Smart questions
Smart answers
Smart people
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Member Login




Remember Me
Forgot Password?
Join Us!

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips now!
  • 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!

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

Donate Today!

Do you enjoy these
technical forums?
Donate Today! Click Here

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.
Jobs from Indeed

Link To This Forum!

Partner Button
Add Stickiness To Your Site By Linking To This Professionally Managed Technical Forum.
Just copy and paste the
code below into your site.

sparxicus (Electrical)
31 Jan 07 4:40
I have set up a test rig to test out Temperature controllers. An SSR is activated to switch on a 240V LED when the T/C is calling for Heat. Trouble is that even when the SSR is not switched on there is a leakage current across it that lights the LED anyway. I spoke to the SSR manufacturer (Crydom) who said "yes there will be leakage across due to the internal snubber, enough to light a 10mA LED". They suggested either to use a snubberless SSR or put a power resistor in parrallel with the LED to null the leakage current. I cant remember my maths and what ever resistance I use across the LED, it only dims it very slightly. Any advice on solving this problem, formulae / resistor size / or any other advice greatfully recieved.
Skogsgurra (Electrical)
31 Jan 07 5:08
If you have a resistor/LED combination that operates at 240 V (UK?), and if you have a 10 mA leakage through the snubber. Then, to reduce voltage across R+LED to one tenth, you need a parallel resistor close to one tenth of the R+LED value. Assuming that your LED runs at 10 mA, that would mean around 240/0.01 = 24 kohms in the R+LED. If you put one tenth of that (2.4 kohms) parallel, you will probably dim your LED sufficiently. But, you will have 240^2/2400 = 24 watts in the resistor when SSR is on. Not a very good solution.

But, hey! You have your heating elements connected already? They should load the SSR enough to prevent the LED from turning on. Why do you see the LED? Load not connected?

Gunnar Englund
www.gke.org
--------------------------------------
100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

itsmoked (Electrical)
31 Jan 07 6:50
sparxicus;  Can you not use a 25W light bulb - pick a fun color.  The wildly non linear aspect of a light bulb also lets you gauge the actual leakage of the SSR to boot.

The problem you are encountering drives engineers nuts constantly, as the techs or the customer go out with their trusty DMM and then start calling us with "Hey the SSR is ON even when the control to it is off!"  No. That's just the snubber leakage.

Keith Cress
Flamin Systems, Inc.- http://www.flaminsystems.com

MacGyverS2000 (Electrical)
31 Jan 07 6:56
Maybe I misunderstood the question, but wouldn't a lightbulb defeat the purpose of preventing something from lighting up?

Dan - Owner
http://www.Hi-TecDesigns.com

Helpful Member!  OperaHouse (Electrical)
31 Jan 07 7:38
Since this is a test jig, the solution should be small and not produce heat.  How about a capacitor.  Fight that snubber with another snubber!  Suggest a .25-.47 uF capacitor in series with 220 ohm half watt resistor. This will be in parallel with the LED  Use an X2 UL line rated capacitor.  A .1uF 250V is common, use three in parallel to start.  
Mike2468 (Electrical)
31 Jan 07 8:35
Since it is only a test set, and the objective "might" be small/simple; I have used a simple piezo bender disk instead of a SSR + load.  The dc logic from the controller will pulse the piezo "beeper" on and off.

OR

other manufacturers have an LED that represents the control input status.  Just watch that LED, and you are done!  Just google: "solid state relays" and then click IMAGES.  You'll see lots of pictures of SSRs.  Pick one that has an LED.  We prefer the models with a green LED that means ON.
nbucska (Electrical)
31 Jan 07 15:42
Your SSR input is a LED == connect your indicating LED
IN PLACE OF the input of the SSR.

Plesae read FAQ240-1032
My WEB: <http://geocities.com/nbucska/>

sparxicus (Electrical)
1 Feb 07 8:36
Nice one OperaHouse. Fighting one Snubber with another worked almost perfectly (there was the tinyest illumination but you had to look hard for it!). Yes this was a Temperature Controller Test Jig which would have no loading on it. Thanks again Sparxicus.

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!

Close Box

Join Eng-Tips® Today!

Join your peers on the Internet's largest technical engineering professional community.
It's easy to join and it's free.

Here's Why Members Love Eng-Tips Forums:

Register now while it's still free!

Already a member? Close this window and log in.

Join Us             Close