How to power 250W LED with Li-Ion batteries (DIY flashlight), need help

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Mocarny
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How to power 250W LED with Li-Ion batteries (DIY flashlight), need help

Hi, I need a help with this topic. I need a way to power a LED from 18650 or 21700 batteries, this is a DIY project, I want to build a flashlight from scratch. I need to know a way of powering the LED, and this is a ~ 250W LED so I can’t just buy a flashlight driver. I want the flashlight to have constant brightness as long as possible. It would be great to have different modes like 1% – 10% and so on.
Is boost converter a good solution with 9S batteries? LED operates at 40V and 8A as an absolute maximum and has Vf of 30-40V.

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Edited by: Mocarny on 09/29/2022 - 15:29
Argo
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I use a PMW for electric motor to drive my custom flashlight.
I don’t know if this is the best option but it’s very cheap so with 3$ I can drive my led.

Mocarny
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I would rather not use a PWM for my LED, I don’t want it to flicker.
Does a boost or buck converter allow LED to have the same brightness during battery discharge, or it will shine dimmer as the battery discharges?

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Agro
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You need any constant current driver.

How about something like https://www.aliexpress.com/item/32877219145.html?

Bort
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Have you considered buying a 250Wh power station and plugging it into that?

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Mocarny
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Agro wrote:
You need any constant current driver.

How about something like https://www.aliexpress.com/item/32877219145.html?


I was considering it. But do you know if it provides constant led brightness through all battery life, or brightness decreases as cell voltage decreases?

Bort wrote:
Have you considered buying a 250Wh power station and plugging it into that?

I need it to be compact, so ideally something like 8S 4P battery pack + electronics + cooling stuff + DIY enclosure

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thefreeman
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With a Vf of 30~40V then with a boost driver you would need 7S (29.4V max) or maybe 6S depending on the minimum duty cycle, with a buck driver you would need 15S or higher which is a lot of cells.
What size does it need to be ? I don’t know if there are many off the shelf suitable drivers, on aliexpress and Co you can find CC/CV boost converters dimmable with a potentiometer, they’re quite large though and of unknown performance.

Talskled has boost drivers like Ultraboost
It’s a direct application of the example circuit in the LT3756 datasheet, an asynchronous multi topology LED driver IC, but 250W (6.25A 40V) might be too much for it according to the efficiency measurements on the page at 24Vin.
It has analog dimming (with a potentiometer on taskled driver), you can use a voltage from an external MCU to control it (DAC or filtered PWM), also can be dimmed with PWM.
If you’re willing to design and make a driver you could try using it with beefier components (low side FET, diode, inductor), though being asynchronous the diode will always dissipate a lot of heat.
Add a MCU for modes, thermal regulation etc, if you don’t code then Anduril can be used.

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What’s the LED? Bunch of the big LEDs come with a simple circuit so you just connect them to mains electricity…

Mocarny
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thefreeman wrote:
With a Vf of 30~40V then with a boost driver you would need 7S (29.4V max) or maybe 6S depending on the minimum duty cycle, with a buck driver you would need 15S or higher which is a lot of cells.
What size does it need to be ? I don’t know if there are many off the shelf suitable drivers, on aliexpress and Co you can find CC/CV boost converters dimmable with a potentiometer, they’re quite large though and of unknown performance.

Talskled has boost drivers like Ultraboost
It’s a direct application of the example circuit in the LT3756 datasheet, an asynchronous multi topology LED driver IC, but 6.25A 40V might be too much for it according to the efficiency measurements on the page at 24Vin.
It has analog dimming (with a potentiometer on taskled driver), you can use a voltage from an external MCU to control it (DAC or filtered PWM), also can be dimmed with PWM.
If you’re willing to design and make a driver you could try using it with beefier components (low side FET, diode, inductor), though being asynchronous the diode will always dissipate a lot of heat.
Add a MCU for modes, thermal regulation etc, if you don’t code then Anduril can be used.


You are right, a 7S will be the right option.
If I decide to use a boost driver, can I somehow add Anduril? I was thinking about using Arduino to have basic modes ant temp regulation, but I don’t know if it’s a good idea.
gravelmonkey wrote:
What’s the LED? Bunch of the big LEDs come with a simple circuit so you just connect them to mains electricity…

No, this is just a LED and I need a driver.

Another question is, if this LED has 2 power sections (so the led is divided into 2 independently sections, with 2 “+” terminals and 2 “-” terminals) is it better to use 2 boost converters and feed 4A to each section, or use one bigger boost converter and connect 2 sections in parallel and set 8A on converter?

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thefreeman
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Agro wrote:
You need any constant current driver.

How about something like https://www.aliexpress.com/item/32877219145.html?

I quickly looked at this test : https://robojax.com/learn/arduino/?vid=robojax_400W_boost
Asynchronous boost converter with 8.5mΩ switch FET and mbr20100ct diode.
He only tested 10Ain max, not sure why but he probably mentionned it in the video, which at 24Vin 36Vout gives 6Aout with 94%, 14W to dissipate (quite a lot already).

Mocarny
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thefreeman wrote:
Agro wrote:
You need any constant current driver.

How about something like https://www.aliexpress.com/item/32877219145.html?

I quickly looked at this test : https://robojax.com/learn/arduino/?vid=robojax_400W_boost
Asynchronous boost converter with 8.5mΩ switch FET and mbr20100ct diode.
He only tested 10Ain max, not sure why but he probably mentionned it in the video, which at 24Vin 36Vout gives 6Aout with 94%, 14W to dissipate (quite a lot already).


Thank you for the link. So if I understand correctly, this solution (or this exact type of boost converter?) is not really good?

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thefreeman
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Mocarny wrote:
You are right, a 7S will be the right option. If I decide to use a boost driver, can I somehow add Anduril? I was thinking about using Arduino to have basic modes ant temp regulation, but I don’t know if it’s a good idea.

The taskled/LT3756 takes a voltage for analog dimming, same as all Anduril compatible drivers, on my anduril drivers I use the DAC of a T1616, but usually it is a PWM signal with a low pass filter to convert it in an analog signal, so you can do that with an arduino.

For the aliexpress boost converter it might also be possible but that requires analysing the circuit, without doing that the potentiometer could probably be replaced with a digipot controlled by the arduino.

Quote:
Another question is, if this LED has 2 power sections (so the led is divided into 2 independently sections, with 2 “+” terminals and 2 “-” terminals) is it better to use 2 boost converters and feed 4A to each section, or use one bigger boost converter and connect 2 sections in parallel and set 8A on converter?

With the drivers listed in the thread, yes it should be better to use two.

Mocarny
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Thank you thefreeman, it helped a lot. It might be a silly question, but does the LED “know” how much current it need? Let’s say I am going to connect my led to a boost board, so I set voltage and current to zero and after connecting I will increase only the voltage to e.g. 38V,and the current will increase as well to perfect value? Do I need to adjust current on boost board after reaching 38V?

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SammysHP
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That’s not how electronics work. Wink For LEDs you need a current source. Due to Ohm’s law you can’t force the voltage to be something different than required.

Mocarny
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SammysHP wrote:
That’s not how electronics work. Wink For LEDs you need a current source. Due to Ohm’s law you can’t force the voltage to be something different than required.

My knowledge in this topić is very low. I don’t even know if it exists. Silly
So when connecting to boost board, which potentiometer should I adjust to not fry the LED?

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Mocarny
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Would it be possible to use one analog/digital potentiometer with both boost boards? Like if I desolder both and then wire both to one potentiometer?
I’m going to need a double the resistance one, or half the resistance, or the existing one will work the same?

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