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.

Yes, that's 24VAC applied to the two wipers on the latching relay.
And the two Com's are indeed common to each other and to the 24VAC common.

The 32VAC fuse rating is not appropriate for the 115VAC motor. You need one rated for at least 115VAC.

We'd have to understand exactly how the motor connection works to comment further on the use of only one relay.
Certainly if you add some electronics (which you stated you didn't want to do) then you could likely reduce the number of relays, even do away with the latching relay.

 

Yes, that's 24VAC applied to the two wipers on the latching relay.
And the two Com's are indeed common to each other and to the 24VAC common.

The 32VAC fuse rating is not appropriate for the 115VAC motor. You need one rated for at least 115VAC.

We'd have to understand exactly how the motor connection works to comment further on the use of only one relay.
Certainly if you add some electronics (which you stated you didn't want to do) then you could likely reduce the number of relays, even do away with the latching relay.

Thanks! I thought any AGC fuse would work, with the proper amps rating of course, until I read the fine print. Will continue to look.
The puzzle is that I didn't see any boards in the Liftmaster because I don't think they used them then. I have a second unit that I will dissect tomorrow.

 

The fuse voltage rating is related to breaking the arc that forms when the fuse opens. A low voltage fuse may not be able to break this arc, leading to very high currents before the fuse ultimately disintegrates, stopping the current.

 

Th.e fuse voltage rating is related to breaking the arc that forms when the fuse opens. A low voltage fuse may not be able to break this arc, leading to very high currents before the fuse ultimately disintegrates, stopping the current.

I would propose using a microwave fuse 125vac 20a. Does this sound ok?
I was able to get to the gate today. Soon after starting to build your circuit, I realized that while I had 120v at the site, I had no amps. I traced the problem back to the pole and called the electric company. They diagnosed a bad neutral and fixed it. Apparently at the meter there was a mixture of copper and aluminum wiring which he said happens all the time. Go figure. This is Cape Cod near the water with salt air! He showed me a terminally corroded aluminum wire which he had removed at a restaurant and said they had serious equipment damage as a result.
I wonder how much of my original circuit could have been damaged by this. Anyway, I put the old circuit (with board) back together so I could see if anything worked after the neutral fix. It didn't of course but wanted to be absolutely sure. I really have no idea how long the neutral has been bad but seeing correct line voltages with a non-working gate would never have led me to suspect that this could be complicated by a current issue!
I didn't have time to restart building the new circuit but will do so next week and report back.
Here are the resistance measurements I took on the motor with leads unattached (except capacitor left in place): wht-brn .5 ohms, red-blu 4.6 ohms. Do these sound plausible? Let me know if you or Max would like me to look at other pairs.
Again, thank you.
Frank

 

How about wht to red and wht to blu, and while you are at it brn to red and brn to blu.

 

How about wht to red and wht to blu, and while you are at it brn to red and brn to blu.

Sure Mike. I will get them as soon as I get back next week.

 

Where is the resistance check and maybe eliminate the guess work?
Max.