Single Phase motor wiring question

[ProDave]

My guess would be L to one thick cable, N to the other thick cable Start capacitor to the thin cable.  Then you will have to try other side of start capacitor to N and if that does not work other side of start capacitor to L

 

[mecheng46]

i will try you suggestions Dave, thanks.

What size capacitor shall i try with this motor?

 

[roys]

Wild guess, try a 10uf 450V 

try tryping cbb60 as well when you do a search, think I got my last one from Amazon, cheap as chips.

 

[ProDave]

I would have said about 4 or 5 uF  make sure it IS a motor start capacitor usually rated at 400V ac.

 

[mecheng46]

I went through the pictures I took yesterday and I just noticed that the resistance readings I got from the starting windings yesterday are not healthy, unless I am missing something?

My only hope is if there is a centrifugal switch in the motor somewhere that might be the culprit. Otherwise i might have to ignore the starting widnings and wire only the run windings directly on an SDST switch and push start it every time i want to use it.

Shame as is not an easy task finding a brand new single phase 240v 1HP bench grinder, for some reason manufacturers don't make heavy duty single phase grinders anymore. Heavy duty usually goes with 3 phase. 

 

[Tony S]

A centrifugal switch is of no use without a capacitor to give a starting phase shift.

 

[mecheng46]

A centrifugal switch is of no use without a capacitor to give a starting phase shift.

I was referring to the issues with the high resistance readings from the windings.

I am currently trying to identify the problem with the starting windings, which it will either be a dodgy centrifugal switch or an open circuit on the windings. A capacitor will be required anyway.

 

[ProDave]

It might just be a lower power winding as it's only needed to start so there might not be anything wrong at all.

 

[Tony S]

I was referring to the issues with the high resistance readings from the windings.

I am currently trying to identify the problem with the starting windings, which it will either be a dodgy centrifugal switch or an open circuit on the windings. A capacitor will be required anyway.

The start winding resistance is always higher than the run winding, it’s only used for less than a second.

 

[mecheng46]

From memory resistance should be a kilo ohms number at the most? I hope i am wrong.

I took it apart and i found the contactor/brush broken in half. The brush is a shaft mounted type same on the picture below. I can only find couple of pictures of this type on the internet, this must not be a common type. The bottom round part is the weight that pushes the brush away from the switch when it goes up to speed. It is spring loaded by a small spring going through it to keep it in contact with the switch at low speed. I am guessing this part won't be available to buy these days? 

 

[roys]

Just as a by the way, I have taken apart loads of single phase motors with centrifugal switches and I have never seen that type with the brush except in text books.

Now that I have said that I will probably get one to look at next week

 

[Tony S]

It’s a repulsion start motor.

Covered in the forums Knowledgebase.

 

[mecheng46]

any help finding spares for this centrifugal switch will be much appreciated.

Does Black and Decker stock this kind of spares or are any other manufacturers use this type of centrifugal switch these days? 

 

[Tony S]

In 40 years I’ve never come across a repulsion start motor, they’re an American thing.

 

[Geoff1946]

What's broken? If its the carbon piece itself it shouldn't be too hard to make one from a larger carbon brush, such as one for a car starter motor.

 

[mecheng46]

It's the brush holder

 

[Geoff1946]

I've never seen anything like that. It looks hard/impossible to replicate. Is it bakelite?  I guess it contacts, and shorts out, a pair of slip-rings when stopped (?).

If so, the only fix I can think of is to bring out the connections and make up a manually operated OFF/START/RUN switch, (to work a bit like a delta star starter).

 

[roys]

Mmmm 3D printer job, don’t know if the plastic used in the printer would stand up to the heat and stress of its duty though.

 

[mecheng46]

I will try ABS material from a 3D printer and see how it goes. I glued the original part with superglue but I am not super confident with it. It feels ok but I don't want to strip it down in 2 weeks time.

Whilst I am trying to source this part I will need to source capacitor this bench grinder need.

Depending who i ask i get a different number anything from 4uf to 550uf.

Since the motor has a centrifugal switch I need a start capacitor on the starting windings. From a quick look on the internet the capacitor for a 240v 1HP motor should be anywhere between 138 to 182uf (240v or more), am i missing something?

 

[mecheng46]

Update on this:

I printed the broken part on a 3D printer (ABS) and I used a 140-170uf starting capacitor.

All working well now, thanks for your help