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I have SRD-05VDC-SL-C relay that I got for my ATMEGA and I noticed that it says on the relay:

   10A 250V/AC 10A 125VAC
   10A 30VDC   10A  20/DC

Then I was reading this article and found this line:

  Output:
  Connect a load, DC 30V/10A,AC 250V/10A

This is where I get lost, as far as I understood these are maximum ratings, but what does the relay output AC 220V or DV 30V?

Basically I want to power 9A 20V DC LED panel. In order to do this I still will need AC to DC converter and transform the 220v to 20v, correct? Thanks!

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    \$\begingroup\$ A relay is a magnetically controlled switch so it outputs either an open circuit or a closed circuit. \$\endgroup\$ – Andy aka Oct 29 '16 at 16:36
  • \$\begingroup\$ @Andyaka so basically it's literally a switch and I still will need transformer, correct? \$\endgroup\$ – 0x29a Oct 29 '16 at 16:37
  • \$\begingroup\$ You will need a converter to convert from from 220V AC to 20V DC but there is no guarantee that is correct without reviewing the data sheet for your LED panel. \$\endgroup\$ – Andy aka Oct 29 '16 at 16:40
  • \$\begingroup\$ Do you want to use the relay to switch the mains for the LED panel power supply? \$\endgroup\$ – Andrew Morton Oct 29 '16 at 18:39
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Since a Relay>2A has special conductive high temp tungsten or other plating alloys , it is designed to withstand a certain amount of >10,000'K arc temperatures for so many times at so many milliseconds or microseconds depending on the load reactance and current.

You supply the voltage, not the relay. But the load also affects the switch off voltage and current or starting surge current to big caps.

Since AC normally quenches current at or near the Zero crossing , it has a higher rating, but DC motors for example act as generators when switched off and thu current is sustained like an SCR until quenched or until the current drops below the holding current when opened.

For this reason , DC ratings are lower than AC ratings on all switched contacts.

For those who wish to research this further , see all of OMRON's Application Notes on Relay Contacts

example

another example

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