LED Lamp Build

Thread Starter

Projectus Plentyus

Joined Jun 27, 2021
11
Hello everyone, I am trying to do some research for a maker project. I want to take a cheap old lantern and turn it in to a battery powered LED lantern. The overall idea is to use a number of 5mm leds in a radial pattern inside the lantern, which will throw light in all directions. Imagine four leds in four vertical rows arranged 90 degrees apart. I want it to be battery powered and also have a dimmer switch instead of a regular on/off. Any ideas on how to set this kind of thing up? They are pretty small lamps so more than likely one would have a AAA pack and the other a AA. Thanks in advance.
 

SamR

Joined Mar 19, 2019
3,498
Welcome to AAC!

What is the current draw of your LEDs, how many total LEDs, do you know what the mAh rating of your batteries is, and do you understand that LEDs are typically dimmed used PWM and not a dimmer? LEDs are current devices, not voltage... Also, do you have a preliminary schematic that we can work from?
 

Thread Starter

Projectus Plentyus

Joined Jun 27, 2021
11
First off let me apologize for the crude drawing that will accompany this post. The lights I have decided to use are warm white leds which have a forward voltage of 3-3.2v and a draw of 20mA. Total leds required would be 12-16 (2 different sized lanterns, one small (12) one medium (16)). Power source would be 4x duracell batteries for a total of 6v and 11,400mAh. The intent of this project is to build a battery powered lantern from an old kerosene one. The objective is to have one that can put out various levels of light by way of some sort of dimmer with a knob. The knob would need to be mounted on the former fuel cap for the best appearance. I have also included a picture of the end item. I still haven’t figured out how I am going to mount the leds. I was thinking of using a flexible thin sheet of plastic that could be rolled in to a cylinder and glued together, which all the wiring on the inside going down through the tank area to the switch and battery.
 

Attachments

LowQCab

Joined Nov 6, 2012
1,110
With this setup, there will not be a Knob, but a miniature, 3-position, Toggle-Switch.
A proper Pot controlled Dimmer would require a small Circuit-Board,
but You probably have room for it in the Tank.
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LED Lantern  FLAT  .png
 
Last edited:

bertus

Joined Apr 5, 2008
21,549
Hello,

4 leds of 3 - 3.2 volts in series will not work on 6 Volts.
Use 3 batteries and one led with current liminting resistor on a branch.

Bertus
 

Thread Starter

Projectus Plentyus

Joined Jun 27, 2021
11
Welcome to AAC!

What is the current draw of your LEDs, how many total LEDs, do you know what the mAh rating of your batteries is, and do you understand that LEDs are typically dimmed used PWM and not a dimmer? LEDs are current devices, not voltage... Also, do you have a preliminary schematic that we can work from?
Welcome to AAC!

What is the current draw of your LEDs, how many total LEDs, do you know what the mAh rating of your batteries is, and do you understand that LEDs are typically dimmed used PWM and not a dimmer? LEDs are current devices, not voltage... Also, do you have a preliminary schematic that we can work from?
Please see the information below as a reply to your post. This was my first actual interaction with a forum message board and I did not see the reply button.
 

Tonyr1084

Joined Sep 24, 2015
6,269
Forgive if this is something you already know; but why leave things to chance. IF you put four AAA batteries (or any batteries) in parallel you get the same voltage and four times the amp hour rating (as shown in the attached). IF you put them in series you get four times the voltage at the same amp hour rating.
1624797984954.png
As someone already stated; LED's with a Vf (forward voltage) of 3Vf in series the resulting forward voltage drop will be 9Vf. A 6V source will not have sufficient voltage to light these LED's. If you use a 6V setup you can only run each and every LED in parallel. That's 12 to 16 LED's and 12 to 16 current limiting resistors. In this case, a desired amperage of 20mA would require (at 6V) 150Ω resistors on each and every LED. You COULD go the route of using a single resistor to power all the parallel LED's but I don't know if that would work. I've only successfully put about 6 LED's in parallel all through a single resistor. I have the video to prove it if anyone challenges me.

To put three LED's in series you'd need more than a 9V source. At this point it would be recommended you use 18650 Lithium Ion batteries; four of them. Each cell is about 3.8 volts. When fully charged they're 4.2 volts. Battery management is crucial as they MUST be charged in a proper profile. You can't just throw a voltage at them and let them go. They can go BOOM! Also, a good BMS (Battery Management System) will also cut the batteries off before they drop their voltage below (I think it is) 2.8 volts. If they go below that voltage they can suffer damage and become useless, and potentially dangerous as well. So good BMS is crucial.

Do you know how to calculate the resistance needed for LED's at a given voltage supply? If not - we can help.
 

Thread Starter

Projectus Plentyus

Joined Jun 27, 2021
11
Forgive if this is something you already know; but why leave things to chance. IF you put four AAA batteries (or any batteries) in parallel you get the same voltage and four times the amp hour rating (as shown in the attached). IF you put them in series you get four times the voltage at the same amp hour rating.
View attachment 242265
As someone already stated; LED's with a Vf (forward voltage) of 3Vf in series the resulting forward voltage drop will be 9Vf. A 6V source will not have sufficient voltage to light these LED's. If you use a 6V setup you can only run each and every LED in parallel. That's 12 to 16 LED's and 12 to 16 current limiting resistors. In this case, a desired amperage of 20mA would require (at 6V) 150Ω resistors on each and every LED. You COULD go the route of using a single resistor to power all the parallel LED's but I don't know if that would work. I've only successfully put about 6 LED's in parallel all through a single resistor. I have the video to prove it if anyone challenges me.

To put three LED's in series you'd need more than a 9V source. At this point it would be recommended you use 18650 Lithium Ion batteries; four of them. Each cell is about 3.8 volts. When fully charged they're 4.2 volts. Battery management is crucial as they MUST be charged in a proper profile. You can't just throw a voltage at them and let them go. They can go BOOM! Also, a good BMS (Battery Management System) will also cut the batteries off before they drop their voltage below (I think it is) 2.8 volts. If they go below that voltage they can suffer damage and become useless, and potentially dangerous as well. So good BMS is crucial.

Do you know how to calculate the resistance needed for LED's at a given voltage supply? If not - we can help.
I have some electrical troubleshooting experience but it’s mostly limited to which component is not working. I haven’t really gotten the chance to work with diodes, leds and other such components. Mine are relays and switches normally. Knowing what the intent of the project is, are there any single leds that could be used with a battery pack that would produce a 2200-3000K light with enough lumens to light a small room?
 

Audioguru again

Joined Oct 21, 2019
3,542
My computer room is lit with 72 LEDs all pointing downwards. 30 LEDs would be dimmer but probably would be OK.
Of course they are power by mains electricity, not by a battery.
 

BobTPH

Joined Jun 5, 2013
3,679
You are not going to light room with a few AAA cells for very long. Lets do a calculation.

A 60W equivalent LED bulb would dimly light a small room. It uses about 8W of power.

An AAA battery is 1.5V at 1Ah or 1.5 Wh. So 4 give you about 6WH. If you could use the 4 batteries with 100% efficiency, which you cannot, and the batteries could really produce 1.5Wh at that power level, you would get 45 minutes out of them.

Bur battery capacity ratings are calculated at a current draw that would last 20 hours, and the capacity declines when you draw more current.

So my guess, is you are looking at 15 minutes battery life.

Bob
 

ElectricSpidey

Joined Dec 2, 2017
1,809
Personally I would look into a flicker circuit.

And, you will get much more efficiency out of using fewer LEDs and not losing power across all those resistors. (wait you say "what resistors")

Yes resistors...you will need resistors.
 

Thread Starter

Projectus Plentyus

Joined Jun 27, 2021
11
Personally I would look into a flicker circuit.

And, you will get much more efficiency out of using fewer LEDs and not losing power across all those resistors. (wait you say "what resistors")

Yes resistors...you will need resistors.
Can you explain a “flicker circuit” more please? I know resistors will be needed and I can figure out what ohms and wattage? that they need to be.
 

LowQCab

Joined Nov 6, 2012
1,110
2- LEDs, in series, both with a ~3.2V Forward-Voltage-Drop, which adds up to ~6.4V-FVD,
will operate just fine on a ~6-Volt Battery Pack, WITH NO CURRENT LIMITING RESISTORS.

They will have slightly less Light Output, compared to being run on the full ~6.4-Volts / ~20ma.,
but the bonus of not wasting so much power,
and not increasing complexity with Resistors or Current-Limiting-Circuits,
is very attractive.
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