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Dual Relay


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I've got 2 dual relay bricklets attached to a brick and for some reason when i power up the 240V side of the relays they work for a few times and then the brick stops repsonding. If i reset the master brick everything is fine, and then it stops responding again. If i remove power from the 240V side then everything works as normal after the reset until I turn the power back on. The wiring is definately correct on the switched side of the relay.


This originally happened over the chibi extension, however I have tried it directly connected to usb and the same thing happens.

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How many 240V devices do you have attached to the Dual Relay Bricklets? Does this happen with one already?


And what do you use to power the Master Brick? I expect that the Master Brick does not get enough power through the USB port in your case. There is a thread in the German forum with a similar problem, he could get it working with a Step-Down Powersupply.

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I thought this might be the case. I have tried connecting only one relay block at a time, but the same thing happens. I have tried cycling the relays with no load connected for about 100 cycles each and everything is fine.


I have a small heater (100W) and a small pump (20W) connected to each brick - the resistive load seems to switch fine - i think the problem may be with the inductive load of the small motor (20W) as switching it seems to give the error. Is it possible that it could be giving some sort of feedback which is causing an error on the master brick?


Edit: This definately seems to be the problem. I have tried several resistive loads with no problems. I have also tried 4 different inductive loads which all give the same error

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  • 1 month later...
  • 7 months later...

Hi all,


I've recently bought a set of 3 dual relay bricklets to use with diverse devices like, amongst others, two electrovalves. Since these work with solenoids at 12V DC I guess I'll have trouble with current feedback as reported. This is my first electronic project (I'm computer engineer, used to take care of software part) so I'm trying to learn fast. After reading a lot I've arribed to 2 conclusions:


1) For a 12V DC valve, I'll have to put a 12 VR diode in parallel to the valve, facing forward to positive polarity.

2) For a 240 VAC, 2A fluorescent I'll have to put a 380V Varistor in parallel to the fluorescent. A snubber circuit would also be good for this one, since the varistor will burn a lot of energy at the beggining but won't last for long. But currently I don't know how to calculate the snubber circuit so I'm waiting to confirm I need it before doing it.


I just wanted to share this with you english speakers on this forum, since this topic was forgotten 6 months ago (discussion followed in the german forum, unfortunately I can't understand a word, not even with translators) and more people might found theirselves in this very stressing situation of discovering this 2 relays you bought won't be able to switch an inductive load.


Also, for the record, if nothing of this works, Solid State Relays might be an alternative I guess (probably random turn-on SSR), could we get a SSR bricklet in the long term?

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Hi Nifty,


Thanks for answering. Happy to have someone who had the same problem once to talk to!


As far as I know (which is not much) the Snubber will take a lot of the feedback current generated by an inductive load, but it needs a few milliseconds to warm up to take the energy. In that very first milliseconds you need something else which works quick and absorbs the initial voltage peak, so that what the Varistor is used for. I understand you tried the snubber + varistor, or just the snubber alone? In case of the second, do you think it may be worth it to try the snubber + varistor? (i.e. is this dangerous, like it could burn the dual relay bricklet or master brick, or will it just create software problems on the brick until reset?)




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