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Solid State Relay

walkboneswalkbones Posts: 30
edited 2005-10-27 00:46 in BASIC Stamp
I'm using a Basic Stamp to control an SSR to switch a·fluorescent light with an electronic ballast off and on. The fluorescent light flickers every couple of seconds when the relay is off. Is the snubber circuit of the SSR causing this? I'm lookng for a way to prevent this flicker assuming it will shorten lamp life over time.

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Comments

  • dandreaedandreae Posts: 1,375
    edited 2005-10-25 21:42
    Can you try using a 60 watt light bulb and check to to see if it turns on/off properly in your circuit?· This will help determine if there is an issue with the load regarding the circuit.· Some relays need a sufficient load inorder to turn off.

    Dave

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    Tech Support
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    Http://www.parallax.com

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  • walkboneswalkbones Posts: 30
    edited 2005-10-26 18:24
    I tested the SSR with a 60 watt 120vac lamp and bypassed the Basic Stamp and the SSR didn't flicker the lamp. I also added the incandescent lamp to the fluorescent and switched both with the SSR and the flickering of the fluorescent went away. It appears I need a dummy load in parallel with the fluorescent light to prevent the flicker. Any suggestions on what to look out for when selecting a resistor? 100 watt, 2ohm resistor, possibly?
  • Beau SchwabeBeau Schwabe Posts: 6,568
    edited 2005-10-26 18:43
    walkbones,

    I suspect that what you are seeing is a result of the "open circuit" nature of a fluorescent light.

    At 120V, you’re going to have about 60Amps across your 2 ohm resistor....."POP"

    For a reference:
    A "Cold" 100Watt bulb measures about 9.5 Ohms (As the filament heats, this value increases)
    A "Cold" 75Watt bulb measure about 13 Ohms. Again this changes as the filament heats.

    ....You could probably get away with a little 4W night light. Sorry, I don't have one to measure,
    but I would guess it to be about 40 Ohms.

    In fact, you may find that you can get away with a load of several K Ohms that would solve your problem.

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    Beau Schwabe

    IC Layout Engineer
    Parallax, Inc.
  • walkboneswalkbones Posts: 30
    edited 2005-10-26 19:02
    Oh, sure, using V x V\R = Watts formula, I'll need a 3k ohm, 5watt resistor. Sounds good, thank you.
  • Alan BradfordAlan Bradford Posts: 172
    edited 2005-10-27 00:46
    Hi,
    I think your problem is the leakage current through the Triac in the SSR. It is 1-2 MA. I am not an expert on what makes a flourescent lamp work, but this current is most likely charging up a capacitor in the ballast circuit. When this charge gets high enough to discharge through the lamp, the flash occurs. As the voltage dops to 0, the cycle repeats.

    I have had this problem when interfacing AC SSR's to equipment with opto-isolators. The leakage current will latch the optos on. A 5-10 k resistor across the load will·usually cure it. A 1 -2 watt resistor shouldnt get too warm. You may need to experiment to see how large a resistor will get rd of the problem.· Good old E=IR time.

    Hope this helps,
    Alan Bradford
    Plasma Technologies
    www.plasmatechnologies.com
    ·
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