Film-Tech Forum ARCHIVE: Problem With a Smart 3K Dimmer

This is topic Problem With a Smart 3K Dimmer in forum Film Handlers' Forum at Film-Tech Forum ARCHIVE.

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Posted by Don Furr (Member # 1469) on 02-01-2015, 10:11 PM:

With the low light trim pot turned completely to "dim", the lights still have a low glow. I need the lights completely off. Is this fixable?
http://www.film-tech.com/warehouse/manuals/SMARTDIMENSION3K.pdf

Posted by Chris Markiewicz (Member # 1415) on 02-02-2015, 09:50 AM:

Just a few thoughts:
What kind of load are you driving? is it all incandescent or are there any CFLs or LEDS in there?
With the dimmer set to low, check the AC volts between load neutral and load out. What is the reading?
Still at low, you can try and tweak the mid level trim down just a bit and see if your bulbs go out. Sometimes the trim controls interact with each other. If not, return the mid trim to where it was.
Good luck!

Posted by Gordon McLeod (Member # 33) on 02-02-2015, 10:16 AM:

A triac or SCR or SSR block dimmer can not actually fade completely to zero or actual go to 100% output
If the fireing device operates below the threshold that establishes a holding current through it the up fade will in fact have a very large jump in it in a snap effect
on the other end the fireing pulse is not allowed to actually get to the maximum fireing angle in case it overshoots and goes into the next half cycle
Also there is a voltage drop across the filter chock
All that said the trigger circuit of various manufacturers varries in design and some allow more level of control than others
I remember that the SMART was very similar to the HiTech dimmer
One could if they wanted to be cleaver remove the Low pot from the board and add a resistor in series with its high side equal to the pots value this would decrease the reference voltage range to a lower value
That may cause some flicker I dont have a schematic handy anymore but Oscar may chime in as I remember having many discussions as it was being designed
But remember that at the lowest level the dimmer still has to be be conducting and at the lowest one at least needs to see a very small glow in the centre of a lamp filament

Posted by Don Furr (Member # 1469) on 02-02-2015, 02:38 PM:

Chris the load drops from 112.0 to 7.8 volts. I guess that almost 8 volts is keeping the bulbs lit.

Posted by Gordon McLeod (Member # 33) on 02-02-2015, 06:44 PM:

at the lowest most dimmers are 2.5-3volt true RMS

Posted by Don Furr (Member # 1469) on 02-02-2015, 11:11 PM:

I have given up on the idea of dimming the UV black lights. I've just put 'em on a switch. On or off....simple enough! The End.

Posted by Oscar Neundorfer (Member # 458) on 02-04-2015, 12:14 PM:

I don't have the schematic of that dimmer at hand, so I cannot give meaningful advice. However, as I recall, (and I may be wrong since it hs been MANY years since I designed it), the trim pots had a resistor between the low end of the pot and ground to prevent them from being trimmed all the way to off. If I am right, just shorting that resistor may allow a full off setting.

If I can find the schematic, I will update this post.

Posted by Don Furr (Member # 1469) on 02-04-2015, 03:51 PM:

Thanks Oscar!! You're a scholar.