Dremel scroll saw DC motor

[Martik]

Posted here a while ago re: broken speed control: Well they sent me a new
one - no charge! but the damn thing still won't work. The motor just hums in
all positions of the control. I measured 100VDC going to 2 of the 4 wires to
the motor. The motor bearings and brushes look good. Any ideas what further
diagnosis I could pursue?

 

[James Sweet]

Posted here a while ago re: broken speed control: Well they sent me a new
one - no charge! but the damn thing still won't work. The motor just hums in
all positions of the control. I measured 100VDC going to 2 of the 4 wires to
the motor. The motor bearings and brushes look good. Any ideas what further
diagnosis I could pursue?

There's 4 wires to the motor? I had assumed the brushes would be in series
with the field coil, you need voltage to both pairs of wires for the motor
to run.

 

[Martik]

There's 4 wires to the motor? I had assumed the brushes would be in series
with the field coil, you need voltage to both pairs of wires for the motor
to run.

The 2 wires to the brushes have the 100VDC, I do not know what the others
are for.

Here is a picture, the red and blue wires go to the brushes:

http://www3.telus.net/martik/motor.jpg

 

[James Sweet]

The 2 wires to the brushes have the 100VDC, I do not know what the others
are for.

Here is a picture, the red and blue wires go to the brushes:

http://www3.telus.net/martik/motor.jpg

Can't really see much there, that's definitly the commutator of a universal
motor though. As I said before, you need power to the stator windings for
the motor to run, otherwise you'll just burn up the armature.

 

[Jim Adney]

news:zy%Hd.13338$Os6.4292@trnddc08...

The 2 wires to the brushes have the 100VDC, I do not know what the others
are for.

Here is a picture, the red and blue wires go to the brushes:

http://www3.telus.net/martik/motor.jpg

While most small DC motors that I'm familiar with these days have
permanent magnet stators, 2 extra wires imply that there must be a
stator field coil. Your photo is very good, but it's too close up to
see the whole motor and how it's built.

I suspect, however, that it has field windings which are not getting
any power. It needs voltage across BOTH the brushes AND the field
windings.

-

 

[Ross Herbert]

The 2 wires to the brushes have the 100VDC, I do not know what the others
are for.

Here is a picture, the red and blue wires go to the brushes:

http://www3.telus.net/martik/motor.jpg

It appears that the white and yellow wires are possibly connected to
some other item (thermal sensor ??) on the other side of the
fibreglass pcb which is clamped under the brush housings. Can you
remove the pcb to have a look?

 

[Bill Jeffrey]

I would bet that the extra pair of wires bring variable power to the
stator, providing a variable magnetic field and thus varying the speed.
With no power on these leads (no power on the stator), there is no
field, so the motor won't turn, of course.

Since you just got a new speed control unit from Dremnel, you have to
assume that the speed control unit is OK. This leads you to suspect
that the problem is in the wiring inside the motor, or the cord from the
speed control unit to the motor (assuming you didn't get a new one with
the new speed control). So start at the speed control - does it put
power on the yellow and white wires, as well as on the red and blue
wires? If so, does the power make it through the cord to the pcb
mentioned in another post? If so, does it make it to the motor?

Find out where you are losing power in the yellow / white wire circuit.

Bill Jeffrey
===========================

 

[Martik]

I would bet that the extra pair of wires bring variable power to the
stator, providing a variable magnetic field and thus varying the speed.
With no power on these leads (no power on the stator), there is no field,
so the motor won't turn, of course.

Since you just got a new speed control unit from Dremnel, you have to
assume that the speed control unit is OK. This leads you to suspect that
the problem is in the wiring inside the motor, or the cord from the speed
control unit to the motor (assuming you didn't get a new one with the new
speed control). So start at the speed control - does it put power on the
yellow and white wires, as well as on the red and blue wires? If so, does
the power make it through the cord to the pcb mentioned in another post?
If so, does it make it to the motor?

Find out where you are losing power in the yellow / white wire circuit.

http://www3.telus.net/martik/

Referring to the above pics:

Motor1 is the PSB, the small white connector (upper right) with grn,brn,blu
goes to the speed control. There is continuity to all 3 wires and voltage
(2-3 v) and resistance (4-7k) vary when adjusting the control. The large
white connector goes to the motor with 100v between the blu and red; 50v
between blu and yel; 50 v between blu and wht, ov between wht and yel with
NO change when adjusting the control for both 100 and 50v readings

Motor2 shows the pcb in the motor. I get 100v between blu and red and 50v
between blu and wht, 50v between blu and yel with no change when adjusting
the speed control. I cannot see any connection under the pcb between the
red/blu and wht/yel wires.

So, I conclude that all the wiring for those 2 connectors is ok but don't
understand why there is no change when adjusting the speed control.

Motor3 show closeup of wiring from pcb to 'end cap'

Motor4 shows other side of end cap with magnetic disc

Motor5 shows commutator inserted

Motor6 shows housing and armature. Those odd shaped thinks in the housing
are just washers.

Thanks again for your help!

 

[Ross Herbert]

http://www3.telus.net/martik/

Referring to the above pics:

Motor1 is the PSB, the small white connector (upper right) with grn,brn,blu
goes to the speed control. There is continuity to all 3 wires and voltage
(2-3 v) and resistance (4-7k) vary when adjusting the control. The large
white connector goes to the motor with 100v between the blu and red; 50v
between blu and yel; 50 v between blu and wht, ov between wht and yel with
NO change when adjusting the control for both 100 and 50v readings

Motor2 shows the pcb in the motor. I get 100v between blu and red and 50v
between blu and wht, 50v between blu and yel with no change when adjusting
the speed control. I cannot see any connection under the pcb between the
red/blu and wht/yel wires.

So, I conclude that all the wiring for those 2 connectors is ok but don't
understand why there is no change when adjusting the speed control.

Motor3 show closeup of wiring from pcb to 'end cap'

Motor4 shows other side of end cap with magnetic disc

Motor5 shows commutator inserted

Motor6 shows housing and armature. Those odd shaped thinks in the housing
are just washers.

Thanks again for your help!

A great set of phoros...

The motor is definitely a permanent magnet motor, so no field
winding...

Since you know the controller is ok the problem can only be in either
the armature or whatever is hooked up to the yellow and white wires on
the brushes pcb in the end cap. Since the armature is new it is
unlikely that there is an internal short in the winding, but this is
still a possibility. My guess is that whatever is connected to the
yellow and white wires provides some sort of feedback to the
controller and if this device is not working then the controller
doesn't know what to do.

 

[Ross Herbert]

A great set of photos...

The motor is definitely a permanent magnet motor, so no field
winding...

Since you know the controller is ok the problem can only be in either
the armature or whatever is hooked up to the yellow and white wires on
the brushes pcb in the end cap. Since the armature is new it is
unlikely that there is an internal short in the winding, but this is
still a possibility. My guess is that whatever is connected to the
yellow and white wires provides some sort of feedback to the
controller and if this device is not working then the controller
doesn't know what to do.

PS.

Found this page http://www.scrollsaws.com/General/Chosing.html


Extract.

"Subject: Dremel scrollsaw
Date: Fri, 03 Aug 2001 08:16:16 -0600
From: Rik White <[email protected]>
To: [email protected]

Have you had the opportunity to use this piece of junk? I've been
through 3 since March. All suffer the same problem, they just plain
quit running for no apparent reason. The saw has many flaws but this
is the most frustrating. I thought you might want to add a review of
this paperweight to your website. Rik. "

It seems that someone else isn't too impressed with Dremel scroll saws
either.

 

[Martik]

PS.

Found this page http://www.scrollsaws.com/General/Chosing.html


Extract.

"Subject: Dremel scrollsaw
Date: Fri, 03 Aug 2001 08:16:16 -0600
From: Rik White <[email protected]>
To: [email protected]

Have you had the opportunity to use this piece of junk? I've been
through 3 since March. All suffer the same problem, they just plain
quit running for no apparent reason. The saw has many flaws but this
is the most frustrating. I thought you might want to add a review of
this paperweight to your website. Rik. "

It seems that someone else isn't too impressed with Dremel scroll saws
either.

Well, I'm getting pretty close to just bypassing the whole PS and replacing
the motor with an AC induction motor. Don't need the variable speed anyway.

 

[Martik]

A great set of phoros...

Amazing what a macro setting and high F-stop(8), no flash and a self-timer
can do

The motor is definitely a permanent magnet motor, so no field
winding...

Since you know the controller is ok the problem can only be in either
the armature or whatever is hooked up to the yellow and white wires on
the brushes pcb in the end cap. Since the armature is new it is
unlikely that there is an internal short in the winding, but this is
still a possibility. My guess is that whatever is connected to the
yellow and white wires provides some sort of feedback to the
controller and if this device is not working then the controller
doesn't know what to do.

Could you suggest a way to just bypass the controller and run at full power?

 

[Jamie]

Amazing what a macro setting and high F-stop(8), no flash and a self-timer
can do





Could you suggest a way to just bypass the controller and run at full power?

get a rectifier of lets say 5 amps or morw and can handle 160 V AC or
better.
P.S.
if you really don't know the actual max voltage to the brushes you
could burn out the motor giving it direct source via a rectifier.
you will know if it seems to really wind up faster then normal before
the smoke comes out.
oh btw, legion has it, if you let the smoke out then its a total lost!

 

[James Sweet]

get a rectifier of lets say 5 amps or morw and can handle 160 V AC or
better.
P.S.
if you really don't know the actual max voltage to the brushes you
could burn out the motor giving it direct source via a rectifier.
you will know if it seems to really wind up faster then normal before
the smoke comes out.
oh btw, legion has it, if you let the smoke out then its a total lost!

He said it hums though and measures 100v at the motor? That would seem to
indicate that the speed control is fine (heck he replaced it right?) perhaps
it got overheated and demagnetized the field magnets? I can't think of
anything else that could be the problem unless the thing is physically
jammed or he's measuring wrong.

 

[Martik]

He said it hums though and measures 100v at the motor? That would seem to
indicate that the speed control is fine (heck he replaced it right?)
perhaps
it got overheated and demagnetized the field magnets? I can't think of
anything else that could be the problem unless the thing is physically
jammed or he's measuring wrong.

It turns freely and the field magnet is very strong. When I assemble the
brushes and commutator in place I get zero (instead of 100) VDC between red
and blue. Somehow that pcb on the motor end is blocking the voltage but I
can see no traces on the backside of the pcb???

 

[Martik]

He said it hums though and measures 100v at the motor? That would seem to
indicate that the speed control is fine (heck he replaced it right?)
perhaps
it got overheated and demagnetized the field magnets? I can't think of
anything else that could be the problem unless the thing is physically
jammed or he's measuring wrong.

I thinks it's the power supply: If i connect a 14v battery to the commutator
the armature become strongly magnetized, however when I connect it directly
to the red and blue leads from the main PCB it is NOT magnetized even though
I read 300vdc from these two leads. Not enough amperage? I cannot check this
as I have no amp meter.