Speed controller Very slow!

[Martin King 2Participant @martinking2]

Hi all,

I need to slow down a Powerfile by a lot to stop it burning the material being sanded. I have almost zero knowledge of electronics so cannot build anything. Is there an off the shelf unit that would do with damaging the file? The slowest speed on the unit is waaaay to fast.

Regards, Martin

[Martin King 2Participant @martinking2]

Want to slow down a B&D Powerfile

[Roger Provins 2Participant @rogerprovins2]

Search eBay and you'll find dozens. No idea which is best … here is just one but caveat emptor.

**LINK**

Edited By Roger Provins 2 on 13/08/2016 08:50:53

[Martin King 2Participant @martinking2]

Roger, thanks for that. As I am so out of my depth with electronics my concern is how safe these things are in use for the file and the user. The file needs to go really slowly.

Martin

[Tim StevensParticipant @timstevens64731]

Have you considered the use of an old-fashioned manual file? I find it easier to go slowly after the first five minutes …

Cheers, Tim

[Les Jones 1Participant @lesjones1]

Hi Martin,
If the speed control on the powerfile is an electrical control (As opposed to a multi speed gearbox) then it may not work with an external speed control. An internal speed control will probably be a phase angle type speed control which is the same as the ones in Roger's link. A light dimmer switch uses the same method and could be used provided it has a suitable power rating for your powerfile. It could be that an internal electrical speed control is designed so it cannot go too slow for the fan to cool the motor properly. I am basing these comments on the assumption that it uses a series wound (Universal) type motor as you have given no details.

[Nick WheelerParticipant @nickwheeler]

Doesn't a Powerfile already have a speed controller?

I'm sure my some-made-up-brand copy does. It's not something I use very much, mainly for weld prep and finishing in tight spaces like door-shuts.

[BazyleParticipant @bazyle]

As said above you can't put a second speed control on the thing that already has one. They may have set the control to a not so slow minimum to ensure it still gets some airflow.

[Martin King 2Participant @martinking2]

Hi all,

Thanks for the replies,

Yes it does already have a speed control but the slowest is still way to fast and causes burning.

As I thought the motor will be going too slow to be cooled.

Hand sanding is obviously an option but difficult access to the corners etc which the file reaches nicely.

Seems like my idea is a non starter! Never mind!

Regards,

Martin

[BazyleParticipant @bazyle]

Perhaps time for one of those vibrating saw thingies with a custom sanding pad. Not sure if they don't also go like the clappers though.

[Michael GilliganParticipant @michaelgilligan61133]

Martin,

This is probably not appropriate, given your self-professed lack of knowledge; but someone's got to mention it:

It should be possible ['though maybe not easy] to bypass the existing speed control, and then use an external controller.

Give us the exact model number, and maybe someone can find an exploded view.

MichaelG.

[RobboParticipant @robbo]

Martin,

Get yourself an oscillating sander. The Fein Multimaster is the leader and very expensive, but these days cheap variants are available (from Aldi, Screwfix etc)

Variable speed and with the correct sanding head can get into tight corners.

[Ian S CParticipant @iansc]

I just reassembled the speed controller I built for Mums electric spinning wheel today. The max speed with the controller in place is just a bit over 50%, and I had the bottom speed set to about 25%. It was used on a sewing machine motor, and worked very well. Dad had a similar speed controller on his Black & Decker, and he used that with a B&D attachment wood lathe, end result, burnt out armature. The problem I see with electronic speed controllers is that as the speed reduces the flow of cooling air reduces, but the heat increases, it all sounds a bit daft, but this is the reason I have a strong dislike of this type of machine control (variable speed lathe). I imagine the power file is really designed for wood work.

Ian S C

[Howard LewisParticipant @howardlewis46836]

In the past, I have used a Variac to slow a cheap jigsaw, but with the knowledge that reduced speed = reduced power and seriously reduced cooling.

Speed reduction by voltage control is likely to increase current draw, more than expected, since at lower speeds, the motor's back emf will be reduced, resulting in a greater voltage drop across the motor.

The Power vs Speed relationship for a fan is non linear. Being similar to a marine propellor, it is probably to the power 2.8, so halving the speed probably reduces the flow of cooling air by a factor of between 7 and 8.

So only short periods of use, under light load, are feasible, if damage is to be avoided.

Howard

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