Variable voltage for underwater lighting

[rmathews]

We are building an underwater lighting system that runs off batteries for a film project.

The system operates between 36 and 60V, optimally at 48V, we have connected 4 12V car batteries to provide the power but want to be able to vary the light output by varying the voltage. Is there an easy way to do this? at full power the lighting system draws 10A.

Any ideas would be much appreciated, we're on a very tight schedule with this project as we go underwater next week!!

Cheers

Rich

 

[alec_t]

Are the lights of the normal filament type or some other type?
Does the variation have to be continuous (smooth) or could it be stepped?

 

[rmathews]

The lights are LED solid state tubes (designed to replace standard fluorescent tubes), ideally smooth but stepped would be fine if there is enough variation.

 

[Reloadron]

You may want to think about using a PWM (Pulse Width Modulation) system to control the intensity of the light tubes if they are LED type. It would involve using a simple PWM circuit to drive what is called a MOSFET so you actually pulse the LED tubes. The more data you can provide on the tubes the more help you will get.

Also welcome to the forums.

Ron

 

[rmathews]

thanks, just did a few more tests and discovered that we can vary the resistance to vary the output (not sure why it took this long to discover but it has been a number of very late nights to get this sorted) so i think the best option is a potentiometer but it needs to be rated for 10A, had a quick look and I've not discovered anything that suits yet...

not sure what info you want about the tubes. they have had the transformers removed so they run on DC and consist of two strips of high power LEDs (300 ish i cannot remember off the top of my head). I will find the original documentation for the lights if i can. I'll have a look at PWM but the lights are being used for film so there can be no flickering like normal fluro tubes as this will show up. The system looks a bit like this https://vimeo.com/28317446 but has been modified a bit since and consists of 8 lights on a bank

 

[Reloadron]

If you can get the actual data sheet for the lights that would be great. The problem with using a pot to vary the voltage starts with as you mentioned a pot capable of 10 amps.

As to flickering. A conventional fluorescent lamp runs at a frequency of 50 or 60 Hz. The lamp actually flickers 50 to 60 times per second. PWM uses much, much higher frequencies. While I am not a videographer I doubt that with a high PWM frequency that there would be any flicker. The big merit is you are not looking for a monster pot. While high power pots do exist, they can be expensive. The need for the data sheet is to determine the LED tube voltage and the actual LED current required. I wouldn't rule a pot out, it just may not be the best venue.

Ron

 

[KeepItSimpleStupid]

This is worth while looking at to modify: https://www.jameco.com/webapp/wcs/stores/servlet/Product_10001_10001_120539_-1

You should get lots of hits using "PWM motor control"

Next wwek doesn't leave much time.

 

[Boncuk]

When trying to calculate the power of the LEDs I used the nominal voltage of 48V and 10A of LED forward current.

That means the LEDs have a power of P=V*If, in numbers P(W)=V(48V)*If(10A)=480W.

If you use a pot "killing" excessive voltage it will have to dissipate a lot of power, meaning you are working with a tremendous amount of wasted energy. Additionally that pot has to be huge and certainly also has a lot of weight.

A smart solution would be using PWM which almost does not waste energy (except for the power dissipation within the power MosFet-transistor. The power dissipation can be reduced by selecting a transistor with a very low RDS(ON) value, e.g. 0.01Ohm which means the transistor will dissipate 1W of power.

There are tiny power control circuits used in R/C model flying, boating and racing cars capable of controlling up to 125A.

I recommend to use one of those. All you have to do is providing the voltage supply and a PWM signal which is the easiest part.

Boncuk

 

[KeepItSimpleStupid]

This: https://www.electro-tech-online.com...r20Speed20Control20Spec20Sheet20-20200820.pdf

pretty much meets your specs, but it still needs some effort to make it work. Heatsinking, waterproof/water resistant? Who controls the brightness? The guy in the water or someone topside? Fusing etc.

 

[OlPhart]

If people are immersed/involved, I hope you've Real confidence in your wiring... 50+VDC with any good ion carrying fluid means lethal power to someone closely connected to ground (50Vs' reference).

I'd check floating voltages (no pun), just to be sure nothing bad is happening. <<<)))

P.S. with 4 batteries, you won't have a problem. I'm cautioning about line powered supplies.

As limited time maybe check: **broken link removed**.
You'd have to split your lighting into 2 circuits, but also have more control.
I Googled "LED dimmer", took all of 30 sec.