Controlling the RPM of a DF64 with a VFD - Page 2
-
ltanzil (original poster)
- Posts: 44
- Joined: 2 years ago
for the time being no. i leave the 10uf running capacitor.spopinski wrote:Do you also bypass the capacitor and use all 3 output wires to drive the motor? Effectively remove all the grinder electronics?
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
- Posts: 853
- Joined: 2 years ago
Okay, I'll calm down about finding a half-speed version of the same motor. *sigh*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.
Has anyone ever posted a complete teardown of the DF64?
-
Giampiero
- Posts: 856
- Joined: 8 years ago
-
ltanzil (original poster)
- Posts: 44
- Joined: 2 years ago
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?
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)
- Posts: 44
- Joined: 2 years ago
as promised. this is the photo of the connection of the wire for vfd.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?
the unit will still working fine when you plug it to wall socket. you just need external switch for on/off.
no soldering needed!
-
GDM528
- Posts: 853
- Joined: 2 years ago
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?
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
- Posts: 856
- Joined: 8 years ago
No, has been easy, in effect the flange did separate by the ball bearing in a flash.
-
ltanzil (original poster)
- Posts: 44
- Joined: 2 years ago
Update. i have bypassed and remove all electronic including the 10uf capacitor. and connected the VFD directly. 3 wire out of the motor directly connected to the VFD.spopinski wrote:Do you also bypass the capacitor and use all 3 output wires to drive the motor? Effectively remove all the grinder electronics?
results. way stronger torque at low rpm. now i can grind consistently down to 400 rpm. no stalling. but caution must be observed. at 400 rpm the current output of the VFD can be as high as 5.2 amps. this peak current can be maintained for about a minute. after 1 minute VFD drop the current to about 4 amp to prevent burn out. since DF 64 has no active cooling, low rpm torque boost has to be use wisely.
-
basiecally
- Posts: 24
- Joined: 4 years ago
Hey!
Interesting read. I've been planning to make an RPM controller for my DF64 as well (I also have the cast burrs by the way, nice!). I*m still confused as to what type of motor is in this grinder though. From the looks of it, with the capacitor and the windings, isn't this a syncronous three phase motor with a running capacitor? I mean, you being able to run it off of a three phase VFD implies that it is as well. Or is you VFD single phase?
I'm not too familiar with electrical motors though so please forgive if I confuse the terminology. Is there any sign that this is indeed a brushed motor? It would seem very impractical as there is no way to get at the brushes to change them out if they wear down.
I've considered if this might be an asyncronous motor, universal motor or syncronous motor with running cap. So I feel like I'm all over the place. All these require different means of speed control so I feel like working out what I've got is an important starting point.
Interesting read. I've been planning to make an RPM controller for my DF64 as well (I also have the cast burrs by the way, nice!). I*m still confused as to what type of motor is in this grinder though. From the looks of it, with the capacitor and the windings, isn't this a syncronous three phase motor with a running capacitor? I mean, you being able to run it off of a three phase VFD implies that it is as well. Or is you VFD single phase?
I'm not too familiar with electrical motors though so please forgive if I confuse the terminology. Is there any sign that this is indeed a brushed motor? It would seem very impractical as there is no way to get at the brushes to change them out if they wear down.
I've considered if this might be an asyncronous motor, universal motor or syncronous motor with running cap. So I feel like I'm all over the place. All these require different means of speed control so I feel like working out what I've got is an important starting point.
