Electronics Repair (sci.electronics.repair) Discussion of repairing electronic equipment. Topics include requests for assistance, where to obtain servicing information and parts, techniques for diagnosis and repair, and annecdotes about success, failures and problems.

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Old September 8th 18, 05:27 PM posted to sci.electronics.repair
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Default Power tool armature repair - Followup

On 9/7/2018 6:20 PM, Bob Engelhardt wrote:
[...]
The windings at the back of the commutator are wrapped in string &
coated.* I'm thinking that I can cut back the string & get at the winding.


With a small bit in a Dremel I excavated behind the segment, down to its
connecting wire. There was no continuity from that wire to other
segments! Then I noticed what had been staring me in the face all along
- the connecting wire exposed and broken:
https://imgur.com/a/jhIcgqf

Its connection to the segment also came loose, so I soldered in a jumper:
https://imgur.com/a/yiBcCit

It surprised me that the original connecting wire was steel. I don't
know why steel would be used, but it made soldering difficult.

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Old September 8th 18, 06:31 PM posted to sci.electronics.repair
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Default Power tool armature repair - Followup

On Saturday, September 8, 2018 at 12:28:41 PM UTC-4, Bob Engelhardt wrote:
On 9/7/2018 6:20 PM, Bob Engelhardt wrote:
[...]
The windings at the back of the commutator are wrapped in string &
coated.* I'm thinking that I can cut back the string & get at the winding.


With a small bit in a Dremel I excavated behind the segment, down to its
connecting wire. There was no continuity from that wire to other
segments! Then I noticed what had been staring me in the face all along
- the connecting wire exposed and broken:
https://imgur.com/a/jhIcgqf

Its connection to the segment also came loose, so I soldered in a jumper:
https://imgur.com/a/yiBcCit

It surprised me that the original connecting wire was steel. I don't
know why steel would be used, but it made soldering difficult.




Flux is your friend. I don't solder *anything* anymore without touching the connection with a bit of liquid flux. Today's solder is garbage, and a bit more flux makes it flow so much better.
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Old September 9th 18, 01:19 PM posted to sci.electronics.repair
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Default Power tool armature repair - Followup

On 2018-09-08 18:27, Bob Engelhardt wrote:
On 9/7/2018 6:20 PM, Bob Engelhardt wrote: [...]
The windings at the back of the commutator are wrapped in string &
coated. I'm thinking that I can cut back the string & get at the
winding.


With a small bit in a Dremel I excavated behind the segment, down to
its connecting wire. There was no continuity from that wire to
other segments! Then I noticed what had been staring me in the face
all along - the connecting wire exposed and broken:
https://imgur.com/a/jhIcgqf

Its connection to the segment also came loose, so I soldered in a
jumper: https://imgur.com/a/yiBcCit

It surprised me that the original connecting wire was steel. I
don't know why steel would be used, but it made soldering difficult.


Congrats! Now that the connection is done, make sure to touch up the
worked area with epoxy to protect it from vibration and from being
sandblasted. Since it's going back into a drill and drilling dust is
highly abrasive at typical rotor velocities, neither the wire nor the
soldering should be exposed. The epoxy coating should be made smooth so
that the "bump" over the rework does not stick out too much into the air
and dust stream. When applying epoxy, try not to leave any unfilled air
pockets underneath as far as practical.
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Old September 9th 18, 01:22 PM posted to sci.electronics.repair
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Default Power tool armature repair - Followup

On 2018-09-09 14:19, Dimitrij Klingbeil wrote:
On 2018-09-08 18:27, Bob Engelhardt wrote:
On 9/7/2018 6:20 PM, Bob Engelhardt wrote: [...]
The windings at the back of the commutator are wrapped in string
& coated. I'm thinking that I can cut back the string & get at
the winding.


With a small bit in a Dremel I excavated behind the segment, down
to its connecting wire. There was no continuity from that wire to
other segments! Then I noticed what had been staring me in the
face all along - the connecting wire exposed and broken:
https://imgur.com/a/jhIcgqf

Its connection to the segment also came loose, so I soldered in a
jumper: https://imgur.com/a/yiBcCit

It surprised me that the original connecting wire was steel. I
don't know why steel would be used, but it made soldering
difficult.


Congrats! Now that the connection is done, make sure to touch up the
worked area with epoxy to protect it from vibration and from being
sandblasted. Since it's going back into a drill and drilling dust is
highly abrasive at typical rotor velocities, neither the wire nor
the soldering should be exposed. The epoxy coating should be made
smooth so that the "bump" over the rework does not stick out too much
into the air and dust stream. When applying epoxy, try not to leave
any unfilled air pockets underneath as far as practical.


P.S. From the picture it looks like a neighboring wire lead is exposed
and already partially abraded down. Make sure to re-protect it as well.
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Old October 14th 18, 02:04 AM posted to sci.electronics.repair
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Default Power tool armature repair - Followup followup

On 9/8/2018 12:27 PM, Bob Engelhardt wrote:
With a small bit in a Dremel I excavated behind the segment, down to its
connecting wire.* There was no continuity from that wire to other
segments!* Then I noticed what had been staring me in the face all along
- the connecting wire exposed and broken:
https://imgur.com/a/jhIcgqf

Its connection to the segment also came loose, so I soldered in a jumper:
https://imgur.com/a/yiBcCit

It surprised me that the original connecting wire was steel.* I don't
know why steel would be used, but it made soldering difficult.


With it "fixed", it still sparked like crazy! It took a while, but I
finally found a transformer that I could re-purpose as a growler. With
that I discovered that the armature had shorted windings. Sigh.

I took it as an opportunity to do something new: rewind an armature.
There's a number of YouTube videos showing it and it doesn't seem too hard.

First, I needed the parameters: size of wire, number of turns in each
winding, and the connections of the windings to the commutator segments.
It was easy on the videos - you just unwind the old and record the
parameters. Not so on mine - the windings were potted with epoxy. With
some careful destruction I got some of it unpotted, but not the
connections to the commutator. So I trashed it.

Part of the commutator connections problem was that there were jumpers
from the commutator to the windings. Most (?) armatures have their
windings loop around a lug on a commutator segment and continue. I.e.,
each lug is the start point of one winding and the end point of another.
On mine there were 2 commutator segments per rotor slot; the jumper on
one connected to a winding wire, but the jumper on the other connected
to _2_ winding wires! How could there be 3 connections per slot?
Bizarrely asymmetrical.

I'm disappointed that it wasn't more doable.



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Old October 14th 18, 03:02 AM posted to sci.electronics.repair
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Posts: 10,203
Default Power tool armature repair - Followup followup

On Sunday, 14 October 2018 02:04:13 UTC+1, Bob Engelhardt wrote:
On 9/8/2018 12:27 PM, Bob Engelhardt wrote:


With a small bit in a Dremel I excavated behind the segment, down to its
connecting wire.* There was no continuity from that wire to other
segments!* Then I noticed what had been staring me in the face all along
- the connecting wire exposed and broken:
https://imgur.com/a/jhIcgqf

Its connection to the segment also came loose, so I soldered in a jumper:
https://imgur.com/a/yiBcCit

It surprised me that the original connecting wire was steel.* I don't
know why steel would be used, but it made soldering difficult.


With it "fixed", it still sparked like crazy! It took a while, but I
finally found a transformer that I could re-purpose as a growler. With
that I discovered that the armature had shorted windings. Sigh.

I took it as an opportunity to do something new: rewind an armature.
There's a number of YouTube videos showing it and it doesn't seem too hard.

First, I needed the parameters: size of wire, number of turns in each
winding, and the connections of the windings to the commutator segments.
It was easy on the videos - you just unwind the old and record the
parameters. Not so on mine - the windings were potted with epoxy. With
some careful destruction I got some of it unpotted, but not the
connections to the commutator. So I trashed it.

Part of the commutator connections problem was that there were jumpers
from the commutator to the windings. Most (?) armatures have their
windings loop around a lug on a commutator segment and continue. I.e.,
each lug is the start point of one winding and the end point of another.
On mine there were 2 commutator segments per rotor slot; the jumper on
one connected to a winding wire, but the jumper on the other connected
to _2_ winding wires! How could there be 3 connections per slot?
Bizarrely asymmetrical.

I'm disappointed that it wasn't more doable.


motors with partial short can be run in series with a 3kW heater - but not now.


NT


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