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I'm looking for a 5 V relay, low current (Arduino)- DPDT and I found chinese one - RY5W-K in Aliexpress

I'm trying to understand the pinout schematic:

  • where is the + and - of the control pin (one of 1\16)?
  • what pin is shorted to what pin when on \ off?

I'll be happy for guidance,

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3 Answers 3

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There is no +/- for the coil pins 1 and 16, it's an electromagnet so is not polarized, you can connect it either way. If a relay has a polarity sensitive coil it will normally be marked as such in the datasheet.

The schematic on page 7 shows the connections.

The contacts are what is known as Form C. This has a common connection, one normally closed contact that is connected to common when the relay is not energized, and one normally open contact that is connected to common when the relay is energized. These are often denoted as COM, NC, and NO on schematics.
One set of Form C contacts is known as SPDT (Single Pole Double Throw). When two sets of these contacts are controlled by a single actuator, as they are in this relay, it is known as DPDT (Double Pole Double Throw).

First set of contacts:
Pin 4 - common
Pin 6 - normally closed
Pin 8 - normally open

Second set of contacts:
Pin 13 - common
Pin 11 - normally closed
Pin 9 - normally open

relay contact schematic

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  • \$\begingroup\$ Some relays like the Panasonic DS2Y series have a bias magnet to increase sensitivity. These specify a coil polarity. As usual, the datasheet will advise if this is the case. \$\endgroup\$
    – Kartman
    Apr 14, 2022 at 13:35
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I found chinese one- RY5W-k in Aliexpress

If you are buying something that is claiming to be that relay from AliExpress, then be prepared that it could be counterfeit or totally different.

Regarding interpreting the datasheet that you linked (and another one which seems to apply to the genuine relay is here) this is the relevant diagram from it, with my annotations in red:


Annotated image from relay datasheet linked in the question


Looking only at the top row of contacts and after enlarging the image, you can see:

  • There is no contact shown for the pin 4 connection, so this is the COMmon pin.

  • Relay datasheet show it in an un-energised state, so the contact shown connected on pin 6 is the Normally Connected (NC).

  • And the contact shown open on pin 8 is the Normally Open (NO).

(You can see the same pattern on the lower set of contacts.)

There is no indication that the coil (pins 1 & 16) has a required polarity, so either polarity should work.


As mentioned above, especially if you are buying the relays from anything other than a legitimate distributor, you will need to perform your own tests on the actual relays you receive to ensure that their pinout does actually match the datasheet.

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  • \$\begingroup\$ If my former colleagues from Fujitsu were to read this, they might be offended by your prejudging everything from Alibaba with conflation of Chinese clones. Takamisawa is a well-known Japanese brand, which manufactures electromagnetic relays. They merged with Fujitsu components in 1995, but retained the Brand name. Even Alibaba might be disappointed as they also provide Buyer Protection. Still there may be some shlockers around with sub-standard components but rare for JP. \$\endgroup\$ Apr 14, 2022 at 13:38
  • \$\begingroup\$ "Takamisawa is a well-known Japanese brand [...] They merged with Fujitsu components" Yes, I'm aware of that. But in defending Fujitsu & Takamisawa you must therefore be assuming that something labeled "Takamisawa" sold on AliExpress, will be manufactured by them. I stand by my warning to the OP not to assume that. There are many documented examples of counterfeit components being sold on AliExpress (Amazon Marketplace, ebay etc.). (P.S. Your former colleagues at Fujitsu can say "Hi" to my former colleagues there too!) \$\endgroup\$
    – SamGibson
    Apr 14, 2022 at 13:46
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Here's another representation of the pin / contact configuration.

enter image description here

The following table shows the pins that are in contact in relay off / on positions.

enter image description here

The coil pins 1 & 16 may be connected either way (no polarity).

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