Monoliths, Robors and Settes have a gearbox as I'm sure do many more I don't know.

Ira

Power (Watts) is an instantaneous thing. Work (Watt-seconds) is what it takes to grind an amount coffee.

A hand-crank generator is reported to be somewhere around 10 W, so maybe 20 W input. So, a "20 W motor" is sufficient to grind coffee as evidenced by all the successful hand grinders. It will take a lot longer to do the work than a shop grinder that can supply more power.

buckersss wrote:
im curious what the effect of rpm has on all of this - to your point on grind time. if you need 200W at 120rpm for those 68mm conicals, but instead the rpm of the motor jumped up 4 times, to close to 500rpm (many conicals are around there). At that point, shouldnt you need 200W x 4 = 800W just to maintain the power per revolution you were achieving before? so while you are quicker, you arent any stronger persay.

I'm not quite sure what you meant by "stronger", in our grinder case however, strength = power rating, meaning the work a person (or a machine) capable of putting out in unit time, measured with units like watts, Kgfm/s, horsepower, torque*rpm, and so on.

The total energy (or work) needed for a grinder to put out to grind a certain dose of beans of certain roast is
E = torque * rpm * time

Noted in the above equation, torque * rpm = power rating of the grinder, it does seems for a given dose of same beans, a more powerful grinder will finish the job sooner, assuming the total work E remains constant.

rpm is part of the equation, but it does not have a direct bearing in the mix by itself.

There is also inertia, especially with something like a bigger Mazzer grinder, once that motor is spinning at full speed it's going to take a lot to bring it to a halt, which is why some lower powered grinders suggest turning them on before adding the beans. How good the burrs are at feeding also makes a huge difference in the power required.

Ira

Sure, those larger motors have more inertia, and the fact that you're out of the "pull up torque" range. Iv'e been doing a lot of testing/work these past few years and a lot of "forum knowledge" about motors, grinders, burr sizes/types and speeds, doesn't quite work out in practice....what does happen is fully explainable by Physics though.

Thanks to all if you for the great read. And please excuse my lengthy post

There are many different kinds of motors out there with very different characteristics. A 200w AC motor is very different to a 200w DC motor. The 200w are only the peak wattage. The characteristic is very different. A DC motor has the highest torque at the lowest speed and looses torque gradually with increasing speed. An AC motor has quite low torque at startup and a much higher torque at a specific speed, but the startup is the issue. There are some electronics tricks that help with the startup but the characteristic doesn't change significantly.
To be able to grind beans during startup AC motors need to have much more Watt than DC motors.

I actually didn't research any of this but I am pretty sure most boutique grinders have DC motors and most commercial grinders have AC motors. I believe the reason for this is that AC motors have a pretty significant benefit, they stay at a defined speed automatically by design, while DC motors need to have a speed controller to ref up without load or small load. Electronics got so good that this is really insignificant, but an industry doesn't change that quickly.

Personally I like the oomph of an EK or similar and dislike the sound of the changing speed of an eg-1. Would I get an eg-1 if I would win the lottery, sure!

There is a new kid in town though. The Ultra has a different kind of motor which basically has full torque from almost startup and you can set the speed and it won't need to hunt to stay there exactly. Obviously this comes with a drawback, the electronics are much more complicated than even the speed controller of a DC motor. I personally prefer my grinders to be as simple as possible and hence find the Ultra to be overengineered, but it is a great concept and I appreciate it's existence and I can't say I am not tempted at times.

On the other hand there is a completely different discussion happening at the same time, the speed of grinding. There are people arguing that lower grinding speed is better for the coffee. Actually different people have very different arguments for it, like temperature or uniformity of grinds. Nonetheless as pointed out previously lower grind speed needs less torque needs less Watts.
In this context I am still waiting for a vibratory conveyor to feed the beans into the grinder

The torque required seems like it will be primarily related to the type of bean, roast level, burr cut (force) and burr diameter (lever arm). There's another impact of larger diameter as, in many designs, you've got more grinds being sheared or shattered at the same time (increasing total force).

coffeeOnTheBrain wrote: A DC motor has the highest torque at the lowest speed and looses torque gradually with increasing speed.

A DC motor has quite low torque at startup and a much higher torque at a specific speed, but the startup is the issue.

There are some electronics tricks that help with the startup but the characteristic doesn't change significantly.

To be able to grind beans during startup AC motors need to have much more Watt than DC motors.

Did you mean to say AC instead of DC in the underlined part above?

Yes, thank you!

Will edit it above.

Laura wrote: I haven't read negative reviews over Ditting machines but recently pretty negative reviews on kaffetek and levercraft machines.

I've yet to read a negative review, or even a negative comment, about a Kafatek machine. It's almost boring. What have you seen?