Cleaning an armature and field

Reply

  #1  
Old 12-04-18, 06:39 PM
XSleeper's Avatar
Group Moderator
Thread Starter
Join Date: Dec 2004
Location: USA
Posts: 21,105
Cleaning an armature and field

So I have a Fein MultImaster (FMM250Q) that is about 10 yrs old or so. I have used it pretty hard and it has been great. I have noticed the last year or so that it gets very warm when using it... almost too hot to hold onto.

Well today it started slowing down and smoking/stinking so I shut it off... it was really hot this time and took forever to cool down. Once I took it apart, I find that there is lots of drywall dust inside it... (I knew it was going to be dirty!) Found that the armature is fairly clean and the brushes look like they will need replacement soon (5/16" long) but the field appears to be very dirty inside and out. The wires making up the field winding are pretty caked with drywall dust. There also appears to be some heat damage (black blistering) around each of the four the "windows" of the winding (see photos... bottom photo shows one of these "windows"). All 4 look similar to this one.

I guess I'm wondering if I should try to carefully grind down these blisters with a rotozip/sanding drum? Seems i have to because the armature won't slide in and out wit hour rubbing on the blisters.

And then secondly, what should I clean the field up with? Only electrical cleaners? It's slightly rust too. I just wonder if it's salvageable or not... and where the problem lies. If it is just so dirty that the heat buildup eventually caused the blisters... and if the blisters are what caused it to fail?
 
Attached Images   
Sponsored Links
  #2  
Old 12-04-18, 06:45 PM
PJmax's Avatar
Group Moderator
Join Date: Oct 2012
Location: Northern NJ - USA
Posts: 47,695
The windings are enameled coated copper.
Once the enamel starts to melt..... the windings start to short out and it gets worse quick.
 
  #3  
Old 12-04-18, 06:49 PM
XSleeper's Avatar
Group Moderator
Thread Starter
Join Date: Dec 2004
Location: USA
Posts: 21,105
So what you're saying is that since the enamel has started to melt, its a goner... and I probably should look into replacing the winding?
 
  #4  
Old 12-05-18, 10:32 AM
XSleeper's Avatar
Group Moderator
Thread Starter
Join Date: Dec 2004
Location: USA
Posts: 21,105
I tested the field coil and the armature with a multimeter... both seem to check out ok. Strange...
 
  #5  
Old 01-10-19, 03:16 PM
Member
Join Date: Jan 2019
Location: usa
Posts: 28
actually, fields dont 'look' bad....sometimes the 'blisters' are just the enamel for the winding process. My concern at this point would be the armature...check to see if there has been any excessive wear/sparking on the edges of the commutator bars...that could indicate opens/shorts in your armature windings.
Bearings and their fit are also a consideration if it appears the arm. has been rubbing on the stator.
 
  #6  
Old 01-11-19, 02:36 PM
XSleeper's Avatar
Group Moderator
Thread Starter
Join Date: Dec 2004
Location: USA
Posts: 21,105
Actually this field DID look bad as the picture and a side by side comparison attests to. The blisters are not present on the new field, pictured below. And the blisters on each end of the field were so bad they prevented the armature from sliding out easily... as mentioned earlier, the armature and field both test out fine. And there is nothing wrong with the bearings.

However, after replacing the brushes and replacing the overheated field with a new one, it still acts like it wants to overheat quickly and is not getting the right voltage (speed variations are not smooth as the speed control dial is turned up and down, and it never reaches high speed) I have only run it for a few seconds as I dont want to melt this new field so I am going to assume the variable speed switch is the culprit of this entire problem. Unfortunately that switch is just one more $60 part.
 
Attached Images  
  #7  
Old 01-14-19, 09:07 AM
Member
Join Date: Jan 2019
Location: usa
Posts: 28
ok...so the new fields didn't fix the problem....which doesn't surprise me....did you use a 'growler' to test the armature? An ohm test isn't very useful. I would definitely do that before I spent $60. Not saying that's the problem, and you never addressed the comm bar inspection, just how I would approach it. Lastly, did you check both the stator and armature for grounds?
 
Reply

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Thread Tools
Search this Thread
Display Modes