Relay control PCB

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#1
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Hi All

 

I would like your advice on the following

 

I am using a latching relay G5RL-U1-E (https://docs-emea.rs-online.com/webdocs/1370/0900766b81370782.pdf) and controlling it using H-Bridge IC DRV8837C from TI. I have attached a screen shot of my 2L PCB. For this example the TI IC is on anther PCB. I have attached my design. The relay will be powering 250V AC devices.

 

I am now thinking about creating a PCB with multiple relays, but with same power source which will be 250V AC.

 

Can you please advice me if i was to keep the bottom layer's for a copper pour to 250V  so that all relays have the same power source, would this cause any issue? And then have a output connector for each device i need to power?

 

When using copper pours with 250v AC , do i need to keep anything else in mind? I am aware if i was using traces, the copper thickness and width would need to be considered .

 

 

Thank You

 

Regards

 

DJ

 

 

 

 

Attachment(s): 

Thanks

Regards

DJ

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djoshi wrote:
the copper thickness and width would need to be considered .

Thickness and width STILL needs to be considered when using pours, as you did not state how much current at 250vac your attempting to handle....

Also the spacing between the 250vac trace and that of the control (coil) terminals must be far enough apart to prevent a flash over. 

Seek these answers from your governing authority (in the US, it is UL)

With HV AC, do not use square corners, as the these sharp points are good spark emitters, use rounded corners in your copper pour areas.  

 

  Jim

 

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Don't pour under the input signals.  And there's supposed to be at least 8mm between any 240VAC and any low-level (like the relay drive) signal on the same layer, but I'd be a lot happier with more like 15mm.  Note that the signal input areas don't have to be square.

 

How many amps of AC are you throwing around, anyway?  16A is a lot for a PCB.  Multiple relays on the same board?  Hmm.  S.

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I am still waiting for the confirmation on power rating of the devices that need to be controlled.

 

There will be a 12V water pump, connected using a AC-DC power adapter.

And a fan, this fan is 250V AC,

 

I should have this information shortly. 

 

I will keep the control signal about 15mm away.

 

Great i will add round corners. 

 

Yes there will be about 3-4 Relays.

 

I guess i need to confirm how much current before progressing any further. 

 

Ideally what should be the thickness of the copper?

 

 

 

Thanks

Regards

DJ

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Or are there any other option of mounting relays onto a design instead of a PCB?

Thanks

Regards

DJ

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djoshi wrote:

Or are there any other option of mounting relays onto a design instead of a PCB?

 

There are, but they're typically not much fun.  Think screwing them to a board and using lots of wires with spade lugs on them.  Think an automotive relay and you'll get the idea.  There are also other tricks, like leaving off the solder mask and soldering down wires over all the traces and things like that.  Time-consuming.

 

Something else odd I noted about that spec sheet - You're using the SPDT version, and it includes the bizarre little detail that the NC (normally closed) position is only rated for 5A, while the NO (normally open) position is rated for 16A, and I couldn't find in that (highly abbreviated!) spec sheet how long you're supposed to hang around closed in the NO position.  I would have thought that given a latching relay, both contacts would have the same rating, but it seems to me that they don't. Hm! 

 

Hmmm indeed.  S.

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Scroungre wrote:

Something else odd I noted about that spec sheet - You're using the SPDT version, and it includes the bizarre little detail that the NC (normally closed) position is only rated for 5A, while the NO (normally open) position is rated for 16A, and I couldn't find in that (highly abbreviated!) spec sheet how long you're supposed to hang around closed in the NO position.  I would have thought that given a latching relay, both contacts would have the same rating, but it seems to me that they don't. Hm! 

 

I must have missed that.

 

I think i will change the relays to  G5RL-U1A-E, this should solve the issue. 

 

My footprint PCB was a simple prototype i made, but for my actual PCB i will use G5RL-U1A-E. 

 

I should have a confirmation for my current usaage, but i doubt it will be above 3-4A at 250 V AC, but its best to be sure before starting any work.

 

The aim is to have one port, where i supply the 250VAC and then have ports next to each relay that outputs and the earth and nutral can be connected directly from the power source to each device.

 

Is there any good guide i can read on PCB ,RELAYS and 250V AC design?

 

 

 

 

Thanks

Regards

DJ

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djoshi wrote:

I guess i need to confirm how much current before progressing any further. ... Ideally what should be the thickness of the copper?

 

You can't answer that until you know the current it needs to carry.

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When switching 230Vac with a relay there is always a chance of switching transients getting back coupled into the low voltage circuits.These transients may be big enough to endanger reliability of your uC or even destroy uC pins, even though there is galvanic isolation.

 

An isolation creapage gap of 8mm has already been mentioned. If this can not be met it is common to make cutouts in the PCB. Regulations may very in the country you are living or selling this prodeuct to.

 

Chinglish in an Omron datasheet?

 

Doing magic with a USD 7 Logic Analyser: https://www.avrfreaks.net/comment/2421756#comment-2421756

Bunch of old projects with AVR's: http://www.hoevendesign.com

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djoshi wrote:
Is there any good guide i can read on PCB ,RELAYS and 250V AC design?

Consider CLEARANCE (shortest path through air) and CREEPAGE (shortest path along surface) criteria for PCB design:

http://blog.optimumdesign.com/clearance-and-creepage-rules-for-pcb-assembly

.

This calculator maybe useful for creepage:

https://pcbdesign.smps.us/creepage.html

 

Majid

Last Edited: Tue. Mar 5, 2019 - 02:39 AM
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An excellent solution, though not only for piecemeal use, will be a little expensive. We have purchased something similar to the enterprise, but we have serially soldered printed circuit boards. Drawings for the production we do.

Last Edited: Wed. Mar 6, 2019 - 06:04 PM
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I can confirm max current will be 6A . But we can design for 10A.

I am thinking if it's possible to place a small relay board in power socket enclosure so that a device can be plugged in directly without cutting wires and making it as 2way switch so it can be operated manually.

Thanks

Regards

DJ

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djoshi wrote:

I am thinking if it's possible to place a small relay board in power socket enclosure so that a device can be plugged in directly without cutting wires and making it as 2way switch so it can be operated manually.

 

I am not very bright, but I do not understand that at all.  Here would be an excellent place to draw a schematic of what you want.  Picture == 1k words.  S.

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Sorry, what i meant to say was , that if i would like create a small relay switch and place it inside 

https://www.screwfix.com/p/bg-13a-1g-switch-socket/35096

 

This way, i can configure it as a two way switch so power can happen manually and i can simple plug my device instead of cutting wires/

 

Thanks

Regards

DJ

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I see there are many ready made relay boards? Are they a good design?

Thanks

Regards

DJ

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djoshi wrote:
I see there are many ready made relay boards? Are they a good design?
DJ, I see there are many students studying engineering. Are they good students?

 

Can you see how ridiculously broad both of our questions are? Neither can be answered in any meaningful way.

Ross McKenzie ValuSoft Melbourne Australia

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Thanks

 

I have correct the PCB and now kept some extra spacing. Please see the image attached. My H-Bridge is external driven by a TI's DRV8837C.

 

When it comes to creepage, should my design have some slots ? Would this be necessary.

 

The (N.O) will always be in use so that i am always using the 16A contact, instead of the 5A contact, even though i do not see the device being powered being more then 5A.

 

When it comes to the thickness of the copper, the PCB will be either 1ox or 2oz from the PCB company's proto service, therefore i will select the 2oz option, i am thinking that i can also keep the tracks exposed and added extra solder to thicken it up. The pins on the relay are only 1mm, while the tracks are 3mm and 5mm. I am not sure, but should both layers be used for the tracks? This would it give a total thickness of 4oz

 

I can then spray some insulation coating to insure that it never touched, even though the relay will be placed in IP6 enclosure.

 

Is there any additional protection that could be added? As its a H-brdige, design diodes would not be useful. 

 

 

 

Thanks

Regards

DJ