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

Cool. Thanks! One more question... If I get raw cells and a BMS, any idea how I should enclose that stuff to fit in the area of the four SLA batteries? Are there any good Battery boxes out there that fit in same dimension as a 12SLA?
 
First you are going to want to know the size of the cells you choose, then determine how many you will group together, then find/make a box that size. For instance, here is an image of 16x 135ah cells in an 8x2 configuration. This layout measures 13.5" wide and 15.125" long, and 7.25 high (plus wiring on top). These are 135 amp hour cells, 100's would take up even less room. I just didn't have the 100's already in a file so I used what I had. It also depends what you buy as some are tall and narrow and some are short and wide.

135ahx16lifepo4.png
 
After looking into building my own and the cost, I think I may end up going with the 100AH Ampere. Four of these would be 48V at $2000. It would provide plenty of current and is plug and play with the existing battery storage. Given that four new SLA batteries would run me $700, it seems like a no-brainer. If my calculations are correct, it likely would last the life of the mower if I well maintain them. Building my own wouldn't save me much from what I'm thinking.


Does that seem to make sense? $499 for 12V 100AH with a 100A BMS (280A peak) sounds pretty reasonable right?
 
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That 280 peak is only for 5 seconds so if you pull over 100 amps going up a hill, you might not make it all the way to the top. That said, I believe you took some readings and came to the conclusion you wouldn't be pulling over 100 anyway even up hill. Worst case scenario is you do not mow on the way up, just on the way down if it comes to that. So yes, those batteries look like they will do what you want.

I'm the type who like projects and since I have sourced from China before, I do not mind spending a lot of time asking questions and getting quotes. I would expect to pay less than 900 for 16 cells delivered with a bms for another 150. To me, it's worth the money difference but I completely understand those whose time is better spent to them doing something else.

BTW, it's really cool that you have an electric zero turn. I didn't know there was such a thing until your post.
 
If you need 48v, then get or build an actual 48v battery. Some manufacturers are OK with series connecting their 12v LiFePO4 batteries, some aren't.

I doubt that the 280 Ah cells will fit your compartment, but just for comparison, I bought eight 280 Ah cells (including shipping, taxes, fees) for just over $900. That's 2.8 times the capacity of a 100 Ah cell for about the same money you're looking at in an off-the-shelf battery.

If it was me, I would max out the available space in the compartment with the largest cells I could buy.
 
HRTKD said:
If you need 48v, then get or build an actual 48v battery. Some manufacturers are OK with series connecting their 12v LiFePO4 batteries, some aren't.

I doubt that the 280 Ah cells will fit your compartment, but just for comparison, I bought eight 280 Ah cells (including shipping, taxes, fees) for just over $900. That's 2.8 times the capacity of a 100 Ah cell for about the same money you're looking at in an off-the-shelf battery.

If it was me, I would max out the available space in the compartment with the largest cells I could buy.
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Great point. I had forgotten that some of the pre-builts do not handle being wired in series. I'm also in complete agreement with the rest of what you said.

Edit to add: 16x280's in the above configuration would measure 23"x14"x9 high if you are wondering if it would fit in the amount of space you have available.

Additional add: the batteries OP linked to can be wired in series up to 48v.

From the reviews-
"Q: Can this battery be wired in series for 24v applications?
A: Yes. This battery can support wired in series for 24V application;
And This battery can support maximum wired in series for 48V applications, if you have demands on 48V, you can wire 4 modules in series to support 48V."
 
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Yes, it's allowed up to 48V by the manufacturer. I won't be bogging down if I have full voltage. That couple second 100A draw was when I was reading 40-44V. I'm expecting these batteries to average around 50A and peak at around 80A worst case. There really is no point in going past 100AH. I'm cutting 1.25 acres of grass and that will likely get me cutting 4 acres with 100AH Lithium. I also can't wait until mid-summer to get the batteries. I briefly looked at 120AH cells from AliExpress (recommended by Will on his site) that could ship from US but I'd be at $1700 just for the cells. And then I'm not sure what to build the box out of. Is it OK to use Wood? Really, capacity above 100AH does nothing for me. $900 for cells sounds good for cells but how long would that take to receive?
 
Also, regarding zero turn electric mowers... This wasn't available when I got the Ryobi but EGO just came out with one that is run off of their standard Lithium 56V battery packs! Range isn't as good as the Ryobi though. Up to 2 acres.

egopowerplus.com

POWER+ 42” Z6 Zero Turn Riding Mower

The EGO Power+ 42” Z6 Zero Turn Riding Mower produces Power Like No Other ZTR out there, gas or cordless.
egopowerplus.com egopowerplus.com
 
AMDPower said:
Yes, it's allowed up to 48V by the manufacturer. I won't be bogging down if I have full voltage. That couple second 100A draw was when I was reading 40-44V. I'm expecting these batteries to average around 50A and peak at around 80A worst case. There really is no point in going past 100AH. I'm cutting 1.25 acres of grass and that will likely get me cutting 4 acres with 100AH Lithium. I also can't wait until mid-summer to get the batteries. I briefly looked at 120AH cells from AliExpress (recommended by Will on his site) that could ship from US but I'd be at $1700 just for the cells. And then I'm not sure what to build the box out of. Is it OK to use Wood? Really, capacity above 100AH does nothing for me. $900 for cells sounds good for cells but how long would that take to receive?
Click to expand...

On a mower, I would be reluctant to build a box out of wood. Aluminum perhaps.

45 days is about the average shipment time frame from China by ocean freight. Less if you choose air freight.
 
You might be able to find some off-the-shelf battery boxes to contain/protect the cells.

I would be tempted to build a metal or fiberglass box to replace the existing battery tray. It all depends on how much space there is and how much I like the existing set up. Since you are replacing heavy lead with something less heavy, the weight of a metal box may be insignificant
 
Another way to go about it is to look on alibaba for what you want and then contact supplier and request a quote for door to door pricing (DDP) to your location. The prices are regularly better than aliexpress.

By the way, what are the dimensions of the battery compartment?
 
The battery tray is made to hold four SLA batteries exactly with minimal space between them. So it's around 28" Long by 15" Wide by 8.5" High. It's a metal cage and there is a picture shown at the beginning of this post that somebody clipped.
 
In the meantime to get you through some mowing -- have you ever thought that your existing agm's are out of balance, and may have been charged badly by the mower itself? Did they sit on the mower's charge circuit and cook, or did you leave them uncharged for 6 months at a time...

Have you considered charging each one individually with a charger that has an agm-setting externally to the mower's own circuit - at least once to make sure they get a true full charge and are in as much balance as they can be? Look for faulty / corroded / loose battery connections.

It's stuff you can do now to get you through, prior to your conversion.
 
Thanks. I'll do that. I need to take it apart to get the true measurement of the compartment anyway. They always sit on the charger as recommended. I measured voltage and they were all even at full and at "dead" using the regular charger but I assume that it will balance on draw anyway. How do you recommend I do a proper balancing? Should I run them down and then fully charge using an external charger?
 
Regarding a case for your build, if you were to get the 100ah cells linked in post #10 by Jim, 16 would fit in this milk crate. The crate measures 12x18 internally while the pack would measure 11.4x15.4. You would have to sawzall the top off as it is a bit high at 11" and said you have 9". The batteries in the link are just under 5.25" tall so plenty of room on top to add BMS. It would be good to ask them for size verification while checking for door to door pricing.

Just some thoughts.
 
AMDPower said:
Thanks. I'll do that. I need to take it apart to get the true measurement of the compartment anyway. They always sit on the charger as recommended.
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Fine. Your onboard mower charger might be becoming flaky, or in many cases inadequate to start.


AMDPower said:
I measured voltage and they were all even at full and at "dead" using the regular charger but I assume that it will balance on draw anyway. How do you recommend I do a proper balancing? Should I run them down and then fully charge using an external charger?
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NO, do NOT run them all the way down. Simply charge each one up *individually* with an external charger once. Use a decent one, not a wall-wart. Set for agm (I'm assuming they are agm and not gel) That will bring them and their internal cells into balance. Now operate as usual, and use the mower charger for regular storage and charging, because individually charging every time you want to mow is not practical! :)

Now you'll reduce some variables. Either your bank got out of balance, or it may simply point to the fact that you wore them out from normal use. But inadequate charging and premature death from abuse is more common.

I just don't want your grass growing too tall while you are shopping for LFP! :)
 
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Thanks for everyone's help on this! I ended up getting in on a group buy discount with Michael and went with Ganfeng 100AH cells and an Overkill 48V 100A BMS. I'm currently searching for an ABS flight case that I might be able to use to house everything. Excited to get everything!
 
AMDPower said:
Thanks for everyone's help on this! I ended up getting in on a group buy discount with Michael and went with Ganfeng 100AH cells and an Overkill 48V 100A BMS. I'm currently searching for an ABS flight case that I might be able to use to house everything. Excited to get everything!
Click to expand...

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.
 
AMDPower said:
.... I live in Ohio....
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Are you by chance the guy who hit me up on craigslist for the blue 90ah cells I have a few months back? Someone was doing the EXACT same project you are, and lives close by.
 
No, that wasn't me. That's pretty funny though. I'm still waiting on the cells unfortunately. I ended up going with an overkill solar 16S 100A BMS. It will be plenty. It's 100A continuous and peaks much higher than that for up to 30s. I have the BMS and a Pelican case that I'm using to house everything. All I have is a shipping label thus far.
 
AMDPower said:
Nice picture. Yep. That's exactly it. But 280ah! Damn... I'd be able to cut the whole neighborhood with that. That would seem to be expensive no? Any suggestions/links on a low cost 100ah+ cell and a a good housing that I can strap these together in?
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Believe it or not... usually it's way cheaper.
 
AMDPower said:
No, that wasn't me. That's pretty funny though. I'm still waiting on the cells unfortunately. I ended up going with an overkill solar 16S 100A BMS. It will be plenty. It's 100A continuous and peaks much higher than that for up to 30s. I have the BMS and a Pelican case that I'm using to house everything. All I have is a shipping label thus far.
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When I was looking into an electric mower I kept balking at the lead acid batteries in the ryobi.


Then I looked at the lithium cub cadet and laughed at the price.

Then I bought a gasser cub cadet and am pretty happy about it. In hindsight, I could have put a few solar panels out back and would have been happier, but here we are.

Knowing what I know now, I'd have done exactly what you did and just upgrade to lithium after a few years.
 
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