Murphy door

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James L

James L

Senior Member
Location
Kansas Cty, Mo, USA
Occupation
Electrician
I wired a Murphy door yesterday. It's a "hidden door" bookcase door with magnetic catch. It has 2 buttons, one outside the room (in the bookcase) and one inside on the wall. The two buttons are 2 feet apart, so I ran one 18/2 cable to the door jamb and split (option #1 in the diagram)

After I powered it up, I tested from the inside button and it worked. So I packed up all my things to go, then had a thought to check the other button. Now it doesn't work at all, even from the inside button.

120 volts is good.
No power at "C + NC"
No power at "C + 12v"

GC chatted with door manufacturer, and they asked if I tried wiring option #2 - no, I didn't.

They're saying if I rewire to option #2 that usually fixes the problem. I'm saying that makes no sense. If power in is good, but there's no power out on either the feed-thru or the relay output, rewiring won't help.

But I'm sure the whole box is full of electronics, which just might be my weakest skill set.

Any thoughts?Screenshot_20230926_105754_Adobe Acrobat.jpg
 
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If you don't have power between COM and +12, then IMHO the box is toast. Could also check for voltage on the CONTROL+ and - terminals, but it's probably zero, too.

Those things are usually under $20 on amazom prime ("Access Control Power Supply for Door") or get a replacement from Murphy.
 
If there is no +12VDC power (I'm assuming the output is DC), then it sounds like the rectification circuit in the box is toast. Unhook your button wires from the box just to see if it makes a difference, but I don't think it should.
 
junkhound said:
Only guess would be that the switch has a diode, thus polarity a factor?
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I thought about polarity because the connections say "push" and "ground" but I didn't notice any markings on the switches.

Honestly, that's not sinking in why it would use the ground terminal.
 
zbang said:
If you don't have power between COM and +12, then IMHO the box is toast. Could also check for voltage on the CONTROL+ and - terminals, but it's probably zero, too.

Those things are usually under $20 on amazom prime ("Access Control Power Supply for Door") or get a replacement from Murphy.
Click to expand...
Thanks. I think I'll buy one ($16) and take it with me whenever I go back. Seems like cheap insurance
 
The only predictable cause of failure I can see is to wire one of the buttons in parallel with the load instead of in parallel with the other button. Pushing that button would then short out the +12V, damaging the supply.
 
4x4dually said:
If there is no +12VDC power (I'm assuming the output is DC), then it sounds like the rectification circuit in the box is toast. Unhook your button wires from the box just to see if it makes a difference, but I don't think it should.
Click to expand...
I wondered about the rectifier, too 🤔
 
James L said:
I thought about polarity because the connections say "push" and "ground" but I didn't notice any markings on the switches.

Honestly, that's not sinking in why it would use the ground terminal.
Click to expand...
The "Push" terminal is probably "pulled up" internally using a pull up resistor. The button actually "grounds" out the "push" terminal in order to activate the release. That way, if a button or wire got grounded out, the doors would auto-magically stay released instead of staying closed in case the box was mounted inside the hidden room. Fails "open" so to speak.
 
GoldDigger said:
The only predictable cause of failure I can see is to wire one of the buttons in parallel with the load instead of in parallel with the other button. Pushing that button would then short out the +12V, damaging the supply.
Click to expand...
Me too.
I made sure to mark which cable went to the two buttons (they share one cable to the jamb) so that I didn't short the power supply
 
4x4dually said:
The "Push" terminal is probably "pulled up" internally using a pull up resistor. The button actually "grounds" out the "push" terminal in order to activate the release. That way, if a button or wire got grounded out, the doors would auto-magically stay released instead of staying closed in case the box was mounted inside the hidden room. Fails "open" so to speak.
Click to expand...
Okidoki that's really good info. Thanks.
 
I've been looking at the pictures of the power supply, and I watched a video of the Amazon unit (looks exactly the same)

I just noticed a time dial. How much time could be the highest setting on the dial?

Wondering if it was still de-energized after I loaded up yesterday (15 minutes) and if it's been working since 🤦‍♂️
 
Wanted to give an update.
I bought a replacement power supply from Amazon ( thanks @zbang ) and installed it. I disconnected the button leads first as @4x4dually suggested, and it made no difference as was expected.

I disconnected the leads at the magnet so I could connect all the cables on the power supply without a load.

I connected power first, and checked for voltage at the power supply terminals. All good.

On the button + ground terminals, there was 5vdc so guessing @junkhound was correct about polarity on the buttons. Still didn't see any markings, so I figured I'd try it.

I connected the magnet leads and everything worked as it was supposed to.

I appreciate all the input
 
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