Dimming

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Dimming

In a basic way all SSR are On/Off at their core. Some are not dimmable as they are what is called zero cross triggered.

This means they can only be switched on or off at the point in an AC cycle where the voltage goes to zero (ZC = Zero Cross). These cannot be dimmed but can turn power on and off.

Random triggered SSRs (what we build here) can be turned on at any point in the AC cycle but will only turn off at the ZC.

With these points in mind here is how dimming works with random triggered SSRs and a standard dimmer:

The SSR is triggered at some point in the cycle. It can be at the very beginning and it will then stay on during the whole cycle until it turns off at the end ZC (remember it only will turn off at this point no matter where it was turned on). This would give us 100% power 100% of the time for full on.

Or we could wait till half way thought the cycle and it would give us 100% of the power 50% of the time for an average of 50% of the energy to the light. This will dim the light.

We could never trigger it and it would give us 100% of the power for zero percent of the time and the light will not come on.

This is a basic description and there is a little more to it. But in simple terms this is what happens.

The zero cross triggered SSR will only turn on at ZC and off at the next one, so it is either 100% of the time or zero percent of the time so you end up with on or off.

Hope this helps.

RJ


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