using resistors on color kinetics PDS150e with colorblast 12's

[topjimmy]

Color Kinetics ColorBlast 12’s max out at 50watt and a power supply (PDS150e) obviously being 150 watts total.

In theory, I could probably do the following then. If I wanted to run 6 ColorBlast 12 fixtures off a single PDS150 and maxing the fixtures at 25 watts (somehow) I should be able to run 6 CB 12’s without any problem. I know and understand CK won’t recommend nor support such a configuration but technically should work. Here’s the situation, I’d like to use the CB12’s in uplighting for weddings however, I don’t need to run beyond the 25 watt for the halls I’d be using them for anyway, so, if I could restrict the power source to each fixture to only 25 watts I could then power 6 CB12’s with a single PDS150 technically speaking. Perhaps, just using a 25 watt resistor on each connector...

any thoughts or any concerns here ?

 

[epimetheus]

Wont work. At all.

The electronics in the units need the full voltage to operate. All adding a resistor at the connector would do is reduce the voltage.

I would recommend getting the proper wattage power supply. That said, how about just not setting the units above 50%?

 

[Chris15]

Even if it was to work, which it won't, think about this:
LED1 25W + R1 25W = 50W
LED2 25W + R2 25W = 50W
LED3 25W + R3 25W = 50W
=150 watts total = zero gain on present...

 

[MNicolai]

I would recommend getting the proper wattage power supply. That said, how about just not setting the units above 50%?

I believe this would be a bad idea for the same reasons you cannot run 4.8kw of tungsten lighting on a 2.4kw dimmer by running them at 50%; the light source is actually somewhere around a perceived (by the human eye) brightness of 25% or 30% when electrical current is at 50%.

The relationship between perceived brightness and electrical current isn't linear. 10% of this is not 10% of that.

Somewhere on these forums are actual numbers and maybe graphs (I thought Derek or Ship ran an experiment on this at some point) showing the relationship between perceived intensity and electrical current, but I expect the physics may be somewhat different with an LED source than with a tungsten source.

 

[epimetheus]

I believe this would be a bad idea for the same reasons you cannot run 4.8kw of tungsten lighting on a 2.4kw dimmer by running them at 50%; the light source is actually somewhere around a perceived (by the human eye) brightness of 25% or 30% when electrical current is at 50%.

The relationship between perceived brightness and electrical current isn't linear. 10% of this is not 10% of that.

Somewhere on these forums are actual numbers and maybe graphs (I thought Derek or Ship ran an experiment on this at some point) showing the relationship between perceived intensity and electrical current, but I expect the physics may be somewhat different with an LED source than with a tungsten source.

Yeah, I understand that. My last suggestion (maybe I didn't preface it enough - it's still not a very good idea, but it would work) was to not set the fixtures higher than what ever setting you start to see problems at. It would be fairly difficult to measure the overall output wattage at any given setting without making a custom scroller cable and hooking up a DC ammeter. You could experiment though. For example, if you determined that a 25% setting was sufficient for your needs, than it's a reasonable assumption (in my mind) that you could run that off a 150W PSU.

Just to clarify, again, this is not the best idea. Get the appropriate psu if possible.

 

[church]

The idea does not work at all. LEDS are a junction semiconductor device that require a forward bias voltage for the junction to conduct. If the bias voltage is below the turn on voltage the device is "off" and the LED does not emit anylight.

I have just repaired a forty eight LED fixture using 3W LEDs and it used a very common design approach where the LED fixtures uses parallel strings of LEDs each string has 8 LEDs in series. Each string of LEDs is controlled by a pulse width modulated device which ensures the LEDs always see the same forward voltage the only thing that changes is the period of time this voltage is "on". When the PWM is at 100% the LEDs are on 100% of the time, at 50% the LEDs are only on 50% of the time and appear dimmer. One approach that is frequqently used to do this is a programmable regulator - the modulator output drives the regulator control line and turns the regulator "On" or "Off" as required. The regulator voltage is preset by the circuit design. If you reduce the supply voltage by a factor of two you will almost certainly cause the regulator to "drop out" which means the supply voltage is too low for the circuit to operate and the regulator will remain in a non conducting state and the LEDs will never turn "on".

This is also why if one LED fails you also lose the entire string of LEDs

 

[derekleffew]

...Somewhere on these forums are actual numbers and maybe graphs (I thought Derek or Ship ran an experiment on this at some point) showing the relationship between perceived intensity and electrical current, but I expect the physics may be somewhat different with an LED source than with a tungsten source.

Perhaps you're thinking of this formula
lumens/LUMENS = (VOLTS/volts)^3.4
from the collaborative article Mathematical Formulas for Lighting - ControlBooth ?

This graph

illustrates the above formula, but still doesn't take into account the human eye's perception of intensity as it varies with voltage.
------
topjimmy, you could cut your power draw in half by using CB6's instead of CB12's, but obtaining a larger power supply is certainly the best option.

 

[jfleenor]

Hi! Doug Fleenor here, borrowing Janell's screen name.

ColorBlasts use a fairly linear dimming curve. Running a CB12 at 50% will consume approximately 25W. If you do a color fade (Red to Green to Blue) with only one color at full at a time, you should be able to run six CB12 on a PDS-150. Similarly, if you run a fixed color, with the three percentages of R, G, B adding up to less than 150, you should be fine (i.e. red at 50%, green at 75% and blue at 5% = 130). Or you could buy one of our LED300 or LED600 power supplies!

Doug

Color Kinetics ColorBlast 12’s max out at 50watt and a power supply (PDS150e) obviously being 150 watts total.

In theory, I could probably do the following then. If I wanted to run 6 ColorBlast 12 fixtures off a single PDS150 and maxing the fixtures at 25 watts (somehow) I should be able to run 6 CB 12’s without any problem. I know and understand CK won’t recommend nor support such a configuration but technically should work. Here’s the situation, I’d like to use the CB12’s in uplighting for weddings however, I don’t need to run beyond the 25 watt for the halls I’d be using them for anyway, so, if I could restrict the power source to each fixture to only 25 watts I could then power 6 CB12’s with a single PDS150 technically speaking. Perhaps, just using a 25 watt resistor on each connector...

any thoughts or any concerns here ?