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i am controlling Ceiling fan through Panasonic AQH2332A SSR, but getting voltage across fan terminals even if SSR off. The voltage across terminals is about 35v.

i tried to reduce snubber capacitor to 0.01uf, this reduces the voltage to 18v. How can i reduce voltage further.

1> Further reducing capacitor can increase over voltage across SSR, i guess.

2> increasing resistance of snubber doesn't affecting voltage

schematic

simulate this circuit – Schematic created using CircuitLab

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You aren't going to get it down to 0V. The capacitor will leak some amount of current by it charging and discharging. That current will create a voltage drop across the load. You can reduce the voltage by reducing the resistance by adding a resistor in parallel to the fan.

Reducing the capacitor will defeat the purpose of the snubber, which is to reduce the voltage spike on switch off of the inductive load. So you are working with a lower limit on the size of the cap you should use.

If you actually want the voltage to be exact 0 then you need another switch between the snubber and the load that closes sooner and opens later. The switching current on that one can be lower because the snubber will restrict the current after the main SSR is off.

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  • \$\begingroup\$ Thanks for sharing your words with me, yeah i know voltage cannot be down to zero, i am just trying to minimize it. I had used R=39, C=10nf , this is giving me 18v and SSR is working fine on full load. Should i try to reduce cap value and test further?? \$\endgroup\$ – vikas goyal Jul 13 '17 at 9:22
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It's a common fact for all SSR with snubber, because the capacitor is leaking current. If you connect the load, let say ceiling fan, the voltage will be very small and it won't turn the fan, I guess. There is no remedy for that, so sorry. But I don't understand why is this causing troubles to you, if any? Perhaps you are just a little surprised?

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  • \$\begingroup\$ Thanks for your comment. I want to apply for CE and BIS certification for my product , and i have no idea about their standards yet. So i want to make sure that the voltage i am getting shouldn't trouble me while testing and certification. \$\endgroup\$ – vikas goyal Jul 13 '17 at 9:19
  • \$\begingroup\$ You should use capacitor rated for that AC voltage. Determining the inductance and resistance of the load you can calculate the RC components. It may happen that ideal snubber has the C of tens of nF and the R of few kOhms. \$\endgroup\$ – Marko Buršič Jul 14 '17 at 7:24

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