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

Hedges said:
Unfortunately, I don't think NTC can be paralleled. Needs all its material thermally joined. (PTC, for fuses, I think could be paralleled.)
So you need a big enough one. And by the way they run HOT ?

Some batteries have built-in inrush circuits.
I think some of the Signature Solar server-rack batteries may have.
The issue is whether it meets needs for any given inverter a customer uses it with. External inrush, people can do their own.
But motor likely has less capacitor than big home inverters.
Click to expand...
Yeah, noticing that about the NTC.

The Signature Solar NG4-WP 48V, 100Ah, with its 200A BMS is actually the most surprising to see needing the pre-charge circuit be added...as with its 200A BMS and 350A short circuit safety, I thought it would be more than enough to handle the in-rush...considering we are looking at over ~9600W Steady, and ~16800W short being handled by its BMS.

If I do some quick math (with estimates)...taking 1hp = ~750W, the ZT540e being at most ~8hp we see 6000W this is absolute maximum as that would be at 48V 125A, and risking the fuse.

If we take this, and calculate what *could* be acceptable for the previous lead-acid batteries in short bursts....could the in-rush be roughly 400-550A, 19,200-26,400W?
 
Salmon said:
Yeah, noticing that about the NTC.

The Signature Solar NG4-WP 48V, 100Ah, with its 200A BMS is actually the most surprising to see needing the pre-charge circuit be added...as with its 200A BMS and 350A short circuit safety, I thought it would be more than enough to handle the in-rush...considering we are looking at over ~9600W Steady, and ~16800W short being handled by its BMS.

If I do some quick math (with estimates)...taking 1hp = ~750W, the ZT540e being at most ~8hp we see 6000W this is absolute maximum as that would be at 48V 125A, and risking the fuse.

If we take this, and calculate what *could* be acceptable for the previous lead-acid batteries in short bursts....could the in-rush be roughly 400-550A, 19,200-26,400W?
Click to expand...
To add, how are you folks with custom battery packs and external BMS? Do you also need the pre-charge circuit? If not, what BMS is used? Does it have overcurrent/short-circuit protection, and if so, what are the current levels set to trigger them?

This info can greatly help us "drop in" folks know what to look for when selecting pre-configured modules.
 
100 Ah AGM, someone measured 4000A short-circuit current. You can calculate internal resistance from that, add whatever wire resistance in the mower. That would give peak inrush into a large capacitor bank.

Charging a capacitor from a voltage source, there will be a peak current and tail-off, with integral of I^2R ("R" from the fuse) depositing energy that might melt the fuse.

For BMS, using MOSFET resistance you would get the energy deposited in them. BMS may tolerate some over-current for a brief time. If contactor, it bounces and can weld.

Unless there is some current limit, it is likely to trip a BMS with any good size capacitor.
If going directly to a motor, winding resistance would be high compared to what a capacitor presents.
Mower might power blades directly, but BLDC is popular these days, would likely limit current. Drive wheels would be variable speed, VFD.

Those server rack batteries were meant to power ... servers. They weren't designed for inverter and motor applications. So long as a load does NOT start drawing current immediately, all that would be needed is a time or current based circuit to gradually ramp up gate voltage. Power dissipation in MOSFET could be made arbitrarily low, also deposited energy. But only so long as the load is patient, doesn't turn on.
 
Hedges said:
100 Ah AGM, someone measured 4000A short-circuit current. You can calculate internal resistance from that, add whatever wire resistance in the mower. That would give peak inrush into a large capacitor bank.

Charging a capacitor from a voltage source, there will be a peak current and tail-off, with integral of I^2R ("R" from the fuse) depositing energy that might melt the fuse.

For BMS, using MOSFET resistance you would get the energy deposited in them. BMS may tolerate some over-current for a brief time. If contactor, it bounces and can weld.

Unless there is some current limit, it is likely to trip a BMS with any good size capacitor.
If going directly to a motor, winding resistance would be high compared to what a capacitor presents.
Mower might power blades directly, but BLDC is popular these days, would likely limit current. Drive wheels would be variable speed, VFD.

Those server rack batteries were meant to power ... servers. They weren't designed for inverter and motor applications. So long as a load does NOT start drawing current immediately, all that would be needed is a time or current based circuit to gradually ramp up gate voltage. Power dissipation in MOSFET could be made arbitrarily low, also deposited energy. But only so long as the load is patient, doesn't turn on.
Click to expand...
4000A short circuit for deep cycle!? wow, I wouldn't think the in-rush for this mower comes close to that...but who knows.

With these mowers motors its ~6 (4x 80V 470uf + 2x 80V 220uf on the deck motor controllers, drive motor controllers are covered) capacitors per motor controller, and in my case, 5 total motor controllers. The in-rush is those ~30 capacitors immediately needing current as soon as the operator turns the key to run and the main relay completes the circuit.

Many drop in LiFePO4 batteries with built-in BMS have 2-3 stage overcurrent protections, the first 1-2 the BMS will operate in for 5-10 seconds, then the last being the full short circuit protection and usually shutting the battery off <0.1ms, we are seeing the in-rush from the capacitors hitting the short circuit protections.

And yes to your last point, that's why the pre-charge circuit works in these cases. What I am trying to figure out, is for anyone who is looking to do a Lithium conversion upon one of these mowers, in the simplest way possible, what would that look like now, so I can explain that to people near me.

Therefore I need to know if going "drop-in" replacement route for LiFePO4, a pre-charge circuit will be fully necessary, alongside a good recommendation to replace the charger, as well as what batteries to recommend.
 
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I think the successful builds that do not require a precharge circuit inadvertantly employed a BMS with automatic reset after a short circuit is detected. My theory is If your BMS requires a dumb charger to reset itself after a short is detected, you will require a precharge bypass or similar. If your BMS auto-resets, it will just work.
 
noride said:
I think the successful builds that do not require a precharge circuit inadvertantly employed a BMS with automatic reset after a short circuit is detected. My theory is If your BMS requires a dumb charger to reset itself after a short is detected, you will require a precharge bypass or similar. If your BMS auto-resets, it will just work.
Click to expand...
Willing to stand corrected here, but would the BMS going into short/reset at all cause the main relay to re-open (due to lack of power to solenoid), shutting the mower off, then close again upon restarting, turning the mower back on?

May not be an issue, but I would think it could be something notable if it does occur.
 
Salmon said:
Willing to stand corrected here, but would the BMS going into short/reset at all cause the main relay to re-open (due to lack of power to solenoid), shutting the mower off, then close again upon restarting, turning the mower back on?

May not be an issue, but I would think it could be something notable if it does occur.
Click to expand...
I think that would depend on the responsiveness of the BMS, right? seems like it would depend on how long until current is reapplied, but I am just speculating based on observations in the thread. Who knows..

What it doesn't seem to have anything to do with, though, is the rating of the BMS itself, a couple people with 150a+ rating ended up facing the same issue.
 
noride said:
I think that would depend on the responsiveness of the BMS, right? seems like it would depend on how long until current is reapplied, but I am just speculating based on observations in the thread. Who knows..

What it doesn't seem to have anything to do with, though, is the rating of the BMS itself, a couple people with 150a+ rating ended up facing the same issue.
Click to expand...
Right, solenoid relays are quite quick though.

Notably to the second part...in post #696 I believe, @NightStorm is having the issue with the in-rush current with the EG4-WP: https://signaturesolar.com/eg4-wp-lithium-battery-48v-100ah
Which has a BMS at 200A, and short circuit rating of 350A

It's so far been the highest current rated BMS I've seen here, and it still trips.

Another wonder of mine is if you want to avoid DIYing a pre-charge circuit, while going drop in, is if it is going to be worth it. As we could start looking at $2000 and up for LiFePo4 batteries with inbuilt BMS above 500A for short loads
Like this one: Vatrer Power 105ah 200A BMS
 
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I am pretty sure someone also tried a Chins 48v as a drop in, which comes with a 500a peak discharge rating with the same challenges. There's really no telling if that $2000 option would fare any better.

I am leaning towards these myself, if I don't just cave and build my own:

There is a review from 2022 that implies they are drop in, but I am waiting for feedback from @Julie EVD. They took the plunge last week. Hopefully these are a suitable choice.
 
Cover over key switch, and lifting the cover enables precharge?

Precharge enabled by weight on seat?

Key switch has a "key left in ignition" contact, and that enables precharge?
"Insert key and wait until light goes out before starting".

Two-position switch, "Accessories" and "Run". "Turn to first position, wait until light goes out before starting." Same as my diesel.
 
noride said:
I am pretty sure someone also tried a Chins 48v as a drop in, which comes with a 500a peak discharge rating with the same challenges. There's really no telling if that $2000 option would fare any better.

I am leaning towards these myself, if I don't just cave and build my own:

There is a review from 2022 that implies they are drop in, but I am waiting for feedback from @Julie EVD. They took the plunge last week. Hopefully these are a suitable choice.
Click to expand...
The Chins 48V from what I read have a 500A short circuit trip

The Vatrer has a 600A-3 second Overcurrent with 750A short circuit trip.

If you could fab room...there's this beast:
Cloudenergy 48V 150Ah with a 1000A short circuit trip.

The data point I would like to know is just what kind of inrush are we talking?

the more I read the more I am seeing the pre-charge is looking to be almost inevitable...making some YouTube videos like Aging Wheels "easy route" recommendation at the end...a bit misleading.
 
Do you happen to know the 'short circuit trip' rating on the Overkill BMS? I couldn't find it easily on their website, but I am the quintessential layperson.
I'd be curious to know because that one seems to be unfazed by the issue. I was able to confirm the Overkill is able to reset itself without user intervention after a short, however.
 
noride said:
Do you happen to know the 'short circuit trip' rating on the Overkill BMS? I couldn't find it easily on their website, but I am the quintessential layperson.
I'd be curious to know because that one seems to be unfazed by the issue. I was able to confirm the Overkill is able to reset itself without user intervention after a short, however.
Click to expand...
It's programmable to my knowledge, which is why I was trying to ask any folks who used it what they may have set it to, if that is the case...

@AMDPower did you use the overkill BMS?
 
So after doing estimation math for too long, and consulting a eentsy bit of AI to scour the web for the specs of Ryobi's motors and motor controllers.

Given AI's ability to make up facts, take all following with doctors recommended doses of salt.

The estimated inrush current I have is 370-400A

Given this;
BLUF: Any LiFePo4 battery package with at least peak amperage of >400A should be good to "drop in" without a pre-charge circuit

The CHINS 48V 100ah Battery should be specced Ok to drop in WITHOUT a pre charge circuit, but at 500A peak, it is close, and this is reliant on some speculation both due to possible AI shenanigans, and inconsistent marketing from CHINS:
On Amazon: Peak Amps "500A"
On CHINS website: Peak Amps "300A"???

The Vatrer 48V 105ah Battery is well above what's needed to run at 700A [correction 600A-for 3 Seconds, 700A was a Typo] peak with no pre charge circuit, and may just be a "safe" bet, less reliant on speculation due to a higher buffer.
[Correction 2, Some inconsistent marketing with Vatrer exists, as their website does not have the 600A spec, only the amazon listing does, Thanks @MowerConversion for the catch!]

All Ampere/Li Time package BMSs that I have seen have 250-300A peak current and will require a pre-charge circuit

The EG4 48V 200A battery short circuits at 350A, just below 370A, and needs a pre-charge circuit
 
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chazman113 said:
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.
Click to expand...
I'm in my 4th season with a 42" Ryobi ZTR (100AmpHr). Since purchase I've observed an "in house" rule of stopping mowing at or before 50% depth of discharge. Battery life and mowing time was fine thru the first three seasons of use. Now in the 4th season, I'm getting only 20 minutes or so of mowing run time when I reach 50%. So the research has begun regarding how to convert to Lithium. I'm leaning toward a single 48V, 96AH battery, new (matching, for lithium) charger and new charge indicator. I'd rather not "fiddle" with four 12V batteries and balancing - hence the single 48V battery intention. I've been reading with great interest about "pre-charging" the capacitors. I'm going to have to learn fast - the old SLA's are nearing end of useful life.
 
Ed C said:
I'm in my 4th season with a 42" Ryobi ZTR (100AmpHr). Since purchase I've observed an "in house" rule of stopping mowing at or before 50% depth of discharge. Battery life and mowing time was fine thru the first three seasons of use. Now in the 4th season, I'm getting only 20 minutes or so of mowing run time when I reach 50%. So the research has begun regarding how to convert to Lithium. I'm leaning toward a single 48V, 96AH battery, new (matching, for lithium) charger and new charge indicator. I'd rather not "fiddle" with four 12V batteries and balancing - hence the single 48V battery intention. I've been reading with great interest about "pre-charging" the capacitors. I'm going to have to learn fast - the old SLA's are nearing end of useful life.
Click to expand...
Well I will be biting the bullet on my own math soon and installing a Vatrer 48V 105A (more for features and an included 22A charger)
I have a buyer that wants to repurpose my current Li-time 12V 100ah batteries, so I will be using those funds to buy the Vatrer

If it's all correct you may not have to build a pre charge circuit, see post #739 above yours
 
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Salmon said:
So after doing estimation math for too long, and consulting a eentsy bit of AI to scour the web for the specs of Ryobi's motors and motor controllers.

Given AI's ability to make up facts, take all following with doctors recommended doses of salt.

The estimated inrush current I have is 370-400A

Given this;
BLUF: Any LiFePo4 battery package with at least peak amperage of >400A should be good to "drop in" without a pre-charge circuit

The CHINS 48V 100ah Battery should be specced Ok to drop in WITHOUT a pre charge circuit, but at 500A peak, it is close, and this is reliant on some speculation both due to possible AI shenanigans, and inconsistent marketing from CHINS:
On Amazon: Peak Amps "500A"
On CHINS website: Peak Amps "300A"???

The Vatrer 48V 105ah Battery is well above what's needed to run at 700A peak with no pre charge circuit, and may just be a "safe" bet, less reliant on speculation due to a higher buffer.

All Ampere/Li Time package BMSs that I have seen have 250-300A peak current and will require a pre-charge circuit

The EG4 48V 200A battery short circuits at 350A, just below 370A, and needs a pre-charge circuit
Click to expand...
@Salmon thank you for exploring this and providing your thoughts on the common drop ins suggested. I also am very interested in a drop in for my 54” ZT model that won’t require a pre-charge circuit.

Curious though, where do you see that the Vatrer battery has 700A peak? I’m seeing the rating listed as “continuous discharge current up to 200A (Peak 400A 35S)”. Maybe I’m misunderstanding something about “peak”?

Thanks!
 
MowerConversion said:
@Salmon thank you for exploring this and providing your thoughts on the common drop ins suggested. I also am very interested in a drop in for my 54” ZT model that won’t require a pre-charge circuit.

Curious though, where do you see that the Vatrer battery has 700A peak? I’m seeing the rating listed as “continuous discharge current up to 200A (Peak 400A 35S)”. Maybe I’m misunderstanding something about “peak”?

Thanks!
Click to expand...
Yeah I think I need the inconsistent marketing on that one too, now that I take a second look
The Amazon Listing has "200A Continuous, 400A 35s, but adds "600A 3s" in the "About this Item" Section

As for the 700A Short circuit Peak...It looks like that was a typo that was in my excel spreadsheet I was using to keep track of this stuff...correcting all now. Good Catch!

I have made the plunge on it, so will update when it arrives and is installed.
 
Salmon said:
Well I will be biting the bullet on my own math soon and installing a Vatrer 48V 105A (more for features and an included 22A charger)
I have a buyer that wants to repurpose my current Li-time 12V 100ah batteries, so I will be using those funds to buy the Vatrer

If it's all correct you may not have to build a pre charge circuit, see post #739 above yours
Click to expand...
So your thinking is that the 48V battery will provide enough short term current supply capacity for the current "in rush" when the main switch is turned ON without tripping out and requiring a re-set?
 
Ed C said:
So your thinking is that the 48V battery will provide enough short term current supply capacity for the current "in rush" when the main switch is turned ON without tripping out and requiring a re-set?
Click to expand...
Certain ones, yes, including the Vatrer.

There are some assumptions to my claim, and I will report results here when the battery has arrived and I am able to test it.
 
NightStorm said:
I should think that your choices should work, but am new to this myself and far from an expert. Your location says "NY" so I don't know how you store your mower in the winter but be careful not to ever charge these batteries when the temp. dips below freezing. Doing so will likely ruin them. Some batteries have low-temp. cut-off to prevent this, many do not.

I went with a single 48v battery that I bought from Signature Solar, intrigued by getting a unit both with low-temp cutoff and with a 200A BMS. I've had to monkey around to implement a capacitor precharge that kicks in for the first few seconds the mower key is turned on, if I don't do this the battery goes into a "PROTECT" state that you can't get it out of w/o another 48v DC source. Personally I'd not recommend this battery 'cause it way too sensitive and goes into PROTECT state very, very easily. As such it is too easy to get stuck with a dead mower way a long way from a 48v power source (and no, the battery charger will not work to take it out of PROTECT mode). The battery has an app that connects via bluetooth but no controls in the app. (I suggested such an app enhancement t in a call to Signature Solar but that seemed to fall on dead ears).

Also, the stock 48v charger that came with the mower works with my battery just fine, my guess is it would work with yours as well.

Good find on the plug, do you know if it fits?
Click to expand...
Thanks for responding. I will keep the mower in a conditioned space that won't dip below 50 degrees F.
NightStorm said:
I should think that your choices should work, but am new to this myself and far from an expert. Your location says "NY" so I don't know how you store your mower in the winter but be careful not to ever charge these batteries when the temp. dips below freezing. Doing so will likely ruin them. Some batteries have low-temp. cut-off to prevent this, many do not.

I went with a single 48v battery that I bought from Signature Solar, intrigued by getting a unit both with low-temp cutoff and with a 200A BMS. I've had to monkey around to implement a capacitor precharge that kicks in for the first few seconds the mower key is turned on, if I don't do this the battery goes into a "PROTECT" state that you can't get it out of w/o another 48v DC source. Personally I'd not recommend this battery 'cause it way too sensitive and goes into PROTECT state very, very easily. As such it is too easy to get stuck with a dead mower way a long way from a 48v power source (and no, the battery charger will not work to take it out of PROTECT mode). The battery has an app that connects via bluetooth but no controls in the app. (I suggested such an app enhancement t in a call to Signature Solar but that seemed to fall on dead ears).

Also, the stock 48v charger that came with the mower works with my battery just fine, my guess is it would work with yours as well.

Good find on the plug, do you know if it fits?
Click to expand...
Thanks for the note on the temperature. Fortunately, our barn is heated. Even without the heat, it doesn't get down below about 45 degrees.
 
Good afternoon Gentlemen. I haven't tried the new batteries yet. I wanted to get a good mow in before I started fooling around with the upgrade. As I've been preparing. I've taken some measurements on the mower in operation that should give us some better data. First and foremost, is the energization curve shown. It peaks at about 312 amps, and is above the rated current (100 amps) for a total of 9 microseconds. That's what the BMS has to hold in for. I put a DC clamp meter on the mower and ran it, and it seemed to reliably stay below 70 amps even in the heaviest grass. That's high speed run and high speed mow. Next weekend I'll try the upgrade.
 

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Interesting, about 5 microseconds per sample, which is very coarse for 10 microseconds per division.
"Fluke Scopemeter", guess that's why.

But here I read 125 MS/s


What is the meaning of an envelope that goes +/- hundreds of amps?

The 312A surge is motor starting? Or connecting battery to load (maybe a capacitor bank of motor drive)?
If capacitor inrush, might be higher with lithium.
 
Julie EVD said:
Good afternoon Gentlemen. I haven't tried the new batteries yet. I wanted to get a good mow in before I started fooling around with the upgrade. As I've been preparing. I've taken some measurements on the mower in operation that should give us some better data. First and foremost, is the energization curve shown. It peaks at about 312 amps, and is above the rated current (100 amps) for a total of 9 microseconds. That's what the BMS has to hold in for. I put a DC clamp meter on the mower and ran it, and it seemed to reliably stay below 70 amps even in the heaviest grass. That's high speed run and high speed mow. Next weekend I'll try the upgrade.
Click to expand...
Ok that's on the ZT480, Thank you So much!

I have a ZT540e which does have 1 additional deck motor so can reasonably assume a higher inrush during those microseconds, I would say my estimates would likely be decently accurate at 370Amps for the ZT540e, and this gives me much more confidence with my decision.
 
Hedges said:
Interesting, about 5 microseconds per sample, which is very coarse for 10 microseconds per division.
"Fluke Scopemeter", guess that's why.

But here I read 125 MS/s


What is the meaning of an envelope that goes +/- hundreds of amps?

The 312A surge is motor starting? Or connecting battery to load (maybe a capacitor bank of motor drive)?
If capacitor inrush, might be higher with lithium.
Click to expand...
To answer your question the 312Amp load is the inrush upon connecting the batteries to the capacitor banks of the motor controllers.
 
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