Replace electromechanical circuit

Thread Starter

csfahey

Joined Nov 2, 2015
5
I have a 1/2 hp radial arm saw from the 1930's that uses a capactor and a magnetically driven mechanical switching arrangement to power the secondary windings of the electric motor. The capactor has burned out and I really don't want to deal with the mechanical switch as I am pretty sure it is going to be very noisy and heat up given how it looks like it works. Besides the thermal protection circuit breaker no longer works and the manufacturer cannot recommend a replacement that fits. So, what I want to do is replace the mechanical part with a solid state arrangement which I am pretty sure can be done using some diodes, resistors and a replacement capactor. What I am not sure of however what this type of circuit is called so I can research it and build it. My first thought was that it was an AC recitifier but that doesn't seem to be it nor does it seem to be a phase splitter or inverter. Can anyone point me in the right direction?
 

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Brownout

Joined Jan 10, 2012
2,390
Your switch looks like a normal relay, and should work. After all, it's been working since the 1930's. But if you really hate it, you can replace it with a similarly spec'ed Solid-State relay.
 

MaxHeadRoom

Joined Jul 18, 2013
19,754
There are external current relays for motor start windings, these replace the normal centrifugal switch version, if that is what the original function is.
Max.
 

PackratKing

Joined Jul 13, 2008
847
There are good odds, that your original equipment, is only crusted with sawdust and wood-resins... and a thorough cleaning will likely put you back on track, with only a new capacitor...
 

Thread Starter

csfahey

Joined Nov 2, 2015
5
Yes, I am pretty sure that it only requires a new capacitor, but there is also a chance that the mechanical relay might be worn out as well after all it is 80 years old. In either case, this relay will be noisy and will probably get hot which is why I suspect that the thermal protection was in the circuit. Since I cannot keep it original which I had wanted to by replacing the circuit protection, I might as well make it work quieter, cooler and more reliably. So I would rather replace the mechanical relay than keep it. I have looked at relays and the configuration appears to be of the SPDT type. I will look into potential relays as well. If I decide to keep the original mechanical relay would a RC Snubber circuit help with the noise and heat?
 

Thread Starter

csfahey

Joined Nov 2, 2015
5
This does not appear to be a potential relay nor does it appear to have a centrifugal switch. I am having a hard time wrapping my head around how it works but I believe it works like this. During a positive current and voltage, the solenoid causes the contact to close the circuit to one set of windings as well as the capacitor. Then the current and voltage reverses which causes those contacts to open and the other circuit to close where the capacitor begins to discharge, charging the other windings until the current reverses again which switches the contacts on the relay again repeating cycle.

Using the pictures I have included, can anyone confirm that this is how it works?
 

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MaxHeadRoom

Joined Jul 18, 2013
19,754
Can you trace the wiring out and post it?
It appears to be a potential relay action looking at the files.
I only see one relay contact.
Max.
 

Thread Starter

csfahey

Joined Nov 2, 2015
5
I will try. I need to take apart the relay at the wire connections to see if there is a hidden connection first.
 

Thread Starter

csfahey

Joined Nov 2, 2015
5
Thanks. The site had some good information. My machine is a little older than their but I think I can find the diagrams in there somewhere.
 
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