JD
Well-Known Member
Most modern commercial dimmers these days use SSRs (Solid State Relay) for the power end, as compared to discreet SCRs or Triacs. Basically, a monolithic device that contains the opto isolator, firing circuit, and thrysistor all in one part. At its heart, that thrysistor could be a triac or set of SCRs, but unless the part manufacturer tips his/her hat, we will never knowI stumbled across this thread looking for technical documentation on one of these dimmers because I bought it used and like many other folks it had several shorted channels.
I happen to own some really old NSI equipment and it is sad to see how they have 'cheapened' their product offering over the years. I have never been a big fan of triacs for dimmers. I always preferred a dual-scr design. Sure a triac is nothing more than two SCR's packaged into one case but if you look at the thermal capacity of a dual-scr design vs a triac the dual-scr design always wins out even with the same current rating.
I have an NRD-8000 and an ND4600, both of them a virtually indestructible. Each individual SCR has a large heat sink per device, then you look at the D4DMX it has one single heat sink shared by 4 devices and then also relies on the heat to be distributed to the back mounting cover yet there is no heat sink grease to help conduct the heat to the rear panel.... very poor design indeed...
If there is only one good thing about the design it's that they still included chokes on each channel. I've seen really cheap Chinese crap with no filters at all or a single filter for all channels... those things put so much garbage on the line I've seen some of them actually generate enough noise to throw the gating/ramp signal into a tither within the dimmer pack itself.
Back to the "shoebox" NSI, as long as you have 25 amp triacs in there, they hold up pretty good. Shame they come with 15's. Modern triacs and SCRs are better at handling some of the real high current spikes the the old beasts, but I must admit, it was pretty hard to take down some of those old back-to-back SCR dimmers.