Control/Dimming Crydom Relay Dimmers

[Ken Yanczer]

Is anyone using Crydom D2425 relays as dimmers?

 

[DavidNorth]

Well, a number of people probably use that relay, but most of them may not know that they do.

Is there a specific issue we can assist with? Is this in a specific manufacturer's system? I happen to know something about this part.

Thanks,

David

 

[Ken Yanczer]

Well, a number of people probably use that relay, but most of them may not know that they do.

Is there a specific issue we can assist with? Is this in a specific manufacturer's system? I happen to know something about this part.

Thanks,

David

Dave, I am building a dimmer pack and using a demultiplexor that puts out 0-10 vdc. Not enough to drive the relay to full capacity. Any suggestions? The relay is rated 3-32 vdc input.

 

[DavidNorth]

Ah. Well, this could be an interesting series of posts. Are you placing a load on the relay? Without enough holding current through the relay, it may not fully or correctly fire - 150mA minimum according to the datasheet. The control voltage of 3-32vdc is not the range of control for dimming - its the firing voltage range. Keep in mind that this is a relay and it is either on or off and the control voltage range gives you a wide range of voltages at which you can fire this to full. Off is below 3vdc and on is anywhere between 3 and 32vdc.

To make a dimmer, you need to use a circuit that provides a PWM signal based on voltage zero crossing detection, and use a different relay which is a D2425-10. A D2425 can only be used as a relay, not a dimmer.

Let me be clear about a couple of things. Designing dimmers is not to be taken lightly and I highly recommend that you exercise caution working with this level of current. Issues such as fault current, arc flash, control isolation and creepage and clearance all need to be understood and accounted for. If you do not know how these all work and play into the design of a dimmer, I suggest you not continue.

Does that help?

David

 

[JD]

As David mentioned, there are two types of Solid State Relays. The first type have a built in zero-cross-detector which insures that once the needed control voltage is reached, it will turn on at the beginning of the AC cycle. These could never be used to build a dimmer. The second type can be turned on at any point during the AC cycle. These are the type used in dimmers. There is a lot of control electronics needed to turn one into a dimmer. Most modern dimmers use a microprocessor to achieve much of this. On the input side, you have either a number delivered by a data source (like DMX) or a DC voltage (often 0 to 10 volts) to tell the circuit how bright you want the light. The circuit then starts counting whenever it gets the signal that a zero-cross is detected. When the count hits a certain number, it toggles the control voltage to the solid state relay. A low count gives you a bright output as most of the waveform is allowed through. A high count gives you a dim output as the device is turned on much later. As you can see, there is a bit more to this than feeding a variable voltage directly to the SSR.