...What I can't figure out is how is it on when the master
power switch to the pack is off??? We did open the pack up and didn't see anything obviously wrong (mostly to see if there was a big burned section and/or anything dangerously wrong).
Am I right? And any ideas why it's staying on even with the pack off?
You must have one of the Chinese
shoebox dimmers. In the past we have had posts from folks that have noted that the
shoebox dimmers are dangerous because the main
power switch on the pack is only rated for a few amps. Truth be told, in those
dimmer packs the
power switch only controls the
circuit board and has nothing to do with the triacs. The triacs are wired direct to the incoming
power, through the fuses.
In your case the
triac popped into the always on, or shorted mode when the lamp shorted internally. This is pretty common in the small
dimmer packs with fuses and triacs, rather than the rack modules with breakers and solid state relays, although they also die of shorted filaments, it just doesn't seem to happen as often. Of course they can also die in the open position, where the light won't come on at all.
The fact that
shoebox dimmers have the triacs wired directly to the incoming
power, means that they are powered all of the time, when
power is present at the outlets that they are plugged into. One might question if they could be a fire hazard if left on when the building is not occupied. When asking this question, realize that the SSRs in a
dimmer rack are also powered all of the time, unless the main
disconnect is turned off. In most School auditoriums, and many theatres, the
dimmer rack is turned on 24/7. In theory, both
dimmer racks and
dimmer packs have either fuses or breakers on each load, that should prevent any fire hazard problems. I quess it is just the nature of knowing how most of the
shoebox dimmers are constructed as compared to
dimmer racks, that makes me less trusting of the
dimmer packs.
To replace the triacs in a
dimmer pack is pretty easy to do if you have any electo/mechanical skills. I have repaired quite a few for the various theatres in my area. I now keep a supply of 20amp triacs on my work bench. The real weakness of most of the lesser expensive
dimmer packs is the poor quality and low amperage of the triacs. If these are replaced with a high quality and much larger amperage
triac, they tend to last longer.
Speaking of the less expensive Chinese "
Shoebox dimmers", there is quite a large disparity in quality between the various packs. Most of the packs are manufactured by Irradiant, a sub company of NEO-Neon. They manufacture many different qualities based on who is relabeling the product.
A few years ago, I purchased 3 Matrix dimmers from
bulb america. They advertised as BulbAmerica dimmers, but they are famous for sending you whatever they have the most of. The initial 3 Matrix dimmers, are great. They are pretty well made, with a decent
thickness of metal and with chokes on each
channel. Based on the success of these 3 packs, we ordered 5 more. In this case we were sent the Matrix Pro. With the company suggesting that we got a better deal, because of added features. The Matrix Pro is pure crap. There are no chokes, and the metal is much thinner and the dimming curve is a real mess.
Lightonics, NSI and
Leprecon, are American companies that have made reasonable if not great quality
dimmer packs for many years. They are American made and have most of the right stuff. Although lately, NSI packs appear to be relabeled Chinese packs. Lightronics is offering both their own American made packs and the Chinese imports.
While I would prefer to have nice
dimmer racks with many circuits, the "
shoebox dimmer" really has a very usefull purpose as well. It has just become difficult to know in
advance when purchasing small
dimmer packs what you are buying. Price isn't always the answer as to the best quality. But the bargains are becoming more difficult to identify.
Tom Johnson