Using a rectifier for a simple control circuit - will it work?

Thread Starter

CamaLamaDD

Joined Aug 23, 2015
9
So here is the scoop. I am an automatic door technician. I install lots of electrified door hardware, and control wiring for automatic doors. Typically, to power our electrified door hardware, such as mag locks or electric strikes, we install a dedicated power supply. The downside of this is they are often too large to fit inside of an automatic door cover, making it more difficult to install in retrofit applications.

On a job a couple of months ago, we installed an automatic door operator for the City. We also supplied the logic controller for the door hardware, automatic door, and key card system. Our automatic door operator provides 12 volt AC power, which we typically use to power the magic controller. However, in this application, the key card installer was responsible for providing the power to the electric strike. Instead of putting in its own power supply cabinet, he built a rectifier to convert AC to DC voltage. I have never used or seen a simple diode rectifier before. It powered the electric strike beautifully. Obviously, AC powered electric strikes provide that annoying buzzing sound.

Today, we installed another pair of automatic door operators. After the job was complete, they inquired about adding electric strike so that they can wirelessly unlock the door. I found a rectifier from my Supplier, but all it says is that it is a 50 VA rectifier.

This particular automatic door provides 24 volt AC output on its board, which I have already used for a receiver for the wireless push buttons.

Questions:

1) can I use this $12 rectifier to power my electric strike? (12 or 24v, ac or DC, 250mA)

2) what would happen if I put the 120V line voltage do this rectifier? Would it melt?

3) does the 50 VA rating mean that I can safely put 2 amps at 24 volts ac into this? Would it been put out 2 amps at 24 volt DC?

4) would it be wise to protect this electric strike with a fuse somehow? Could it be done on the rectifier?

Any general information to help me understand this better would be awesome! This would be very handy for future installs so that we can minimize the expense of power supplies.
 

dl324

Joined Mar 30, 2015
10,945
1) can I use this $12 rectifier to power my electric strike? (12 or 24v, ac or DC, 250mA)
Show us a schematic for the circuit(s) in question.
2) what would happen if I put the 120V line voltage do this rectifier? Would it melt?

3) does the 50 VA rating mean that I can safely put 2 amps at 24 volts ac into this? Would it been put out 2 amps at 24 volt DC?
Diodes are rated by maximum current and reverse voltage; not VA.
4) would it be wise to protect this electric strike with a fuse somehow? Could it be done on the rectifier?
What are you protecting it from? Diodes aren't current limiting devices, but could be used for clamping voltage. But that's not a rectifier diode, it's a Transient Voltage Suppressor (TVS) diode which is sometimes used with a series fuse to protect the diode.
 

Thread Starter

CamaLamaDD

Joined Aug 23, 2015
9
Crude drawing:20180802_195524.jpg

Dry input triggers relay one, followed by relay ttwo

1) so this manufacturer only puts 50 VA as specs... What do I presume then?

Model is Camden CX-5024

Sorry, I appreciate your explanation about the diodes, but it's over my head.
 

dl324

Joined Mar 30, 2015
10,945
Cropped, edited image:
upload_2018-8-2_20-4-27.png

I assume you want to use the 24VAC to generate a DC voltage for the electric strike. Does the AC come from the logic board? What is it's excess current capacity, what voltage is the striker power supply, and what is current rating for the DC supply?

When you rectify 24VAC, the peak DC voltage will be 1.414 times that (without using a calculator, a little less than 36V DC).
 

Thread Starter

CamaLamaDD

Joined Aug 23, 2015
9
Cropped, edited image:
View attachment 157451

I assume you want to use the 24VAC to generate a DC voltage for the electric strike. Does the AC come from the logic board? What is it's excess current capacity, what voltage is the striker power supply, and what is current rating for the DC supply?

When you rectify 24VAC, the peak DC voltage will be 1.414 times that (without using a calculator, a little less than 36V DC).
Yes, I want 24 volt DC for the electric strike. No, typically we power the strikes with an external power supply, which is what I am trying to eliminate.

The logic board can be powered by 12 or 24 volt AC. Model is Camden CX -12. https://www.camdencontrols.com/products/CX_12_Switching_Network

Our external power supplies are usually 12 or 24 volt selectable DC, and the door hardware are usually 12 or 24 volt AC or DC.

Two amp power supplies are usually sufficient, because door hardware is typically not more than 250mA.

So basically, the electric strike could at some point get up to 36 volt DC? That sounds like it would damage it, would it not?
 

Thread Starter

CamaLamaDD

Joined Aug 23, 2015
9
Sorry, to clarify, the logic controller needs power coming in, which we usually steal from the door operator. They typically provide 12 volt out. The power for the door hardware we use external power supplies
 

dl324

Joined Mar 30, 2015
10,945
Yes, I want 24 volt DC for the electric strike. No, typically we power the strikes with an external power supply, which is what I am trying to eliminate.
What is the voltage tolerance of the strike and how much current does it draw?

Obviously it work in the case you mentioned in your initial post, but we don't know the power supply voltage/current capacity or the voltage tolerance/current requirement of the strike.

If it will tolerate 1.5 times the AC voltage, a simple rectifier could work. But that will provide a half wave rectified, pulsing DC source and the strike won't be receiving power for about half of the time. If it can't switch 30 (or 25) times per second, an unfiltered half wave rectified power source could be okay.
 
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