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Power an LED from PowerBoost 500 or 1000
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Power an LED from PowerBoost 500 or 1000

by Systembolaget on Fri Dec 21, 2018 11:16 am

Hej,

I want to power a 360mA 5V LED with 280lm output from PowerBoost 500 or 1000 with a 3.7V 3000mAh Li-Ion battery.

High brightness LEDs require constant current. How could I modify or add to the PowerBoost in order to achieve a constant current output for my LED?

In the worst case, I could use a NeoPixel stick with 8 warm white RGBW LEDs, but how many lumens do they output together?

Thanks!

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Re: Power an LED from PowerBoost 500 or 1000

by adafruit_support_bill on Fri Dec 21, 2018 11:31 am

a 360mA 5V LED

5v is not a typical Vf for a LED. Your LED may already have a current limiting resistor built-in. Do you have a link to the spec sheet for your LED?

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Re: Power an LED from PowerBoost 500 or 1000

by Systembolaget on Fri Dec 21, 2018 3:44 pm

Thanks!

I have no spec sheet, because I assumed (from modelmaking forums) that this is what is popular (maybe it is not, as you say). Since the PowerBoost outputs 5V max. and many LEDs I saw need 90 - 350mA constant current, I assumed I need to find a 5V LED (but as you say none might exist on the market).

If, plan A, I can find one with around 300 lumens with 4V or 3V that would also be ok, I guess, if I find out how to make the PowerBoost output a constant current.

Or, plan B, if an 8 pixel NeoPixel RGBW strip outputs around 300 lumens, I could just use that?

By the way, can the PowerBoost also charge 2S or 3S Li-Ion battery?

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Re: Power an LED from PowerBoost 500 or 1000

by adafruit_support_bill on Fri Dec 21, 2018 4:03 pm

A typical 1W white LED has a forward voltage (Vf) of about 3.2 volts. (350mA * 3.2v = 1.1 watts)

Powering a led with those specs from a 5v source would require a series resistor to limit the current. You would need a 5.6 ohm/1 watt resistor.

By the way, can the PowerBoost also charge 2S or 3S Li-Ion battery?

No. The PowerBoost 500C or 1000C can charge a 1S LiPo or Li-Ion cell

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Re: Power an LED from PowerBoost 500 or 1000

by Systembolaget on Tue Jan 08, 2019 5:24 pm

Happy new year 2019, first of all!

I found the Nichia NVSW219CT LED series with 2.9 - 3.1V and 700mA, outputting 280 - 300lm, which is ok-ish.

I finally received the Adafruit PowerBoost 500 and 1000 chargers, and an Adafruit Lithium Ion Polymer Battery - 3.7V 2500mAh.

So, that way, I can charge the battery and/or drive the LED.

How would I now need to modify the PowerBoost 500 or 1000 Charger so the LED draws a constant current of 700mA @ around 3V?

Many thanks in advance!

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Re: Power an LED from PowerBoost 500 or 1000

by adafruit_support_bill on Tue Jan 08, 2019 5:34 pm

If you plug those numbers into one of the LED calculators like this one: http://ledcalc.com/
It says you need a 1W 3.3ohm resistor wired in series with your LED.

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Re: Power an LED from PowerBoost 500 or 1000

by Systembolaget on Wed Jan 09, 2019 2:43 am

Thanks!

That's a lot of energy wasted, ouch!

I read some more on the forum and should better use a step-down converter to get from 5.2V to the LED's voltage & current for better efficiency, ist that right or just an opinion?

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Re: Power an LED from PowerBoost 500 or 1000

by adafruit_support_bill on Wed Jan 09, 2019 7:58 am

For maximum efficiency, you probably would want to avoid the boost stage altogether. No sense boosting the voltage to 5v - only to regulate it back down to 3v.

If you were to take the 3.7v directly from the battery, you could use a 1/2 watt 1.3 ohm resistor for less wasted power.

There are also very efficient 'buck' type current regulators designed specifically for driving LEDs. Mouser, DigiKey and LED specialists such as LedSupply.com will carry "Buckpuck" or similar LED drivers in a variety of current ratings.

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Re: Power an LED from PowerBoost 500 or 1000

by Systembolaget on Wed Jan 09, 2019 8:33 am

Thanks, very much appreciated!

To obtain an "all-in-one system" from my Adafruit PowerBoost/Adafruit battery combination (I very much like the fact that one can charge and/or power something concurrently), how would I have to modify the PowerBoost to "circumvent" the 5.2V output stage and tap the 3.2V from the battery directly?

Are there some parts on the PowerBoost I could "disable" by desoldering and instead soldering on new parts?

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Re: Power an LED from PowerBoost 500 or 1000

by adafruit_support_bill on Wed Jan 09, 2019 8:49 am

You can bypass the boost stage by tapping into the BAT and GND pins. Or you could switch to the #390 "Solar" charger which uses the same charge controller chip: https://www.adafruit.com/product/390

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Re: Power an LED from PowerBoost 500 or 1000

by Systembolaget on Wed Jan 09, 2019 11:52 am

"You can bypass the boost stage by tapping into the BAT and GND pins."

That sounds good; I already bought PowerBoost 500 and 1000 and rather want to use these. Good to know that bypassing is so straightforward. I thought BAT is the battery INPUT only...

All right, I saw you answered a similar request already viewtopic.php?f=19&t=135957

Thanks again for all your answers!

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Re: Power an LED from PowerBoost 500 or 1000

by Systembolaget on Fri Jan 11, 2019 11:10 am

I used the calculator you suggested and got to a different resistor value (supply voltage 3.7V, voltage drop LED 3V, desired current 700mA).

I guess the schematic below is how it'll work.

If I tap into the battery as suggested - bypassing the boost circuitry - will the battery be cut off when it is too depleted, or will I now have to add some battery protection circuitry to protect the battery from being deep discharged?

Thanks!

Skärmbild.png
Schematic screenshot
Skärmbild.png (41.63 KiB) Viewed 169 times

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Re: Power an LED from PowerBoost 500 or 1000

by adafruit_support_bill on Fri Jan 11, 2019 1:44 pm

If you are using one of our LiPo cells, the built-in protection circuit will cut off the output if the voltage drops below a safe value.

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Re: Power an LED from PowerBoost 500 or 1000

by Systembolaget on Fri Jan 11, 2019 4:16 pm

Good to know, thanks!

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Re: Power an LED from PowerBoost 500 or 1000

by Systembolaget on Tue Jan 22, 2019 11:29 am

Got my Adafruit parts together, as always robust and reliable produce!

Now I want to make a change and drive a 500mA 9.4V (typ.) and a 350mA 9.2V (typ.) LED.

I need to change the above circuit by putting a constant current boost converter in between the Adafruit PowerBoost and the LED; should I use the already boosted 5V output or use the "directly from battery" method from the first solution? Would I lose too much battery by boosting twice? What would you suggest?

Thanks again, so far very helpful help!

Systembolaget
 
Posts: 131
Joined: Wed Mar 08, 2017 1:01 pm

Please be positive and constructive with your questions and comments.