SSR not switching dimmed load - Page 1
Forum section: electronics / projects

author: nicnoc
author_rank: Newbie
timestamp: January 15, 2016, 01:43:21 pm
content: Hey everyone.I have a system where there is a "master dimmer" (an 800W dimmer designed for household lighting). From that master dimmer, I have a few SSRs switching 40W incandescent light bulbs.The idea being you can control the brightness of all of the lights with one dimmer.However, the SSRs are only switching reliably when the dimmer is on full brightness, or set to very dim. Dimming mid way results in some lights just 'sticking' on.Could the dimmer be messing with the zero crossing detection?The SSR in question is thishttps://www.openhacks.com/uploadsproductos/g3mb-ssr-datasheet.pdfAnd the dimmer (it's the 800W model)http://www.vetionline.co.za/products/rotary-dimmer-moduleAny help would be much appreciated

author: Zero999
author_rank: Super Contributor
timestamp: January 15, 2016, 04:12:10 pm
content: Yes, it does sound like the dimmer is affecting the zero crossing detection. Try swapping it for a solid state relay with a MOSFET output stage.

author: nicnoc
author_rank: Newbie
timestamp: January 15, 2016, 05:35:44 pm
content: Thanks for the reply!Will the above mentioned SSRs still have zero crossing? My concern is that switching at a non-zero part of the sine wave will cause noise (this system is near audio equipment), as well as a greater inrush current.(If you're wondering, I wrote an earlier response but realized I had misread you - this is an updated version)

author: Seekonk
author_rank: Super Contributor
timestamp: January 15, 2016, 05:44:33 pm
content: The dimmer isn't working right because it likely isn't seeing a load. One quick way to see is to put a small lamp on the output of the dimmer or a RC load of like 1uf and a 10-50 ohm resistor. This will allow the dimmer circuit to work. This can also wirk with non dimmable LED.

author: nicnoc
author_rank: Newbie
timestamp: January 15, 2016, 05:58:27 pm
content: Hey seekonk.Thanks for the reply.The dimmer is working fine, since once an SSR is latched on, I can still dim it with the dimmer

author: macboy
author_rank: Super Contributor
timestamp: January 15, 2016, 06:07:27 pm
content: Quote from: nicnoc on January 15, 2016, 05:35:44 pmIf this is your concern then you must read up on how basic dimmers work... you may not like it!

author: wraper
author_rank: Unknown
timestamp: January 15, 2016, 06:20:28 pm
content: Quote from: Hero999 on January 15, 2016, 04:12:10 pmThis has nothing with mosfet or non mosfet SSR. You can get SSRs either with zero crossing or without it (random turn-on).http://www.crydom.com/en/tech/newsletters/solid%20statements%20-%20ssrs%20switching%20types.pdfHowever, this most likely is something else. Zero crossing could not allow to turn them on. Exactly opposite to being unable to switch off.IMO this is because those SSRs lack any snubber in them, and the dimmer outputs high voltage spikes because of inferior or faulty filter (like dead X class safety rated capacitor, happens quiet often in dimmers). Usually there is some kind of coil (though cable inductance can be enough for causing the problem too) to reduce interference caused. This inductance can cause high voltage inductive kickback. And phototriac optocouplers (in SSR), especially types without zero crossing, are very easy to trip if exceeding the peak voltage. I've seen this when repairing dimmers. X class cap in the snubber fails, and then dimmer just cannot turn off after setting it on, even if phototriac optocoupler is not faulty, it just gets tripped on by the inductive kickback.EDIT: Which particular SSR model? In the datasheet there are SSRs with or without a zero crossing, with or without a snubber. The other question is if those SSRs are genuine or "china special" from ebay/shady place.

author: wraper
author_rank: Unknown
timestamp: January 15, 2016, 06:26:18 pm
content: You could try to attach a snubber across the SSR terminals. Like 47-100 ohm 1-2W resistor in series with 47n-100n X class capacitor. And/or MOV too.

author: Monadnock
author_rank: Contributor
timestamp: January 15, 2016, 08:22:46 pm
content: I must be missing something, but why do you have the bulbs on separate circuits? Why not just wire them all up to the master dimmer? It's good for 800W.