0-10v dimming question

[TDwyerReflex]

I'm working at a school. Some classrooms that have lets say 9-12 led fixtures. In some classrooms when dimming the lights, maybe one or 2 fixtures will either dim to a level that doesn't match the others or will appear to be off. I don't have the print in front of me but I have a suspicion most of these troubled fixtures are at the end of a daisy chain if that makes any sense. Does anyone have any ideas. I haven't tried any troubleshooting yet.

 

[synchro]

I'm working at a school. Some classrooms that have lets say 9-12 led fixtures. In some classrooms when dimming the lights, maybe one or 2 fixtures will either dim to a level that doesn't match the others or will appear to be off. I don't have the print in front of me but I have a suspicion most of these troubled fixtures are at the end of a daisy chain if that makes any sense. Does anyone have any ideas. I haven't tried any troubleshooting yet.

Because the current sourced by each fixture on the 0-10V lines is at most a few miiliamps, it's unlikely that your issue is being caused by a wiring problem. But if there was a significant series resistance somewhere in the chain, the voltage at the end where the dimmer is located would have the lowest voltage because the dimmer sinks current to pull the voltage down to the required dimming level. And so the lights closest to the dimmer would have the lowest voltage and therefore lowest brightness, or be totally off. However, it's more likely that the few lights that aren't matching are either defective or are another model, manufacturer, etc.

 

[gar]

211202-2407 EST

I believe most 0-10 V dimmers are a current source, or approximately, and clamped at a maximum voltage of about 10 V.

Two ways this type of dimmer can be controlled --- a variable resistor, or a source voltage. The resultant input voltage will determine the dimmer output ON time per cycle.

To use resistance control of paralleled 0-10 inputs means the choice of variable resistance range is defined by how many inputs are parralleled. For voltage control the source has to handle up to the maximum load current of all those inputs in parallel.

If the wiring resistance is low compared to the equivalent adjustable control impedance, then all dimmers should see about the same control voltage.

Set your dimmer control for about 50% brightness. Then go around to the various dimmers and measure the input control voltage of each. Should be nearly the same for all at each dimmer.

.

 

[dpcarls1598]

Brand name fixtures or something else? I rarely have issues like that with Lithonia or Hubbell but did with a knock off brand one place bought online. Also, many manufacturers aren’t designed to dim to off. The ones I’m using in classrooms only dim to 15% so I have to set the dimmer control to that or a little above to avoid some being dim and others off.

 

[Flicker Index]

I'm working at a school. Some classrooms that have lets say 9-12 led fixtures. In some classrooms when dimming the lights, maybe one or 2 fixtures will either dim to a level that doesn't match the others or will appear to be off. I don't have the print in front of me but I have a suspicion most of these troubled fixtures are at the end of a daisy chain if that makes any sense. Does anyone have any ideas. I haven't tried any troubleshooting yet.

Do the control wires run in the same conduit with power? Some LED ballasts are more sensitive to cross-talk from capacitive coupling with AC. Also make sure each ballast's control wires are connected in matching polarity. In proper polarity, every connected luminaires should be at full output when the dimmer's control connections are left disconnected. Every fixture should come to the lowest output when you short the two control wires. If the general behaviors are correct but you're seeing differences between fixtures, that's just the way the fixtures are. The variations are more visually noticeable at the lowest end.

There's no industry standard transfer function between luminous output vs control terminal voltage and it doesn't have to be linear.
Read on: https://www.lutron.com/TechnicalDocumentLibrary/048587_Web.pdf

 

[GeorgeB]

There's no industry standard transfer function between luminous output vs control terminal voltage and it doesn't have to be linear.

In an open loop system it is almost impossible to have a "standard transfer function" that is reliable at a 100% level. As long as it is 100% electric or electronic, perhaps; 0-10V to 0-60Hz, yeah, ALMOST perfect. 0-10V to 0-1800RPM, no. Close the loop, you can get REALLY CLOSE. With light, even closing the loop is problematic as color temperature and intensity both have perceived "level" effects. I see no solution to this other than a photocell per fixture, or at least per fixture type, wired into the controllers, one per type at least.

 

[hillbilly1]

I was talking to an engineer with a major lighting manufacturer, and he said it has a lot to do with the programming of the driver. They can set minimum levels specific to the customer, along with rate of dimming.

 

[Flicker Index]

In an open loop system it is almost impossible to have a "standard transfer function" that is reliable at a 100% level. As long as it is 100% electric or electronic, perhaps; 0-10V to 0-60Hz, yeah, ALMOST perfect. 0-10V to 0-1800RPM, no. Close the loop, you can get REALLY CLOSE. With light, even closing the loop is problematic as color temperature and intensity both have perceived "level" effects. I see no solution to this other than a photocell per fixture, or at least per fixture type, wired into the controllers, one per type at least.

It's certainly possible to get it in the ballpark, but they don't. Did you read the Lutron article? It's just a matter of not being standardized. For example, 4-20mA usually sets 4mA as zero, 12mA as 50%, 20mA as full, much below 4mA as open circuit fault, hence 4-20 rather than 0-20.

 

[GeorgeB]

It's certainly possible to get it in the ballpark, but they don't. Did you read the Lutron article? It's just a matter of not being standardized. For example, 4-20mA usually sets 4mA as zero, 12mA as 50%, 20mA as full, much below 4mA as open circuit fault, hence 4-20 rather than 0-20.

In the ballpark, yes, but how large a ballpark? Yes, I read the article. I deal with a different type of drivers, often using 0-10, +/-10, 4-20, 0-20, and indeed (-20)-(+20) as inputs and (usually) valves or at least solenoid operators as outputs. I'd guess that perhaps half or a few more are open loop.

Manufacturing tolerances come into play; if the driver is part of the controlled device, the manufacturer can typically match the replaced with new within (WILD GUESS) 10% over the input range of 15% to 85%. The ends are more difficult. But if the user needs to replace a brandA with a brandB, even these are very difficult. and intensity

Let's take the lighting controller. Please accept I know almost noting about lighting, I'll assume a 0-10 command. Perhaps with the initial 40 fixtures in a facility all are "identical" and give 3200K and 200 lumens at 10%. This same fixture, new, outputs 3600K and 2000 lumens at 90%. Six months later a forklift knocks 3 to the floor and new ones, similar part number, are purchased. How's odds the color temperature and intensity will be "the same" visually as the existing. (How's likelihood anyone will care?)

But my point is there is no (practical) way to correct these differences.

 

[Flicker Index]

You can't get an absolute perfect match, but we're talking something different. The LED string current is already internally monitored in the ballast so it's not difficult to define open circuit / 10v as 100%. However, if the minimum dimming of the LED ballast is say 25%, how should the ballast controller map it 2.5v =25%, and dead travel between 0-2.5 or set 0v as 25%? Linear or logarithmic curve? There's no standardization and that's the problem I am speaking of. Each manufacturer does whatever they feel like it. Some don't even map the curve themselves and those would just follow whatever default transfer function that is pre-programmed into the LED ballast controller IC and not all of them offer programmable transfer function curve.

LED ballasts are not rated with "ballast factor", however fluorescent ballasts are. Common ballasts are 0.88 while there are a very few that are 1.00.
If they were defined as 10v for 1.00 BF, and 5v for BF 0.5, then, the dimming ballast that maxes out at 0.88 would simply respond to changes between 10v and 8.8v, while the 1.00 rated ballasts would dim between 1.00 and 0.88.