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lighting a room with array of LED's on 9v

T

Tanoshimi

Junior Member
Well, that basically says it all. See, I have a dream of embedding an array of flashlight quality LED's running on 9 volt batteries (possibly rechargeable ones that can be recharged by a solar cell). In my research, I see that you can run 25-30 LED's on a single 9 volt (in parallel), but I have no idea for how long. I know the more you have, the faster it will drain the battery. I have not tested this to see how many I need, but am figuring on 1 for each square foot, so (small room) maybe 50-60 total, on two 9 volts (or 4 if that will get me longer battery life). Figuring on using a room in the dark for 2-4 hours per night (less in the summer), I'd like to get at least one month out of the batteries, so 60-120 hours.

Ask me anything you like about computer programming, in any language you like, and I can give you the answer, but when it comes to electronics and designing circuits and schematics, I'm not quite qualified to call myself a noob.

If someone can design a layout that would meet this description, and let me know what I can expect as far as battery life, I'd appreciate it. Feel free to improve upon my idea (change the LED, change the battery, etc). I certainly wouldn't mind having 4-6 rows of LED's, each row containing 10 or 20 LEDs on a rheostat, powered by a batteries recharged by a solar cell.

Thanks,
-Tanoshimi
 
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I soldered a board with an array of 144 LEDs in parallel. It drains a 9v in about 5 minutes, so I have it running with an AC adapter. If you want to light an entire room, battery power isn't the way to go.
 
Rakehellion: Super quick response! Thanks for getting back to me. I know it can drain them pretty fast, but we're looking at about 1/10th of the LED's you had connected. Sill if that's a regular progression, then that means 50 minutes total life. still not realistic.
 
Simple, Forward Current: 20 mA x the number of LEDs is the current draw. Compare that to the MAH rating of the battery and that will give you an approximate run time.
 
Rakehellion said:
I soldered a board with an array of 144 LEDs in parallel. It drains a 9v in about 5 minutes, so I have it running with an AC adapter. If you want to light an entire room, battery power isn't the way to go.
Click to expand...

Wow, if you don't mind me asking, what was 144 LED's for? And how bright did that get? The flashlight design I saw is based upon 8 leds, so I figured less than 100 to do a room. Again, it's a small room. And I'm interested in
a) having the light without affecting the electric bill.
b) having light even during a blackout.

What about using rechargeable batteries on solar cells? If I can get 6-8 hours from the battery, it *should* recharge the next day?
 
Gillbot said:
Simple, Forward Current: 20 mA x the number of LEDs is the current draw. Compare that to the MAH rating of the battery and that will give you an approximate run time.
Click to expand...

So 20 mA x 10 LED's = 200, and the battery is about 570. About 2, almost 3 hours. Not really good.
 
Rakehellion said:
6 AA batteries in series might be better. 9 volt batteries aren't really for high current use.
Click to expand...

Would that drain slower, or last longer than 9v? Or are we still looking at about 2-3 hours?

And if I did hook this up to the house's grid instead, would this cost me less than 4 light bulbs in the room?
 
Tanoshimi said:
Wow, if you don't mind me asking, what was 144 LED's for? And how bright did that get? The flashlight design I saw is based upon 8 leds, so I figured less than 100 to do a room. Again, it's a small room. And I'm interested in
a) having the light without affecting the electric bill.
b) having light even during a blackout.

What about using rechargeable batteries on solar cells? If I can get 6-8 hours from the battery, it *should* recharge the next day?
Click to expand...

It's blinding. Also, I didn't us a resistor, so the battery life could have been extended some. If you just want a flashlight, then a 9v might work.

But if you're using rechargeable batteries and there isn't a power outage, then you're wasting electricity by keeping the batteries charged.
 
Why do you want it on battery power?
Your line voltage (110v in U.S.) is much cheaper than any battery power.
 
But if you're using rechargeable batteries and there isn't a power outage, then you're wasting electricity by keeping the batteries charged.
Click to expand...

Sorry for the confusion. The plan is (was) to use the battery powered ALL the time, not just in an outage (but certainly then), so the batteries just need to get us through one night, and then get recharged the next day. Looking to take the lights off the house's electric bill, and I saw a web of led's and thought I could run that on batteries and embed it in the ceiling.
 
edro said:
Why do you want it on battery power?
Your line voltage (110v in U.S.) is much cheaper than any battery power.
Click to expand...

I thought it might be cheaper to replace a 9 volt battery every 2-6 months than it would be to run 4 bulbs on the 110. Guess that's not the case, and I can't get 2-6 months off the batteries anyway!
 
Spot on Rakehellion. If I could run it on 9v or AA batteries I had to replace, fine, but since all bedrooms have windows (it's a requirement) then I figured I could put some solar sensors out there and run rechargeable batteries.

I have driveway lights that work that way, but I'd be looking at a lot more that that. Basically all 10 of my driveway lights in my room, but with the solar sensors outside.
 
Why bother with a rechargeable 9V battery then? If you tear it apart, you'll discover that it's actually six 1.5V batteries. http://www.youtube.com/watch?v=C1KQgE9HJD8

I suggest that instead of a 9V battery, you purchase a 12V battery (car or perhaps marine) and recharge that using solar. Or, at the very least, use an array of rechargeable AA batteries instead. 9V rechargeable batteries simply do not last that long.
 
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Lighting a room? Are you talking about regular usable light, or emergency lighting?

If regular lighting, you're going to need a lot of those.
- Those have a 15° viewing angle, which will produce a small spot on the floor.
- One of those LEDs will give you less than 1 lumen.
- Colors of objects in the room will not be very good with an LED like that, and you're likely to get very cool light, something beyond 7000K. (Very blue.)
- Assuming the original LED, each one will use 0.066 watts. Assuming no losses, and assuming that a NiMH 9V performs perfectly, you'll get about 2.1 watt-hours out of the battery = 31.8 hours. For one LED. 50 LEDs = 3.3 watts. About 38 minutes. In reality, it will be less - as you increase the current load on a battery, its usable capacity declines.
More likely, you'd need to run the LEDs in strings of only 2 LEDs each, for a total of 25 strings in parallel, each one at 20mA, with a current limiting resistor. So that's going to be 25 * 0.020mA = 0.5A current draw, at 8.4 volts (nominal voltage of a 9V NiMH) = 4.2 watts.
- A very rough guess would be that you'd need more than a thousand of those LEDs to start to reasonably light up a small room.

I'm thinking that this particular method isn't going to be practical. 😉



My living room is 19x11ft. It is lit by:
- 256 watts of LEDs. (Luxeon CoB and Luxeon Rebel)
- 150 watts of CFL. (1x65W and 1x85W)





Tanoshimi said:
I thought it might be cheaper to replace a 9 volt battery every 2-6 months than it would be to run 4 bulbs on the 110. Guess that's not the case, and I can't get 2-6 months off the batteries anyway!
Click to expand...
Nope, not even close. 🙂 (Well...maybe incandescent. But you certainly won't get months of runtime out of a 9V battery, even if it was only running a single LED at perfect efficiency.)

NiMH: First, you buy the battery, and then the charger.
Then the charger takes 120VAC, converts it to what the battery needs for charging, as well as something to run the regulator circuitry, and charges the battery. There are some losses here and there as well. Feel a charging battery. The warm temperature is just wasted energy. Then from the battery, you need to regulate the power, either with constant current drivers or with resistors. A switching circuit current driver is more efficient, but more complex. A linear driver or a resistor simply converts the excess power to heat. Any method's purpose is to ensure that the LEDs do not draw too much current, which can lead to overheating of the die, and thermal runaway.


Powering off of 120VAC: This will go into a switcher circuit that converts and regulates the output, and then provides constant current to the LED source. Done.
There are fewer stages here for efficiency losses.
 
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Gillbot said:
Simple, Forward Current: 20 mA x the number of LEDs is the current draw. Compare that to the MAH rating of the battery and that will give you an approximate run time.
Click to expand...

That would be true, except that, to achieve greater efficiency, in most products using ultra-bright LED's in serious lighting applications, they use a high freqency step up switching circuit to generate very high pulses for very short periods of time. The voltage is high enough that it would fry the LED's if it were sustained.

Because the circuit steps up the voltage, they don't need the battery to maintain a voltage higher than the forward voltage of the LED or string of LED's. That gives them much longer battery life because they can generate the required voltage from a battery that is almost discharged.

This is usually done with an LED controller IC and possibly an external switching FET. I just got to this thread, and I haven't had time to do a deep search, but here's a description of one such circuit that includes this schematic.

p247-fig1.jpg

Rather than laying out a circuit board, you may be able to find one or more models where the manufacturer can has an evaluation board ready to apply power and LED's. Searching Google for battery powered switching led driver will give you some good direction.

Hope that helps. 🙂
 
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What is your budget?
That would be the determining factor.
9V does not have much capacity and is certainly not a contender for medium and high drain applications.

A handful of 18650 lithium-ion cells from a laptop battery connected to a PWM driver will drive a very efficient array of Cree XML emitters.

On a tight budget you can cannibalize a disposable camera for its photoflash components and build a joule thief! 😎
 
Tanoshimi said:
Would that drain slower, or last longer than 9v? Or are we still looking at about 2-3 hours?

And if I did hook this up to the house's grid instead, would this cost me less than 4 light bulbs in the room?
Click to expand...
It all depends on the capacity of the batteries.
Jeff7 said:
Lighting a room? Are you talking about regular usable light, or emergency lighting?

If regular lighting, you're going to need a lot of those.
- Those have a 15° viewing angle, which will produce a small spot on the floor.
- One of those LEDs will give you less than 1 lumen.
- Colors of objects in the room will not be very good with an LED like that, and you're likely to get very cool light, something beyond 7000K. (Very blue.)
- Assuming the original LED, each one will use 0.066 watts. Assuming no losses, and assuming that a NiMH 9V performs perfectly, you'll get about 2.1 watt-hours out of the battery = 31.8 hours. For one LED. 50 LEDs = 3.3 watts. About 38 minutes. In reality, it will be less - as you increase the current load on a battery, its usable capacity declines.
More likely, you'd need to run the LEDs in strings of only 2 LEDs each, for a total of 25 strings in parallel, each one at 20mA, with a current limiting resistor. So that's going to be 25 * 0.020mA = 0.5A current draw, at 8.4 volts (nominal voltage of a 9V NiMH) = 4.2 watts.
- A very rough guess would be that you'd need more than a thousand of those LEDs to start to reasonably light up a small room.

I'm thinking that this particular method isn't going to be practical. 😉



My living room is 19x11ft. It is lit by:
- 256 watts of LEDs. (Luxeon CoB and Luxeon Rebel)
- 150 watts of CFL. (1x65W and 1x85W)





Nope, not even close. (Well...maybe incandescent. But you certainly won't get months of runtime out of a 9V battery, even if it was only running a single LED at perfect efficiency.)

NiMH: First, you buy the battery, and then the charger.
Then the charger takes 120VAC, converts it to what the battery needs for charging, as well as something to run the regulator circuitry, and charges the battery. There are some losses here and there as well. Feel a charging battery. The warm temperature is just wasted energy. Then from the battery, you need to regulate the power, either with constant current drivers or with resistors. A switching circuit current driver is more efficient, but more complex. A linear driver or a resistor simply converts the excess power to heat. Any method's purpose is to ensure that the LEDs do not draw too much current, which can lead to overheating of the die, and thermal runaway.


Powering off of 120VAC: This will go into a switcher circuit that converts and regulates the output, and then provides constant current to the LED source. Done.
There are fewer stages here for efficiency losses.
Click to expand...
This ^
Harvey said:
That would be true, except that, to achieve greater efficiency, in most products using ultra-bright LED's in serious lighting applications, they use a high freqency step up switching circuit to generate very high pulses for very short periods of time. The voltage is high enough that it would fry the LED's if it were sustained.

Because the circuit steps up the voltage, they don't need the battery to maintain a voltage higher than the forward voltage of the LED or string of LED's. That gives them much longer battery life because they can generate the required voltage from a battery that is almost discharged.

This is usually done with an LED controller IC and possibly an external switching FET. I just got to this thread, and I haven't had time to do a deep search, but here's a description of one such circuit that includes this schematic.

p247-fig1.jpg

Rather than laying out a circuit board, you may be able to find one or more models where the manufacturer can has an evaluation board ready to apply power and LED's. Searching Google for battery powered switching led driver will give you some good direction.

Hope that helps. 🙂
Click to expand...

Now you are over thinking it. I have two strips of LEDs for lighting the stairs in a power outage. They are simple LED strips that have a built in resistor coupled to a battery pack, relay and trickle charger. Power goes out, relay switches and the battery takes over lighting the stairs. There is very minimal light and I'd bet there are about 15-20 LEDs on each strip. Basically just barely enough to see where you are going but nowhere near enough to light a room.
 
Gillbot said:
It all depends on the capacity of the batteries.

This ^


Now you are over thinking it. I have two strips of LEDs for lighting the stairs in a power outage. They are simple LED strips that have a built in resistor coupled to a battery pack, relay and trickle charger. Power goes out, relay switches and the battery takes over lighting the stairs. There is very minimal light and I'd bet there are about 15-20 LEDs on each strip. Basically just barely enough to see where you are going but nowhere near enough to light a room.
Click to expand...

That's what I get for being a diode head and reading his OP as wanting to light an entire room and run it on rechargable solar cells. I admire his ambition, but he's in for some serious energy scavenging, harvesting and efficiency issues to achieve his goal.
 
Harvey said:
That's what I get for being a diode head and reading his OP as wanting to light an entire room and run it on rechargable solar cells. I admire his ambition, but he's in for some serious energy scavenging, harvesting and efficiency issues to achieve his goal.
Click to expand...

Yeah, it's a nice idea, but there are too many unneeded constraints on his system. The solar panels he would need would be fairly big and would not be very efficient unless they were mounted outside facing south at the right angle. Personally, I'd just buy a reasonably priced LED fixture, put it in a lamp, and put the lamp on a cheap UPS if I really wanted a battery backup. I'm not sure how expensive he realizes battery/solar power is compared to straight house power. It varies of course, but we're still looking at somewhere between 10 and 25 cents a kW/hour. At 25 cents a kW/hour, that 11 watt Philips LED bulb costs about .275 cents an hour to run, so a penny a night at most or $3.50 a year. The battery backup would be the biggest expense using house electricity. This UPS would probably power that Phillips LED for a couple hours or more even: http://www.amazon.com/CyberPower-CP3...525017&sr=8-11
 
Harvey said:
That's what I get for being a diode head and reading his OP as wanting to light an entire room and run it on rechargable solar cells. I admire his ambition, but he's in for some serious energy scavenging, harvesting and efficiency issues to achieve his goal.
Click to expand...
And I've been there too. 🙂
It made me think of my middle school or high school days: Ambitious or interesting projects, but not even enough money to build a proper prototype. I'd just try to dive right in and hope that Version 1 would work.

All the fun toys were too expensive. Or didn't exist yet. (Blue LEDs weren't even invented until 1994. I finally got one in high school. Then a friend promptly turned it into an orange LED, briefly, by hooking it directly to a 9V battery. :'()
In those days, a simple analog multimeter was a rather significant purchase for me - and I didn't have anyone around to explain to me why I couldn't use it to determine the amp output of an outlet or a lead acid battery, or why doing those things would result in sparks and a blown-up fuse.



Now.....well, put it this way: I have >200 watts of LEDs in my livingroom. 😎
 
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