LiftMaster Door Operator

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synchro said:
Have you measured the resistance of the 2 ohm resistor that's in series with the capacitor between main and auxiliary windings of motor to confirm it's close to that value?
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Yes. At least on my old unit. It was within spec, and it's not easy measuring 2 ohms! I understand what that RC circuit is for and it would appear to be working normally, at least the two components are within spec. I haven't checked the new unit, but it is a NEW unit...I'll go check them both again. I have no reason to suspect product defects at this point, especially since the new one is doing virtually the same thing as the old one. It was to eliminate this problem that we replaced the old one with a new one Now one could say that sounds like something is going on in my house wiring but check this out: we've been having this same problem with both old and new gate units for the last 6 years at least, and the house wiring has changed at least three times, during that period, including going from fulltime on the grid to installing a full Tesla system that we run on almost 100% of the time, so surges and voltage swings from grid aren't present...we're on the Tesla, not the grid. And even when the gate was wired directly to the grid at the meter box on a relatively short run compared to the current setup, it did this same 'stall' baloney. And as I mentioned, I don't think load is the issue. The gate rolls very freely, no binds, no rough spots. Is a 1/2 hp motor not enough? What would cause it to behave so erratically? How about spurious signals from the radio receiver? No one has answered that yet, not from Chamberlain or LiftMaster. I had the installer here two days ago and we got it to stall just once and that's really not enough to troubleshoot it unless you know it inside out. Keep brainstorming, please? Sooner or later someone is going to say "check the darn red wire" or something like that and that will be the solution. The odds are in our favor! And a heartfelt thank you.
 
hbiss said:
Exactly what garage door operators will do if there is some binding of the door or something gets in the way. Many have some kind of switch scheme to sense when the operator is being overloaded or the door jammed but I see no reason that it can't be done by monitoring the motor current. Even though the gate seems to be moving freely, that operator isn't designed for it and it may be having trouble moving it. There is normally an adjustment that sets the sensitivity on the operator.

-Hal
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Where is this adjustment on this unit? And what sensitivity are we speaking of? The radio is receiving the remote signals, no problem. Is it some other sensitivity? You're the first one to mention this so you have my curiosity aroused. Please explain more?
 
If your voltage is dropping to 112 that is too low. Since you have had the problem with two units I would check the wiring connections. Is this on it's own dedicated circuit? I think voltage drop is the issue as @hillbilly1 mentioned
 
kwired said:
That is not a capacitor start motor, the two motor windings are identical and the capacitor is placed in series with one winding in one direction and in series with other winding in the other direction.

I'm still leaning with contactor not closing all the proper contacts for some reason (especially if motor hums but doesn't always turn) or something is happening in the control circuit. to essentially issue a "stop" in mid cycle.
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You're the first one to point out that the cap is not a starting cap, but part of the reversing circuitry. Interesting. So this motor doesn't have a starting capacitor? The RC circuit is just to obtain the phase shift needed for rotation, yes? So could it be the motor is really on the edge of its performance envelope? These same units are used all over our island for this exact same purpose. Everyone can't be having this same problem, so I'm kind of coming up a little empty. Let me throw one other issue at you, since it seems you understand a lot about electricity: on our Tesla system, the Hz of the house power floats between 60Hz when the system is just on idle on the battery, to the range of 61-64Hz which is how the Tesla system controls the PV array. If less power is needed and the battery is charged, the Hz will rise within that range to throttle down the PV array. We don't sell back. Before the Tesla the Hz was whatever the local power company put out. Since we are having the same problems under either scheme, it would seem the minor fluctuation in Hz isn't a factor. What do you think? Thanks very much for your info about the capacitor.
 
Eddie702 said:
If your voltage is dropping to 112 that is too low. Since you have had the problem with two units I would check the wiring connections. Is this on it's own dedicated circuit? I think voltage drop is the issue as @hillbilly1 mentioned
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It's on a fairly long run now but it did the same thing on a run 1/3 the length of the current one. It's on a 20a line with nothing else on that line. Standby voltage is steadily 117-120, if it drops to 112, it's running. Draw when running is 4+amps, draw when stalled is 8+amps, voltage drops to 103.
 
hbiss said:
Exactly what garage door operators will do if there is some binding of the door or something gets in the way. Many have some kind of switch scheme to sense when the operator is being overloaded or the door jammed but I see no reason that it can't be done by monitoring the motor current. Even though the gate seems to be moving freely, that operator isn't designed for it and it may be having trouble moving it. There is normally an adjustment that sets the sensitivity on the operator.

-Hal
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His wiring schematic he posted shows terminals for a "RPM" sensor board. I think that is what is used on more recent models to sense jamming.

There is a slotted wheel on a shaft and an optical sensor to detect speed, have had cases before of the sensor (PCB device with radial leads) that had leads bent and was not properly sensing the wheel.
 
caribconsult said:
Where is this adjustment on this unit? And what sensitivity are we speaking of? The radio is receiving the remote signals, no problem. Is it some other sensitivity? You're the first one to mention this so you have my curiosity aroused. Please explain more?
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My post # 7 the clutch on it, the big pulley is on a shaft with a castle nut on it!


“ shoot low boys their riding shetland ponies”
 
caribconsult said:
You're the first one to point out that the cap is not a starting cap, but part of the reversing circuitry. Interesting. So this motor doesn't have a starting capacitor? The RC circuit is just to obtain the phase shift needed for rotation, yes? So could it be the motor is really on the edge of its performance envelope? These same units are used all over our island for this exact same purpose. Everyone can't be having this same problem, so I'm kind of coming up a little empty. Let me throw one other issue at you, since it seems you understand a lot about electricity: on our Tesla system, the Hz of the house power floats between 60Hz when the system is just on idle on the battery, to the range of 61-64Hz which is how the Tesla system controls the PV array. If less power is needed and the battery is charged, the Hz will rise within that range to throttle down the PV array. We don't sell back. Before the Tesla the Hz was whatever the local power company put out. Since we are having the same problems under either scheme, it would seem the minor fluctuation in Hz isn't a factor. What do you think? Thanks very much for your info about the capacitor.
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It not a starting cap, but not exactly part of reversing circuit. Unlike many higher torque motors that have a definite main and aux winding this one is low enough torque both windings are made same and have same overall impedance. They just switch which winding they put the capacitor in series with which ends up determining which direction it will run, but once that direction is selected it is no different than the run capacitor in a PSC motor.

Many linear actuator motors and a few other low torque but often reversed motors use similar concept to change direction.

Can't help you a lot with the Tesla issues no experience with them not that I may not understand it if I knew more about exactly what is typical with them, I do have some knowledge of what happens in PV systems but no experience servicing or installing those either.
 
On pg. 9 of the document below they describe a clutch adjustment like McLintock pointed out.
Also the RPM sensor board (aka A.R.S.) that kwired mentioned is shown as item 7 on pg. 18. As described on pg. 9, if it senses that the clutch is slipping too much it will stop or reverse the door movement.
They also list a part number for the clutch disc on pg. 21 if yours is worn out (try a clutch adjustment first).

 
Is it possible that there is some mechanical play or backlash in the system so that the motor sometimes starts unloaded and sometimes has to start moving the gate with its locked rotor torque? The starting torque of this capacitor-run motor with symmetric windings is lower than for a capacitor start motor.
Or is the clutch assembly supposed to prevent this?
 
kwired said:
It not a starting cap, but not exactly part of reversing circuit. Unlike many higher torque motors that have a definite main and aux winding this one is low enough torque both windings are made same and have same overall impedance. They just switch which winding they put the capacitor in series with which ends up determining which direction it will run, but once that direction is selected it is no different than the run capacitor in a PSC motor.

Many linear actuator motors and a few other low torque but often reversed motors use similar concept to change direction.

Can't help you a lot with the Tesla issues no experience with them not that I may not understand it if I knew more about exactly what is typical with them, I do have some knowledge of what happens in PV systems but no experience servicing or installing those either.
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I only mentioned the Tesla issues to show that this erratic behavior was happening before we went Tesla, so I don't think the slight fluctuation in the system Hz is the problem. You did see that in another post in this thread? The Tesla system controls the output of the solar panels by raising the system Hz (to throttle down the PV array) to 61-62-63-64Hz and lowers it back to 60 as the sun goes down and there's no more solar panel. Prior to Tesla we had whatever the local grid gave, 60Hz mostly. So I doubt this is a factor. So back to the RC circuit. I understand the phase shift business and how that determines the direction of rotation. So am I correct in the idea that there's no 'true starting capacitor' to give the motor a little kick on startup? Could that be the cause of the erratic 'stalling?' Would changing the values of those parts be of any use? The cap is 40µf and the resistor is 2 ohms. Would changing these have any beneficial effect, or just cause the motor to run faster or slower or maybe continue what it is doing? Thanks as always for your input.
 
synchro said:
On pg. 9 of the document below they describe a clutch adjustment like McLintock pointed out.
Also the RPM sensor board (aka A.R.S.) that kwired mentioned is shown as item 7 on pg. 18. As described on pg. 9, if it senses that the clutch is slipping too much it will stop or reverse the door movement.
They also list a part number for the clutch disc on pg. 21 if yours is worn out (try a clutch adjustment first).

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The clutch is not slipping. When stall occurs, there is NO movement from the motor, the clutch, none of the pulleys and gears. It is not a drivetrain issue as far as I can see. The motor just hums, pulls double the amperage, and refuses to start turning. And is there an RPM sensor in the schematic I posted previously? I didn't see one. Thanks as always to those replying.
 
GoldDigger said:
Is it possible that there is some mechanical play or backlash in the system so that the motor sometimes starts unloaded and sometimes has to start moving the gate with its locked rotor torque? The starting torque of this capacitor-run motor with symmetric windings is lower than for a capacitor start motor.
Or is the clutch assembly supposed to prevent this?
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I suspect this motor is on the low-torque end, because that's exactly what seems to be happening....there's not enough 'starting kick' to get the motor turning. Once it starts to turn, it runs correctly.
 
hbiss said:
Exactly what garage door operators will do if there is some binding of the door or something gets in the way. Many have some kind of switch scheme to sense when the operator is being overloaded or the door jammed but I see no reason that it can't be done by monitoring the motor current. Even though the gate seems to be moving freely, that operator isn't designed for it and it may be having trouble moving it. There is normally an adjustment that sets the sensitivity on the operator.

-Hal
Click to expand...
It's not binding anywhere. The gate rolls smoothly on ball bearing grooved wheels, the chain is greased regularly, you can move it with one hand if you disengage the motor drive with the chain supplied...it disengages some part of the drive train and the gate can be moved manually. The gate probably weights over 500lbs but it moves smoothly and the load isn't a great deal different than rolling up or down a warehouse door, which was the original design intention of LiftMaster for this unit. Down here in PR they have figured out how to use this to operate a rolling gate and these same units are all over. Probably the most commonly used in a place where rolling gates are popular. We call it a "portón."
 
kwired said:
That is not a capacitor start motor, the two motor windings are identical and the capacitor is placed in series with one winding in one direction and in series with other winding in the other direction.

I'm still leaning with contactor not closing all the proper contacts for some reason (especially if motor hums but doesn't always turn) or something is happening in the control circuit. to essentially issue a "stop" in mid cycle.
Click to expand...
Where is this 'contactor' of which you speak and is it accessible to some cleaning or maintenance?
 
GoldDigger said:
Is it possible that there is some mechanical play or backlash in the system so that the motor sometimes starts unloaded and sometimes has to start moving the gate with its locked rotor torque? The starting torque of this capacitor-run motor with symmetric windings is lower than for a capacitor start motor.
Or is the clutch assembly supposed to prevent this?
Click to expand...
There's usually a bit of slack in the drive chain, so it would appear the motor isn't under full load at the start, There's a small but measurable gap in the load until the slack is taken up, and that should allow the motor to begin turning. "Should" is obviously a dangerous assumption here. Would playing around with the values of the RC components have any beneficial effect? I know they are principally to generate the phase shift which determines rotation direction. My guess is that altering the value of this circuit would change something in the way the motor turns but I don't know enough about that to take an educated guess. Does someone out there know about this RC circuit business, like KWired? Is there anything that could be done to provide a little more kick to the startup? Like adding 1 capacitor in immediate series to each of the Red and Yellow inputs of the motor? I'm good enough with a soldering gun to do this and I've built way more complicated stuff than this, so no fear of tinkering here. THANKS TO ALL
 
caribconsult said:
Where is this 'contactor' of which you speak and is it accessible to some cleaning or maintenance?
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Physically in the unit, not certain. On your schematic you posted near bottom right of the page is two boxes representing them, one for open (OP) one for close (CL) each has two "coil" terminals and 9 terminals for power leads, or three sets of COM/NO/NC contacts.

Most commercial operators I have dealt with they are usually easily field replaceable definite purpose contactor style unit. Residential operators it may be more of a PCB relay, probably because the residential ones usually have smaller motors and the commercial ones are big enough the PCB relays won't have heavy enough contact rating.

Adding more capacitance would increase phase shift and give the motor more torque. Too much will smoke it, though on a short duty cycle like this has there is a lot of in between that gives more torque but still will eventually end up with shortening life of motor. But presuming nothing is wrong and you do need more torque then what you have is undersized for the task at hand. before messing with the capacitor I would want to know if both motor windings are drawing current when this thing is not working. If one is but other one is not - I'd still suspect open relay contact that is supposed to be closed. Capacitor isn't that prone to being something that intermittently works relay contact much more likely to be intermittent. I say this because you said the motor hums but won't turn. If nothing happened at all, not even brake release, then the issue probably more likely in the control circuit.

You asked about RPM sensor as well. It doesn't show details of it, just the terminals that interconnect to the control circuit, they are on lower left of the first image in the post with two images.
 
Change RPM broad/ sensor and logic broad


“ shoot low boys their riding shetland ponies”
 
caribconsult said:
There's usually a bit of slack in the drive chain, so it would appear the motor isn't under full load at the start, There's a small but measurable gap in the load until the slack is taken up, and that should allow the motor to begin turning. . . . '
Click to expand...

If there is more than one chain link of slack some designs will allow the sprocket to skip a chain link, try to grab the next one, and bind.
 
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