# Push mower EV conversion, still worth it?



## rochesterricer (Jan 5, 2011)

Btw, I found this thread by dimitri very interesting and helpful, but he spent a lot more on it than what the commercially available models go for.


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## MN Driver (Sep 29, 2009)

I thought it was worth it. I bought one of the 120 volt plug-it-in type B&D units, turns out it has a failed top bearing so I went to the hardware store and got a real bearing rather than the little spoked sleeve junk it came with. Used it a few times to make sure it worked fine while hauling the extension cord around. Then I had 54 cells of good 30 amp rated 6.5Ah NiMh cylindrical cells laying around that I thought would work great with it. It's 64.8 volts nominal but in reality it is higher even at the end of mowing for me.

The reason why I went with the ones you plug into the wall is that the ones that run off the lead-acid batteries are expensive to buy used(which was my goal) and disappeared FAST when I saw one up for sale or listed to be in a garage sale. ..so after seeing all these plug in models for cheap because people realize that carrying around an extension cord looks stupid and is a complete PITA, I decided to check it out. They use a universal motor and run off of DC. I tested it by connecting my hobby charger directly into its plug that you normally hoook the extension cord into, held the on level of the mower and started NiMh charge mode at 3 amps and it spun right up.

If I had more NiMh cells the performance would be even better, some guys are running these with 80 volts of lithium polymer 5Ah cells(it's where I got the idea). It's up to you how you do it though. I just happened to have the NiMh around but after doing this I'm converting a 120v electric plug-in snowblower with lithium polymer cells for next winter. It's not exactly that cheap but at the same time I like the freedom of being able to snowblow at midnight or mow super early in the morning knowing I'm not waking the whole neighborhood up.


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## rochesterricer (Jan 5, 2011)

Hmm, interesting. I hadn't considered converting a plug in model. A quick search of Craigslist shows lots of them going for cheap. 

How strong is the motor? Does it work ok when the grass gets long and/or wet? Is the performance drastically lower with the relatively low voltage? 

I've looked into battery electric snow blowers before as well. The decent models from companies like Ariens seem to start around 800 bucks and go up from there.


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## Ziggythewiz (May 16, 2010)

My plugin works great. I'm lazy so it tends to get fairly long, and I don't mow when wet, but that's more about keeping the buildup down than being able to cut. Mower's definitely an area where lithium could really help out with the reduced weight on a conversion.


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## MN Driver (Sep 29, 2009)

rochesterricer said:


> Hmm, interesting. I hadn't considered converting a plug in model. A quick search of Craigslist shows lots of them going for cheap.
> 
> How strong is the motor? Does it work ok when the grass gets long and/or wet? Is the performance drastically lower with the relatively low voltage?
> 
> I've looked into battery electric snow blowers before as well. The decent models from companies like Ariens seem to start around 800 bucks and go up from there.


When it was plugged into 120v I was able to walk about as fast as I could through grass tall enough to be seeding and it wouldn't flinch. I never try to mow when its wet because I like to avoid needing to unclog a mower deck. I'm thinking it would perform fine. This worked out fine for me and I mounted the batteries up on the handlebar area to balance the weight but to still have most of it on the front to hold it to the ground, make turning a breeze and still lighter in total weight with the NiMh cells(a little under 20 pounds for the cells).

Performance isn't drastically lower, the blade doesn't spin as fast so for my 64.8 nominal voltage pack, I need to walk about the pace I would walk for a self propelled mower and that speed doesn't really bog down. I would say with an 80 volt pack that you could walk at a reasonable pace and cut through most tall grass patches without slowing down more than you would with a conventional mower.

For what it's worth, there are people who have used a 12v battery hooked to a power inverter. If you already have a 1500w rated power inverter and a good charger, that might work out if you want to do it cheap with lead-acid. No guarantees over weight/handling, fitting the battery, how long you can mow, etc.


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## Joey (Oct 12, 2007)

I bought a used B&D 24V for $200. The circlip that held the motor shaft together had failed and the brushes needed to be replaced. Also the contactor was done, and replacements are very expensive. I made my own starting switch with a contactor and that works really well. $60 for refurbing. When the SLA are done (4 years old) I'll think about Lithium just to lighten the mower. It is heavy with lead. I won't go back to a gas mower.


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## Salty9 (Jul 13, 2009)

Definitely worth it as far as POME (Poor Old Mother Earth) is concerned. Small gas engines pollute more than todays cars.


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## MN Driver (Sep 29, 2009)

I disassembled the pack before winter so I can condition the 9 subpacks(6 cells for subpack) of NiMh cells at the beginning of the season(NiMh self discharge and memory issues leaves me with cell drift city if they are inactive too long), so the pack is currently not attached but let me know where to lay the tape measure and I'll post pictures if you want more details of the 120v version of the B&D. I can post in a few days, it's buried in the garage a bit as mower is out of season at the moment in MN.


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## rochesterricer (Jan 5, 2011)

I'm not sure where in MN you are, but here in Rochester it is looking like I will need to break out the mower soon. What a crazy winter and spring this has been. 

I would love to see some pics if you get a chance. 

About how long can you mow on a charge with your pack? The 5ah you mention above seems kinda small. IIRC, the lead acid B&D models are 10ah right now.


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## MN Driver (Sep 29, 2009)

I like in the Twin Cities suburbs, roughly 100 miles drive from Rochester.

To be honest about how long I can mow. I'm really not sure what the range is of this thing. I had 12 subpacks(72 cells 6.5Ah) of reject worn out NiMh laying around that were going to be used for an ebike but then I killed the bike it was going into and never found a good package for the right price to go through with it and so my plans changes for the batteries. I more or less just charged the good subpacks(9 are good, 3 are shot) up, assembled them in a very crude package with a fuse and used it. I have a quarter acre lot and I'm pretty sure I walk fast enough to get in done in under 45 mins. I haven't bothered to setup any form of monitoring or anything with these NiMh cells as these cells aren't worth much to me. They've never run out on me yet. I'll have to see when I condition them if they are still good for this years mowing or not.

If they die I'll go with Lithium Polymer, which I would monitor Ah drawn out and use a good hobby charger to charge and balance them appropriately. I'd use the same Lithium Polymer pack but with more cells in an electric 120v plugin snowblower that is basically the generic version of the Toro Powercurve 1800 called the Snow Devil that I bought from Menards when they had a 3 day sale for $100. I bought it with the intention of converting it to LiPo, when I do that, the NiMh gets 'parked'. http://www.toro.com/en-us/Homeowner...c/Pages/Model.aspx?pid=1800-Power-Curve-38381


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## rochesterricer (Jan 5, 2011)

I've thought about an electric snowblower like that one, but I'm unsure how well it would work for me. Last winter was a nightmare and our driveway got plowed in real bad every time we got big snow. I have to wonder if one like that would have enough power, especially in the deep stuff. 

To be honest, with the layout of my house I could probably do fine lugging a cord around for blowing snow. That is, if the blower was powerful enough.


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## rochesterricer (Jan 5, 2011)

When you guys talk about other builds people have done, is this from other forums or just from random places on the internet? I'm just wondering if there are communities dedicated builds like this, that I haven't found.


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## rochesterricer (Jan 5, 2011)

http://www.wind-sun.com/ForumVB/sho...120V-AC-corded-lawn-mower-with-litium-battery

This guy is claiming 2.5 hours of battery life on a 20S pack with only 5ah of storage. Does that seem really high to anyone else? Such a pack could probably be built with about $200 worth of lower performance lipoly cells from the RC world.


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## Joey (Oct 12, 2007)

rochesterricer said:


> http://www.wind-sun.com/ForumVB/sho...120V-AC-corded-lawn-mower-with-litium-battery
> 
> This guy is claiming 2.5 hours of battery life on a 20S pack with only 5ah of storage. Does that seem really high to anyone else? Such a pack could probably be built with about $200 worth of lower performance lipoly cells from the RC world.


 
My black and decker mower (8-10 years old) draws 16 amps to spin the cutter blade, no load, from 24 volts of a SLA battery pack. 16 amp*24 v = 384 watts. The capacity of the pack is 17 amp hours. Capacity = 24 v*17 ahr = 408 watt hours. The run time to a flat pack is at most 408 whr/384w = 1.06 hours. The time under load (dry grass) is about 45 minutes, and wet grass 30 minutes.

A 20 series pack has about 80 volts (a generous 4 volts/cell). With 5 amp hour capacity, the pack has 400 watt hours. To last 2.5 hours the power draw would have to average 160 watts. On my mower it would have about an hour of run time.


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## rochesterricer (Jan 5, 2011)

Joey said:


> My black and decker mower (8-10 years old) draws 16 amps to spin the cutter blade, no load, from 24 volts of a SLA battery pack. 16 amp*24 v = 384 watts. The capacity of the pack is 17 amp hours. Capacity = 24 v*17 ahr = 408 watt hours. The run time to a flat pack is at most 408 whr/384w = 1.06 hours. The time under load (dry grass) is about 45 minutes, and wet grass 30 minutes.
> 
> A 20 series pack has about 80 volts (a generous 4 volts/cell). With 5 amp hour capacity, the pack has 400 watt hours. To last 2.5 hours the power draw would have to average 160 watts. On my mower it would have about an hour of run time.


Thanks, that helps me quite a bit. After some playing around on Hobby King, it looks like such a pack could be built for less than $160. If you wanted to get close to a full 120V you could add a couple more 5S packs for a total of under $240. Not bad IMO. Personally, I might be fine with the 20S pack.


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