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Dimming 7 series connected lights independently

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whiterabbit

New Member
I am not knowledgable in electronics, please bear with me. I have been trying to explain what I want to manufacturers of solid state controls but I dont know the lingo.

What I first wanted to do is connect 7 12V 50W lamps in series to std 120V power source then use a dimmer to over or under volt. 0-16V is what I want to deliver to each lamp and alot of std controls exist for this.

I would prefer, however, to (lamps still in series) be able to over or under volt each lamp individually.

Is this possible?

If so can you elaborate a little.


Thanks very much
 

Chippie

Member
"I would prefer, however, to (lamps still in series) be able to over or under volt each lamp individually"

Cant be done. Only way to dim each lamp independantly is to have each one on its own...


7 * 12 lamps in series = 84 volts worth...fed from a 120v supply......hmm wont last long....Feeding each lamp with 16 volts is not good either. Thats a 133% increase in voltage, overruning them they wont last long..


You best have think about what you are doing, perhaps there is a better way of achieving your goal
 

whiterabbit

New Member
Thanks, actually there is a reason for what I am doing.

At 16V the lamps have a 200 hour life span and a color temp of 6000k. For production purposes that is not bad and being able to control color temp is very crucial to our application. lamps are only $6 a pop compared to $30 for average photo lamp and are not run constantly. Anyway I supply the lamps so better for me

Why in series. Because I need to put 14 lamps (2 strings of 7) on one std 15 amp circuit. This is a portable on location kit and assumes worst case scenario...no power.

The max voltage to ever reach the lamps will be limited to 16V and most of the time this would be run between 12V (2000 hour life span 4700k) and 15V (300 hour life span 5500K at which point daylight film is balanced)

It, seems like should be a way to create 7 series points that step down the voltage by 16 or so volts each and within each point have another circuit that can split the 16V between the lamp and a resistor or something.

that is the general idea. What do you think?
 

Gene

New Member
Just thinking..... I have heard of 500 watt photofloods but do your 50 watt, 12 volt bulbs put out enough light to be useful?
 

mechie

New Member
Series regulators

I have two theories on how to achieve this...

If each lamp had a voltage regulator in parallel with it then it could be dimmed by reducing the regulator's setting. A complication here is that there must be a current limiter in series with the lot whose main purpose is to 'waste' the excess voltage, this makes the whole rig run at a constant (maximum) current even when everything is at minimum brightness. The lamps will never really see zero volts as some voltage drop will be required across the regulator circuit to power it.

If each bulb is connected to a three-wire regulator such that as the regulator is 'dimmed' the bulb effectively taps off lower voltages from its regulator (like a rheostat, common, wiper-to-bulb, track-top, sort of thing). The circuit will then (hopefully) not require the current limiter circuit mentioned in idea 1. It could be possible to go right down to zero volts with this but I suspect the circuit will end up more complicated in this configuration.

NOTE -- Both options will generate a fair amount of heat as each of the seven circuits will dissipate some 50W (a total of 350W).
 

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stevez

Active Member
The power consumed by each bulb is dependent on the resistance of the filament. If there is a significant difference from bulb to bulb then powering them in series may result in more color temp variation than you want. The same is true if you put them in parallel across a common supply. I know little about the variability of bulbs but would want to understand that if color temp were critical and I had no way of "tuning" the voltage to a bulb.
 

bogdanfirst

New Member
ok, related to figure thaory_2 i think that i might have an idea. if you can put a variable resistor in series with thel bulb and one in paralel with the bulb and the series resistor, and mecanicly connect the variable resistors so that when the series increases and so the lamp looses intensity and the paralel will descrease so that the whole circuit will have a constant resistance and will not affect the other lamps.
here is a figure of my idea, but the resistors can be replaced by a simple transistor circuit wich will make it better.
 

bogdanfirst

New Member
o, thanks for the tip....
but how do i attach files in General electronics Chat?
it says that i can't....but some others can...
 

hantto

Member
I think that only "higher rank" moderators can attach files in General Electronics. You should propably ask electro tech admin to get the right to attach files in here.
 

whiterabbit

New Member
I have been out in the jungle filming just got back.

It sounds like it would be possible to do this then. I will look into these replys further and determine if this is going to be a true benefit.

As for the 50W putting out enough light. 1 lamp, No, but 14, yes and with precise control. Also at higher voltages its more like 90W. The 500W lamps have to be conditioned. By the time your done you can cut as much as 90% of the light, its a frustrating way to work, time for things to change.

Thanks,

jp
 
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