Workzone "dremmel" low revs and faultering

[N_Cook]

I replaced the triac with similar rating and same symptom.
Runs perfectly smoothly, bypassing the control pcb, feeding 60V,.15A DC
bench ps. Pot and Rs ok, DB3 diac tests ok dropping +/-30V on droppered
35V supply. Even checked the switch current carrying . Just leaves 2
caps, that I've not ESR'd or LCR'd yet.
A better triac match required?

 

[N_Cook]

100nF, 250V, X2 class block cap, across the 2 wires to armature and
stator, good ESR but only about 50nF.
Perhaps spark eroded away and now arcing across internally, anyway will
find a replacement for that and retry on mains

 

[whit3rd]

On Thursday, January 28, 2016 at 5:24:00 AM UTC-8, N_Cook wrote:

I replaced the triac with similar rating and same symptom.
Runs perfectly smoothly, bypassing the control pcb

Ordinarily, stuttering means the brushes are sticky or dirty,
and not making consistent commutator contact. It could be,
though, that your triac is false-triggering (there ought to be
a gate-to-cathode resistor or resistor+capacitor that prevents
false triggering).

Are you sure that component is a triac? There are similar devices
called 'quadracs' that have an inbuilt trigger.

 

[Clifford Heath]

On 29/01/16 01:52, N_Cook wrote:

100nF, 250V, X2 class block cap, across the 2 wires to armature and
stator, good ESR but only about 50nF.
Perhaps spark eroded away and now arcing across internally, anyway will
find a replacement for that and retry on mains

My Dremel sometimes fails to start, but runs ok once push-started. Bad
at low speed. Commutator looks ok, so I was assuming internal shorts in
the armature, rather than problems with the controller. Am I wrong?

A similar problem to yours however...

 

[Jon Elson]

Clifford Heath wrote:

My Dremel sometimes fails to start, but runs ok once push-started. Bad
at low speed. Commutator looks ok, so I was assuming internal shorts in
the armature, rather than problems with the controller. Am I wrong?

If there are shorted turns in the armature, the motor will run slow, vibrate
and get very hot. The shorted turn is acting like a brake. An open in one
wire will make it lose torque, and possibly have a dead spot where it won't
start, but otherwise will mostly run.

Jon

 

[N_Cook]

On 29/01/2016 00:24, whit3rd wrote:

On Thursday, January 28, 2016 at 5:24:00 AM UTC-8, N_Cook wrote:
I replaced the triac with similar rating and same symptom.
Runs perfectly smoothly, bypassing the control pcb

Ordinarily, stuttering means the brushes are sticky or dirty,
and not making consistent commutator contact. It could be,
though, that your triac is false-triggering (there ought to be
a gate-to-cathode resistor or resistor+capacitor that prevents
false triggering).

Are you sure that component is a triac? There are similar devices
called 'quadracs' that have an inbuilt trigger.

Main control is a Z0409MF triac.
If a short in the windings then it would not work well on DC, even if
only 60V. I'll try a diode on a variac while the pcb is removed to check
for higher V internal arcing.
In a couple of hours I'll put in a new 100nF and crack open the old one
and look for errosion of the film metalisation.
Generally I'm very impressed with this Workzone WCT 135, I bought a
second for a spare luckily. Just 2 safety issues, needs a shroud around
the on/off switch and a brake on the pot knob from vibrating around,
both easily modified.

 

[N_Cook]

On 29/01/2016 04:17, Jon Elson wrote:

Clifford Heath wrote:



My Dremel sometimes fails to start, but runs ok once push-started. Bad
at low speed. Commutator looks ok, so I was assuming internal shorts in
the armature, rather than problems with the controller. Am I wrong?
If there are shorted turns in the armature, the motor will run slow, vibrate
and get very hot. The shorted turn is acting like a brake. An open in one
wire will make it lose torque, and possibly have a dead spot where it won't
start, but otherwise will mostly run.

Jon

no overheating or smoke/smells.
Cold testing showed consistent <>12.5R segment to segment, consistent
<>50R across brushes and <>120R overall, while turning the rotor

 

[N_Cook]

With a 1n4006 on a variac, perfectly happy with 70% mains , quasi DC ,
presumably about 180V peaks.
Autopsy on the cap. No obvious smoke trails inside or burning smell,
just a "chemical" hot polyester clothing out of a tumble drier sort of
smell. Minimum metalisation mid way into the bulk of the layup, only 1/3
of width of metal remaining, so presumably local heating there so run
away and the metal there looked very suspect , grey, not mirror and
microscopic pin holes

 

[N_Cook]

Back to perfect working order. Quite a bit of space in there but no
100nF 400V(decided to up from 250V rating) cap laying around, but 4x
..47uF 100V in series went in there with room to spare. This will be a
stock fault with these nice compact drills, I use mine on a daily basis
it seems. While in there a better idea of anti-vibration fudge for the
pot knob, simply a small O ring over the pot shaft, before replacing the
knob, to bind slightly as it is compressed slightly when fitted in the
casing.
I left the TIC226 triac in there as running perfectly normally.