Confused about grinders - Page 9

Grinders are one of the keys to exceptional espresso. Discuss them here.
unfiltered

#81: Post by unfiltered »

AssafL wrote:Actually, the Versalab is very stable in RPM using a back-emf industrial speed controller. So you definitely can control speed without the hall-effect sensors of a BLDC.
I was referring to the qualities of induction motors/BLDC over brushed DC regards holding RPM constant under load. The simplicity of the single phase AC circuit and its low noise no contact operation are benefits. The additional stuff required to run BLDC is the main negative for me but if I was going to the hassle of using a controller, I'd be using it on a BLDC rather than a a brushed.

unfiltered

#82: Post by unfiltered »

Jake_G wrote:The trick Option-O went with is to use a motor compatible with rectified line voltage, rather than stepping it down to 20, 24 or 48V, like many motors require.

This allowed for a standard brushless driver to be incorporated into a small power supply board. With :D ~170V bus voltage, the required current for 300W is quite small (less than 6 amps) and with it, the size of the rest of the components. I believe the motor driver they sourced is rated for 700V and up to 50A of saturated current and supports both encoder feedback as well as running encoder-less using field-oriented-control (FOC).

The trade off is that the motors themselves are not terribly small for their rated power output, but that doesn't seem to be a problem.
I have noticed that the unofficial-official line on the market readiness of the upcoming DF64S is now as below....


"Not yet. Probably making some changes that will push it out a couple months"


I wonder if the post by Jake_G has given them an idea and now some design changes are in order..... :lol: :lol:

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AssafL

#83: Post by AssafL »

unfiltered wrote:I was referring to the qualities of induction motors/BLDC over brushed DC regards holding RPM constant under load. The simplicity of the single phase AC circuit and its low noise no contact operation are benefits. The additional stuff required to run BLDC is the main negative for me but if I was going to the hassle of using a controller, I'd be using it on a BLDC rather than a a brushed.
What "qualities"?

1. Induction needs slip. Without slip no current is induced (hence "induction") in the cage. So the rotor speed is always lower than the phase speed. it isn't constant at all. It depends on the required torque. With quite a bit of clever circuitry (frequently referred to as VFD - variable frequency drive) - one can control phase speed and thus the motor speed. One would also need some feedback (an encoder, a hall effect sensor, a reed switch) to detect the rotor speed for the VFD. Or use a pre-programmed curve and hope the motors are similar in specs. VFD are expensive - but I buy NOS from eBay for cheap.

An added disadvantage and is the reason grinder use big induction motors is that the slip/torque graph is inverted at first. Induction motors love to stall. Hence they like zero startup torque applications like fans.

Induction motors probably have the longest lifetime of all motors since they are simple and have no brushes.

2. BLDC. Are DC motors almost identical to PMDC except they are complex. They are a bit better in that you can get extremely high startup torques than PMDC (assuming you design them well - most are very similar in their behavior). Speed is regulated by the electronics - not by the motor itself. Timing is critical for commutation hence they typically have multiple (3) hall effect sensors, etc. In theory, BLDC have a very long lifetime since they have no brushes. In theory as long as Induction. But they rarely are. Even if shock etc. doesn't eventually get the connectors/hall effect sensors, etc. Capacitors age and will eventually fail. Far before the bearings do.

3. PMDC. Simple, but have mechanical commutation. Hence very noisy on the power lines. Unregulated speed unless you add electronics or a governor (like in the old cassette tape players which had a really cool centrifugal governor). Startup torque is maximal - almost as high as BLDC.
In theory - PMDC should have a short lifespan due to brushes. In theory because I have at least 10's of PMDC motors salvaged from old discarded devices. Even vacuum cleaners whose motors are abused heavily. I've only encountered two devices which had worn out brushes.
On the 13 year old Versalab which is used daily for 2-4 cups - the brushes have eroded less than 5%. So that means the brushes will outlive me. But I am not sure the electronics will - but they are Industrial Standard COTS so easily replaced.

So I don't buy into the fads of the "better motor technology". Sure there are applications (e.g. EV) where you need the strongest motor, perfectly controlled, regenerative as well, and for that you get into induction with reluctance slits etc. Now hauling a car and a family (a ton if not more) - up to a ski resort on tiny motors and a LiIon battery - now that is indeed cool. One day they'll make one and market a grinder that has a "motor like in your Tesla".

So what - is it needed? It is hardly our use case here. Why not spend the money on burrs and alignment instead of wasting it on fancy motors where an inexpensive one would work just as well?
Scraping away (slowly) at the tyranny of biases and dogma.

malling

#84: Post by malling »

While I don't disagree with what you write. I also think it's important that we point out that those grinders using said fancy motors happens to be those same grinders using the fancy burrs and that has the better build and lower tolerance, the same grinders not needing to use annoying ugly bellows. Additionally many of those have RPM control so their choice of motor make perfect sense.

The ones using brushed is just the same grinder that are either constructed for commercial use and or made cheap like the DF's with lower build, less precision and cheaper burrs, like Italmill. Obviously you can make them work there tons of grinders thar run years on end.

I would love to see a P64 ripped off RPM and tossed in a cheaper motor for a lower entry price, but it's unlikely to happen.

Bar (original poster)

#85: Post by Bar (original poster) »

Wow. This post hit the jackpot on replies. So which will be greater the improvement from the Breville built in grinder to the least expensive Orphan or the improvement from the Orphan to a Niche Zero?

I paid my ante and saw the first round of bets, now I need to decide if I want to fold, save my money, and limp along with subpar espresso drinks or invest in a grinder. I am willing to spend some time in getting my puck prep up to speed.

Where is the best place to buy a Niche anyway? I suppose the Orphan you would just get on Amazon?

Thank you.

ira
Team HB

#86: Post by ira »

Probably the Breville to the OE grinder will show a larger improvement, especially if you can find a Pharos.

unfiltered

#87: Post by unfiltered »

Nice summary of motors. "Constant" might not have been the best word to use but the rpm difference between a loaded/unloaded induction motor isn't comparable to changes in brushed DC rpm under load.

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AssafL

#88: Post by AssafL »

malling wrote:The ones using brushed is just the same grinder that are either constructed for commercial use and or made cheap like the DF's with lower build, less precision and cheaper burrs, like Italmill. Obviously you can make them work there tons of grinders thar run years on end.
Are the Titus and the Versalab "lower build, less precision and cheaper burrs"?

At the extreme, some of the best values in grinders ditch the motor and are manual. One can afford a morse tapered - centered and aligned - with a reasonable size burrs. Obviously - you can't drive a 4 burr DRM style or a 98mm flat burr with your hand.

Again - nothing against BLDC. I was reminded today of the first BLDCs I saw - 1980's Videos heads in VCR's were able track much faster than the belt driven heads that came before them. I used to repair them for friends and liked the utility of the BLDC design.
Scraping away (slowly) at the tyranny of biases and dogma.

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AssafL

#89: Post by AssafL »

NR
Scraping away (slowly) at the tyranny of biases and dogma.