Modifying an LED lightpanel for low power - is this possible/feasible?

First of all, I confess that I am new to all this stuff so forgive my ignorance. My last physics/electronics class was almost 15 years ago :-
D
I want to modify an LED lightpanel to use less power than it already does so that it would last longer. The LED lightpanel is being used to backlight a billboard with power supplied by 12V-20Ah battery. The lightpanel has 360 pure white LEDs (180 left - 180 right) inserted along both the left and right edges of a 1.5m x 1.0m light guide plate and uses about 30W, which is too high.
An engineer friend suggested that I could reduce this by dividing the LEDs into "multiplexed" groups and cycling through them (so that only one group is on at a time) at high frequency i.e. 75Hz - 100Hz. According to him, at this frequency (the "flicker fusion rate") the human eye can be fooled and the panel would only need a small fraction of the power to effectively light the billboard.
Is this possible? And if possible, how can it be done and what would I need to do it? How would it affect the LEDs?
Thanks!
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
In article

Forget about it! Unless there is something you are not telling us that causes loss that you can eliminate you are subject to conservation of energy. If you can beat that, you can build a perpetual motion machine, but don't bet your house on that.
Bill
--
An old man would be better off never having been born.

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Hello Bill,
Thanks for replying. Novice though, so I may need some more info than that. For example, isn't this something that could operate on the same principle as a typical LED dimmer i.e. with Pulse Width Modulation?
Thanks!
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Sure, you could do that and it will use less power, but it will be dimmer too.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
In article

Sure! If you will be happy with less light you can do with less power. that is why it is called a dimmer and not a brightener.
Bill
--
An old man would be better off never having been born.

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Excellent. As I said, I'm not very conversant with this but it *may* be a reasonable tradeoff - I do not need it to light up a room so it need not be very bright.
Thanks.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Babangida wrote:

[snip]
Maybe a bit higher. If this sign is going to be visible by moving observers, some flicker might be noticed. If its a computer monitor or TV set, this might be OK.

But it will be dimmer. 25% duty cycle (4 groups alternately lit) will look just as bright as running all the LEDs at 25% of normal current. There is no free lunch.
If you can come up with some grouping that satisfies a fixed brightness requirement, that will work. But what do you do if you want to vary the brightness? Rewire the groups?
Use pulse width modulation (PWM). Vary the duty cycle from 0 to 100% and set it to the desired brightness.

Driving 360 LEDs from a 12 volt supply (directly) means breaking them down into 90 series strings of 4 per string. One way or the other, the total draw will be 2.5 A which can be handled by a MOSFET or IGBT and controlled from a microcontroller or even a 555 variable duty cycle oscillator.
Take a look at the existing LED connections and see how they are connected now. It would be best to adapt your design to this because rewiring 360 LEDs is not a trivial task.
--
Paul Hovnanian mailto: snipped-for-privacy@Hovnanian.com
------------------------------------------------------------------
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Most of the higher power LED stuff I've seen made to run off 12V uses a boost converter. The losses in the converter end up being a lot less than the losses in all the series resistors that would otherwise be required.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Why a boost converter? Starting at 12V, a buck regulator is much simpler.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
snipped-for-privacy@att.bizzzzzzzzzzzz wrote:

Because with a boost converter you can run a long string of LEDs in series with a single resistor. A buck converter is great for 1-3 LEDs, but each individual string requires a separate current limiting resistor.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
James Sweet wrote:

Charge pump (multiplier)?
--
Paul Hovnanian mailto: snipped-for-privacy@Hovnanian.com
------------------------------------------------------------------
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Paul Hovnanian P.E. wrote:

Those are used occasionally where small size is the highest priority, backlights for very small LCD screens, LED flashlights, etc, but the inductor type boost converter is more common where space allows the slightly larger components.
Dallas/Maxim has a good selection of LED driver ICs along with many application notes and documentation to help one choose.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

And with correctly regulated converter is it possible to get rid of that traditional series resistor. Use a switch more power supply in constant current mode and you can get rid of that traditional current limiting resistor and losses caused by it (constant current power supply does the current limiting).
--
Tomi Engdahl (http://www.iki.fi/then /)
Take a look at my electronics web links and documents at
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
wrote:

Sure, but his point is that you still would want a series string to minimizing the number of switchers. This likely means a boost regulator.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
wrote:
|> An engineer friend suggested that I could reduce this by dividing the |> LEDs into "multiplexed" groups and cycling through them (so that only |> one group is on at a time) at high frequency i.e. 75Hz - 100Hz. | | Maybe a bit higher. If this sign is going to be visible by moving | observers, some flicker might be noticed. If its a computer monitor or | TV set, this might be OK.
Maybe a lot higher. I've seen flicker to 200 Hz in LEDs.
--
-----------------------------------------------------------------------------
| Phil Howard KA9WGN | http://linuxhomepage.com/ http://ham.org/ |
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Polytechforum.com is a website by engineers for engineers. It is not affiliated with any of manufacturers or vendors discussed here. All logos and trade names are the property of their respective owners.