Design considerations for using multiple relays...?

[rascalseven]

I am building a unit for a friend of mine that will need 12 DPDT small signal relays (Omron G5V types) and, at some point, all 12 may be active (though rarely, I'm sure).

I've never used so many relays in a design before and am concerned about possible problems with all the parallel resistances of the coils when all are active (assuming they will be driven all from one voltage source).  What problems am I likely to encounter, and what kind of solutions can I use to get around them?

I appreciate any and all advice and info.

Thanks and peace,

JC

 

[AMZ-FX]

Recent discussion along these lines:

http://www.groupdiy.com/index.php?topic=49423.0

regards, Jack

 

[audiomixer]

Hi JC,

If I understand your problem correctly your relays are switched independently, so the drive current on the individual transistors will not be a problem. driving them directly via a uController seems a weird idea anyway.... the uControllers are not build to drive that large currents, and the max combined drive current is usually in the range of 200/ 300mA.  a simple transistor driver will solve all of these issues. the total drive current required for your relays will be 12 x 30mA so this is not really a problem for a simple power supply.

cheers,

Michael

 

[PRR]

> I've never used so many relays in a design before

But you have had zero to twelve lamps turned-on at once.

Same issue.

If you have a dozen large lamps on the far end of the ranch, fed through a too-long too-thin extension cord, or powered by a bicycle generator, they get dim when all on. Or if you overcompensate, excess voltage on low loads.

You are not powering large lamps. Audio relays, any practical number can be fed with the thinnest hookup wire that will stand mechanical abuse. #22 is fine.

You don't want the power source to soar or sag. If these are "12V" relays, you want to stay below 16V when just one relay is on, and above 10V when all are on. This means knowing the _current_ each relay demands. Unregulated supplies are simplest to build. Regulated may be easier to over-build with assured voltage.

 

[jwhmca]

Same issue for me... I'm using 40 relays that may be all on at once.

Are there any issues with the DCR or other coil issues or is it purely a function of "If the power supply has enough current"?

I'm using an LM317 which can supply 1.5A

I have built one prototype sub-pcb and measure 65mA with ALL relays on.  There will be 8 of these, so 520mA if everything is on.

My supply has enough current , I'm just wondering if there are other issues with all those coils in parallel?