DC switching

[patm72]

I have a 20A DC power supply to switch ON and OFF. What to use? SSR or regular contactor?

The 24VDC generated by this power supply will feed solenoid valves, contactors, pilot lights and other small stuff.

 

[analogkid2digitalman]

Are you switching the DC output or the AC (I am guessing) input to the supply?

Wheels within wheels / In a spiral array
A pattern so grand / And complex
Time after time / We lose sight of the way
Our causes can't see / Their effects.

 

[patm72]

I'm switching the output. My PWS is 3 phase to 24 VDC. I need to switch off a big part of it upon pressing an E-Stop button. I thus need a part of that 24VDC even if my E-stop is pressed.

 

[buzzp]

I would use a DC contactor rated for with the 'break' ratings of your loads that you will be switching off. It is important to make sure you look at the break ratings of the contacts as you have several loads which will bite back (generate a higher voltage than that apllied when the circuit is interrupted), like the solenoid valves and contactor coils. Of course, you could take measures to reduce this by placing, in its simplest form, a diode across each coil. This will reduce the generated transient when breaking the load. This also affects operate and release times of said devices so if timing is an issue, look at that close as well. You can use an RC circuit across the coil as well. There are many schemes which will work but all affect operation times to some degree.

The SSR is an option too but still have to watch DC break ratings. Putting a diode, or whatever method you choose, across the coils of the devices is probably more important using an SSR than a contactor just depends on the ratings of the SSR.

 

[itsmoked]

Remember SSRs can and do short closed so they are NOT a safety device. A contactor would be better.

 

[Mike2468]

A SSR can give you a fast disconnect. We have used some:

http://www.power-io.com/products/hdd.htm

in ATE applications.

 

[melone]

Does the power supply have GPIB interface?