....................
(3) The contact rating issue on the relays still looms. Max had suggested a very heavy duty P&B relay (50a) for the power relays but I wondered if I could get by with less for a 1/2hp motor. The 1800w starting current figure that I saw for a 1/2hp capacitor start motor would suggest that 16a is adequate. It's also very hard to find a latching relay with a contact rating of greater than 16-20a, and those are generally resistive not inductive. Your thoughts?

If you follow the circuit I posted, the latching relay only carries relay coil current so can be a small device.
For safety reasons it's advisable to not put line voltage on the limit switches as you show. Also they may not be able to handle the motor current.
As I previously noted, the latching relay needs to be an alternate-action, impulse type.

 

Sorry, yes, should have read reverse one pair WRT the other.
Max.

Thanks Max for your info on the relay contacts issue. I think I am all set there for now. But I now have a burning question for Max, Crutschow, Mike or whoever wants to take a stab. I most unfortunately cannot locate the schematic for my old Liftmaster (the GD opener, not the gate opener, which is an Allister) but when I look inside the Liftmaster I see only one relay (clearly latching) not three! How do they do it? The GD opener circuitry and the proposed gate opener circuitry certainly could be made pretty much identical, I would think. A quick reading of amps (motor not operating) shows .07. I hear a soft buzzing. I assume that would be from the 24vac transformer which I assume is always energized, but could it also be that a motor coil is always energized as well, as in my proposed (criticized) circuit in post #29? Try as I might I can't see any other way to do this with only one latching relay, which seems to be the case in the Liftmaster design.
I will certainly consider using Crutschow's circuit, but it would be much nicer to only have to employ one relay.
Will look to your comments. Thanks again. Frank

 

This is how the GD operator motors I have worked on are wired.

 

If you follow the circuit I posted, the latching relay only carries relay coil current so can be a small device.
For safety reasons it's advisable to not put line voltage on the limit switches as you show. Also they may not be able to handle the motor current.
As I previously noted, the latching relay needs to be an alternate-action, impulse type.

I apologize for my recent posting which I made prior to reading this, but you might want to address my question of how Liftmaster seems to get away with only one relay.
Now to the above: I missed the point about the latching relay carrying only relay coil current, a sign of my incomplete knowledge of things (which is why I had to come here to consult the experts.) I now fully see this. As to your second point, I will need to look at your circuit again to understand that it does not put line voltage on the limit switches or subject them to motor current, another huge oversight on my part.

 

This is how the GD operator motors I have worked on are wired.

View attachment 86298

Hi Mike-
I can only tell you that the schematic I posted (showing four wires) was the one that was shown in the Allister Twist'r manual. I do need to do an ohms check on the windings but it will be several days until I have access to the motor.
Frank

 

Any possibility that the fourth wire is a brake? 120Vac is applied to the extra wire to release the brake?

 

I apologize for my recent posting which I made prior to reading this, but you might want to address my question of how Liftmaster seems to get away with only one relay.
Now to the above: I missed the point about the latching relay carrying only relay coil current, a sign of my incomplete knowledge of things (which is why I had to come here to consult the experts.) I now fully see this. As to your second point, I will need to look at your circuit again to understand that it does not put line voltage on the limit switches or subject them to motor current, another huge oversight on my part.

Now I understand everything!! I will almost certainly be using your circuit because it is clearly very safe and conservatively designed. I guess that means that the Liftmaster single relay design must be less so (see post #42) but I will await your comments.

 

Any possibility that the fourth wire is a brake? 120Vac is applied to the extra wire to release the brake?

I have no idea how to answer that. Best left to the others. Could you explain what you mean by a "brake" in this setting?

 

I have no idea how to answer that. Best left to the others. Could you explain what you mean by a "brake" in this setting?

Sure, what do you want a garage door to do if it is stopped at some intermediate level? Assuming the door springs perfectly compensate for the door weight, then the door will stay put. However, if it is like 99% of the doors I have played with, the door is "heavy" at some point of its travel such that the weight of the door might back drive the motor and its gear train.

Putting a "band brake" on the motor shaft would arrest the motor and keep the armature from free-wheeling. Application of 120V to the fourth wire on your motor could be actuating a solenoid that releases the band brake... That is what your posted schematic diagram implies...

 

One of the largest G.D. opener controllers in N.A. is Chamberlain, and they tend to use the motor with the alternate use windings.
This is a schematic of an older one.
Max.

 

One of the largest G.D. opener controllers in N.A. is Chamberlain, and they tend to use the motor with the alternate use windings.
This is a schematic of an older one.
Max.

Looks like the three wire motor diagram I posted above. Note that regardless of direction, the full line voltage is across one winding, while the other has the capacitor in series with it (current leads).

Anybody else want to speculate what the fourth wire is for???

 

Speculation. Perhaps the motor is wired as shown here? Presumably having the two ends of both windings accessible allows greater wiring freedom.

 

Speculation. Perhaps the motor is wired as shown here? Presumably having the two ends of both windings accessible allows greater wiring freedom.

The connections in the link indicate reversing two windings that are permanently connected as a main and a phase shift winding.
Unlike the previous which show both windings doing double duty.
In the case of the double duty motor, it can be configured either way, as long as both ends of both windings are available.
The double duty motor, the windings are identical.
Max.

 

The connections in the link indicate reversing two windings that are permanently connected as a main and a phase shift winding.
Unlike the previous which show both windings doing double duty.
In the case of the double duty motor, it can be configured either way, as long as both ends of both windings are available.
The double duty motor, the windings are identical.
Max.

Is the reason you must speculate on the function of that fourth wire because there's no way to tell from the schematic what's on the board and how it's wired? (Probably a naive question.)
BTW, hopefully I will have access to the motor over the next couple of days and will post the resistance readings as soon as I do.

 

Is the reason you must speculate on the function of that fourth wire because there's no way to tell from the schematic what's on the board and how it's wired? (Probably a naive question.)
BTW, hopefully I will have access to the motor over the next couple of days and will post the resistance readings as soon as I do.

Basically a motor dia that just shows 4 wires disappearing in to it is open to speculation.
Hopefully the resistance test may clarify it.
Max.

 

If you follow the circuit I posted, the latching relay only carries relay coil current so can be a small device.
For safety reasons it's advisable to not put line voltage on the limit switches as you show. Also they may not be able to handle the motor current.
As I previously noted, the latching relay needs to be an alternate-action, impulse type.

A few quick questions about your circuit before I implement it (hopefully tomorrow or Thursday.) I thought I understood everything but I am now a little confused about the way in which the 24vac is applied to power the coils in the two power relays. Specifically, the 24vac from the transformer is used to activate the coil on the latching relay, that is clear. But the two wipers appear to be tied together, with "24VAC" noted to the left. I guess I misunderstand what you are trying to say here. That *is* supposed to be 24vac across the wipers, isn't it? Also are there any more common points? (I assume the two "Com"s are tied together.) Just want to be 100% sure.
I will be fusing the motor line with a 20a fuse. I picked up a 20a AGC fuse and holder but the fine print said "up to 32vac." I now have no idea what I should be using.
I haven't checked this whole thread before writing this, but I didn't notice anyone explaining how the Liftmaster *seems* to get away with just a single latching transformer, at least that is all I could see.
Thanks again for all your help (and others). If this ever gets done it will be surreal.

 

Sure, what do you want a garage door to do if it is stopped at some intermediate level? Assuming the door springs perfectly compensate for the door weight, then the door will stay put. However, if it is like 99% of the doors I have played with, the door is "heavy" at some point of its travel such that the weight of the door might back drive the motor and its gear train.

Putting a "band brake" on the motor shaft would arrest the motor and keep the armature from free-wheeling. Application of 120V to the fourth wire on your motor could be actuating a solenoid that releases the band brake... That is what your posted schematic diagram implies...

Thanks. I will have the resistance measurements soon, but will that answer the question? My guess is it doesn't have a brake but I have no real idea.

 

Thanks. I will have the resistance measurements soon, but will that answer the question?

Well it sure won't hurt!

IF the motor has a brake, you would not be able to turn the shaft.
With the Chamberlain drive mechanisms, it is virtually impossible for the motor to back feed, as the drive mechanism is worm and pinion.
Max.

 

Well it sure won't hurt!

IF the motor has a brake, you would not be able to turn the shaft.
With the Chamberlain drive mechanisms, it is virtually impossible for the motor to back feed, as the drive mechanism is worm and pinion.
Max.

Hi Max-
Pretty sure the shaft would turn when everything was working properly awhile back.

 

Hi Max-
Pretty sure the shaft would turn when everything was working properly awhile back.

Could you possibly look at the circuit in post 33 which Crutschow designed for me and answer my questions which appear in post 56? Crutschow may post later but I am concerned I won't get the answers before I start to work on this tomorrow. Thank you.