Relays with RC-4

[tintin]

Hi all,

Long time reader, first time poster!  I am using the RC-4 boards to switch low current solenoids at 110V AC.  I would like to use the Crydom CX241 SSRs (due to their low AC hold-on load current) with the RC-4.  The input specifications are as follows:

Control Voltage Range                4-10 Vdc
Nominal Input Impedance          300 Ohm
Typical Input Current @ 5 Vdc    15 mAdc
Must Turn On Voltage                 4.0 Vdc
Must Turn Off Voltage                 1.0 Vdc

Would such relays be compatible? It is my understanding that the chip on the RC-4 can safely source/sink ~ 30mA per i/o thus capable of activating the relays...

Any help in this regard is immensely appreciated!

Thank you,
Frank

[JonnyMac]

To be honest, you're going to have to give it a try -- so just buy one at first (if I had one, I'd test for you).  Since the SX on the RC-4 needs to be protected from manual input circuitry that could be used we have additional current limiters on the board, this can reduce the sensitivity a bit.  The next rev of the RC-4 will probably eliminate the manual inputs (since nobody seems to use them) which will allow us to drive the relays directly and use a wider range of Crydom relays.

Oh,  we still have lots of RC-4s in stock so the update won't be happening any time soon.

[tintin]

Thanks for the great info Jon.

I have followed your suggestion and yesterday received one of the SSRs -- it seems to work perfectly with the RC-4.  However, I am currently just using one relay and am concerned with the total current drain once I have 4 of such relays on the board (all active at once).  Again, each CX241 SSR consumes 15mA as opposed to the 3mA of the D2W series.  Do you see this as a potential problem?

The reason for my concern is that I must purchase 20 SSRs (that's 5 RC-4s). I would be very grateful for any advice.

Thank you,
Frank

[JonnyMac]

That won't be a problem -- if one works, all four will.  I was just concerned that there may not be enough current (due to the limiters on the RC-4) to activate the relay.  Each pin on the SX can sink/source 30 mA and with the additional limiters on the board you're not going to be pulling 15 from each pin.  Short version: You're good to go.