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Topic # 147084 8-Jun-2014 17:38
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looks interesting

http://www.ebay.com/itm/281205997347

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  Reply # 1061393 8-Jun-2014 18:24
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I bought a Raspberry Pi with the PiFace board to do something similar but with fewer I/O ports (more can be added).

The relays on this are rated at 250v as are the ones on the PiFace board.  The PiFace PCB itself however is not rated at 250v and I think the documentation says stick to 12v (from memory).  There is no indication that this equipment is rated for 250v.

^^^  CAUTION ^^^




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  Reply # 1061398 8-Jun-2014 18:36
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the relay board on the oeezee says its rated at 250V. looks ike the control board is 5v. you can buy the relay boards seperatly for $19 USD for an 8 way board. the ralys are only 10A so youd have to watch what you switched with them otherwise use contactors for the heavier loads.

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  Reply # 1061578 9-Jun-2014 00:35
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Unless all the low voltage circuitry is isolated inside the enclosure with no external connections, you cannot safely use these relays for mains.  For the form-C contacts the common pin is between the coil pins with about 5-6mm clearance, not the 3cm required for appliances.

The relay is rated only 3A for inductive loads, specs printed on it is for resistive loads: http://www.sanyourelay.ca/public/products/product_list_new.php?series=43&listby=0

Note that (other) relays that can handle large inductive loads are not suitable for switching signals (or LEDs etc.), because they need a high current in order to keep the contacts clean - it is a requirement of the contact plating.




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  Reply # 1061601 9-Jun-2014 06:50
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Pity they didn't build it with SSRs instead of mechanical relays



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  Reply # 1061978 9-Jun-2014 17:24
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SSRs have thier issues too. i prefer relays for this sort of thing.

The 3cm rule is stupid because every relay out there has less than 3cm clearance internally, (and  anything it mounts to.) also as its not an appliance but mounted in a sub board type enclosure the rules may be different anyway, just like wire sizing inside a SW board..
another option is to desolder the relay and break it out to an LY2N type relay for instance.

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  Reply # 1062290 10-Jun-2014 06:20
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The 3cm clearance rule is for surface contamination.  A physical barrier or a sealed enclosure is also good.  On a PCB if you have slots routed in the board then the path is measured around the slot, not through the air.  Or a double insulated product also works.  It is about preventing high voltage breakdown to the user.




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  Reply # 1062341 10-Jun-2014 08:22
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I have just been playing around with an Arduino + 4xrelay board (looks very similar to these relay boards). With an ethernet shield and using MQTT I have a very reliable way of switching the relays, and monitoring digital input pins. Plan to put one inside my alarm panel to give me IP monitoring of alarm state and triggers (panel only has a dialler, no IP module). Also going to hack a spare RF dongle and use the relays to allow me to arm/disarm via my home automation system. Will also allow me to open/close the garage door.

That is all low voltage so no issues switching, and I can even power the Arduino from the alarm 12V supply. 

Not bad for a $US8 Arduino + $US8 ethernet shield + $US5 relay board!


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  Reply # 1062774 10-Jun-2014 17:39
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Ive had nothing but issues with ethernet shields stopping arping and dropping off the lan.




Richard rich.ms

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  Reply # 1062821 10-Jun-2014 19:39
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richms: Ive had nothing but issues with ethernet shields stopping arping and dropping off the lan.

I am not surprised after looking at EMC/EMI issues from Beagle Bone which claims to meet compliance, but then discovering it was done by overdamping the DDR bus out of spec, and running the memory interface at it's slowest which is not what the released firmware does.  "Experimental" boards do not have to meet any form of compliance as long as they have a disclaimer that it is for lab use only, despite selling thousands/millions.




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  Reply # 1063255 11-Jun-2014 11:03
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Richms - how often does this happen for you? I have just setup an Arduino + Ethernet shield in a test config running an MQTT client. I will be notified if the device loses connection with the MQTT broker so will leave this running for a few days and see how it fares.

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  Reply # 1063256 11-Jun-2014 11:06
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20-30 mins with 4 phones hitting it regularly. Few days with a single pc hitting it.





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  Reply # 1063264 11-Jun-2014 11:18
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What are you using these for?

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  Reply # 1063342 11-Jun-2014 13:14
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Just serving a page with a temperature from a couple of 1 wire sensors in aquariums.




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  Reply # 1063685 11-Jun-2014 22:04
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Try a different power supply, it might be too noisy.  Or run the power supply close to rated load, EMC compliance is done only at no-load and at full load so manufacturers don;t care what comes out of them at part load.




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  Reply # 1064355 12-Jun-2014 19:43
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running power supplies at very low load is flakey. you get all sorts of harmonics int the supply that seems to get dampened at closer to spec loads.

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