SSR Operation Question

Greg Norton

Hello All,

I am trying to design something to operate as a switch on an electric skeet thrower using a BS2 pin as a control. The problem I have is there are many varieties of these machines and some are AC operated, while others are DC operated with car batteries. My control circuitry will be battery powered seperately (using AA batteries).

My original thought was to use a mechanical relay big enough to handle the voltage and current of either the AC or DC case. However, the switch will need to stay closed for indefinite periods and I don't want to draw the coil current from the AA batteries for a long time to avoid draining the batteries.

My next thought was that this sounds like a job for an SSR. This would have the advantage of low current requirements to activate the relay. However, I don't know enough about them. Will an SSR designed for AC carry a DC signal as well? It seems logical to me that it would, but I'm hoping someone here can confirm or deny whether this is true. I also read something that seemed to imply that conduction of an SSR is related to the voltage across the two load terminals. This is creating much confusion for me.

Are there other considerations I haven't thought of? I see many types of SSRs available and I'm not sure which to choose for this application.

Thanks for your help.
Greg

skylight

Using the fact that the triac inside the SSR consists of back to back SCR's and that once gated they will continue to conduct until the threshold current drops below their specification it may be to your advantage to drive a DC machine without any more intervention from the control circuit, ie you could turn it off (once triggered) until you wish to use a device to disconnect the output circuit and turn off the SSR's triac. Of course only one of the triac's SCR's will conduct depending on polarity, also because the circuit "free runs" once triggered i'd suggest a stop switch is incorporated in the output circuit especially if driving a motor.

Peter KG6LSE

I have seen MOSFET/IGBT SSRs . but they are $$$
and unlike Mech Relays the are Polarty sesitive to the output .

skylight

A simple thyristor (SCR) would suffice driving a DC machine, use the battery to gate the SCR (just takes a quick pulse say from a button as a starter) and as mentioned above a disconnection device on the output to turn the SCR off.