Dimmer Pulsation

[ChrisM94]

Hi

 

I'm working in a venue with 4 Cell Molefays on a FOH Truss which has socapex lines ran from there to an Avolites Rack with Dimmer Modules in it. The problem is that at low percentages of say 10-30% the moles pulsate quite quickly and so have a very unpleasant effect. When faded up past 30% they operate quite happily as normal. We've tested all of the dimmer modules with a fixture local to the rack and there doesn't seem to be any problem with the dimming there. So it narrows it down to the cable and the fixtures but the moles have operated perfectly fine when not used on the FOH Truss. To me it seems impossible that the cabling could cause any effects like this. It may just be an intermittent problem.

 

I was just wondering if anybody else has had this problem and if so how to fix it.

 

Thanks in advance

[timsabre]

Does the DMX to the dimmer rack continue on into the truss?

 

Are any other fixtures/dimmers affected when the moles play up.

 

Sounds like it could be a DMX fault being made worse by noise from the dimmers...

 

If it's a recent avo rack, look at the DMX values for the moles channels on the display when the problem is happening, are they steady?

[Wingwalker]

Have you extended the length of the extension cables to put the units into their new position? I'm wondering if there is just enough of a voltage drop to make a difference.

[itiba]

Following on from Tims advice do they do the same thing if you remove DMX from the equation completely ie manually fade them up from the dimmers themselves on test mode?

[themadhippy]

could the soccas be adding capacitance to the output of the dimmers causing them to oscillate? bit like naim amps of old

[PaulDF]

When you say you tried the dimmers with a fixture at the dimmer pack was it with a mole?

[niclights]

I would speak to Avo. I've seen this before where some channels flash at full at increasing rates proportional to intensity level. This was with Art racks on hire so I have never been able to investigate but JB Toby said he thought this would happen with a neutral fault, presumably within the rack itself.

[ChrisM94]

The DMX only feeds to Avo Rack but that feed most likely comes from some sort of splitter. I wouldn't have thought it would be a DMX issue though as the problems only occur with the Moles and nothing else.

 

We had thought possibly something to do with capacitance or inductance of the long cable run from the dimmer rack - probably about 200m.

 

It seems to have stopped happening for now at least, which is frustrating as nothing has actually changed with he system.

[alistermorton]

Could it be a failing capacitor on the ramp generator?

[timsabre]

Assuming these are recent avo racks, it's all done in software, there are no ramp generators.

 

If it's not DMX, and as nothing else is affected it seems unlikely to be, then it must be a triggering problem on the power circuit.

I would agree that contacting Avo service is probably the best thing to do as they may have heard of it before.

[csg]

I had a similar problem last september with an Art rack, I isolated the issue back to the individual channel. As you describe, the fault manifested itself as a regular flicker / strobe at low intensities. The load was only a couple of source 4 pars. A quick re-patch onto a spare channel sorted the issue out.

[gnomatron]

Does this still happen if you use the test pots on the rack? Sounds like the sort of fault I've seen caused by dodgy faders on lighting desks. Probably isn't, but worth asking. Definitely worth asking avo though.

[csg]

in my case, certainly not, the problem was with the module itself. A "dodgy fader" would likely produce a more random flicker, and in my case, we could look at the DMX.

[James Remo]

Likewise, I've seen a couple of art 2k racks with channels pulsing at low drive, with a 4 lite hanging off the dimmer. Very interested to find a fix

[csg]

Funnily enough I think it was one of your racks James, a Renegade job at the Copperbox back last september.