Wolf 6" bench grinder capacitor

[Bsmith]

My 40 year old little grinder as above suddenly went to about half speed and little power while I was using it last week. I took it apart looking inside for brushes like an idiot (I don't know much about these things but felt I couldn't make it worse). No brushes in there and all looked good, tried it after changing the capacitor and off it went to full speed. The cap I took off was a 10uf and the washing machine one I put on is a 8uf so it's a bit slower at coming up to full speed. Just for fun I tried a 200uf cap which brought it up to speed much faster but I also noticed when I switched it off that it slowed to a stop faster. I thought caps were for starting and wouldn't affect stopping.

 

[roofman]

My 40 year old little grinder as above suddenly went to about half speed and little power while I was using it last week. I took it apart looking inside for brushes like an idiot (I don't know much about these things but felt I couldn't make it worse). No brushes in there and all looked good, tried it after changing the capacitor and off it went to full speed. The cap I took off was a 10uf and the washing machine one I put on is a 8uf so it's a bit slower at coming up to full speed. Just for fun I tried a 200uf cap which brought it up to speed much faster but I also noticed when I switched it off that it slowed to a stop faster. I thought caps were for starting and wouldn't affect stopping.

sounds like the charged cap is acting as a magnetic brake

 

[Bsmith]

sounds like the charged cap is acting as a magnetic brake

Thanks roofman, I changed it back to washing machine one, it's a bit slower starting but ok.

 

[rtbcomp]

There's probably some residual magnetism in the motor which makes it act like an alternator, the capacitor will load it and slow it down.

 

[Rig Pig]

A Wolf from the days when Wolf was a quality brand, very nice! I'm on the lookout for a quality replacement for my nasty 8" far eastern dump find!

 

[Bsmith]

There's probably some residual magnetism in the motor which makes it act like an alternator, the capacitor will load it and slow it down.

Thanks rtbcomp, so if I had that cap back on, would it be sitting live while the grinder is turned off?

 

[rtbcomp]

No. There may be a charge left in the capacitor, depends where in the mains cycle the mains is switched off.

 

[Bsmith]

A Wolf from the days when Wolf was a quality brand, very nice! I'm on the lookout for a quality replacement for my nasty 8" far eastern dump find!

It's done a lot in it's time and still going good.