| Posted: Tuesday Mar 30th, 2010 06:20 pm |
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1st Post |
Treworgey
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| Joined: | Thursday Jan 11th, 2007 |
| Location: | United Kingdom |
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Hi, I have a question about the electrical characteristics of zone inputs.
I am using an output to drive a relay which switches an AC load. These is also a mechanical switch that switched this relay on - in parallel with the open collector output. Now what I want to do is be able to detect when this relay is activated via the mechanical switch.
There are several options:
1. Connect the switch to a zone and get Comfort to activate the relay. However I am concerned this may introduce a delay and is not fail safe if Comfort doesn't behave as expected.
2. Use a double pole relay and use one pole to connect to the zone input. Not happy mixing 240v AC and 12v DC in the same relay.
3. Connect another relay to isolate Comfort from the first relay. - Trying not to introduce any more relays - running out of supply anyway!
4. Use a current sensor to detect the load current. - Trying to keep it simple.
So is it possible to connect the output directly to an input? The problem is when the relay is off 12V will be applied to the input - is this safe? Would this be ok if I use a RIO instead - according to the manual it will accept 25V continuously.
Finally when using relays should I connect a diode across the coil to prevent back e.m.f.?
Thanks in advance for any help.
Kind regards,
Chris Williams
Worcester
England
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| Posted: Wednesday Mar 31st, 2010 01:31 am |
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2nd Post |
slychiu
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| Joined: | Saturday Apr 29th, 2006 |
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You cannot connect a Comfort Output directly to an input. The open collector output does not go low enough for the input to detect a low level
Anyway Comfort knows the state of all outputs using the Get Outputs action, so there is no need to test the output state
I suggest you use the TWS01 Module which has a mains-rated relay and current sensor. The relay contacts are connected to a two way switch to your load so that both the mechanical switch and the Comfort output is able to control the load. Even if Comfort is switched off, the mechanical switch would be able to work
see http://www.cytech.biz/Default.aspx?cmd=ID%2ftW5Xw2bTCO626ZAAInw%3d%3d&productid=59&categoryid=6&pageindex=
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| Posted: Wednesday Mar 31st, 2010 05:39 am |
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3rd Post |
Treworgey
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Hi Slychiu,
Thanks for your reply. I have considered using a current sensor (I already have several relays) but I wanted to keep things as simple as possible. I do not need to detect when the output is low ( as you say I already know the state of the output ) but I do need to know when the external switch in on which will pull the output to to 0v. If you are saying that the 12v will be too high for the input then that is an issue. However is this also the case for the RIO? Also I don't need 2 way switching, i.e. I don't need Comfort to be able to overide the external switch. In this case the switch is a hot water flow sensor and the load is a pump.
Thanks again.
Kind regards,
Chris
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| Posted: Wednesday Mar 31st, 2010 06:07 am |
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4th Post |
slychiu
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It is not advisable to connect the switch and rel;ay coil to the Comfort input. The Comfort input circuit will impose volatges to the relay coil and you may find that the relay is permanently on
For the RIO, the specification Input overvoltage protection of 25V does not mean the input will work correctly at 25V, it means that the input is protected
I suggest to use a current sensor, it may be the simplest workable alternative
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