Rechargeable Battery Pack solution for a single LED

Thread Starter

PFAB

Joined Mar 27, 2024
10
Hi All,
I’m trying to create a very simple circuit with one LED bulb which is battery-operated. (I know, this all sounds like LED 101)
There are several examples of this type on your site. However, I am looking for a bit of a different solution to my problem.

I had purchased some LEDs on Amazon in 2018 to create a proof of concept for a project. The one I am using is a 5mm 6v Pre-Wired Amber/Orange LED - Ultra Bright (3v, 4v, 5v, 6v) amber/orange LED, that I would like to power for very long periods (10 days at least). The LED I have is rated at 3v-6v, so my first attempt was to run this with a 5v battery pack, similar to the ones used to recharge cellphones. This works fine, but 99% of these charges have an auto-switch-off feature that turns off the charge if it doesn’t sense enough draw, which is the case with a 20mA bulb. The chargers turn off after about 30 secs on average (depending on the make).

Since this was not working, I then researched other options and came across some slightly different phone chargers, made by a company called VOLTAIC, which sells chargers of different capacities, all with a common feature of having the charger always on, no matter what the draw is. This solved my problem partially. The problem is that if I leave the LED on continuously, I will at most get about 2 and half days before the battery is completely drained. This surprised me given that the total battery capacity is rated at 6.4Ah*3.7V = 23.68Wh

From the manufacturer:
"The total capacity of the battery is actually the 6.4Ah*3.7V = 23.68Wh because 3.7V is the lithium ion battery cell voltage. The 5V USB output is the regulated output voltage and therefore is not the correct voltage to calculate capacity. Additionally, this is the nominal capacity assuming no losses. In practice we see that it is closer to 18-20 because of variation in the cells actual capacity, losses in the regulated output, and a low voltage buffer set at around 5% remaining capacity."
Still, one would think that that tiny bulb could run for longer. So, I am not sure why this might be happening.

I’ve now recently been experimenting with small votive candles that run on a CR2032 battery and seem to be able to stay on for as long or longer actually. How can a coin-sized battery provide longer power than a big brick?? This is a total mystery to me. The LEDs are 3V on these.

So here’s my question, if anyone would be so kind as to help me answer, and so that I can keep the little amount of hair that I haven’t yet pulled out from the top of my head:

Is there a way to:

-Power a single Amber colored LED from a rechargeable battery.
-Be able to have that LED stay on for long periods. (10, 15 days)
-If only used for a few hours initially, be able to come back to a battery that has not drained after a few weeks of not being used (which happens with the current battery).

-Optional cherry on top: If the bulb could have a fading/breathing pattern, that would be tops.

Thank you for reading this far,
Any insight or help would be super appreciated. Any suggestions on a different approach would also be very welcome.

Cheers,
Fabrice

Here’s a picture of my latest set-up:

Screenshot 2024-03-25 at 2.08.27 PM.png
 

MisterBill2

Joined Jan 23, 2018
18,986
getting 5 volts from a 3.7volt cell or cells requires some sort of voltage boosting circuit, and that has an efficiency of less than 100%. So there is part of the problem, at least. In addition, many battery capacity claims are "Rather optomistic" to use a polite term.
Besides that, have you verified the actual current taken by the LED to really be 20.0 mA? Certainly LED current is voltage dependent.
 

mdagli1

Joined Dec 4, 2012
18
Assuming LED = 1W and Battery = 24Wh
24 divided by 1 = 24 hours

When boosting a lower voltage to a higher voltage for a DCDC converter, the current draw on the low side also increases for the same wattage.
 

MisterBill2

Joined Jan 23, 2018
18,986
Some bad news is that boost types of switch regulators are among the least efficient ones. And a question: Have you measured the actual current used by that "6 volt" LED assembly?? Have you tried using actual "High Brightness" LEDs? I suggest a bit of experimenting with actual components that have actual specifications claimed. An LED with a forward voltage of 1.85 volts would work with two in series and a 3.70 volt battery and no resistor wasting power. That could provide some useful information about both the LEDs and the batteries. And certainly there is no claimed efficiency level for the boost converter circuit, although we can guess that it was designed with minimum cost as a design target. So if you are able to accurately measure the current draw from the internal battery pack, and to the LED assembly, it may provide some clues.
 

Thread Starter

PFAB

Joined Mar 27, 2024
10
getting 5 volts from a 3.7volt cell or cells requires some voltage boosting circuit, and that has an efficiency of less than 100%. So there is part of the problem, at least. In addition, many battery capacity claims are "Rather optomistic" to use a polite term.
Besides that, have you verified the actual current taken by the LED to really be 20.0 mA? Certainly LED current is voltage dependent.
Thank you for your observations, which all make sense. This is indeed what the manufacturer of the battery seems to be suggesting as well, on top of the fact that additionally, when the battery has a USB-A plug plugged into it, it activates the "Always-On" mode, which in and of itself draws 6 to 7 mA without anything connected to it. Overall, my config is messy at best. Ideally, a 3v battery with a 3v LED would be optimal. Finding that LED is the easy part, finding a *safe* rechargeable 3V battery with enough capacity to last 10 to 15 days is proving to be more difficult, or I may just not be looking in the right place.
 

Thread Starter

PFAB

Joined Mar 27, 2024
10
Do you realize that you 3-6V LED will run for less time at 5V than at 3V?
I'm realizing that now Thank you for confirming my messy set-up. Looking at strictly 3V bulb options now, but still can't seem to find a rechargeable battery that can provide about 10 to 15 days of always-on capacity.
 

crutschow

Joined Mar 14, 2008
34,689
I'm realizing that now Thank you for confirming my messy set-up. Looking at strictly 3V bulb options now, but still can't seem to find a rechargeable battery that can provide about 10 to 15 days of always-on capacity.
Have you measured how much current is actually drawn by the LED?
 

MisterBill2

Joined Jan 23, 2018
18,986
At one time there were catalog pages of LEDs that included color, light output, current, and forward voltage at tghat current. The benefit of those listings was the ability to discover the devices that met one's requirements. Digikey had those pages, with the added advantage that they were honest and safe to deal with. I have not looked at their catalog recently, but it was very educational, and free. So that would be one way to do LED research. AND then they sell the stuff as well,
And for batteries, consider that with most batteries, as they discharge, the voltage drops and so the light output and current will also drop.
And we still have no hint about the application of this long-life LED device. Consider now that a blinking LED would only consume power while lit. THAT may be a way to get the longer illumination time.
 

MisterBill2

Joined Jan 23, 2018
18,986
Certainly measuring the current and the voltage together, along with the intensity, will help with the selection of both the LED and the battery for the secret new product.
 

Thread Starter

PFAB

Joined Mar 27, 2024
10
At one time there were catalog pages of LEDs that included color, light output, current, and forward voltage at tghat current. The benefit of those listings was the ability to discover the devices that met one's requirements. Digikey had those pages, with the added advantage that they were honest and safe to deal with. I have not looked at their catalog recently, but it was very educational, and free. So that would be one way to do LED research. AND then they sell the stuff as well,
And for batteries, consider that with most batteries, as they discharge, the voltage drops and so the light output and current will also drop.
And we still have no hint about the application of this long-life LED device. Consider now that a blinking LED would only consume power while lit. THAT may be a way to get the longer illumination time.
Thank you MisterBill for the Digikey reference. Indeed, they have quite a bit on their site. I found an interesting variation of an LED, not quite the right color, but it has a "breathing" effect to it, so not quite blinking, which would work better for my application. The blinking on/off would not. I'm also just seeing that the different colors of these small LEDs have different consumption ratings. And my apologies for the "secrecy" of it all, I'm reluctant to share that on a public site for all to see. All the same, your help is greatly appreciated.
 

Ya’akov

Joined Jan 27, 2019
9,236
You might consider Sodium Ion cells instead to the Li Ion. Na Ion cels have an open terminal voltage of 3V and an energy density about the same as LiFePO₄ cells. They come in typical form factors including cylindrical (18650, 21700, &c.) and prismatic.

To top it off, they don’t use a flammable electrolyte, so no flamethrower failure mode. You can get them from AliExpress for a bit more than Lithium cells, but nothing outrageous. There are fewer “fake” capacities because they are new enough that the fraudsters aren’t making them—yet.

I believe you can find them on Amazon as well. So: 3V, safer*. not outrageously expensive—a 2S1P or 3S1P battery might be a solution.
 

Thread Starter

PFAB

Joined Mar 27, 2024
10
You might consider Sodium Ion cells instead to the Li Ion. Na Ion cels have an open terminal voltage of 3V and an energy density about the same as LiFePO₄ cells. They come in typical form factors including cylindrical (18650, 21700, &c.) and prismatic.

To top it off, they don’t use a flammable electrolyte, so no flamethrower failure mode. You can get them from AliExpress for a bit more than Lithium cells, but nothing outrageous. There are fewer “fake” capacities because they are new enough that the fraudsters aren’t making them—yet.

I believe you can find them on Amazon as well. So: 3V, safer*. not outrageously expensive—a 2S1P or 3S1P battery might be a solution.
Amazing suggestion, didn’t know that was even a thing. Will look into it for sure. Thank you
 

kaindub

Joined Oct 28, 2019
132
Lets look at the optimal situation
Led draws 20mA and it needs to run for 15 days
15 days is 360 hours
Battery needs to be 7.2 Ah if you drain it fully
With inefficiencies youll need 10Ah. Thats not a small battery.
Then how long will it take to recharge and where will the energy to recharge come from?
This is not an impossible problem, but I think you need to revisit the solution or redefine the problem.
 

Ya’akov

Joined Jan 27, 2019
9,236
Lets look at the optimal situation
Led draws 20mA and it needs to run for 15 days
15 days is 360 hours
Battery needs to be 7.2 Ah if you drain it fully
With inefficiencies youll need 10Ah. Thats not a small battery.
Then how long will it take to recharge and where will the energy to recharge come from?
This is not an impossible problem, but I think you need to revisit the solution or redefine the problem.
This would be exceeded by 4 3000mAh cells in series. That’s not a large battery pack. Keep in mind that the discharge rate is quite low and it is most likely that cells would exceed their ratings which are measured at a higher rate. 3S or even 2S may well be enough at a modest 3Ah per cell.

If not, 4Ah cells are available—a 10Ah battery is not a very large one in the scheme of things, and it‘s probably more than required. That is, if the consumption is held to 20mAh/h. I suspect the TS‘ problem is the 20mA is more than that and he’s using battery time to heat a resistor unnecessarily.
 
Hi All,
I’m trying to create a very simple circuit with one LED bulb which is battery-operated. (I know, this all sounds like LED 101)
There are several examples of this type on your site. However, I am looking for a bit of a different solution to my problem.

I had purchased some LEDs on Amazon in 2018 to create a proof of concept for a project. The one I am using is a 5mm 6v Pre-Wired Amber/Orange LED - Ultra Bright (3v, 4v, 5v, 6v) amber/orange LED, that I would like to power for very long periods (10 days at least). The LED I have is rated at 3v-6v, so my first attempt was to run this with a 5v battery pack, similar to the ones used to recharge cellphones. This works fine, but 99% of these charges have an auto-switch-off feature that turns off the charge if it doesn’t sense enough draw, which is the case with a 20mA bulb. The chargers turn off after about 30 secs on average (depending on the make).

Since this was not working, I then researched other options and came across some slightly different phone chargers, made by a company called VOLTAIC, which sells chargers of different capacities, all with a common feature of having the charger always on, no matter what the draw is. This solved my problem partially. The problem is that if I leave the LED on continuously, I will at most get about 2 and half days before the battery is completely drained. This surprised me given that the total battery capacity is rated at 6.4Ah*3.7V = 23.68Wh

From the manufacturer:

Still, one would think that that tiny bulb could run for longer. So, I am not sure why this might be happening.

I’ve now recently been experimenting with small votive candles that run on a CR2032 battery and seem to be able to stay on for as long or longer actually. How can a coin-sized battery provide longer power than a big brick?? This is a total mystery to me. The LEDs are 3V on these.

So here’s my question, if anyone would be so kind as to help me answer, and so that I can keep the little amount of hair that I haven’t yet pulled out from the top of my head:

Is there a way to:

-Power a single Amber colored LED from a rechargeable battery.
-Be able to have that LED stay on for long periods. (10, 15 days)
-If only used for a few hours initially, be able to come back to a battery that has not drained after a few weeks of not being used (which happens with the current battery).

-Optional cherry on top: If the bulb could have a fading/breathing pattern, that would be tops.

Thank you for reading this far,
Any insight or help would be super appreciated. Any suggestions on a different approach would also be very welcome.

Cheers,
Fabrice

Here’s a picture of my latest set-up:

View attachment 318575
You might want to check the following video on YouTube:

I've been using it for my Solar lights for years and works like a charm. Even during the winter where there isn't much sunlight.
If you need the led to be constantly on, just remove the transistor and connect your LED permanently to power.
If you need it breathing, look for circuits on Ali Express or on the Internet. They don't need a lot of power.
 

Ya’akov

Joined Jan 27, 2019
9,236
You might want to check the following video on YouTube:

I've been using it for my Solar lights for years and works like a charm. Even during the winter where there isn't much sunlight.
If you need the led to be constantly on, just remove the transistor and connect your LED permanently to power.
If you need it breathing, look for circuits on Ali Express or on the Internet. They don't need a lot of power.
Welcome to AAC.

Big Clive is a great resource for LED-related things. I certainly recommend his channel for people interested. But while Clive’s discovery he describes is interesting, the problem described by the TS isn’t addressed by the video you linked.

The TS is concerned with running the LED continuously from a battery for several days—without concern for time of day or recharging the battery.
 
Welcome to AAC.

Big Clive is a great resource for LED-related things. I certainly recommend his channel for people interested. But while Clive’s discovery he describes is interesting, the problem described by the TS isn’t addressed by the video you linked.

The TS is concerned with running the LED continuously from a battery for several days—without concern for time of day or recharging the battery.
Well, here then, is another Big Clive video, describing a circuit called the "Joule Thief", which runs an LED (forward voltage ~2.5v) on a nearly completely depleted AA cell (0.5v measured):

It works by using flyback voltage from a tiny transformer hand wound on a ferrite bead, and uses only 1 common NPN transistor and a 1K resistor...surely you can make a single LED run for a long time on a rechargeable battery with this circuit. But you can't defeat the laws of nature; the total energy capacity of the battery must be enough to drive the LED at your desired current for the period you want ...this circuit just squeezes the last bit of energy from a battery, and makes it useful, even if the voltage is too low to be used directly.

Hope you find this useful. For more info, a Google search for 'joule thief' might be instructive...
 
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