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I have a handful of relays that I am working with for a project. I'm familiar with 4 pin relays, where there is a coil and switch,but the relays I am working with have 8 pins.

Here is the model# and data sheet

EC2-5NU https://www.mouser.com/ds/2/212/KEM_R7002_EC2_EE2-1104574.pdf

On page 3 there is a diagram, I have the Non-latch type on the left.

Pins 1&12 are for the coil, but the switch pins are a bit confusing to me.

It looks like 3-4 & 9-10 are normally closed, and 4-5 & 8-8 are normally open.

What is confusing me is why there are two sets of switch pins.

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  • \$\begingroup\$ the contacts are all the same ... it is a DPDT configuration ... two circuits ... 4-common, 3-NC, 5-NO ... same type of switch on other side ... there are two sets of contacts because some customers want to use one relay instead of two relays \$\endgroup\$
    – jsotola
    Feb 12 '18 at 0:01
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As others have stated it is a dual/double pole relay. That is there are two independent three-way, or dual-throw, switches inside the relay. It is properly named a Double-Pole-Dual-Throw DPDT relay.

If it helps, the diagram below may be easier to understand.

schematic

simulate this circuit – Schematic created using CircuitLab

Interestingly they numbered the pins to include the missing pins 2, and 11, and left room to include the second coil on pins 6 and 7 for the dual coil latching type. So in effect it is a 12 pin part. Designing your PCB that way makes changing the style of relay later much easier.

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The p/n EC2-5NU is a "Double Pole Double Throw" aka DPDT or 2P2T

So there are two Poles or switches that are ganged.

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Those are double-pole double-throw (DPDT) relays - they can switch two circuits.

If you only want to switch one circuit, you only use one pole of the relay, or you may parallel the two poles, if you wish.

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