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Topic: Bigger capacity SSR = greater leak current? (Read 685 times) previous topic - next topic

Ezra Moore

Okay, I will admit I'm doing this mostly by feel here. Definitely not the most knowledgeable person.

I am trying to switch an AC load (a CCFL bulb in a painters-light housing) using my Uno and an Opto 22 SSR (specifically, the 120D10 or 120D25.

I have read that SSRs have a certain amount of voltage leak, so number one I am concerned with current flowing to my CCFL bulb. Mostly I'm concerned with damaging the bulb (not a huge concern, because they are cheap, but a concern nonetheless), or the bulb not doing out completely (from my experience, this probably isn't much of an issue, but maybe I'm wrong), or somehow cooking something (most importantly myself).

My main question is this: will getting the SSR with a maximum load of 25 amps instead of 10 amps have more leak current, and will that leak current (with the 10 Amp SSR or 25 Amp SSR) have any effect at all on my goals?

The CCFL is 13 Watts. So, if I calculated correctly that is approx. 1/10th of an amp at 120 VAC. Does that sound correct? If that is correct, than I will be seriously underutilizing either SSR, are there any negative repercussions of doing this?


Thanks in advance!


Grumpy_Mike

Check the data sheet for the SSR you want to use, but generally yes bigger capacity ones have more leakage.

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will be seriously underutilizing either SSR, are there any negative repercussions of doing this?

Well it will be more reliable.

Leakage current through a bulb is not a problem for the bulb. The circuit is powerd down it is not off so it could be a problem for you if you touch ant live wires.

Ezra Moore

Thanks Grumpy_Mike, I will take a look at the data sheet.

Am I understanding you correctly that there will be no damage to the bulb and that if there is no exposed conductors there will be no physical danger?

I am planning to just wire an outlet in (so that the light can be plugged in, and so that the project is more versatile), and build it into a box.

Thanks for your quick response, and tolerance of my naivete.

Grumpy_Mike

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Am I understanding you correctly that there will be no damage to the bulb and that if there is no exposed conductors there will be no physical danger?

Yes correct.

dc42

I think there is a possibility that the leakage current will cause the bulb to flicker when it is supposed to be off. The electronics in CCFLs typically have the AC mains feeding a full-wave rectifier and capacitor. So the leakage current may charge the capacitor to a point at which the inverter starts and the bulb lights. But the leakage current will probably not be able to sustain the lamp, so the capacitor will discharge and the lamp will go off. Then the cycle will repeat. Whether this happens or not depends on whether the inverter takes enough current to absorb the leakage before its output becomes high enough for the lamp to light.

I normally prefer SSRs to mechanical relays, however for driving a CCFL, I think a mechanical relay may be better.
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Ezra Moore

Thanks Grumpy_Mike and dc42. Much appreciated. I already have this SSR here, so I'm going to give it a shot. If I notice flickering, I will likely switch to a mechanical relay.

As I understand it, the safest way to use a mechanical relay would still be to optically signal it, is that correct?

Again, I really appreciate your help!

Grumpy_Mike

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he safest way to use a mechanical relay would still be to optically signal it, is that correct?

No if you use a relay then it is isolated enough, you just need to drive it with a transistor.

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