Overheating capacitor on 370watt 240 volt induction motor, driving benchtop sander?

Thread Starter

Davey44

Joined Apr 4, 2020
5
My almost new benchtop sander (as above) stopped working because the (push on push off) switch failed. This was replaced and the machine worked well for a few hours, then smelled of smoke/hot electronics. I investigated and found the capacitor very hot and with a small blow-hole in the top. I changed the capacitor with an exact replacement from the maker. Switched on and within moments the same nasty smell of hot electronics happened again. The capacitor was VERY hot.
Any ideas, please, as to what's wrong and how should I proceed to get my useful sander back in full action?
 

Thread Starter

Davey44

Joined Apr 4, 2020
5
Sorry, am I missing something? Would a photo of the manufacturer's plate - on the machine - help? Sorry if I'm being thick.
 

shortbus

Joined Sep 30, 2009
7,604
Let's see now. Googling "Ferrex" gets hits for a iron pill medicine. Scheppach gets many many pages of wood working tools. So if someone asked you to try and help with the information you gave the forum, could you? Personally my crystal ball is in the shop getting recalibrated this week.
 

MaxHeadRoom

Joined Jul 18, 2013
20,441
A couple of thing it could be, No1: is it a AC motor rated start/run capacitor?
N02: If it is a correct start capacitor the method used to switch it out of circuit could have failed. As previous post #7..
More details on the motor is needed.
Max.
 

Thread Starter

Davey44

Joined Apr 4, 2020
5
Is it a start or run capacitor?
Maybe it's just for starting the motor and not disconnecting
Is it a start or run capacitor?
Maybe it's just for starting the motor and not disconnecting
Thank you very much Rich2 and Max. TBH I'm not sure whether the capacitor is a start or run or both - version. I do know, however, that the new capacitor is correct since it's exactly the same as the original one that I took out of the machine.

I have a horrible idea that what you've both said is correct, in that it's a start capacitor which doesn't get disengaged after fulfilling its function! There is what looks like a solenoid linked into the wiring loom, which would presumably be the device which is meant to trigger the capacitor for starting purposes and then is meant to disengage. I wonder if Scheppach would kindly send me a new solenoid? It's supposed to have a three year guarantee, and only bought in January of this year!

So, thank you once again.

Dave R.
 

MaxHeadRoom

Joined Jul 18, 2013
20,441
There are typically two types of start switch, a centrifugal one on the motor shaft, the second is external and consists of a current sense relay which opens once the start current has decreased.
If a start capacitor remains in circuit it is usually destroyed.
Max.
 

shortbus

Joined Sep 30, 2009
7,604
. TBH I'm not sure whether the capacitor is a start or run or both - version. I do know, however, that the new capacitor is correct since it's exactly the same as the original one that I took out of the machine.
All of this could have been avoided by giving the model number of the machine like you were asked earlier. A brand/maker is nice but ti also needs a model number or name, so the manual can be looked for. If it failed that fast when new, and was replaced with the same type, the original one was the wrong type or value. Most manuals will have a parts breakdown and the cap could be compared to that.
 
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