Variable power 21'' SP-mower

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Hello,

I just purchased the 21'' self-propelled EGO mower.

While mowing, the motor continuously changes its power.  (I don't mean the self-propelled action, just the power of the blades.)  I am not talking about overheating because it starts to do this even after a couple of seconds of mowing.  Is this normal: does the machine adapts its power to the length of the grass somehow?  Yesterday there was a short time the power was so powerfull I think my neighbours might have been expecting a helicopter landing close-by.  The battery was also empty much quicker than the week before when I mowed for the first time.  At other times, the mower barely makes any noise, making me check whether it was actually cutting or doing nothing at all (it was still cutting, by the way).

As I cannot find anything in the manual or on this forum that indicates the power changes all the time, I post this question.

Another question: the manual says to clean the motor ventilation part.  Where exactly is it located?  I clean the blades and remove the grass on the bottom.

Thanks and best regards,

Pieter
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Pieter Schevenels

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Posted 3 years ago

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lmgagliardi

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I have this exact model and mine does not change RPM at all but reading other blogs on this mower and many people complain about out of control RPM on the 20 inch model.
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David Cline

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There have been a handful of isolated reports of this defect on the 20" mower, but the vast majority are not affected.  The 20" mower is a constant 600 watt power, and if you hit a dense spot of grass the blade will bog down since power doesn't increase to compensate like it does on the 21".
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Wrog

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Mine adjusts power output when it hits a patch that's thicker and harder to cut but I wouldn't say it's constantly changing.
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Exrace

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This is normal and how the mower conserves battery power for longer run times. With current blade on the 21 the achieve longer runtimes at the expense of lifting power. If and when the higher lift blade is available in the states you will probably notice this less with that blade installed as that blade  takes more energy to keep the blade at ~2800 rpm's
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David Cline

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The high lift blade will slightly increase the resistance on the blade, and thus increase the power drawn by the motor.  Ego has said to expect a 10-15% increase in power consumption (and thus an equivalent decrease in run time).
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David Cline

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Yes, the power changes on both 21" models, but it goes much higher on the 1,000 watt self propelled version than the 700 watt push version.  If you are cutting dry grass and aren't taking much of the blade off then it is actually slower and quieter than the 20" model.  If you are cutting very thick grass, taking more than 1/3 of the blade off, or the grass is wet then the motor will sense the resistance start to slow the blade down and increase the power.  Once the resistance has decreased, the power will drop back down.

Yes, this makes the battery's run time on a single charge shorter, and if it stays at an elevated power level for most of your mowing then you will notice a significant difference in run time.  The manual may not explicitly explain the variable power feature, but it does explain the expected run time for different types of mowing.
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David HD, Champion

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Official Response
Pieter, if you have nothing "interesting" to read this weekend, then spend your time reading this great article on "What is a Brushless Motor and How Does it Work?" by Chainsaw Journal.  This article breaks down the "how" and the "advantages" of a brushless motor.  This article was written about the EGO 56V Chainsaw, even though I don't own or need a chainsaw, but it was very informative with great exploded views of a "brushless motor."  I am a visual person and this article was perfect for my taste, hope you will enjoy it!

Advantages of the brushless motor:
  • The lack of brushes ensures that there is low friction during the operation of the motor and reduced production of heat, therefore, increasing the durability of the motor.
  • The minimal heat and motor wear due to lack of mechanical contact on the motor vastly improve power transfer and electrical efficiency that leads to increased performance and power.
  • The increased efficiency of the brushless motor helps to prolong battery life up to 50% or more.
  • There is no sparking and the motor produces less electrical noise.
  • Heat dissipation is better since the stator where the windings are located are connected to the case.
Disadvantages of the brushless motor:

The initial cost of the motor is high due to the need for commutating devices such as the encoder and a controller or drive.

https://www.chainsawjournal.com/what-is-a-brushless-motor-and-how-does-it-work/

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David HD, Champion

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TAT, at $490 for just the motor, the backpack leaf blower would probably retail for $900 or higher - that would be "one heck" of a blower!!!!!  Plus, you would need (2) 7.5 Ah batteries to keep up with the demand - but would be nice to try it if they can build it.
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Blue Angel, Champion

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Pretty crazy motors!
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TheAtomTwister

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Actually, you would need 5 7.5Ah batteries to stand the 255 amp current draw. Also, I believe that such a draw would only work in bursts without overheating the motor. It is probably best to run it at 6.5kW, which is still well over the 3.3kW of the Husqvarna 580BTS.  It is also probably better not as a backpack but as a walk-behind blower.
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David Cline

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I have one of those... a gas-powered walk behind. It seemed like a great idea when I got it, but it's actually quite a pain to maneuver if you miss anything in a single pass. Probably would be best in combination with a backpack blower.
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David HD, Champion

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The last time I saw one of those "walk-behind" blowers was when I was in elementary school.  They are powerful but bulky (to David's point) so I don't imagine "residential" use is high vs. commercial.
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bloomz

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Mine rarely changes speed, if it was constantly I'd be calling support.
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David Cline

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How dense is your grass?

Mine drops back down to low power at the end of every pass, whenever I lift the mower to turn, or if I slow down or stop for a moment. The slowdown is pretty quick, but the ramp up is more gradual, so it does seem to constantly be changing—unless I have enough grass buildup under the deck that it doesn't drop back down and just stays high.

You can always call support if you are concerned, but hearing the power modulate up and down on a 21" mower while mowing certainly isn't anything unusual that you should be worried about,
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Pieter Schevenels

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Thank you all for the (quick) comments.  I guess most of them are reassuring.

It is all new grass since July.  The shadow zones have quite high and thick grass and the zones in the sun are easier for the mower as the grass still has to grow dense there.  I guess that explains the change about every minute.  So I guess the noise is decreasing when thicker/higher grass is being mowed as the rpm is lower (but the power higher), as I understood from one of the replies.  While mowing, this didn't seem logically but now it does.

And indeed the first time I mowed at height nr. 5 and yesterday at height nr. 4 which probably explains why the battery was empty faster.

At last, indeed the slow down is quick and the ramp up is more gradual.