Lawnmowing: manual and electric powered

[dogman dan]

Right now the run time is about 2 min. That's how easy the lawn is to mow right now. I need to put the CA on it one of these days when it's hard to mow. That will have to wait for rain. This sure isn't Memphis. Last time we got 1/4 inch of rain was October. Trying to grow a thick lawn here is like driving 100 miles for a gallon of milk. A stupid waste of money. I'm watering just enough to keep it barely green. The front lawn is all desert range grass, and gets mowed about 3 times all summer.

When, this year if, the summer rains come, then the lawn in the backyard starts growing like what you are used to, 6" a week. Mow twice a week or you are screwed if you are getting 2 inches of rain a week. Real rain makes it grow crazy fast compared to water from the city wells.

I expect at least 30-40 min run time out of 15 ah lipo cutting thick grass. I got at least that out of 16 ah nicad.

 

[auraslip]

Ouch - 30-40 minutes isn't that much at all! CA seems like a good thing to try out! If I end up running 6s lipo, then I'm planning on using the power logger.

I'm envious of your desert landscape - no allergies - no grass to mow every other weekend! Even if it puts me out of business...

 

[dogman dan]

Suprisingly, allergies are worse here than most places. At least in town anyway. Dry air keeps 10 year old pollens blowing around in circles endlessly. The worst offender is the pecan farmers. Huge pollen counts when an entire valley full of trees blooms. Then in the fall, they blow the same pollen back into the air in the harvest process. Some days, I look and the valley on the way to work and want to turn back, and call in sick.

Not so bad where my house is now, up on the Jornada de Muerto plateau. Plenty of sand, but much less pollen. It is nice to mow less often that's for sure. I still tend to do it weekly anyway, but it takes very little time till the rains come.

 

[dogman dan]

Still no hard data, but a longer mow time today, and a patch or two of thicker grass.

Ran the 6s 15 ah pack I plan to use all summer, and it held up great in the thick spots. Motor does slow down, but not enough to make me walk slow. Took about 15 min, And expect it to take 30 when all of it is thicker. The pack is back on the charger and at 24.18 volts. I would guess a 6s 15 ah pack would definitely do even pretty large yards, front and back. My lot is a third acre but much of the back is dirt.

Really no sag at all I think, just the motor slowing for the thick stuff, like you slow down climbing a hill. Still have to CA it to prove no sag. When it sagged on lead, you could tell there was a slow return to normal speed. Now it just slows for the very very thick spots, and then back to normal cutting. I can walk with it very fast, using such a light mower.

I say, 6 s is fine, if the size is big. I'd rate this 24v B&D cordless mower on 6s lipo, as equal to a small gas mower. Like the 3.5 hp ones. I buy the 5 or 6 hp ones for at work, where we have about 2 acres of grass. It only trims edges, but might need to do the whole thing if the toro breaks down.

 

[auraslip]

thanks for the update dog man

I'm still town between 8s 2p of headway (power cells) and 6s lipo, but I'm leaning towards lipo now.

 

[dogman dan]

Now charged I have the amount used from the pack, 2.6 ah ran the mower about 15 min this time. It would last a shorter time in thick grass the whole mow of course.

Either way it seems real, non saggy 24v is not too bad in the thick stuff. Whatever you end up using, you could have 2s boost packs for a monster cut.

 

[auraslip]

Not too bad - 5ah per half hour....

That comes out too $70 per half hour of run time... super cheap to upgrade!

 

[dogman dan]

Last summer, using nicads, I was getting 30-40 min of run time out of a 16 ah pack. But the sag was still pretty bad the last half of it. A damaged battery, I doubt I was getting more than 10 ah out of it. I never measured it, I could do the yard front and back and that made me happy enough.

 

[sico]

I recomend starting with 18s and work up from there if you need more speed:

 

[auraslip]

cutting your grass and killing yourself!

 

[amberwolf]

It doesn't have a motor on it, but there is a bike like that in the front yard of a house along one back path to a grocery store north of me. I need to remember my camera someday to take a pic of it.

 

[swbluto]

I saw a comment and keep seeing over the internet that the corded electric lawn mowers are appropriate for small lawns, implying they're less than optimal for larger lawns. What makes them inappropriate for larger lawns? If it's the limited range of the electric cord, couldn't one just use an extension cord?

Also, what would be best for larger lawns?

 

[swbluto]

I recomend starting with 18s and work up from there if you need more speed:

I was thinking about motorizing one of these manual lawn-motors by somehow attaching an outrunner to the helical blades and then running it as 6000 RPM with its potential of 6 kW. That would cut any kind of grass, wouldn't it?

(I know, adapting a regular electric mower would be more sensible, but the mental image is just too entertaining of seeing helical blades spinning at 6000 RPM.)

 

[amberwolf]

Sometimes it's probably just that really long cords are difficult to manage, especially without forgetting and running it over. :lol:

Some of the electric mowers have insufficient cooling for the motor, so the larger the area to cut, the hotter it gets, until finally it will reach a point that may damage the motor (or melt the plastic mounting bits many of them use).

The one problem I see with motorizing a helical cutter is the danger of injury, if you don't have a sufficiently powerful brake on it to stop it instantly if you let go of the handle. Normally it stops very quickly if you're not pushing it, virtually instantly if in uncut grass, but with the motor it could easily just keep chopping bits of you off if you tripped and fell into it.

 

[dogman dan]

Like in the movie frankenhooker. 8) When I cut golf course grass, the reel mowers for greens had a dead man switch in the seat to prevent that. It would stop the pump on the hydraulic powered reels. The big Jacobsen tractor had no such thing, and a throttle set on the dash. 12 reels cutting about 16' wide So if you fell off it, you'd get made into hamburger. Just like plowing with a tractor would if you fell off.

Any more than 100' of cord on electric mowers is a pain, and you get voltage drop if it's not thick cord. But on a small yard, like on the houses built nowdays, a 50' cord is perfect. So is a pushed reel mower. I'm thinking of yards that are perhaps 40'x40' or less. Mines about 40' x 200' in back. I did it with a plug in electric for a few months, but it was a hassle to keep moving where I was plugged in as I went around the house.

 

[PedalingBiped]

 

[fizzit]

Ya can't embed photos from facebook :|

 

[PedalingBiped]

I've done it before, so what now?

 

[fizzit]

Hmmm... I'd say your privacy settings may have used to be "everyone can see photos" and are now at "only facebook users can see photos"

But I can't say for sure. I went to the URL your photo was at and it worked but I had to log in first.

 

[dogman dan]

I put the 15 ah 6 s pack on the 24v B&D string trimmer yesterday, and found it so powerfull it kept tripping the amp limit inside the trimmer. Really cut nice though! The amp limit would trip when the string automaticly advanced, and could stall the motor till the cutter on the guard trimmed it to length. So much power had me burning the string a lot. I find string trimmers work best when run as slow as the cutting job will allow.

I might just have to run the thing on 5s, to better imitate saggy 24v nicad. :lol:

 

[swbluto]

I put the 15 ah 6 s pack on the 24v B&D string trimmer yesterday, and found it so powerfull it kept tripping the amp limit inside the trimmer. Really cut nice though! The amp limit would trip when the string automaticly advanced, and could stall the motor till the cutter on the guard trimmed it to length. So much power had me burning the string a lot. I find string trimmers work best when run as slow as the cutting job will allow.

I might just have to run the thing on 5s, to better imitate saggy 24v nicad. :lol:

Interesting. I was thinking about hooking up my 24volt ping upto an electric trimmer, but I'm now starting to doubt the wisdom of that, lol.

Would you know approximately how many AH the weed eater ate through? I'm curious how many AH of 5s lipo I should order.

 

[liveforphysics]

Run 6s. Solder across the amp-tripping device.

 

[auraslip]

Bypassing the circuit breaker might cause it to over heat. I'm gonna do a thermometer on my motor.... the power logger would be perfect for this....... only goes up to 125c though....
It can monitor RPM, so that should be fun

 

[dogman dan]

Yeah, bypassing the device could lead to smoking the motor. It's cheap, it's brushed, etc. The surge cutoff is preventing damage when the motor gets stalled by the string getting too advanced, or wrapping around a stick that can't cut. So with no controller the thing can draw crazy amps if stalled. Last summer I ran it some on 5s, and it didn't have the problem as much.

I think less is more with string trimmers. More power usually just blows your string. Run string trimmers as slow as possible and still cut, and the string lasts longer. Yesterday I was cutting some freeze damaged grass and ice plant away, so I was revving it up to it's max, and finding uncuttable stuff in the mess.

I don't know how much AH used, I only ran it about 5 min. Last summer, there was no way I could use up a 5 ah pack with the trimmer on a 1/3 acre lot.

 

[swbluto]

Thanks dogman, so it sounds like 5Ah should be plenty for weedeating purposes.

I'm looking into getting a cordless lawn mower and I was looking to adding my own battery pack to it and I need to know how many WH's is typically required for a regular lawn to buy the appropriate battery pack (I was thinking about a123s to take advantage of that 2000+ cycle life and fast charging.)

I was looking http://www.amazon.com/Black-Decker-RB-3610-36-Volt-Battery/dp/B00394E9MY which is a battery for a mower designed to cut upto 1/3 an acre, and I'm guessing that's made of sealed lead? At 28 pounds and $129, that sounds about right...

Wikipedia says that lead-acid gets about 30-40 wh/kg. However, taking into account the puekert affect for this kind of "power application", I'm guessing something like 20 wh/kg would be more reasonable to assume. Since 28 pounds is about 12 kg, that puts the amount of energy used for a lawn at about 240 wh for 1/3rd an acre. Does anyone have numbers to confirm the energy needed to cut a lawn?

I was doing the calculations for a gas lawn motor, and it seems that a typical gas lawn mower uses half a gallon of gas for 1/3 an acre. That's about 6000 wh/energy, and assuming 15% engine efficiency, that's an effective work output of 900 Wh. Hmmm... these two numbers aren't close to each other. I'm wondering what I'm missing...?