Newbie Question: Use of diodes to isolate multiple relay NO outputs

Thread Starter

EUPremier

Joined May 6, 2022
6
Hi Folks,
I've installed ten 220VAC LED floodlights to the outside of a property. They are powered via 12VDC-220VAC relays. The relays are controlled via 'Smart Outputs' on an intruder alarm system (IAS) using a dedicated output card. The output card has 8, 12VDC relays, of which, 4 are currently being used.

The lights are zoned Front, Rear, Left & Right of the property and may be individually controlled via the App for the IAS.

I am using a negative trigger to energise the high-amp relays.

  1. The problem:
The IAS does not provide the option to trigger all four relays simultaneously in any situation other than a full alarm condition, in which case, it's done automatically.

  1. The solution:
I want to use a 5th relay to allow the user to bring on all lights simultaneously, on-demand.

I can do this by, on Relay 5, linking the Common to Ground and the NO to the NO terminals on each of the existing 4 relays.

Configuring relay 5 per User requirements results in all lights coming on.

However, it doesn't take a genius to realise that triggering any of the other 4 relays will then have the same result as the ground back feeds across all relays via Relay 5.

  1. Question;

Can I circumvent this issue using 4 diodes in-line on the wires connecting Relay 5's NC terminal to each of the other 4 relays?

I've read that diodes favour the positive circuit so not sure if it'll work.

If so, can you recommend a suitable diode? I was planning to use BOJACK 1N5349B 5W 12V Power Zener Diodes which I found on Amazon.

If not a diode, can I use anything else to achieve the objective?

Thanks in advance.

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Thread Starter

EUPremier

Joined May 6, 2022
6
Welcome to AAC.

If you use a 4PDT (4 Pole Double Throw) relay it will isolate each of the other relays from each other.

Something like this.
Thanks for your reply:

The isolation issue is in the control relays which are baked into the output card from the IAS manufacturer. As for the high-amp relays, they're already installed and I'd rather work around, if possible.
 

MisterBill2

Joined Jan 23, 2018
11,874
It might also be possible to use diodes to drive each of the four relay coils, but that would require some circuit information that I don't have, and you might not have it either. But certainly a 4 pole relay, with the four isolated sets of contacts, can do it very well.
 

Thread Starter

EUPremier

Joined May 6, 2022
6
It might also be possible to use diodes to drive each of the four relay coils, but that would require some circuit information that I don't have, and you might not have it either. But certainly a 4 pole relay, with the four isolated sets of contacts, can do it very well.
Changing all the relays is major surgery at this stage. Surely the query is fairly straightforward, no? I have, say, two wires, linked to relay outputs A & B, both capable of carrying ground to C, when On.
I’m okay with A getting ground from B but not B getting ground from A.
Can I place a diode on B to ensure ground cannot flow A to B, but can flow B to A?
 

crutschow

Joined Mar 14, 2008
29,755
You could use two diodes to each relay coil (cathode to coil for a 12Vdc positive control signal).
All coils have a common ground.
One diode goes to the individual control signal for that relay, and the other diode goes to the common output of the added relay.
That way the individual signals are isolated from the common control signal.
Make sense?
 

Thread Starter

EUPremier

Joined May 6, 2022
6
You could use two diodes to each relay coil (cathode to coil for a 12Vdc positive control signal).
All coils have a common ground.
One diode goes to the individual control signal for that relay, and the other diode goes to the common output of the added relay.
That way the individual signals are isolated from the common control signal.
Make sense?
Thanks for your reply Crutschow. That’s really helpful.
I think I’ve learned that the onlybway to do this is to use a positive trigger and that diodes don’t work on the ground side.
Thanks a mil. :)
Which type of Diode should Inbuy for this?
 

Tonyr1084

Joined Sep 24, 2015
6,884
You have 8 independent relays. Each can switch high voltage. In your case it's switching 220VAC. You can use a fifth relay to switch a DP4T relay. You don't need diodes as long as you're not crossing voltages. Always switch the hot side. You're using 220V so I'm not real versed in that, but if everything is the same phase then suppose all four relays are off. There's no power going to the lights. But then you energize the fifth relay and it powers a bigger relay, the DP4T relay. It connects each individual output to power. All four lights come on. Even if one of the four relays activates it's not causing any short circuits - it's all the same voltage the same phase. Give me a bit of time and I'll bang out a drawing for you. No diodes.
 

Tonyr1084

Joined Sep 24, 2015
6,884
OK: Relay 1 controls the first light. Ry2, #2 and so on.
Relay 5 controls a 220VAC relay coil that bridges all outputs from the first four relays together AND it provides power to all four lights regardless of Ry 1, 2, 3 or 4. Whenever the fifth 12VDC relay is energized it switches on the 220VAC coil which switches all four lights on at the same time. Again, regardless of the state of the first four relays. AND since they're all tied to the same power source there's no shorting of the 220VAC.

1651876928902.png
 

Thread Starter

EUPremier

Joined May 6, 2022
6
You have 8 independent relays. Each can switch high voltage. In your case it's switching 220VAC. You can use a fifth relay to switch a DP4T relay. You don't need diodes as long as you're not crossing voltages. Always switch the hot side. You're using 220V so I'm not real versed in that, but if everything is the same phase then suppose all four relays are off. There's no power going to the lights. But then you energize the fifth relay and it powers a bigger relay, the DP4T relay. It connects each individual output to power. All four lights come on. Even if one of the four relays activates it's not causing any short circuits - it's all the same voltage the same phase. Give me a bit of time and I'll bang out a drawing for you. No diodes.
Hi Tony,
Thank you for your very detailed reply & drawing. Indeed, introducing a DP4T relay will do the trick. However, I was trying to avoid introducing another high-voltage relay. The current situation deviates slightly from your summary as follows:
I have 8 low-amp, 12VDV relays on the IAS auxiliary Output Board. I’m only using them to energise the 4 bigger relays which power the lights.
So, currently, 4/8 low-power relays drive 4 high-power relays.
What I was hoping to do was use a fifth low-power relay and interface it, in a minimally invasive manner, to the current wiring to allow all lights to come on when it’s activated.
i can easily change the wiring so that the Common on all the low-power relays is +. Connect the magnet in the high power relay to permanent Ground and energise them by putting + out of the NO terminal on the low-power relays, as required.

if I do this, could I not simply connect the NO on the 5th relay to each of the other 4 low-power NO terminals, but use a diode for each of the 4 connections?
My theory is that I can then apply + to each high-power relay simultaneously, by activating that 5th relay as this would make the NO terminals on the other 4 low-power relays go to +.
When individual zones are used and the NO terminal on one or more of the 4 individual low-power relays are active, the diodes prevent the fifth relay’s NO terminal from getting +, preventing the undesirable backfeed to the inactive zones.

thoughts?
 

eetech00

Joined Jun 8, 2013
3,146
Hi

It doesn't really matter which side of the relay is switched for this application as long as it makes sense and the design choice is consistent. What should be avoided is switching BOTH sides of the relay.
Here is the same schematic but modified to switch the positive side of the circuit.

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MisterBill2

Joined Jan 23, 2018
11,874
Post #12 verifies that my thinking was correct. My suggestion requires only the external addition of a single 4 pole relay that would be connected only to the terminals of the existing relay module. And the relay will only be switching the 12 volts to operate those existing power relays.
So there has been "A failure to communicate!"
The coil of the four-pole relay will be operated by that fifth output, as already described. Each of the four N.O. contact sets will then be wired in parallel with the N.O. contact terminals on the terminal strips of the present output board. This means two wires in each of those connection points. No diodes required, and no part changing.
When the 4-pole relay is not operated the function will be identical to the way it had been, but when that 4-pole relay is activated and those four contacts are closed, all four of the high current relays will be activated independently.
You can also get plug-in sockets with screw terminals for the relays that I am suggesting. This will allow a neat and stable installation that will be acceptable to even the most critical inspectors.
 

Tonyr1084

Joined Sep 24, 2015
6,884
Hi

It doesn't really matter which side of the relay is switched for this application as long as it makes sense and the design choice is consistent. What should be avoided is switching BOTH sides of the relay.
Here is the same schematic but modified to switch the positive side of the circuit.

View attachment 266604

View attachment 266605
This would work. This one or even the first one. I needed to look at it closer but I've seen what eetech00 is doing here. You questioned the use of diodes, and this will fit the bill. Initially I had disregarded the use of diodes because I thought you were talking about isolating the high voltage AC with diodes. That wouldn't work, but I now realize you probably already knew that. So I have to agree with eetech00.
 
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