GreenWorks MO12B00 Review

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Best GreenWorks mo12b00 Review

I'm updating this to 5 stars because even given the issues below, I would buy this GreenWorks mo12b00 again over any competitors I could find in this product category of lawn mowers. I've used this for 4 years now and it still works the same as it did new. I remarked below on poor cut quality in some scenarios where blade speed can fall too low which is still a problem, but this really only occurs when mulching. Cutting thick or tall grass with the discharge open improves the pace and cut quality in this scenario but there are limitations, mowing fields is still going to produce a crappy cut no matter what you use.

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 lawn 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 GreenWorks mo12b00 lawn mower at peak output generally costs 8-25c/hour. You also hit an advantage in purchase price as gas or cordless lawn mowers 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 GreenWorks mo12b00? 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 GreenWorks lawn 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 lawn 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 GreenWorks mo12b00 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.

The bad?

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 GreenWorks mo12b00 lawn 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:

Lawn 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 GreenWorks mo12b00). 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 lawn 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 governor setting for push mowers) outputs about 3425W, falling to around 2800W at 3000RPM.

Obviously there are electrical supply limitations to a lawn mower like the GreenWorks mo12b00. 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.

Rating 5/5

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