# Power Supply for Relay Shield **URL:** \ **Category:** Hardware\ **Created:** [June 1, 2016, 1:41am UTC](https://community.particle.io/t/power-supply-for-relay-shield/23354 "2016-06-01T01:41:39Z")\ **Posts on this page:** 6\ **Page:** 1
**Author:** ![jbstcyr](https://sea2.discourse-cdn.com/flex026/user_avatar/community.particle.io/jbstcyr/32/7531_2.png) [@jbstcyr](https://community.particle.io/u/jbstcyr)\ **Post date:** [June 1, 2016, 1:41am UTC](https://community.particle.io/t/power-supply-for-relay-shield/23354/1 "2016-06-01T01:41:39Z")
Does anyone have a recommendation for a wall wart to power the relay shield? I tried using an old Compaq laptop power supply that is rated as 18V at 1.9A. The diagram on the power supply indicated that the center was + and the barrel was -. When I plugged it in I got a curl of smoke. Unfortunately, at this time I don’t have a volt meter. I have ordered one. It should be her in a few days. ---
**Author:** ![rickkas7](https://sea2.discourse-cdn.com/flex026/user_avatar/community.particle.io/rickkas7/32/8681_2.png) [@rickkas7](https://community.particle.io/u/rickkas7)\ **Post date:** [June 1, 2016, 10:40am UTC](https://community.particle.io/t/power-supply-for-relay-shield/23354/2 "2016-06-01T10:40:12Z")
I think this similar to the power supply that I used for my relay board. 12VDC, 1.5A (18W), Barrel Plug, 2.1mm I.D. x 5.5mm O.D. x 11.0mm, Positive Center [http://www.digikey.com/product-detail/en/triad-magnetics/WSU120-1500/237-1393-ND/3094919](http://www.digikey.com/product-detail/en/triad-magnetics/WSU120-1500/237-1393-ND/3094919) They’re widely available, so by no means do you have to order it from Digi-Key; I just provided that as an example (and they have full specs listed on their web site). ---
**Author:** ![ScruffR](https://sea2.discourse-cdn.com/flex026/user_avatar/community.particle.io/scruffr/32/6952_2.png) [@ScruffR](https://community.particle.io/u/ScruffR)\ **Post date:** [June 1, 2016, 3:37pm UTC](https://community.particle.io/t/power-supply-for-relay-shield/23354/3 "2016-06-01T15:37:45Z")
The specs of the relay shield on the [store page](https://store.particle.io/?utm_source=sparkCommunity&utm_content=power-supply-for-relay-shield) do tell this > [@](#): > > Operating voltage: 7 to 15V DC But the silk and the the [docs](https://docs.particle.io/datasheets/particle-shields/#relay-shield-specifications-v3-x-x-) do state 7 ~ 20V This might need clarification. What version of the shield have you got? Was the Photon plugged in correctly? Additionally to voltage and polarity the DC "quality" (ripple & noise) might play a role too. ---
**Author:** ![jbstcyr](https://sea2.discourse-cdn.com/flex026/user_avatar/community.particle.io/jbstcyr/32/7531_2.png) [@jbstcyr](https://community.particle.io/u/jbstcyr)\ **Post date:** [June 1, 2016, 4:49pm UTC](https://community.particle.io/t/power-supply-for-relay-shield/23354/4 "2016-06-01T16:49:34Z")
Thanks for the quick answers. ScruffR, I had not seen the voltage spec in the documentation. I was going by the rating etched on the board. Silly me for believing what I read. I didn’t have the Photon plugged in at all. I didn’t want to lose the chip if the power supply didn’t work. Another question I have in the same vein. Can I still use the USB connection to the Photon if it is plugged into the relay shield and properly powered? ---
**Author:** ![ScruffR](https://sea2.discourse-cdn.com/flex026/user_avatar/community.particle.io/scruffr/32/6952_2.png) [@ScruffR](https://community.particle.io/u/ScruffR)\ **Post date:** [June 1, 2016, 4:53pm UTC](https://community.particle.io/t/power-supply-for-relay-shield/23354/5 "2016-06-01T16:53:19Z")
> [@jbstcyr](#): > > Can I still use the USB connection to the Photon if it is plugged into the relay shield and properly powered? Yes, you can. There is a protection diode that prevents Vin voltage to feed back into USB. ---
**Author:** ![jbstcyr](https://sea2.discourse-cdn.com/flex026/user_avatar/community.particle.io/jbstcyr/32/7531_2.png) [@jbstcyr](https://community.particle.io/u/jbstcyr)\ **Post date:** [June 1, 2016, 4:54pm UTC](https://community.particle.io/t/power-supply-for-relay-shield/23354/6 "2016-06-01T16:54:36Z")
Thanks ScruffR