What is the relay coil current ?

[ahmedadelhosni]

Hello,

I am trying to choose a low coil current relay from mouser. I want a relay which will last for years.

This is RT114005, coil resistance is 62 ohm. but what is the coil current ? if it is 5v/62ohm = 0.080 A, then that's a lot. I always read that the relay will consume 10-15 mA. So do I add a resistance in series ? but also there must be a minimum current for the relay to latch !!

http://eu.mouser.com/Search/ProductDetail.aspx?R=RT114005virtualkey65500000virtualkey655-RT114005

THanks.

[AWI]

@ahmedadelhosni The relay power consumption is 400mW. That matches with 80mA on 5V. These numbers for power consumption do not really influence the relay lifetime. This is mostly determined by the load on the contacts.
If you put a resistor in series the relay will probably not function.
You can search for a lower consumption one or use a solid state relay with consumption as low a 3mA

[ahmedadelhosni]

@AWI Thanks.
The problem is that I am trying to design an AC to DC converter using LNK304 and it has max 120mA to supply the circuit, and I need to have 3 relays. Thus selecting this relay will not help.

If I use a solid state a relay, do you have any experience regarding "safety" ?
Like do I need to add snubber circuit or not ? and what are the values and how to choose them ? etc.

I have already implemented TRAIC circuits before but I have been always afraid that it is not safe. I have also checked this link http://www.esp8266-projects.com/2015/05/p3-wifi-mains-power-dimmer-switch-with.html which has a good circuit design. but I don't know how the value s where chosen in case I changed the TRAIC used in the post.

[AWI]

@ahmedadelhosni If you are designing with LNK304 like this:

You know (or should know) the consequences of (non)galvanic isolation.. Commercial Solid State relays like these are pretty "safe" in that respect.

But a SSR never really switches off like its mechanic brother. It will depend on the usage if that can be considered safe.

[ahmedadelhosni]

@AWI yes I aim to use the LNK and will design a plastic box for isolation and safety. I searched alot and watched teardown videos of some plugs and LED bulbs and they are using non isolating AC-DC converters but within a non conducting case.

Actually I didnt understamd your last phrase. Can you re explain please ?
Also does this SSR needs anything further to power on and off the load ?
Thanks

[AWI]

@ahmedadelhosni As long a you isolate everything from the outside world is should be safe (with respect to accidental touch).

the long version of the last sentence..

A solid state relay (AC) is something like

this means that in in and output of the circuit are 'switched' by means of an electronic component with inherent leakage. Eg. for BT138:

Wheras a 'mechanical' relay, can have an open contact with 'no' leakage.

the "Snubber" circuit meant to protect the Triac for high voltages from inductive loads can be present in both types of relays and is always 'leaking'.

Summarizing: a SSR (or relay with snubber)in OFF position, is not safe in a way that you can touch the contacts (when attached to a high voltage source). But then again: I would not take the risk with any other relay, you never know.... ;-)

[ahmedadelhosni]

@AWI Thanks. I know understand what you meant.

I am also concerned with the safety of not blowing or overheating the device. THat's why I referenced a link to a devicee above because there are several components which I don't really know whether I need it with resiestive loads or not.