Cordless Lawn Mower Adventure

[rscamp]

There have been threads about electric conversions and lithium upgrades to lawn mowers here on the sphere from time to time. I just did a pretty basic LiPo conversion of a new B&D SPCM1936 cordless lawnmower.

The net result in a nutshell is almost 3X the useable run time with a 10 pound reduction in weight.

Just a couple of pics are posted here as I have already posted most of the details in the Off Topic section of BentRider. http://www.bentrideronline.com/messageboard/showthread.php?t=84246 . I'm not sure - registration may be required to view the pics. There is similar information on it over at LawnMowerForum...

The power consumption figures for this 19" mower may be of use to people considering electric lawn mower projects in future. One thing I don't have is motor RPM. I should borrow a strobotach or somehow configure my optical prop RPM meter to get a speed on this puppy...

 

[MikeFairbanks]

I use an electric lawnmower, corded, and like it. No fumes.

 

[chvidgov.bc.ca]

Do you think it would take 48V nominal (Ping), full charge 60V dropping quickly to 53? Is it a brushed motor or brushless? Would the motor take an ebike brushed controller?

 

[Dauntless]

I have a plug in mower, the extension cord is a pain but at least it's not hard starting. I didn't get the cordless because I didn't expect the battery to hold up. A few hundred into LiPo, how long will they last?

 

[rscamp]

Do you think it would take 48V nominal (Ping), full charge 60V dropping quickly to 53? Is it a brushed motor or brushless? Would the motor take an ebike brushed controller?

Can't imagine the motor being brushless - too expensive for a consumer device like this.

Not sure what would happen at that high a voltage - the RPM would be awfully high. I'm not sure you would want to slow it down and run it continuously on a brushed controller - running a speed control around 80% throttle at high loads is hard on it.

If memory serves, the Ping batteries are only 3C. This application would stress them more than the LiPos - how much depends on the capacity of the Ping pack. An equivalent Ping is $200 more for the batteries!

 

[rscamp]

I have a plug in mower, the extension cord is a pain but at least it's not hard starting. I didn't get the cordless because I didn't expect the battery to hold up. A few hundred into LiPo, how long will they last?

People look at cycle ratings and completely ignore all the other factors determining battery life. In a nutshell, I expect this to be trouble-free for about 3 years.

This arrangement is soft-fail - repair is plug and play (with caveats of course).

 

[dogman dan]

How many cycles is RC lipo? Say you only get 200 cycles for example. If your growing season is 6 months, thats only 24 cuts a year. So your lipo lawnmower battery lasts 8 years? Chances are old age is the problem, not cycles.

What I do in practice, is run other things on my 6s lipo packs. I have a 24v B&D mower, and a 24v bike, and can run 12s on other bikes as well. So in the end, the wear and tear I put on a pair of 6s packs to run my mower is pretty minimal.

In this example, he must have a very large yard. 36v 20 ah is a pretty huge pack for a mower. I easily get through my yard with 24v 10 ah. So for my yard, the battery cost is barely over $100. Sure, that's pretty costly compared to gas, but a small price to pay for not walking around pushing a stinker.

Re overvolting a mower with a 48v ping, I don't recomend it. A fast blade speed cuts nice, that's for sure. But it also will throw rocks that much harder. You'd only want to run a faster speed if the cut is particularly tough. I find mowing so easy now with the superlight cordless mower that I don't put it off till it's too tall to cut anymore.

My B&D mower is just a simple brushed mower, with no RPM controll. So it's pull a switch and go. There is a charger inside, But I don't use it. When I ran my mower on 24v nicads, the mower could blow the 20 amp fuse on the pack. So you can pull a nice spike when you hit some thick grass. But a 15 ah ping could handle it I think.

Really love it that I can mow at 6 am, and not wake the neighbors.

 

[rscamp]

How many cycles is RC lipo? Say you only get 200 cycles for example. If your growing season is 6 months, thats only 24 cuts a year. So your lipo lawnmower battery lasts 8 years? Chances are old age is the problem, not cycles.

What I do in practice, is run other things on my 6s lipo packs. I have a 24v B&D mower, and a 24v bike, and can run 12s on other bikes as well. So in the end, the wear and tear I put on a pair of 6s packs to run my mower is pretty minimal.

In this example, he must have a very large yard. 36v 20 ah is a pretty huge pack for a mower. I easily get through my yard with 24v 10 ah. So for my yard, the battery cost is barely over $100. Sure, that's pretty costly compared to gas, but a small price to pay for not walking around pushing a stinker.

Re overvolting a mower with a 48v ping, I don't recomend it. A fast blade speed cuts nice, that's for sure. But it also will throw rocks that much harder. You'd only want to run a faster speed if the cut is particularly tough. I find mowing so easy now with the superlight cordless mower that I don't put it off till it's too tall to cut anymore.

My B&D mower is just a simple brushed mower, with no RPM controll. So it's pull a switch and go. There is a charger inside, But I don't use it. When I ran my mower on 24v nicads, the mower could blow the 20 amp fuse on the pack. So you can pull a nice spike when you hit some thick grass. But a 15 ah ping could handle it I think.

Really love it that I can mow at 6 am, and not wake the neighbors.

Agreed. The LiPos will die of old age before using all the cycles with my usage profile (shallow cycles, low charge/discharge currents). You've got a good dual-use arrangement. Just cycling, my usage profile would probably get thousands of cycles out of these LiPos, not hundreds. So the trick in my case is to minimize aging of the LiPos. My usage profile will have them ready for storage around 50% SOC in a cool place, for example...

Yes, quite a large amount of grass is being mowed in my case. And there's a lot to be said for having absolutely no "range anxiety".

 

[chvidgov.bc.ca]

When I looked at the connection of the BD battery pack to the chassis a few weeks ago, it seemed to have 4 pins for the power - are there two positive and two negative? I'm curious why I saw four connectors on the pack...not sure if it was that particular model.

 

[dogman dan]

Carger in and discharge out would make sense for a bms pack. But seems odd for sla's.

No range anxiety is good. My tired old nicads were not much better than the sla's. Mows a 1/3 acre my ass. 10 ah of lithium has no problem for me to mow front and back. Only about 1/2 of my third of an acre is grass. the rest grows junk.