up to roughly +/- 4A around 50A within a second or so). It generally mows my grass between 25 and 50A, with 50A when doing heavier stuff and 25A just moving and spinning the cutting blades. Is this going to be a problem with batteries with a max continuous discharge current of 50A? Don't know, but I wasn't going to take a chance with a BMS shutdown.

Maybe someone with knowledge of BMS max current shutdown behavior could chime in...

BTW, someone else on the facebook page just bought some 50Ah LiFePO4 batteries but hasn't finished it yet.

We installed our four new 50Ah LiFePo4 batteries to replace the 48v battery pack (after charging each to 100% with a 12v LiFePo4 specific charger) and our RM480e tractor works perfectly. We also ordered a 48v LiFePo4 charger and an EzGo connector. There are only two wires coming from the charger and there are three on the EzGo connector. Did you have to make any changes or modifications to the wiring on to the RM480e to get the LiFePo4 charger to work? Thanks!