300W AC light dimmer mod to 500W

Thread Starter

IvarsOzolsDB

Joined Aug 24, 2012
38
Bought Stairville PAR56 Active 300W and got a bit dissapointed in light output. So I got wondering maybe there is some mod I could do to put 500W 230V PAR56 bulb in it (originally 300W 230V PAR56) and not fry dimmer circuits. I traced schematic (look in attachments) in high voltage part, as it looks like a triac dimmer with some extra fancy mains filtering, did not see the point to trace controller part, as it is optically isolated by MOC3021 and it's own 9V transformer and I suppose works like ac phase control dimmer. Triac is BAT06-800BW.

Changed NTC to 3A, filter choke to same 30mH just 5A one, L1 inductor 3A torodial type. Circuit works with 500W lamp, but at 1-4% dimmer setting, lamp does not turn off, either stutters, stays full on or switches full on and off. Again, my understanding of triacs is none. Googling up showed similar problem when optoisolated triac would not turn off, fix was putting on snubber. Maybe I have to change snubber R3 C3 values accordingly? Anyone have any knowledge of how this works?
 

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Ian0

Joined Aug 7, 2020
1,113
But the inrush will be 20A, and it‘s a large filament to heat up. An 8 Amp triac is just about enough for a PARcan, A 12A triac would be better. Just look for BTA12-600BW.
If the triac won’t turn off, then it has failed, usually because the fuse was overrated and the filament fell across the lamp terminals when the lamp failed. Always use a high-breaking-capacity fuse (with a ceramic tube) with not too high a rating, otherwise the triac fails before the fuse. Getting the right value of fuse takes a little experimentation, use the smallest one that doesn’t blow on the inrush current, and remember that it’s a lot easier to change the fuse than to change the triac.
A filament lamp load doesn‘t need a snubber and a BW is a snubberless triac which will withstand the high dV/dt.
If it won’t work at low dimming levels the the triggering circuit is remaining on past the zero crossing, and that’s probably just bad design.
 

Thread Starter

IvarsOzolsDB

Joined Aug 24, 2012
38
Circuit works fine if a 300W bulb is connected as original design specified. Also I tried shorting coil L1 with 500W bulb and then it's working fine too. What does that coil actually do?
 

Ian0

Joined Aug 7, 2020
1,113
Circuit works fine if a 300W bulb is connected as original design specified. Also I tried shorting coil L1 with 500W bulb and then it's working fine too. What does that coil actually do?
The inductors Filter out the interference.
Triac dimmers are normally very tolerant of different loads. It must just be borderline at 300W load.
I know of problems with retriggering on the sensitive gate triacs (-SW and -TW types) but not the -BW.
 
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Dodgydave

Joined Jun 22, 2012
9,837
It's not the Triac,there must be some zero crossing detection to trigger the optocoupler, what goes into the large connection,,can you post a video of the problem.?
 

Thread Starter

IvarsOzolsDB

Joined Aug 24, 2012
38
Here is the video:

Filmed by potato phone, sorry about quality. Controlling brightness with integrated controller 0-100%. Have not tried even smaller increments with DMX (0-255).

Personally, I have hunch that retrigering is something to do with L1 coil. If I bypass it, circuit functions as intended with 500W bulb.
 
Last edited:

Ian0

Joined Aug 7, 2020
1,113
The trigger pulse should finish long enough before the zero crossing for the triac to switch off. It probably finishes exactly on the zero crossing which would be enough for it keep the triac on into the next cycle.
 

Ian0

Joined Aug 7, 2020
1,113
Practically, no; but if you start to have problems with interference on the mains, you know where it's coming from.
 

Thread Starter

IvarsOzolsDB

Joined Aug 24, 2012
38
No smoke, all works great. Tested with dmx control from 0 (off) to 255 (max) too, all good. Temperatures leaving device full lit for an hour middle of housing where bulb touches metal gets hot to about 125°C with 500W bulb, it was about 110°C with 300W one so it is not too bad. End part of housing, where dimmer lives and control buttons are gets to about 45°C max. For noise testing I connected lamp in the same AC outlet where my PC, several audio amplifiers and crossover gets power, had no issues with any new noise on audio output, so I assume I'm clear there too.

Now all what is left to do is wait to all this damn covid-19 crap gets out of the way and try upgraded lamps out in the field at some gig.

But for those who consider doing the same, don't. It is far much easier to buy dimmer + "dumb" lamp enclosure separately and screw it near on the same light fixture pole. End bill of matherials will be about the same in the end. I did this only because I had bought theese fixtures already and had time to tinker.
 
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