Power 160 LED Video Light Off 12V

[davidjamesi]

Hey there, new to the forum! Have enjoyed lurking and learning stuff, however i have a question for everyone

I have 6 160 LED video lights for videography. However each takes 6 AA batteries. The lights a supper bright...but not for long!
I would like to eliminate the use of SO many AA batteries by figuring a way to power it off a 12v battery that would last MUCH longer and could power all 6 at once.

From my understanding you would need to run a resistor for every led? of course from the photo you can see the 160 leds are run in parallel...
The photos show the unit stripped down, it includes 2 circuit boards. 1 has the 6 leds and a button on the 2nd circuit board that show the amount of power left in the AA batteries. The other circuit board has a few capacitors (16v 220F) and (16v 470F) and another one that reads "C 600" along with a variable control switch (it broke thats why i ripped this one apart to see if powering off a battery was possible, but keep in mind the other 5 units are in tact and have the variable power piece in tact).

Like stated above, my plan would be to have a plug come out of the back of the unit that can be plugged into a battery. If i could keep the variable power that would awesome, i dont necessarily need the battery capacity checker (6 leds that show amount of power left) but i imagine sense its all tied together it would be find to keep together.

I know i am probable leaving a lot of info out but really would love some insight on how this might be possible!

thanks in advance.

 

[betwixt]

Technically you SHOULD run a resistor to each LED but very often for cheapness they are left out. It means it's possible to get an imbalance between LEDs and some may be brighter than others, especially at low brightness.
Some units are designed with the limitation of the battery in mind - the manufacturer relies on the batterys inability to provide much power to prevent the LEDs burning out!

However, it should be possible to adapt the present 9V requirement to 12V quite easily. It looks like the control (or whats left of it!) sets the duty cycle of a pulse width controller. Thats an efficient way of controlling the apparent brightness without wasting too much power as heat. Dropping 3V is actually a challenge when the current demand is so variable but the easiest way is probably just to wire four silicon 1A diodes (1N4001 or similar) in series with one of the external battery wires then connect to the orginal AA battery terminals. Each diode will drop about 0.65V from the 12V so across the original battery terminals you will get about 9.4V which is close enough to what brand new AA cells would produce.

Brian.

 

[davidjamesi]

What a great idea Brian! Appreciate the quick and easy to follow idea
just picked up the diodes and will give it a go tonight!
Ill report back.
Thanks

 

[davidjamesi]

So just to clarify, this is what i have done so far. If the diagram makes sense, is what im doing correct? Also the battery i have in my house right now is 12v 18 amps an hr. I imagine that is way to much for what i am trying to do? It would probable just melt the solder or heat the wire up way to much. What type of 12v battery would work best, and would have a large capacity/is rechargeable?

 

[betwixt]

You have wired it correctly - well done!

The battery capacity is a measure of how much energy it can store, not how much it produces at any time. It means you can draw 1 Amp from it for 18 hours or 2 Amps for 9 hours and so on. It's the number of Amps multiplied by the number of hours it can sustain them subject to some limits on it's actual maximum current before damage. 18AH will work fine, the actual battery type is up to you. For professional video shoots we usually carry 12V 15AH sealed lead acid cells because they are a good compromise between weight, life expectancy and cost. You can use NiMH or NiCd but they work out far more expensive when you need higher capacity.

I'm not sure how much current your LEDs draw, I specified 1 Amp diodes because if it was designed to run on AA cells it can't need too much but you might find they run hot. This is normal, they each dissipate about 0.7W per Amp passing through them. The heat should not be enough to damage them but don't let them contact any surface that might melt or confine them in a small space. If the heat is too much, your only option is to remove it with a finned heat sink or to use a different kind of voltage dropper but see how it goes for now, the other options are far more complicated and expensive.

Brian.

 

[davidjamesi]

Ok, so i have done a few tests, with the 4 diodes attached Its reading about 8.99v give or take a few...The battery is at about 12.64v, however when i attach it all and turn the LED on it will run perfectly for about 9 seconds and then the middle diode will get so hot it melts the solder and falls off! I have tried with a few more diodes attached and of course it lowers the power and led brightness but it didnt seem to melt after a minute or so, still got very hot to touch... Any ideas as to what to do about that? And if i went the heat sink route, would i but 4 small finned heat sinks? and where would i put them, on the diode itself? Also are there bigger diodes that would work better for the amount of current?

Would these work? https://www.amazon.com/Cosmos-Alumi...=UTF8&qid=1364280015&sr=8-3&keywords=heatsink

In the photo below you can see the diode that detached itself, i tried running it to the AA terminals, same story.

Photo (I couldnt upload on this site for some reason) : **broken link removed**

 

[betwixt]

The current must be quite high which accounts for the short battery life.

There are two solutions:
1. remove the heat from the diodes, it would be much easier to use tab mounted diodes (secured by screws) and one heat sink.
2. use a switch mode regulator. This method is considerably more complicated but produces less heat and regulates the voltage rather than just dropping it.

Don't forget that heat is wasted power although the amount needed to melt that solder joint isn't all that much anyway.

For tab mounted diodes you could try something like the GPA1601 which is a 16A diode which has a metal tab and screw hole to mount it to a heat sink. I'm not sure where you are but in the UK they cost about 0.28 (about $0.35 US).
There is no way to avoid the amount of heat being generated when you use diodes like this but ones designed to have heat conducted away from them will run much cooler.

If you want to use a switch mode regulator I suggest using an LM2576 which is fairly cheap but needs some support components. By virtue of the way it works, it should run very cool and probably wouldn't need a heat sink at all. Let me know if you think you can manage a circuit board and I'll give you more information.

Brian.

 

[davidjamesi]

Thanks so much for your time an patience! Seriously, what a cool forum that allows newbs to learn what would take most months in school.

Im going to go the GPA1601 route first and see how that works, i had a few laying around from a couple amps i took apart, however they were mounted to bigger heatsinks, any idea on what size would work well for just one?
Also whats the possibility of making something like the Switch mode regulator, and running 5-6 of these leds off of it? Would each led need their own or would making one be sustainable to put out 9v across the board? If so that would be a great route, mainly because i could just make a little case for that by the battery, and run something like quick disconnect cables to each led (https://www.amazon.com/Battery-Tender-081-0148-25-Disconnect-Extension/dp/B000FW2MWW)
Let me know if that makes sense or would even be doable!

 

[betwixt]

I have a simple philosophy, I was a high school drop-out and completely self taught in electronics. What I learned for free, I pass on for free, and if it helps anyone, all the better. Mind you, I left school a long time ago and I've held some top jobs since then!

Each GP1601 will drop about 0.7V, just like the smaller diodes so you need to use four again. They also produce exactly the same amount of heat but being in a larger package and with that metal tab they can safely move it elsewhere to keep themselves cool. I would look for a heat sink just a little bigger than four diodes mounted side by side. Be careful because pin 1 is internally connected to the tab so you need to electrically isolate at least three of them so they aren't shorted together. You can buy T0-220 isolating washers to mount them on, they conduct heat but not electricity and they are usually provided with a rimmed plastic washer to fit the hole in the tab so the screw itself doesn't short it to the heat sink. You have probably seen these already if you have dismantled amplifiers.

I would be cautious about running more than one of the LED panels per bank of diodes or per switch mode regulator, it's difficult to guess how much current the LEDs actually draw when in use but two or more probably exceed the limits of a single regulator.

If you Google for LM2576 you will find the data sheet. You need the 'variable' schematic and to set the output voltage to 9V. It isn't difficult to build but you must use the correct diode and inductor as specified in the data sheet. SMPS have special requirements when it comes to diode speed and ordinary diodes like the ones you illustrated will not work. It will still need a heat sink but it will produce signficantly less heat than the diodes in series design. There is no reason why you can't run one battery to several regulators with each one feeding one LED panel.

Brian.