Easiest battery lawn mower to convert to LiFePO?

Hello,

I'm new to the forum, but have a quick question and a couple quick searches don't seem to address it directly. I'm looking to buy a battery powered electric lawn mower to cut my yard, about 1/3 acre. I'm considering a Neuton 6.4 and the top end B&D mower nost seriously at this point, but I'm open to other options. I have access to very high quality LiFePO cells and modules and know how to manage them and would like to take a mower with a LA battery and build a couple of LiFePO packs for it, making it lighter and eliminating any possible "range anxiety" or fear of being left in a lurch in the event of a battery failure. 36V units are preferred, but I will entertain 24 and 48V units as well. So here's my question:

What current production mowers would be the easiest to do this with?

Any feedback appreciated!

dh

I have the B&D 24v version from a few years back. It's a beast. Brushed motor, and NO CONTROLLER. Yup, no controller. So it can amp spike the living daylights out of my battery. Thick grass, and I can see 100 amps and more. This mower killed sla, and killed NiCad. I now run it on 10 ah of 30c lipo, potentially allowing 300 amps. But to be honest, it works best on 20 ah of it!

Bottom line, if you get the B&D, be prepared to build it a really big pack unless you have some high c rate cells. However, at 36v, the energy it needs to cut the thick patch will be 1/3 less amps than mine uses. I tried overvolting mine to 36v, but it just caused the internal heat breaker to trip pretty quick.

I DO recommend lipo for these mowers, but if free you can afford to abuse lifepo4 some. With the lipo, 20 ah of 24v gives me enough power to easily mow my relatively large yard front and back in one charge easily. I have 1/3 acre, but not 100% grass. The mower is a dream to use, removing 20 pounds of lead really improved how it is to push. No harder than pushing an empty baby carriage around the yard. Half the weight of a gas mower.

Go for it, whichever mower you choose, it beats gas by a long ways. So light, so quiet. I could mow my lawn at midnight and neighbors would never hear it.

For me, the conversion was pretty easy. Mostly just attaching a couple wires with andersons on them to the original battery terminals. I don't use the on board charger, but the original on off switches still work normally.

Hi Dogman,

Thanks for the reply. I'll be using A123 cells, so they can do this job in their sleep. I would imagine it's safe to assume that any mower with a LA battery is going to have +/- connections and that's it--no sense lines checking individual cell Voltages or other sorts of "mystery terminals". I hadn't considered whether a motor controller would be present. No controller is potentially appealing as long as the design doesnt depend on the LA chemistry for current limiting. Sounds like you're not popping motor fuses with your rig, so that's encouraging. Maybe I'll go the B&D route....they're highly rated and should have more reliable support in the long term than Neuton, who seems to still be largely confined to the NW (I'm in the Detroit area).

You don't have to sell me on the benefits of electric. I already own an electric tiller for my garden and snow blower for my driveway, both plug-ins. The yard's just a bit too awkward and irregular for a plug-in, and I have such a great access to cells it would bother me not to go the battery route for the mower. (Repurposing used automotive cells is a pet project.) I also have a 2009 Prius with a Hymotion L5 Plug-in conversion. I'm looking forward to no longer storing gas in the garage. I'm not a big fan of combustion engines generally, and I hate them on yard equipment.

Thanks again for the reply. Anyone else have any experience with doing this?

dh

What A123 cells ?

999zip999 said:

What A123 cells ?

Click to expand...

I can get any but 18650's, but at this point suspect I'll favor the 32113 or the 26650. Depends on what I end up with mower-wise.

dh

Yeah, 10 ah of A123's should do the trick for sure.

When I got my B&D on the cheap, it came with funky lead that sat on display un charged for a year in the store, no charger, and no on off safety key. So right off the bat, the lead could barely mow 25% of my moderate sized lawn. Switching to 5c nicads, the mower blew the 30 amps fuses immediately. Paralelling them, I was able to carefully mow and keep it under 60 amps and not blow the fuses. Finally switching to lipo, now I let er rip in the thick grass, and see 100-150 amps spikes. Holy moly, that's a lot in a tiny little brushed motor. But it's not that bad in normal grass I mowed last week.

Mostly I just wanted you to know a huge amp spike can come when running a mower with no controller. I have no idea if the other brand is so crude, but the B&D is definitely designed to murder your batteries unless they can put out the amps. If you can mow about every 5 days, you get less thick cut, and no amp spikes. Let it go 10 days, and you might have a heavy mow.

Got the bright idea to look at Craig's List last night (duh) and found a used B&D CMM1200 for $75. I suspect this is the same mower you have, DM. I ran the mower for a moment before buying it, and the LA battery appears to be OK, but clearly limited in its ability to deliver big current. I'll be seeing how much "range" it has shortly as well as lifting the cover to look underneath (don't have access to a Torx bit at the moment.) This should be fun!

dh

wb9k said:

Got the bright idea to look at Craig's List last night (duh) and found a used B&D CMM1200 for $75. I suspect this is the same mower you have, DM. I ran the mower for a moment before buying it, and the LA battery appears to be OK, but clearly limited in its ability to deliver big current. I'll be seeing how much "range" it has shortly as well as lifting the cover to look underneath (don't have access to a Torx bit at the moment.) This should be fun!

dh

Click to expand...

I have one too and the A123m1 cells work fine. You can recharge them real fast during breaks.

You can still get them cheap on ES.

http://endless-sphere.com/forums/viewtopic.php?f=31&t=36589&p=758226#p758226

OK, I used the mower to cut my grass today and the existing SLA pack in the mower was able to do the whole yard on a single charge. This verified what the seller told me--it hadn't been used too much, not at all the last couple years, but the thing had stayed plugged in the whole time. The battery appears to have survived this treatment just fine.

However, it was not all roses with the SLA battery. Most of the things I read complaints about in electric mower reviews were present in full force. The mower would bog down easily in tall or wet grass, and (apparently) went into thermal protection a number of times when I got into the taller stuff. I had to stop a few times when the mower quit turning on during heavier work. Let it sit a couple minutes, and you could pick right up. Letting motor speed recover to max on a very regular basis seems to help with this problem. Bottom line, I would consider the mower just adequate for the job with the SLA battery, at least at this point in its life.

After I had mowed most of the yard, I stopped and took the top off and was amazed at how simple the device is. A 17Ah SLA battery (actually 2 12V batteries wired in series and glued together), a thermal breaker, the motor, and a cable running to the switch on the handle. That's it. I giddily removed the SLA unit and quickly jiggered in a 7S3P 20Ah pouch cell module I had laying around and let 'er rip. HOLY CRAP! Just like that, this thing was unstoppable, able to mow through super-tall weeds and thick grass every bit as well as any gas mower I've ever used. Speed stayed up easily and it wasn't overheating anymore. People think these things are underpowered, but this is the fault of the battery chemistry being used. With good LFP, this thing absolutely screams--figuratively of course; it's actually very quiet.

So I'll have to see what makes the most sense for a permanent Li pack. I have some 26650-based modules that can pretty easily be tweaked into all kinds of shapes and configurations and those will probably be my first choice. A Hymotion module might make a good direct drop-in though too, I'll have to try it. The benefit there would be slight over Voltage at about 26.4V, and 25Ah of capacity--way more than enough to mow my yard, even when it's long. If an 8S module like that will work without causing thermal shutdown problems, that may be the way to go. I would probably never need to charge that pack above about 80% SOC and it would last forever.

I'm stoked!

dh

Yep, lug it enough and just like a hubmotor it overheats, despite a blower cooling it. But feed it 24v that doesn't sag like melting lead and it rips along nicely.

But I did find mine did not like 36v. That just ran it at too fast a blade speed, and even lightly loaded it would overheat. Mine runs good on 25v starting voltage 90% of the time, but in really thick grass later in the summer 7s lipo, at 29v top of charge works better. I never tried 8s though. If it rains this year (hasn't for two) I'll start mowing every 5 days instead of 7.

On mine, after removing the lead, I cut a big hole in the top and dropped a box into the hole. To use my mower, I just drop a battery into the tray, plug in and off I go. That way I can store the battery safe, and charge inside.

The really huge benefit to me in lithium was losing the weight of that block of lead. With just 3-5 pounds of battery, it pushes like a dream.

Can you buy these mowers without the battery?

I think they would go nicely with cellmans 24v 20AH a123 packs



EDIT: google showed me this lithium 19 inch mower available. The link doesn't want to become clickable for some reason.. you'll have to copy paste into your browsers address bar...


http://www.tylertool.com/greenworks-25292-40v-cordless-19-in-3-in-1-lawn-mower/gwkn25292,default,pd.html

The Stig said:

Can you buy these mowers without the battery?

I think they would go nicely with cellmans 24v 20AH a123 packs

Click to expand...

I was just talking with a friend about how I am convinced that if you've got the will and know how (and, in my case, luck) to make a decent Li pack, the way to go is buy a used mower for a fraction of what the new ones go for, most of which still used LA batteries. Convert it to Li and you've got a real killer. I'm kind of excited about this. Most reviews of the mower I bought were very negative, and I can see it with the LA batt, but man.....it really did have all the gumption of my old 3.5 HP gasser, and even the 6 HP gasser I borrowed from a friend recently. Mulched better too. And so quiet, and low vibration. Of course, that was with a barely used Fisker module on board---way overkill....I'm curious to see how small and/or used the cells can get and still deliver good performance. This could keep me busy for a while....

dh

dogman said:

Yep, lug it enough and just like a hubmotor it overheats, despite a blower cooling it. But feed it 24v that doesn't sag like melting lead and it rips along nicely.

But I did find mine did not like 36v. That just ran it at too fast a blade speed, and even lightly loaded it would overheat. Mine runs good on 25v starting voltage 90% of the time, but in really thick grass later in the summer 7s lipo, at 29v top of charge works better. I never tried 8s though. If it rains this year (hasn't for two) I'll start mowing every 5 days instead of 7.

On mine, after removing the lead, I cut a big hole in the top and dropped a box into the hole. To use my mower, I just drop a battery into the tray, plug in and off I go. That way I can store the battery safe, and charge inside.

The really huge benefit to me in lithium was losing the weight of that block of lead. With just 3-5 pounds of battery, it pushes like a dream.

Click to expand...

Thanks for all the great feedback. Sounds like durability has not been an issue for you so far. Do you have any idea how many hours it has on it? These things could well burn up with all the overheating that goes on with that saggy solder battery (I think we just coined a new term), but with a good stiff source they should have much improved longevity.

dh

The Stig said:

Can you buy these mowers without the battery?

I think they would go nicely with cellmans 24v 20AH a123 packs



EDIT: google showed me this lithium 19 inch mower available. The link doesn't want to become clickable for some reason.. you'll have to copy paste into your browsers address bar...


http://www.tylertool.com/greenworks-25292-40v-cordless-19-in-3-in-1-lawn-mower/gwkn25292,default,pd.html

Click to expand...

fixed :wink:

Ypedal said:

The Stig said:

Can you buy these mowers without the battery?

I think they would go nicely with cellmans 24v 20AH a123 packs



EDIT: google showed me this lithium 19 inch mower available. The link doesn't want to become clickable for some reason.. you'll have to copy paste into your browsers address bar...


http://www.tylertool.com/greenworks-25292-40v-cordless-19-in-3-in-1-lawn-mower/gwkn25292,default,pd.html

Click to expand...

fixed :wink:

Click to expand...

Thanks,

So what... we gotta know how to clean up the links before we paste them on the forum?

Ypedal said:

The Stig said:

Can you buy these mowers without the battery?

I think they would go nicely with cellmans 24v 20AH a123 packs



EDIT: google showed me this lithium 19 inch mower available. The link doesn't want to become clickable for some reason.. you'll have to copy paste into your browsers address bar...


http://www.tylertool.com/greenworks-25292-40v-cordless-19-in-3-in-1-lawn-mower/gwkn25292,default,pd.html

Click to expand...

fixed :wink:

Click to expand...

Yes, there are a few Li models out there too and I'm sure they perform very well. Might be more expensive than this other route after the first pack goes south or if you want to buy a spare. Maybe not.

dh

I'm in year 4 of my mower now. Used for perhaps an hour a week, for 5 months a year. So I'm guessing 300- 400 hours now. I try not to go too long, and give it the heavy mow, so I don't overheat it. Mine was "new" when I got it.

dogman said:

I'm in year 4 of my mower now. Used for perhaps an hour a week, for 5 months a year. So I'm guessing 300- 400 hours now. I try not to go too long, and give it the heavy mow, so I don't overheat it. Mine was "new" when I got it.

Click to expand...

Do you find it more difficult to overheat with a Li battery on board? The difference there seemed rather stark to me, but I've only used the thing once.....

dh

I cobbled together an 8S8P pack of used 26650's tonight to try on the mower tomorrow morning. Beginning nominal capacity 18.2 Ah, it presently should be good for somewhere between 12 and 15Ah. I'll characterize it later. The cells are presently at about 40% SOC and I want to see how they perform with that low a charge on them. Also experimenting with a variety of form factors--this one is really two 12V modules rigged up just like the two gel cells that come stock in the mower. After some additional thought, I do not believe this is the best way to go when using these modules, for a couple of reasons. I have quite a bit of experience with this cache of used cells, but not with having them deliver this kind of current. This will mean having to do things a little differently than I have been able to get away with when using these chopped-up modules in the past, only asking 20 or maybe 30 Amps to run my ham radio setup. They do this quite handily, but a 60Ah stack of new 20Ah pouch cells IS noticeably better. It will surely be so with the mower pulling 60 to 100 Amp spikes. Avg cell impedance with this cache generally runs 3 to 5 mOhms for an individual cell--some ten times what you'll read across a new 20Ah pouch. I expect performance that will be plenty acceptable for mowing my yard to realistic lengths, but won't act like a mini brush hog on a whim the way it did with the Fisker module. However there should be some favorable trade-off here as well because I have an additional series element over the Fisker.



dh

i had one of those B&D mowers once.

got it free off CL, their dad had died and they could not make it work when they were going through his stuff because the key was not in the handle/fulcrum spot. so i wired the hinge thing together and it worked fine but was shooting sparks off the brushes like the 4th of july.

i gave it to bill since he had bigger batteries!!

i bet you melt the brush holders with the A123s.

Mowing continuously too long, longer than the lead would last, could do that. I have 1/3 acre, but most of it's not mowed weekly. I water a strip around the back of the house, so about 150' x 12' is my back lawn. The rest is a junkyard . That gets roundup herbicide. Front yard is xeric native grass and wildflowers, and gets mowed about monthly or less.

So for me, letting er rip with lipo is not a problem. At most, a mow takes me 15-20 min tops. And I learned to mow more often in years when water actually falls from the sky. The overheat breaker rarely pops for me. It really only overheated a lot when I tried 36v on it. That overheated very fast. If you have a 45 min mow yard, mow half, have a beer or a lemonade, then mow the rest.

The key thing for avoiding overheat is keeping the blade speed at it's ideal rpm. Sound familiar to hubmotor bike riders? 23-28v seems to be the magic voltage, and above 25v for thick grass. Sharp blades help too, but I'll confess to not sharpening mine in a few years.

New brushes should be easy to find if you need them. An old motor can get so dirty inside, that brushes start sparking right away in use.

Any brushless mowers out there

Some homebuilds in old threads. I'm not aware of any brushless mowers on the market, but only know the guts of the B&D I have.

I have just acquired a Troy bilt model 188, 19" electric cordless mower. It was sold cheap as the 2-3 year old 9 AmpHr Lead acid batteries were done. What I like about it is it uses four 12V batteries in series to give 48 volts same as the pack(s) I use for my Ebike. I have an A123 pack with the 20 AmpHr cells that should work well with it. The motor label says 48 V at 15 Amps. It has a circuit breaker but no controller as far as I can tell.

MADE IN CHINAAA hehe

I guess these brushed motors are good since theres no need for a controller... If only there was some kind of circuitry that would limit the current spike on start up... how bout a to stage switch on start up, where the first stage has a big resistor in line, allowing the motor to get spinning, and then you switch it to the second position "on" which is go! (no resistor)