Control/Dimming Slight flickering when dimming house lights

[Muellergt]

I recently wired up the house lights in our church to (5) 4-channel dimmer packs. Each pack has a dedicated 20amp breaker, and the load per channel is (7) 90W bulbs. That equals 5.25amps per channel at 120V due to my calculations. And we're only using two channels per pack because they say they're 15amp max. We bought cheap dimmer packs, Matrix DMX Pro+.

The problem is I can see slight flickering or flashing when dimmed at all. I'd even say its strobing. It's not extremely noticable, but enough to be distracting. I'm limited in my knowledge of dimmers, but I know that's not normal and it doesn't happen to our PARs which are on the same dmx run...even past the house dimmer packs. Please help.

 

[marmer]

Back in the old days (c. 1990) Sylvania Capsylite PAR38s would flicker when dimmed. It got to where we had to use lamps from a different manufacturer. (I don't think they have that problem now.) I wonder if your house lights have old Capsylites? Seemed like they had some kind of energy-saving design which caused visible flicker when the voltage was reduced. On the other hand, that was more than twenty years ago. (We opened in 1991 and I'm pretty sure that we still have a few original PAR38s and PAR30s in service. Not many, but a few.)

 

[Muellergt]

I do know the lamps we are using are Utilitech Par38s. They are halogen, but I was getting the effect with standard incandescent bulbs. Could it be a grounding problem by any chance?

 

[jhochb]

Good Morning

I would think a neutral issue rather than a grounding issue
Do you have a dedicated neutral for each load?
And is your DMX line terminated?

 

[Muellergt]

The entire load consists of 7 fixtures that share a neutral. Then it is plugged into the dimmer pack, on its own 20amp beaker with a dedicated neutral. I'm not sure if they are all connected inside the breaker box on a buss though. Is that standard?

As far as the DMX goes I assumed that the units automatically terminated the DMX, but I will have to check.

 

[DMXpro]

The entire load consists of 7 fixtures that share a neutral. Then it is plugged into the dimmer pack, on its own 20amp beaker with a dedicated neutral. I'm not sure if they are all connected inside the breaker box though. Is that standard?

As far as the DMX goes I assumed that the units automatically terminated the DMX, but I will have to check.

When you say the 7 fixtures share a neutral, do you mean they're wired together before being plugged into the dimmer? If so, I would try separating them, then plugging them all in with splitters or cube taps. Also, the dimmer pack at the end of the chain is the one you're going to want to terminate; some packs have a built-in selection for termination, which can be very helpful. If this is the case, maybe some packs in the middle of the chain are terminated by accident.

 

[Muellergt]

Yeah. They're wired in parallel using pigtails...as wiring any other circuit. In order to seperate them, I'd have to run a crap load of conduit and new wiring in the ceiling. I think then plugging them into cubes vitually has the same effect if I'm not mistaken. I will however have to check on proper termination of the DMX. All these units are at the beggining of the DMX run though and the units further along, with PAR64s and what-not on them, dim without any problems.

 

[Aman121]

I'd bet that it's a termination thing or maybe an issue with the console.I've had a a similar problem with shoebox dimmers running s4s and it turned out to be a bad terminator block.

 

[derekleffew]

... The problem is I can see slight flickering or flashing when dimmed at all. I'd even say its strobing. It's not extremely noticeable, but enough to be distracting. I'm limited in my knowledge of dimmers, but I know that's not normal and it doesn't happen to our PAR s which are on the same DMX run...even past the house dimmer packs. Please help.

I'm guessing the "strobe rate" is 60Hz? All cheap shoebox dimmer s use triac s rather than SCR s, and most have little or no filtering (see choke, toroidal). A dimmer, phase control is just a very fast switch turning on and off 120 times a second. The smaller a lamp's filament, the more perceptible the "flicker" becomes. The larger filaments of higher wattage lamps, due to the amount of tungsten contained, have more "thermal mass" to counteract the cycling on and off.

Two solutions (neither of which terribly appealing):
1. Buy higher quality dimmers
2. Use larger wattage lamps

I recently wired up the house lights in our church to (5) 4-channel dimmer packs. ...

NEC prohibits portable equipment (such as your 4-channel shoebox dimmers) from powering permanently installed fixtures (your 90W houselights). I know of no 4-channel dimmer pack that is UL Listed for permanent installation.

.....

 

[STEVETERRY]

Err... you generally can't see 60 Hz flicker, even on a small tungsten load.

This is much more likely to be jitter caused by a simple-minded or marginally designed zero-crossing detector ( Dimmer, zero crossing referenced ) in the dimmer, especially if the AC line is noisy.

What [-]kind[/-] make and model of dimmers are being used?

ST

 

[jhochb]

Good Morning

NSI had a 4 pack that was for perminant install. It had knock outs for line & load side wiring. I don't know if Leviton still makes it or not.

 

[Muellergt]

I guess I'll have to try another dimmer pack. I'm using an Optima Lighting Matrix DMX Pro+ dimmer pack, which I know is a cheap pack, but I've used them before with no issues.

 

[dramatech]

I have experienced the same problem with the same dimmers. First that model of dimmer has no chokes. The problems come and go, but the best pattern to the problems that I have so far detected, is small loads, and wiring in older buildings.

As Steve Terry stated, it is probably some thing to do with the zero crossing detection circuit. I have used the control circuit board from those same dimmers and used it to control Solid State Relays with good quality chokes and had problems only with very small loads and dirty power. In general, they have worked quite well with the SSRs and chokes.