# SSR - zero crissing and snubber help

Hi, im building a fridge control with my arduino, i had deceide to use an SSR to control the compressor i had not check its rating yet, i guess its < 10A @ 220vAC
but whats driving me crazy are some mentions to zero crossing devices and a so called snubber circuit, anyone can give me some help on calculations for this and if its really needed in my case?

thanks!

Zero crossing is something that an SSR should do for you, you should not have to bother with it. A snubber circuit is an inductor / capacitor circuit to limit the speed of the rise in current to reduce interference when you switch it on. This is something that should already be in your fridge.

thanks, i hope so, its an old fridge, do you know how can i calculate this RC circuit ?

also, i have a fluorescent lamp near the arduino, when i turn it on, the lcd shows garbage for a while, should i put a capacitor in the SSR input to prevent any possible arduino switch by interference ?

[quote author=Luis Manson link=topic=86275.msg646470#msg646470 date=1326122821] thanks, i hope so, its an old fridge, do you know how can i calculate this RC circuit ? [/quote]

You need to know at least the current draw of the compressor and the SSR commutating dV/dT rating. See pages 12-13 of http://www.fairchildsemi.com/an/AN/AN-3008.pdf. Or buy an SSR with built-in snubber.

[quote author=Luis Manson link=topic=86275.msg646470#msg646470 date=1326122821] also, i have a fluorescent lamp near the arduino, when i turn it on, the lcd shows garbage for a while, should i put a capacitor in the SSR input to prevent any possible arduino switch by interference ? [/quote]

A capacitor across the SSR input isn't likely to make any difference, but may overload the Arduino when the pin switches state. It would be better to find out why the lcd is showing garbage. How are you powering the Arduino and LCD? Does the problem still occur if you power it from a 9v battery connected to the barrel jack? How close does the lamp need to be to make the problem occur?