Controlling the RPM of a DF64 with a VFD - Page 2

Grinders are one of the keys to exceptional espresso. Discuss them here.
ltanzil (original poster)

#11: Post by ltanzil (original poster) »

spopinski wrote:Do you also bypass the capacitor and use all 3 output wires to drive the motor? Effectively remove all the grinder electronics?
for the time being no. i leave the 10uf running capacitor.
i have consider that. but right now i don't have enough data on df64 the start winding. and it work fine with 2 wire.

connecting the start winding directly might provide greater torque. but it might also burn the winding if the current is to big. the running capacitor limit how much current flow to the start winding.

it might also effect the smoothness of the motor. because now the phase shift of the run and start winding is no longer 90 degree but become 60 degree

things that i will do next is increasing the run capacitor from 10uf to 20uf. in my calculation 20uf is more suitable for the motor at 25hz
my new caps should come in the next few days. i will post and update.

GDM528

#12: Post by GDM528 »

ltanzil wrote:i agree with giampiero. swapping the motor is ten times more hassle. i have thought of it. the motor shaft is directly attached to the burr. and stator is press to the grinder body. it is going to be a nightmare.
Okay, I'll calm down about finding a half-speed version of the same motor. *sigh*

Has anyone ever posted a complete teardown of the DF64?

Giampiero

#13: Post by Giampiero »

Apart the various teardown videos, i once even removed the motor flange.

ltanzil (original poster)

#14: Post by ltanzil (original poster) » replying to Giampiero »

hemmmm..... this is interesting i thought the motor is press fit. but i seems form Giampiero photo the stator is only clamped by bolts. this photo also confirm that the rotor is squirrel cage. if the stator is easy to remove. means that rewinding the stator to 3 phase is feasible. i count 24 slot. so winding it to 3 phase 4 pole is possible.

the vfd will work more efficiently and greater torque at low rpm,

that is future project. for now stick with single phase.


Giampiero, is it difficult to remove the motor flange?

ltanzil (original poster)

#15: Post by ltanzil (original poster) »

GDM528 wrote:Okay, I'll calm down about finding a half-speed version of the same motor. *sigh*

Has anyone ever posted a complete teardown of the DF64?
as promised. this is the photo of the connection of the wire for vfd.

the unit will still working fine when you plug it to wall socket. you just need external switch for on/off.

no soldering needed! :D


GDM528

#16: Post by GDM528 »

Cool - thank you for the pictures!

Some high-level observations, corrections appreciated if I got any of it wrong:

1) The body of the DF64 is essentially the motor housing, to the extent it even holds the bearings in place. I wouldn't be surprised if the manufacturer of the DF64 was already in the electric motor business, when somebody suggested they could turn one of their motors into a coffee grinder. Someone with a machine shop could wedge in a different motor, but at that point they might as well just build a grinder from scratch.

2) The large capacitor is a "run" capacitor and can stay in-circuit once the motor is up to speed. I think that implies the VFD must support a simple two-wire connection to the motor with no start function.

What's not clear to me, is why the built-in power switch and auto-off timer had to be eliminated. Can't the VFD be left "on" with no load?

Giampiero

#17: Post by Giampiero »

No, has been easy, in effect the flange did separate by the ball bearing in a flash.