How to isolate two different power supplies inputs to the same locking device.

Thread Starter

Lynne Perry

Joined Aug 5, 2019
6
I have an existing access control system providing 24vdc to power a door to unlock. Client would like to add an intercom door release using 24vdc from their POE switch independent of the access system. I believe that the two power sources need to be isolated from each other but the method is where I need assistance.
 

Thread Starter

Lynne Perry

Joined Aug 5, 2019
6
Is there possibly another name for this type of diode? I'm not coming up with a part number. Thank you!

The drawing was great!
 
Last edited by a moderator:

ericgibbs

Joined Jan 29, 2010
8,841
hi,
You need to know the resistance of the latch or the current required by the latch, so that we suggest a diode type.
E
 

Reloadron

Joined Jan 15, 2015
4,567
Is there possibly another name for this type of diode? I'm not coming up with a part number. Thank you!
When using a plain diode in a circuit like Eric provided the typical naming convention is a "blocking diode". For an everyday basic application like you have generally any of the 1N4000 series of diodes should work as long as the latch current is below 1.0 Amp and most I have worked with are. Look towards a 1N4002 everyday diode.

You also need to consider that a diode, any diode will have a forward voltage drop. Generally what this means is when either power source in your case provides exactly 24 VDC to a latch solenoid, the solenoid will only have about 23.3 volts applied to it. In most cases the drop is insignificant and won't matter.

Ron
 
Last edited:

Thread Starter

Lynne Perry

Joined Aug 5, 2019
6
hi Lynne,
Welcome to AAC.
One option is to fit a series diode in each 24V positive line, link the 0V lines together.
E
I now have an added complication I could use input for.
One power source is 24VDC
the 2nd source is 12VDC from a POE switch they want to wire in series with a 12VDC plug in tranformer for the 2nd 24VDC power.
Whats the up/down side and use of diodes in that case?
 

Thread Starter

Lynne Perry

Joined Aug 5, 2019
6
together.
E
I now have an added complication I could use input for.
One power source is 24VDC
the 2nd source is 12VDC from a POE switch they want to wire in series with a 12VDC plug in tranformer for the 2nd 24VDC power.
Whats the up/down side and use of diodes in that case?
 

Reloadron

Joined Jan 15, 2015
4,567
I am assuming POE is Point of Entry? Locking mechanisms like this, commonly called a striker are normally just a solenoid. Some systems, depending on a security configuration will unlatch if power fails. Some also have a battery backup.

Normally such solenoid strikers are pretty forgiving as to the voltage which is why when using a blocking diode the voltage drop across the diode becomes insignificant. Now when we start doing things like using 12 volts from a POE system in series with another 12 VDC supply like for example a 12 volt wall wart it may be time to consider what the actual current required by the striker solenoid actually is?

Most POE systems just uise a small relay which energizes the striker for a short given period of time like 3 to 5 seconds. A normally open push button switch can be placed in parallel with the relay contacts to unlatch the striker for the duration of the button push. That or your original plan of just adding another power source to the striker solenoid. The end result is as long as you have another source of 24 VDC with adequate current for the striker, as long as it is 24 VDC with enough current. While I don't see this as a good idea yes, it should work with a pair of blocking diodes. Good systems allow for battery backup during a power failure as required.

Ron
 

Thread Starter

Lynne Perry

Joined Aug 5, 2019
6
I am assuming POE is Point of Entry? Locking mechanisms like this, commonly called a striker are normally just a solenoid. Some systems, depending on a security configuration will unlatch if power fails. Some also have a battery backup.

Normally such solenoid strikers are pretty forgiving as to the voltage which is why when using a blocking diode the voltage drop across the diode becomes insignificant. Now when we start doing things like using 12 volts from a POE system in series with another 12 VDC supply like for example a 12 volt wall wart it may be time to consider what the actual current required by the striker solenoid actually is?

Most POE systems just uise a small relay which energizes the striker for a short given period of time like 3 to 5 seconds. A normally open push button switch can be placed in parallel with the relay contacts to unlatch the striker for the duration of the button push. That or your original plan of just adding another power source to the striker solenoid. The end result is as long as you have another source of 24 VDC with adequate current for the striker, as long as it is 24 VDC with enough current. While I don't see this as a good idea yes, it should work with a pair of blocking diodes. Good systems allow for battery backup during a power failure as required.

Ron
I am assuming POE is Point of Entry? Locking mechanisms like this, commonly called a striker are normally just a solenoid. Some systems, depending on a security configuration will unlatch if power fails. Some also have a battery backup.

Normally such solenoid strikers are pretty forgiving as to the voltage which is why when using a blocking diode the voltage drop across the diode becomes insignificant. Now when we start doing things like using 12 volts from a POE system in series with another 12 VDC supply like for example a 12 volt wall wart it may be time to consider what the actual current required by the striker solenoid actually is?

Most POE systems just uise a small relay which energizes the striker for a short given period of time like 3 to 5 seconds. A normally open push button switch can be placed in parallel with the relay contacts to unlatch the striker for the duration of the button push. That or your original plan of just adding another power source to the striker solenoid. The end result is as long as you have another source of 24 VDC with adequate current for the striker, as long as it is 24 VDC with enough current. While I don't see this as a good idea yes, it should work with a pair of blocking diodes. Good systems allow for battery backup during a power failure as required.

Ron
I agree it's not a great idea, I have an insistant IT person. POE in this case is power over Ethernet.
My question would be how to use blocking diodes (if possible) to protect the 12V POE and 12V transformer from each other in series to output 24V or if it's necessary.
 

Reloadron

Joined Jan 15, 2015
4,567
I agree it's not a great idea, I have an insistant IT person. POE in this case is power over Ethernet.
My question would be how to use blocking diodes (if possible) to protect the 12V POE and 12V transformer from each other in series to output 24V or if it's necessary.
Yes, it would be the same configuration, place two 12 VDC sources in series and then a blocking diode as drawn earlier. I would make sure when you get into this they understand this is not a good practice. Power Over Ethernet was never intended for this sort of purpose. Fortunately I worked with great IT people who left things like this to engineering types. Just make sure if things don't work nobody is pointing at you. Another point is when a solenoid coil has power removed and the magnetic field collapses there is an inductive kick. Maybe your IT guy has some thoughts on that? If one is not already installed I would place a diode across the solenoid coil, called a flyback diode.

Ron
 

Thread Starter

Lynne Perry

Joined Aug 5, 2019
6
Okay, so just the blocking diode at the (2) 24v + to the lock. I have a suppressor at the lock so this should resolve kick back.thank you so much!
Yes, it would be the same configuration, place two 12 VDC sources in series and then a blocking diode as drawn earlier. I would make sure when you get into this they understand this is not a good practice. Power Over Ethernet was never intended for this sort of purpose. Fortunately I worked with great IT people who left things like this to engineering types. Just make sure if things don't work nobody is pointing at you. Another point is when a solenoid coil has power removed and the magnetic field collapses there is an inductive kick. Maybe your IT guy has some thoughts on that? If one is not already installed I would place a diode across the solenoid coil, called a flyback diode.

Ron
 
Top