Delta 36-725 Repair help and warning
#28
  Re: RE: Delta 36-725 Repair help and warning by lkomroff (That little white un...)
(12-06-2019, 11:27 AM)lkomroff Wrote: That little white unit looks like a microswitch.  It fan also appears not to be a standard type. Could the fan be 2 piece and part of it should move when motor starts?  If that happened, there is a metal bracket (L shape) that looks like it is pressing on the microswitch, that could move along with the fan, open the microswitch and disconnect the cap. So , if the fan is stuck, bracket needs adjustment, microswitch is bad or the fan section won't move, the start cap will never be disconnected from the circuit.

Possibility or am I dreaming?

Larry

Looks like a potential relay.     Same effect as a centrifugal switch but sometimes used in dirty environments.   It uses induced voltage in the winding to tell when to disconnect the start cap.   Tom can explain it better.   Not sure if that is the problem but very likely.  Roly
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#29
  Re: RE: Delta 36-725 Repair help and warning by Roly ([quote='lkomroff' pi...)
(12-07-2019, 09:58 AM)Roly Wrote: Looks like a potential relay.     Same effect as a centrifugal switch but sometimes used in dirty environments.   It uses induced voltage in the winding to tell when to disconnect the start cap.   Tom can explain it better.   Not sure if that is the problem but very likely.  Roly

That certainly sounds like a possibility.  The black wire from that relay would go one pole of the start capacitor.  And the two blue wires go to one side of the run capacitor.  If that is the case I hope that is a common part?
_____
Darrell
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#30
  Re: Delta 36-725 Repair help and warning by Darrell D. ([size=small][color=#...)
I’ll give it a shot.  With a two-capacitor motor, a potential relay is wired in parallel with the start winding.  Its contacts are normally closed.  As the motor starts and increases rotor speed, the magnetic flux induced in the rotor (hence the term ‘induction’ motor) develops back-EMF which opposes current flow in the windings.  High current flows in the windings without this back-EMF, and as the rotor approaches unloaded speed, EMF increases and opposes current in the windings, which is why the current starts out in the 4-8 times rated current range but decreases down to unloaded value at speed (with no load).

Rotor speed is what governs current flow in the windings, by the way, through the mechanism of back-EMF.  Putting a load on an induction motor slows it a little (just a little over 4% between no load and full load), which reduces the back-EMF, which allows more current to flow in the windings, which strengthens the magnetic fields, which increases the rotor torque to meet the applied load torque.

But while starting, as this EMF increases, it eventually reaches a value in the potential (as in voltage potential) relay coil that causes it to open its contacts and hold them open, which takes the start capacitor out of the circuit.  Same function as a centrifugal switch, but sealed (usually) and much more suitable for dirty environments.

Air conditioning compressors use these because they’re hermetically sealed and you can’t open them to repair a mechanical switch.  

If you’re replacing capacitors, you should also replace the relay, as they wear out too.

Not such a great explanation but it’s all I’ve got.   Sigh
Tom

“This place smells like that odd combo of flop sweat, hopelessness, aaaand feet.”







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#31
  Re: RE: Delta 36-725 Repair help and warning by TDKPE (I’ll give it a shot....)
(12-07-2019, 05:29 PM)TDKPE Wrote: I’ll give it a shot.  With a two-capacitor motor, a potential relay is wired in parallel with the start winding.  Its contacts are normally closed.  As the motor starts and increases rotor speed, the magnetic flux induced in the rotor (hence the term ‘induction’ motor) develops back-EMF which opposes current flow in the windings.  High current flows in the windings without this back-EMF, and as the rotor approaches unloaded speed, EMF increases and opposes current in the windings, which is why the current starts out in the 4-8 times rated current range but decreases down to unloaded value at speed (with no load).

Rotor speed is what governs current flow in the windings, by the way, through the mechanism of back-EMF.  Putting a load on an induction motor slows it a little (just a little over 4% between no load and full load), which reduces the back-EMF, which allows more current to flow in the windings, which strengthens the magnetic fields, which increases the rotor torque to meet the applied load torque.

But while starting, as this EMF increases, it eventually reaches a value in the potential (as in voltage potential) relay coil that causes it to open its contacts and hold them open, which takes the start capacitor out of the circuit.  Same function as a centrifugal switch, but sealed (usually) and much more suitable for dirty environments.

Air conditioning compressors use these because they’re hermetically sealed and you can’t open them to repair a mechanical switch.  

If you’re replacing capacitors, you should also replace the relay, as they wear out too.

Not such a great explanation but it’s all I’ve got.   Sigh
 Good explanation.  I am sure some eyes glazed over, but for us electrical nerds it made sense.   Roly
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#32
  Re: RE: Delta 36-725 Repair help and warning by TDKPE (I’ll give it a shot....)
(12-07-2019, 05:29 PM)TDKPE Wrote: If you’re replacing capacitors, you should also replace the relay, as they wear out too.

That seems to make sense, but what relay to use?  I see a number of "potential relays" and "compressor hard start kits".  THe relays seem to have a ton of connectors.  Assuming that that little white switch is a relay, there are only 4 contacts.  I see on the hard start kits, that those relays seem to typically have 4 connectors.

I still have the motor at a repair guys house.  Waiting to hear back what the issue maybe and what it will take to fix.
_____
Darrell
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#33
  Re: Delta 36-725 Repair help and warning by Darrell D. ([size=small][color=#...)
That, I’m afraid, is not such an easy question. The voltage through the relay coil will depend on the motor and the capacitors, and it has to open at the right motor speed, so they’re not a one size fits all deal. There should be numbers on that little block, again assuming that’s what it is, and either you need to find the same unit based on the numbers, or vary the voltage across it to find when it opens. Assuming the old one opens at the proper value, which is in question since there’s a problem with this motor in the first place.
Tom

“This place smells like that odd combo of flop sweat, hopelessness, aaaand feet.”







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#34
Sad    Re: RE: Delta 36-725 Repair help and warning by TDKPE (What is that white u...)
(12-04-2019, 08:57 PM)TDKPE Wrote: What is that white unit in the middle picture, with the two blue and one black wire to it?
After some thought and searching, that white unit seems to be a micro switch.  I dont have the motor (at a shop, still waiting to get it looked at, ugh,   Sad)

I did some searching for DMC-1220 switch and relay, and this is a common number for micro switches, the one part pictured is from a Ryobi miter saw.

Im thinking the gray steel arm is a lever from a centrifugal switch.  I trips the switch and turns off the start cap and turns on the run cap.

   

   
_____
Darrell
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