Many years ago (possibly 50) you could buy a module that would take the place of a starting relay or centrifugal cut-out for an AC motor. Where do you find them? (I think I sent for one thru Popular Science mag at the time) Thanks
I don't know about a solid state version. But, there are electro-mechanical versions that are quite common on motors less than
1 hp. They control the input to the start winding with a current sensitive relay. When the motor is turned on the inrush current closes the circuit to the start winding. When the motor gets up to speed and the current drops to the run value the relay opens the circuit the the start winding. I believe Klixon made them. You might try and google them.CP
Those relays are [were] commonly used on sealed refrigeration compressor motors, so check out an appliance repair place or a heating/ air conditioning place. Neil S.
Those relays are [were] commonly used on sealed refrigeration compressor motors, so check out an appliance repair place or a heating/ air conditioning place. Neil S.
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Some fridge motors use a PTC thermistor instead of a current sensing relay - once or twice I've successfully bodged motors with failed thermistors by using the thermistor from a CRT TV degauss posistor.
I've seen 3-wire starters that were marked Solid State (triac, presumably), as replacement parts for current-type start relays, typically for refrigeration compressor motors (fractional HP).
Places like Johnstone, or other suppliers for HVAC service folks should have numerous models to choose from. You may need to know a motor's specs, at least the LRA locked rotor amps rating, to be able to make an informed selection of starter devices.
The following is a post from rec.crafts.metalworking..
I bought a couple of used Dayton (1/3 HP) bench grinders recently, and found some Klixon current-type motor starter relays being used instead of centrifugal switches for switching between Start and Run windings in these small split-phase 120VAC induction motors.
I mention these relays because they would be a suitable replacement for damaged mechanical components or switch contacts related to centrifugal switches.
These relays are the types used with refrigeration and air conditioning compressors, and also completely suitable for other split-phase motors. They have a heavy duty winding that the motor current passes thru, not a separate coil like common relays. When the power is turned on, the relay is pulled in, to make contact to the Start winding. The starting amperage of the motor is initially high, but it drops as the rotor approaches Run speed, the relay drops out, connecting the line voltage to the Run winding.
There are charts of different models of the SR start relays (in PDFs at the link above), but I didn't find any type of selector guide for choosing what the appropriate amp ratings would be for various HP ratings. The models of Klixon SRs I was looking at were applicable for motors up to
15A (3CR series), and the next larger series of SRs were for up to 25A, so these ratings would cover nearly all single phase split-phase motors (capacitor start or non-capacitor start) used in a home shop environment.One particular aspect of the SRs is that they are gravity-dependent, and therefore need to be installed with the proper end pointed up. Aside from that, they are highly reliable starting devices, rated for about
1 million cycles.The specific ratings used for a 1/3 HP bench grinder motor use an 11A pull-in (Start) spec and a 6A drop-out (Run) spec. Of course, larger motors would use higher rated specs for pull-in and drop-out currents, and the ratings vary in tenths-of-an-ampere (11.5A/6.3A, etc).
-- Cheers, WB .............
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This was a totally solid state device...like a timed triac that cuts- out after a half second.
This was a totally solid state device...like a timed triac that cuts- out after a half second.
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If the motor is low powered, ie not too much bigger than a fridge motor, you can use a CRT TV degauss unit, there are 2 different types of the 3 pin unit so you have to make sure you know which and wire it accordingly.
The most common type has 2 PTC elements - one is in series with the load (degauss coil - (or start winding)) and delivers a short burst of current which decays as the current through it heats it and causes its resistance to rise.
The second PTC element is wired directly across the mains (after the on/off switch) so that its self heating also heats the first PTC turning the current fully off.
The less common type of degauss unit is a combination PTC/NTC pair, the PTC would go in series with the load as before, the NTC in this case would be in series with the run winding - the NTC element provides inrush current limiting as it has a high resistance at room temperature, falling to a low resistance as the current flowing heats it up.
Once again the self heating of the NTC heats the PTC and switches off its current.
The downside is that degauss units take a few minutes to cool after the motor is switched off.
It is amazing to me that they aren't commonly available!
Google --- PLC module.
HTH
-- Live Fast, Die Young and Leave a Pretty Corpse
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Not even close. This was a small (a little larger than a postage stamp), simple device. I remember using one on a 5 HP motor that wouldn't start. It was for a bakery mixing machine.
Thermistor across the start cap?
-- Live Fast, Die Young and Leave a Pretty Corpse
Already suggested - he seems to be ignoring it.
Murata make a range of motor start thermistors (posistor).
By the look of the picture on the front of the catalogue they may be plug in replacements for existing start winding solenoids.
Back in my youth I went to school for HVAC and got a job with a family owned company who installed Trane. I can remember installing hard start kits. But my specialty was gas fired ammonia systems. Quite a few residential and small office units around. Mostly 5 ton. Hell natural gas was cheap back then. Our local gas company went on strike and I was working on those things 24 hours a day it seemed. So freon-based systems were not part of my routine except for the then emerging residential heat pump units. But I do remember the solid state hard start kits.
I think this Villa dood is somewhat purposefully dense.
-- Live Fast, Die Young and Leave a Pretty Corpse
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There is no starting cap...it would take the place of a centrifugal opening starting switch. I'll Google posistor and see where that leads. (thanks meathead for the comment-helpful indeed)
Never got into actual motor repair except for taking apart 10/15 horse
230 volt single phase repulsion/induction motors, then having the rotor/ stator rewound, the com resurfaced or replaced. Other than that was a simple plugin solid state replacement for a three pin residential AC compressor. There were direct replacements or hard start replacements to give the compressor a month or so longer useful life while the owner scraped up the cash for a replacement.-- Live Fast, Die Young and Leave a Pretty Corpse
There is no starting cap...it would take the place of a centrifugal opening starting switch. I'll Google posistor and see where that leads. (thanks meathead for the comment-helpful indeed)
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AFAIK Murata claim "posistor" as a registered trademark, but the word has found its way into common usage by TV engineers to describe the PTC degauss units for CRTs.
Yeah I mistyped PLC for PTC a couple replies ago.
Still that doesn't replace a centrifugal clutch directly although you could probably jury-rig one.
-- Live Fast, Die Young and Leave a Pretty Corpse
"clutch"?!
Well yeah a clutch, switch, kickout what the f*ck ever you want to cal it.
-- Live Fast, Die Young and Leave a Pretty Corpse
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