×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

DC switching

DC switching

DC switching

(OP)
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.

RE: DC switching

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.

RE: DC switching

(OP)
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.

RE: DC switching

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.

RE: DC switching

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

RE: DC switching

Does the power supply have GPIB interface?

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources