Sparking motor

[GS42]

I've had a Dewalt DWE7485 for a couple of years now, today I noticed the motor was sparking when I start and stop the saw (it's worse when I stop it). I blasted the motor with some air in case something was stuck in there but I'm wondering if it's the brushes?

Any thoughts?

 

[Phill05]

It looks like you need some new brushes and before you put new ones in whilst you have the cover off try cleaning the gap in between the copper commutator use a toothpick size of wood so you don't damage any wiring.

 

[GS42]

Thanks, I'll give that a try.

 

[Phill05]

Thanks, I'll give that a try.

I just had to do it on a small hand sander and now works great, it should sort you out.

 

[GS42]

I replaced the brushes and gave everything a clean, sadly it's still sparking especially when I turn it off. Someone suggested that it could be normal like this but it doesn't look right to me.

 

[Sideways]

https://www.ukworkshop.co.uk/threads/arcing-universal-brushed-ac-electric-motors.137062/

May be worth glancing through ...

 

[GS42]

Thanks I just had another read through and think I've checked most things, when I discussed it with a friend they suggested it could be a design feature - electric brake to slow the blade quicker than it would if left to spin freely.

 

[Sideways]

Unlikely.
https://www.eng-tips.com/viewthread...ly tough to do,Injection Brakes for AC motors.

You can't inject DC into a universal motor to slow it down like you can an AC induction motor - because universal motors run off DC as well as AC.
Is there a largeish resistor in there anywhere that could be used to absorb energy from the motor during braking ?

Some universal motors are just nasty and do spark a lot. And it is a DeWalt ...

 

[GS42]

The saw itself cuts very well - though I've seen a lot of negative reviews for it this is the first 'issue' for me with it. I have searched for others with similar sparking issues and found this on another site -

As advised my our global team the arching is due to the units braking feature were the brake coil needs to generate high reverse current in motor, which causes arching between carbon brush & commutator. This is a safety feature of the product and one that is known.

So all could be normal after all, though I'm not a fan of seeing sparks in the workshop.

 

[Henniep]

The saw itself cuts very well - though I've seen a lot of negative reviews for it this is the first 'issue' for me with it. I have searched for others with similar sparking issues and found this on another site -

So all could be normal after all, though I'm not a fan of seeing sparks in the workshop.

Also, the new brushes will take a while to seat and sparking should decrease.

 

[GS42]

I sent a copy of the video to the local dewalt service centre and received this response...

Looking at the video this is normal.

It is just the electric brake stopping the blade which causes the flash from the motor.

Nothing to worry about.