Twin Relay Control Board on DP5050 PCB

Just for good measure, a breakout board for twin Songle SRD series relays to fit the Dangerous Prototypes standard PCB size DP5050.

Released under Creative Commons Attribution Share-Alike 3.0 License, the schematic and parts of the layout derive from Sparkfun Electronics COM-11041 designed by N. Seidle and Joel Bartlett. Thanks Sleepwalker3 and an anonymous commenter for helpful design suggestions. The latest version of the board (RD02) has the relays in a different orientation to maximize the clearance and creepage between the high voltage traces:

The component values are designed for VCC = 5 VDC. For VCC = 12 VDC, use R4/R5 = 3.3 KΩ.

See the previous post for a single relay on a DP5031 PCB.


Mains electricity can kill. If switching high voltages, make sure to mount this PCB in a well-insulated or grounded enclosure. Apply conformal coating to the finished board for electrical insulation and environmental protection. Make sure your loads are properly protected by fuses.



Anonymous said...

You write you need to have a good insulation, yet you drive the 12VDC just within 1-2mm away from mains (e.g. 230VAC requires at least 5mm airgap to pass the LVD CE approval!). Turn the relay 90 degrees clockwise and do not go with 12VDC signals (or 0VDC for that matter) closer than 4-5mm from mains, by dong this you also have the diode closer to the relay coil. This design is only good for 48VAC (60VDC) or less.

Tom said...

After looking at a couple of other designs, I did decide to rotate the relays. It would be helpful to reference your other statements so that they are easier to evaluate. I used IEC guidelines as evaluated on www.creepage.com to calculate the minimum clearance of 1.5 mm (pollution category 2, 150 V >= nominal mains voltage <= 300 V, Vpeak = 400V, not QC program) and minimum creepage of 0.6 mm (functional insulation, pollution degree 2, material group IIIa/b, working voltage 250 Vrms, coated board).

SuperFabius said...

Hi, you can give a look at http://www.ti.com/lit/ml/slup227/slup227.pdf for an introduction. In your case "Rinforced Insulation" shall be used because you mix a SELV circuit with hazardous voltage (250V AC RMS). So creepage is 5mm (or 4.6mm using interpolation for 230 V AC RMS). See also UL 60950-1 1st edition Table 2L at page 113 and UL 60950-1 2nd edition, Table 2N at pag.127 in conjuction with the text of clause
It took me some days to start to understand....

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