DC thru RC-4

[gadget-evilusions]

I was reading the efx-tek website, here specifically, http://www.efx-tek.com/topics/crydom.html . I read "See www.crydom.com for RC-4 compatible relays that are designed for swtiching DC circuits." I may just be confused, but I thought that the RC-4 couldn't be used with DC. I am probably wrong, but it would be wonderful if with the proper relays I could run DC thru the RC-4. I may also just be mis reading that sentence.

[menehune]

The RC4 can be used with DC.  Unlike mechanical relays than can swith both AC or DC currents, solid state relays cannot be used for both AC and DC voltages.  The D2W203F "relays" that are shown in the efx store cannot switch DC, only AC (the D2W SSRs need the zero cross of the AC sine wave to switch on or off).

If you buy the RC4 board bare and purchase your own CMX200D3 "relays", you could switch DC with the RC4.  Mouser is quoting a price of $39 each for the CMX200D3 relays and they are not in stock.  It's much cheaper to get a windshield wiper relay for $10-$15.

A second consideration is the current capacity of the RC4 traces.  DC motors can draw 10s of amps and the circuit traces cannot handle that level of current.  I wouldn't go above 3 Amps of current for the traces.  You could build up the traces by stripping off the solder resist and soldering 14 or 12 gauge wire onto the traces, but you will void the board warranty and can run into safety issues.

Crydom AC solid state relays:
http://www.crydom.com/en/Products/Catalog/d_2w.pdf
Crydom DC solid state relays:
http://www.crydom.com/en/Products/Catalog/c_m_x.pdf

[gadget-evilusions]

I am not running motors so I don't think current capabilities of the traces are an issue. I am using them to control 12vdc solenoid valves with 20w coils that will be ran at 15 cps, thus the reason for not using a mechanical relay.

I have used similar style dc to dc solid state relays controlled by a prop-1 for this application, but I was hoping to have a carrier for the relays (the rc-4) for ease of mounting.

I was mostly concerned about the routing of the current thru the termianal blocks and thru the relays, hoping to make sure it wouldnt be a problem .

[JonnyMac]

No promises... (because we have a long development list) but would a high-current, solid-state expander board be valuable?  I have this idea for a board called HC-8 that would work like a DC-16 but use high current transistors (e.g. TIP120) instead of ULNs.  It's just an idea, but there is another prop/display building company that we do a lot of work with that is also using high-wattage valves.

Thoughts?

[JonnyMac]

I believe the terminal blocks we use are rated for 5 amps, but I'll have to check with John.

[gadget-evilusions]

I don't know if it would be a viable product to be produced. I know I wouldn't use alot of them, maybe 5 a year. I use mechanical relays with motor applications and where viable with high watt coil solenoid valves. I would use something like that normally with one or two valves and a prop-1 in my machine gun style air cannons. I can not think of any applications where I personally would need 8 high current dc outputs.

[livinlowe]

Jon-
I think that kind of board is a good idea.

[wseay]

I would like to see a relay board.  I have a Kit 74 board that I adapt to different projects.  I also have a Kit 108 that is RS232 controlled.

A relay board gives you the option of AC or DC.  Also with two relays you can build a H-Bridge for DC Motor direction control.

In the EFX-TEK world, it would let a Prop-1 drive a Wiper Motor, Fogger, A/C Spots, Fluorescent Black Light all without letting out the Blue Smoke.

Might make a nice add-on to the EZ-8 as well.