Add a VFD to any single phase grinder??

Grinders are one of the keys to exceptional espresso. Discuss them here.
RTM
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Joined: 1 year ago

#1: Post by RTM »

I had been thinking of trying this for a while; and seeing The DF64v coming out really gave me the gumption to try my theory on my RR45.

Most of our grinders use a Single phase motor. PSC is a type of single phase motor, permanent split capacitor and that's the design name of a motor where the capacitor is always in the circuit.
By design the capacitor is shifting the original phase 90° to simulate a two phase rotating magnetic field. What I am doing is removing the capacitor, and running the motor on variable frequency.

By using a 3 phase VFD the supplied phase angle is 120° apart, but the original winding configuration still works really well ( like a " Scott T" configuration) and actually can correct the 120 to 90°. With this, you get great speed regulation and power.
I am still testing this out, but so far very impressed. I was able to start a loaded grinder at 20hz ( my rr45 uses a 4 pole motor , that's 600rpm!)
This morning I ground at 40hz and the result was a quiet and consistent grind!
Another bonus is you can increase the speed above usual 60hz, I have mine limited to 70hz for my initial testing.. I am thinking to grind at a low speed but use the high speed to " blow" out the chamber.
Anyway, was excited and nobody in my circle cares about coffee grinders that much LOL



Sorry about the messy workspace, I was eager to try it out!
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GDM528
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#2: Post by GDM528 »

RTM wrote: correct the 120 to 90°
Clever!

Where is the phase correction occurring, from the VFD? Can you offer any details on the make/model you're using?

buckersss
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#3: Post by buckersss »

I enjoyed reading that, nice post! Can you taste a difference?

RTM (original poster)
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#4: Post by RTM (original poster) »

GDM528 wrote:Clever!

Where is the phase correction occurring, from the VFD? Can you offer any details on the make/model you're using?

If my understanding of whats happening is correct- the phase correction is happening actually inside the motor- since motors are just transformers with a rotating secondary. Check out the Scott T transformer connection and you can see the similarities.. a split phase motor has a Main and Run winding with different resistances, and by putting power to the common tap 120 degrees out seems to create some inductive reactance that smoothes everything out, sort of like a backwards rotary phase converter

Initially I left the capacitor in and tried to just run it on single phase, but the motor cogged and vibrated really bad. once I hooked it up without the capacitor it sounded and felt just like a 3ph motor on a drive.

The VFD I chose was the smallest/ cheapest on Ebay- a " T13-750W-12H" https://www.ebay.com/itm/363914996749?h ... R4La2oTmYQ
I think any small VFD would work, as long as you can shut off the phase loss detection as the run winding will pull more amperage than the start and could trip a fault otherwise.
buckersss wrote:I enjoyed reading that, nice post! Can you taste a difference?
Thanks! it certainly wasn't any worse, and I enjoyed using it.. I need to hone my barista skills more to truly appreciate what this can do. New burrs really woke up this grinder for me more than anything 8)

jannus
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#5: Post by jannus »

Very cool!
I'm glad someone else is also trying it! I had a fan in my roaster hooked up this way (also disconnected the starting cap), and indeed it seemed fine. I couldn't easily measure if there was excess heat or anything else, and none of my more qualified contacts could give me a yes or no in terms of possible long term effects...so eventually I took it back to single phase.
I also found it ran smoothly for the time I had it running.
A grinder motor is surely working way harder....although also for very short stints. Fact is, there are "single phase VFDs" out there, just not many.
If it's an ineffective process I can live with it, I just don't want to do damage. I'm hoping what you're doing is pointing to the "all ok" direction! :)

ira
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#6: Post by ira »

Depending on the motor it may become very inefficient and get hot at frequencies far from it's design frequency. But other than that, there is no issue with using a VFD.

RTM (original poster)
Posts: 92
Joined: 1 year ago

#7: Post by RTM (original poster) »

jannus wrote:Very cool!
I'm glad someone else is also trying it! I had a fan in my roaster hooked up this way (also disconnected the starting cap), and indeed it seemed fine. I couldn't easily measure if there was excess heat or anything else, and none of my more qualified contacts could give me a yes or no in terms of possible long term effects...so eventually I took it back to single phase.
I also found it ran smoothly for the time I had it running.
A grinder motor is surely working way harder....although also for very short stints. Fact is, there are "single phase VFDs" out there, just not many.
If it's an ineffective process I can live with it, I just don't want to do damage. I'm hoping what you're doing is pointing to the "all ok" direction! :)
Super cool application with the fan- I was concerned with it heat wise aswell- - so far I left it running for about a hour; unloaded of course and it barely warmed up at all.. it almost seems to run cooler than when it had the capacitor.
I do know in other applications the VFD can harm the motor bearings.. I guess I'll see what happens as this grinder was a garage sale bargain to begin with.
this project is certainly headed build an enclosure for the drive and wire in a switch for it than revert back.
What was the longest you ran your setup with the fan for?

jannus
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#8: Post by jannus »

I ran it for several roasts, they usually lasted about 1h30 from start to finish, each. The problem is that it's a roaster, so inherently everything got a bit hot. As such, I could never tell if the fan got hotter than usual, and looking at the cost of a new fan I decided I'd rather just keep it as it was.
I did get the idea that it was less efficient, perhaps less powerful, but I could never get a clear answer on whether that will have a detrimental effect on the life expectancy of the motor itself. That, to me, was the biggest concern.

RTM (original poster)
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#9: Post by RTM (original poster) »

jannus wrote:I ran it for several roasts, they usually lasted about 1h30 from start to finish, each. The problem is that it's a roaster, so inherently everything got a bit hot. As such, I could never tell if the fan got hotter than usual, and looking at the cost of a new fan I decided I'd rather just keep it as it was.
I did get the idea that it was less efficient, perhaps less powerful, but I could never get a clear answer on whether that will have a detrimental effect on the life expectancy of the motor itself. That, to me, was the biggest concern.
That's a pretty good test, in my experience with fans, 4 hours is considered constant duty so if it holds up to a slightly longer test I'd imagine it would run all day long.

So far I'm pretty confident it's not hurting the motor in anyway, but this is only day 3 of having this on here.

Maybe I'll leave the motor running for a few hours and see if it warms up at all.
I ground 3 shots (17g each) this morning and 55g for a pour over, all at 35hz which is around 1000rpm, very happy with it still!

ira
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#10: Post by ira »

If it doesn't warm up in 15 minutes, it's not likely going to ever warm up. But you need to test it at the frequency (RPM) extremes you will use while roasting.