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GreenWorks 25112 13 Amp 21-Inch Corded Lawn Mower
|You Save:||$108.19 (43%)|
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- Powerful 13 Amp Electric Motor delivers enough power to cut through the toughest grass
- Durable steel 21-Inch cutting deck gets the job done quicker and more efficiently
- 3-in-1 feature provides multiple options for grass clippings from rear bagging, side discharge and mulching capabilities for versatile needs
- 7 position height adjustment offers a range of cutting height from 1-3/4-Inch to 3 3/4-Inch for the perfect cut on all grass types
- 10-Inch rear wheels and 7-Inch front wheels
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|Cutting width||21 inches|
|Item Dimensions||23.2 x 17.2 x 31.5 inches|
|Item Weight||53.1 pounds|
|Manufacturer Part Number||25112|
|Shipping Weight||61.65 pounds|
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|Item Dimensions||17.2 x 31.5 x 23.2 in||16.13 x 26.88 x 18 in||15.75 x 28.4 x 20.3 in||16 x 36 x 38.5 in||18.38 x 30.19 x 17 in||16 x 49.5 x 38 in|
|Item Weight||53.1 lbs||56 lbs||37.5 lbs||28 lbs||36.25 lbs||37.5 lbs|
Greenworks, 13 Amp, 21-Inch 3 in 1, Rear Bag, Mulch or Side Discharge, Converts Easily from Rear Bag to Mulch or Side Discharge Electric Lawn Mower, Model # 25112
Top customer reviews
Let's get a few things out of the way, these do not impact the product score, as they are common to all products in this category:
1. This is a corded mower. Dealing with the cord is sometimes a pain. If you have a lot of trees or obstacles you may want to consider something else.
2. Maximum power is limited to a 120V outlet and what can safely make it out an extension cord (about 1650W, for reference 1HP is ~745W).
3. With no batteries to wear out or engines to refuel/re oil, this is very cheap to operate. Running this mower at peak output generally costs 8-25c/hour. You also hit an advantage in purchase price as gas or cordless units with the same features generally cost 50-100% more.
4. Short of hitting something, bogging down an electric motor generally allows it to produce more power and speed back up again (unlike a gasoline engine).
So, what's good about this? Well:
1. 21" Steel deck. The actual blade is 19.5" leaving you a little less than an inch on either side of the deck that won't be cut. You can get a much closer cut with this than the B&D plastic models that have a very thick plastic housing. It's also going to survive rocks/sticks much better than the plastic ones. Both the discharge cover and bag seem to attach easily and solidly. It also makes it look more like a lawn mower and less like a big kid's toy.
2. Light (<55lbs). Since you're not carrying your power source onboard it will be lighter than any other mower in this size class (compare to 75-90lb for gas or battery electric). Larger rear wheels give easy maneuverability. Single lever height adjust works well and is spring loaded so you can raise or lower it with one hand.
3. 3 in one operation - A lot of electric mowers whether they're cordless or corded are limited on power, most get around this by using more efficient blade designs that generate less lift but mulching can be slower. With a reasonably well manicured lawn it doesn't matter much, but cut quality and performance drop off a lot if mulching tall or really thick grass. Since this model has a side discharge that remains an option for thick grass and improves cut speed significantly without wasting your clippings, quite a few electrics don't have a discharge option.
1. Wheels/axles could be shielded a little bit so the cord doesn't tend to wrap around it and go under.
2. Mulching anything thick is slow, mowing through thick grass can take quite a bit of time (and tends to clump the output.) I think this is more related to the blade design, when you move fast through thick patches it will cut but leave a few standing, if it had more lift I think it would draw these up (and also help propel the discharge better). Unfortunately the blade seems to have proprietary mounting holes so that's hard to do.
Now, into the nitty-gritty:
This mower is powered by a brushed DC electric motor (Globe 7080). Brushed DC motors are lighter and cheaper than AC synchronous motors or induction motors. However they're generally less durable or efficient.
The Globe 7080 has a peak efficiency (their spec) of 68%. Peak efficiency at 3500RPM (590W output at 7.3A), Peak power at 2245RPM (860W output at 13A). Here's why that's a problem:
Mowers are generally limited (by agreement) to a maximum blade tip speed of 19000 feet per minute (for safety of items that may be thrown from the mower). Higher blade speeds give more lift helping the grass get lifted into the cutting path and making cleaner cuts. At max efficiency RPM the blade is moving about 17,800FPM on this mower. If you start cutting too fast you'll bog it down. Because it's electric it picks up torque so it will keep spinning but you don't hit peak power until about 11,600FPM. This is far too slow and you'll start seeing missed cuts and ragged lines (I noticed this in actual usage).
So since you can't really cut that slow, maximum usable power is closer to 600-650W, or less than 1HP. By comparison, a Honda GCV160 engine at 3600RPM (a common governer setting for push mowers) outputs about 3425W, falling to around 2800W at 3000RPM.
Obviously there are electrical supply limitations to a mower like this. It's perfectly serviceable but nothing amazing, if they ran a brushless motor in here it would undoubtedly cost more but the efficiency could be much higher (>85%) and could be designed for peak power much closer to the ideal blade speed.
Here's the specs on the motor, some were given others were hand calculated.
Globe 7080 series (120VDC)
No-Load RPM 4490 RPM
No-Load Current 2.0A (provided) 1.16A (measured)
Stall Torque 7.316nm
Stall Current 26.0A
Torque Const 0.305nm/A
Speed Const 37.4 RPM/Volt
Max Efficiency 68%
Torque 1.61 nm
Speed 3500 RPM
Current 7.3 A
Power Output 590 W
Blade Tip Speed 17868 FPM
Maximum Power (assume 50% full stall torque)
Torque 3.658 nm
Speed 2245 RPM
Current 11.99 A (+2A no load) - 14A
Power In 1680 W
Power Out 860 W
Calc Eff 51.2%
Blade Tip Speed 11460 FPM
I just moved to a new house, where I thought a self-propelled gasoline mower might be more suitable. I bought a Subaru, which mercifully died after less than 2 hours of use. It was heavy, awkward to use, and couldn't handle heavy grass as well as the Greenworks.
These tips apply to both models:
1) Place a rubber bumper on top of the safety switch, then strap it down with a zip tie or hose clamp. The mower will now start just by pulling on the power handle. Not as safe as the federally-mandated safety switch arrangement, but still quite safe; if you're dumb enough to work on the blade with the mower plugged in, you deserve the consequences.
2) Wrap the handle with bicycle handlebar tape. The foam padding is fairly delicate, and will tear fairly easily.
3) After every use, put the mower on its side, and wash the cutting chamber thoroughly to flush out grass clippings. Let it dry on its side, in the sun.
My only complaint is that a week after I bought mine, Amazon cut the price by $30 — this mower is a steal at $142.
UPDATE, August 2, 2017 : It's not worth dropping a star, but I recently discovered that the 21" model has been decontented slightly compared with the 20" model that I bought many years ago. The older mower had ball bearings in the wheels, while the wheels on the 21" model have cheap plastic sleeves. I somewhat improved the situation by wrapping .0005" brass shim stock around each axle, then greasing with heavy marine grease. The wheels don't wobble now, and they turn much more smoothly.