Bad relay choice ?

A project log for SPDT16: 16-bits arithmetic unit with relays

Let's imagine I could get about 200 SPDT relays. Of course I would know what to do with them :-D But will 200 be enough ?

yann-guidon-ygdesYann Guidon / YGDES 05/08/2016 at 03:103 Comments

I noticed only now some details I didn't see before: these 3V relays are rated for 150V 100mA max. (under which conditions ?)

Given that it takes 60mA to energise one coil, the amplification coefficient is barely 2 and the design expects more.

It was a good idea to connect coils in series wherever possible. Control signals still require a large fanout and I'll probably have to implement a 2-levels signal tree (with repeaters for each nibble or two).

Given the current handling, it would have been wiser to opt for a higher coil voltage, which reduces the required current, thus a better amplification factor.

That, and DPDT, will be considerations for a next version, if any !


matseng wrote 05/09/2016 at 04:17 point

I guess that a 24 or 48 volt AC relay would be better choice for getting a large fan-out.  But the AC relays might be slower due to the shading coil so in a high speed situation DC relays would be better and then accept the lower switching ratings.

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Yann Guidon / YGDES wrote 05/09/2016 at 04:24 point

For now, speed is not an issue : I just completed a ring oscillator at about 1.6Hz. I'm not sure I can make a difference between AC and DC relays, i've never heard about a "shading coil".

The relays I use are DC-compatible anyway :-) They can switch pretty fast but it's only the beginning of the story...

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matseng wrote 05/09/2016 at 04:51 point

The shading coil is basically just an short circuited internal extra coil on the core that holds the flux alive a bit longer so the relays doesn't hum (or even chatter is fast enough) when run on AC.

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