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Avoiding simultaneous "on" on both channels


knuth
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This is the challenge: An electric heating cable has three connections (L1, L2, and N). Applying AC voltage to L1-N gives one power output, applying voltage to L2-N gives another, lower output. Voltage should not be applied to L1 and L2 simultaneously. Connecting this cable to a double switch is simple: L1 goes to the Q1 output, L2 to the Q2, and N obviously to N. There is, however, nothing that keeps me from switching on both channels, which is the "L1+L2" situation I want to avoid. Using a scene, this can easily be avoided by switching one channel off before turning the other one on. I can even hide the two switch devices in the web interface, and use a virtual device in stead with such internal logic built in. I am still concerned that if the fibaro:call(id1, "turnOff") fails to complete (such things happen!) and the subsequent fibaro:call(id2, "turnOn") succeeds, I may end up with the L1+L2 situation anyway. 

 

The question therefore is: Is there any way to configure the double switch in such a way that the two output channels are never engaged at the same time? If not, does anyone know of a z-wave product which works as a selector, not a switch? That is, where input L is connected to output Q1 or Q2 through a toggle function? In that case I could use that for my two L connections, and have a single switch in series to switch the whole thing off. 

 

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Following this topic as I need the same configuration for 2 cases.

 

1. opening/closing the hatch to my chickens (Controlling 2 12V relays with an actuator connected.

2. Same purpous as your heating cable except that in my case it is the hot water heater. (large and small element and both cannot be on at the same time due to max power consumption of the switch)

 

As you mention a scene would partly solve this.

 

In HC2 I had a VD which did check the switch status, then turn off one, give a gracefull delay, then check if it was actually off and also if the device was still on and not dead (since this one was quite far from the hc and sometimes it failed to execute the command) if all okay switch on the other. (this for opening/closing the hatch) If failed it would try 3 times before sending a message that it failed.

 

This might sound like overkill but needed to avoid blowing fuses and/or overloading the switch.

(and yes end switches to indicate position would also be possible but not solve the case where switch is still on)

 

To have the double switch/relay act as a bistable switch would have been awesome and expanded the use cases for this switch.

This should be at firmware level.

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@knuth

I guess you could use roller shutter instead of double switch. It has two load terminals only one of which can be used at a time. Only thing I’m not sure about is if you can keep them on. Cause normal function for them is to be one for several seconds and go off after it. 
Or you can use two single switches and connect Q1 of one to S1 of the other and vice verse. In this case they will switch off each other. The only problem is that the latest gen of FGS has a bug and sometimes it doesn’t switch state :) So better use Aeotec ones or older models of Fibaro or other alternatives. 
But the option with Roller shutter is more preferable I guess. 

Edited by baskalex
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@Knuth,

Are you sure its giving only power to one cable?

My heather, 2 life wires, works as follow":

L1 >>low wattage

L2>>high wattage (including L1)

 

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  • @Sjakie : The case as presented is simplified (there are more cables and wires involved). So for this exercise the answer is yes, power is applied to one pair or another pair, not to both. 

    The roller shutter is an interesting option, @baskalex , didn't think of that one. I will look into it, to see if the timer and the max current are compatible with my situation. 

     

    And yes, @akatar turning both off is also a necessary option. So three positions in all: only L1 on, only L2 on, or all off. Sorry if that was not clear from the start. 

    Edited by knuth
    Added a response to @akatar
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  • 6 hours ago, baskalex said:

    Or you can use two single switches and connect Q1 of one to S1 of the other and vice verse.

     

    If I get you right, this may also be implemented in the double switch, like this:

     

    Please login or register to see this image.

    /monthly_2020_03/image.png.a242e60d58291e165ef362b195cc1592.png" />

    Here the blue cross-connection is from S1 to Q2, the orange one from S2 to Q1. I think you are on to something here, but I still wonder how this would work. Assume "all off" as the starting position, both switches defined as toggle switches. I then turn on switch 1 (S1) which powers up Q1. This in turn is picked up by S2, which then turns on Q2. Now both loads are on, precisely the opposite of what we wanted. Where did I go wrong? Setting parameter 20 = 2 does not seem to solve the problem either. Would this be any different if you used two single switches in stead? 

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    Hei @knuth, you can use a switch that only turns on one output at any one time, called vekselvender here in Norway.

    If the case in hand is a heating element in floor or any heating device that has an earthed terminal/earthes chasis etc, you must use an all pole as well ( 2 pol bryter here in Norway, NEK400 regulations).

    The 2 pole switch turns power on- off and vekselvender controlls Q1 -Q2.

    Config in parameter switch type. I would also set up a securing scene to check that q1-q2 are not enabled at the same time.

    If the case in hand is for a permanent installation with high ampage i would instead, consider using rele's .

     

    One idea might be to use 2 relays, one with double contacts and 2'nd rele with 2 no and 2 nc contacts. Bothe relays are impuls holding type.

    One output Q1 turns power on and off (impuls power to A1 contact on relenr 1 ) and Q2 (impuls power to A1 contact on relenr 2 ) cycles the rele between 2no and 2 nc. This eliminates the need for a sperate 2 pole switch.

    The 2 nc contacts (rele 2) will be automatically connected when rele 1 turns on so connect lowest load to these contact. Obs, dont try this at home if you dont know what you are doing. Here in Norway you must have a qualified electrician to wire and connect this example.

    Test with other load, fex light bulbs before applying to project.

    I take no reponsibility for any damages that might result from applying this information to your electrical installlation.

      

    As i have said previously, it is absolutely recommended that a qualified electrician should check all of your diy connections.

     

     

     

     

     

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    Edited by MARCUSP.I.L
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    @knuth

    I thought of starting with one on and one off. But it means that one of the outputs is always on. So it was just a bad idea :) I think what @MARCUSP.I.L offers is the best option. I would definitely not rely on a scene here, because a risk of failure is too high. 

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  • @MARCUSP.I.L : Rest assured, I would never install anything like this without using an electrician. My question on this forum was only to get some help in the planning stages. My electrician would like to know how I plan to do things, and then review and revise these plans to ensure that they are according to regulations. Only then would he do the actual installation. 

    Thank you for a constructive solution! Your scheme seems the best so far, using the double switch to activate two relays, one for on/off, the other to switch between loads. One question regarding your diagram: Do you have an example for a relay make/model that would be suitable for each of the two relays shown? 

    Could the

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    be used in stead of the left part of the diagram (Fibaro Double Switch Q1 + your "relay 1"), to control the all-pole on/off function? For the right side, alternating between two outputs, I know of no z-wave relay that does this directly (the Roller Shutter comes close, but is low-amp and single pole). This makes your solution attractive, if you can show me a suitable "non-smart" relay to be used for relay 2.

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    Hei @knuth, good to hear. You can try this model from Hager, el nr: 43 699 56. Max load 16 amps. Other brands to trust , Schneider - ABB - Siemens.

    You could use the Aeotec Heavy duty switch as an alternative  for main power on-off, can handle 40 amps if i have read correctly ?

    I  personally would use a 2 pole NO impuls rele (43 699 51), as indicated in drawing, simply because i would use a double impuls wall switch for manual control. I have not come accross a suitable z wave device to use as an alternative for 2NO-2NC Rele.

    But your suggestion would work fine, especially if you are connecting a 3 fase power supply  L1 + N(L3) for 2 NC contacts and L2 + N(L3) for 2 NO contacts.

    Releays are cheaper and come in many variations NC .-NO 2 pole /4 pole etc etc..

    I use relays where i can as they have better holding points than fibaro switches ( utholdenhet) - contacts are guaranteed to withstand in and out connections for greater loads and duration.

    I am a little hesitant to connect 10 + amps over a z-wave device in a wall box behind a switch .

    Usually i install relays on rail in fuseboks and mount my z-wave devices (also on rail) in the lower part of same fuseboks.

    Mount rubber cable grommets (gumminippel)  for antenna if needed.

    Important point for all DIY electricians, rele/fibaro switches etc need ventilation . Loads exceeding 5+ amps create excessive heat in device and can , in worst case , melt or burn contacts...

     

    Anyway, see enclosed data sheet for Hager impuls relays and consult with your main man..Lykke til

    By the way i dont work for HAGER , but recommend after many years experience.

     

     

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    Edited by MARCUSP.I.L
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