Unique dimming application question...

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RobbieR

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Location
Atlanta
Hey ya'll,

First time back in quite awhile.

I wanted to get your input on a unique application that I've never run into before.

Our client wants (8) fluorescent 2x4 fixtures with a dimmable ballast installed in a Telepresence Room (A virtual meeting room with cameras). They want each fixture to have its own wall mounted dimmer switch for a total of eight dimmers. Basically, a parallel type connection. They want to be able to dim each fixture individually without the need of dimming the entire room. This is to adjust the lighting in the room for the cameras. Keep in mind that they want to stay inexpensive. No fancy lighting controls.

I was thinking about using one branch circuit to power the lights, but I?ve heard of horror stories of shared neutrals and dimmer switches resulting in flickering lights. Since the lighting is sensitive to this room, is it overkill to route a separate branch circuit with a dedicated neutral for each fixture? That is the only way I can think of that would reduce the chance of potential problems.

Thanks in advance!
 
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gar

Senior Member
Location
Ann Arbor, Michigan
Occupation
EE
110214-0910 EST

Why wouldn't there be interaction? You have an impedance, the common wire(s), a change of current and thus a change of voltage. Is it significant, that depends upon the impedance, and other factors.

Will adjustment of one dimmer have a slight effect on another light? Maybe. Will certain adjustments cause flicker? Don't know.

If the ballast is electronic, and the control is via 0-10 V as mentioned above, then there is probably no interaction, or very little. Highly unlikely there would be any flicker effect that was not inherent in a single fixture.

Electronic ballasts with 0-10 V control convert AC to DC and then back to high frequency AC. Intensity adjustment does produce an average change of input current and thus voltage. But this is not the same kind of sub-cycle effect as is a standard phase shift dimmer with a magnetic ballast designed for dimming. A standard phase shift dimmer in combination with an electronic ballast, still AC to DC to high frequency AC, designed for this type of dimmer will probably have an intermediate type of interaction.

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gar

Senior Member
Location
Ann Arbor, Michigan
Occupation
EE
110214-1423 EST

The specification for your ballast look interesting.

From the limited information I conclude that the phase shift dimmer does not need to go much beyond a 90 deg shift for full dimming. This means the rectified DC voltage will probably never drop much below peak voltage minus whatever tolerance is built into the system.

My guess is that dimming is controlled by the phase angle of the voltage from the dimmer rather than the magnitude of the average voltage of the dimmer output.

Conveniently this is a two wire system with wide dimming range.

I suggest you get a couple ballasts and play with them. At a fixed dimmer setting you need to see how much light output varies with variation of input AC voltage.

I do not expect that there is a regulated DC supply within the ballast, but it is possible.

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