LED Lights - Power Supply / Battery

Thread Starter

THRobinson

Joined Jun 7, 2018
55
Hey guys... niece is wanting to build a shadow box with mini light sabers in it.

I got the STL files for Vader/Luke/Obi/Yoda's sabers and got acrylic rods we plan to "frost" so the light shows up. Just a small project.

I am gambling with AliExpress, fingers cross, not had much luck with them. Ordered from places with a 4 week ETA instead of an 8 week. Found 1 seller with pre-wired LEDs, and because of size, grabbed the 3mm ones (blue, red, green). Says 5-12v. I also bought a Type-C usb 5v1A charging module with safety for Lithium batteries. I also have a small switch, and a buck-converter that I can use from another order. Tonne of resistors, I think all 1/4w.

Plan is to make a box/frame for the wall with no wires that can be recharged.

I was looking at something like THIS BATTERY, 3.7v 1000mah, small and rechargeable, cheap and fast shipping. But, 3.7v not 5-12v.

Would I be better off with something bigger? or will the buck-converter set at 5-12v work or do I need this DC-DC BOOSTER? How long would 4 LED's last off that battery? Should I grab other lights? (was trying to find 3v ones pre-wired but didn't see any with 4 week ETA's cheap).

I "think" the plan is to wire the 4x3mm LEDS in parallel, run the wires to the booster, booster to the type-c charger, from the charger to the 3.7v 1000mah battery.

The switch I have on hand, I guess between lights and booster?
 
Last edited:

WBahn

Joined Mar 31, 2012
27,391
I'm confused. You are saying that you want to make a box with no wires that can be recharged, but then want to use a rechargeable battery. How do you plan to recharge the battery?

How long do you want this thing to work for on a fully charged battery.

A buck converter converts from one DC voltage to a lower DC voltage. But you want to go from 3.7 V to at least 5 V. You need a boost converter.

How can we tell you how long four LEDs will last off that battery when you haven't told use either how much current each LED takes are how they are connected (series, parallel, some combination)?

Try to provide that information and we can see if we can move the needle.
 

jiggermole

Joined Jul 29, 2016
63
with it saying 5-12v they may have current limiting resistors already on the die with the led so you may have to look at that. Buck is step down, boost is step up. So I think you meant that one. Making you're own small leds with leads really isn't that bad. So it may be simpler to get like an led sampler from sparkfun and solder on you're limiting resistor right in line with the led. So then you're 3v from two AA batteries would be more than enough voltage to run the leds. Most little 3mm leds are 10-20 ma. And blue is going to be the highest forward voltage, around 3.1V so maybe 3AA batteries. Sparkfun has an LED sampler pack https://www.sparkfun.com/products/15418 . Probably quicker than 4weeks.
The aliexpress mass produced little boost converters are pretty ok in my experience, if you need one.
You need a charging circuit if you're going to work with charging that battery. unless you're going to bury the battery I wouldn't really use that type. I'd probably look at something like the rechargeable AA batteries. That would make you're life quite a bit simpler. https://www.digikey.com/en/products/detail/med/BH2A2S/16604331 would work very decent for this. Then you can just swap out the batteries as they die. If you're set on using a lipo than you'd probably want to look at something like https://www.sparkfun.com/products/15217, Its a usb-c lipo charger. It only charges the lipo.

As far as longevity. You can use watt hours for your battery capacity. Its rough. 3.7V lipo with a capacity of 500mAh is 3.7V x 0.5Ah = 1.85wh. An LED you've properly sized the current limiting resistor for will drop 3.7V and use 20mA (an assumption of forward current on most hobby LEDs) will be 3.7V x 0.02A is 0.074w. that 500mA pack will last very roughly 25hours. In this case I know you don't have to convert, but if you're converting to different voltages and stuff its good to get into the practice. A watt is a watt is a watt.

edit: I committed the sin of wrong your.
 

Thread Starter

THRobinson

Joined Jun 7, 2018
55
Holy cow, $35USD for a handful of LEDs? Yikes.

I debated the AA batteries but wasn't sure how long they'd last, and I'll have to re-check but I think the box frame space isn't quite enough for the thickness.

I ordered this lithium charger, super cheap, $2.10 for 5. Said it has protection so figured be a decent one to use. Then that battery because was small/flat and should fit but also had higher mAh rating than some others at around 80-200mAh. On another project someone mentioned using the buck-converter to go up in voltage, which is why I was confused a bit. Otherwise, I was looking at this step-up board, that I can set to a specific voltage. $1.80 for 5. Can buy singles but hey, so cheap, buy a few and keep in the parts case for future stuff, right?

That all said, I know enough about electronics to solder pots in guitars, and replace caps and IC's if they blow. Stuff like figuring out resistors is voodoo to me. :D

So... would it make more sense to use the 3.7v lithium battery with the USB charger, and not use a step-up, instead just use resistors on the LEDs? My one concern is brightness to light up the acrylic rod.

If the battery holder fits, I could also use these lithium AA batteries.
 

BobTPH

Joined Jun 5, 2013
5,748
3mm round LEDs, if that is what you ordered, are typically indicator LEDs, i.e. they make a little lighted dot meant to be viewed directly. If I understand the effect you are trying to get, making a “light saber” by putting an LED at the end of an acrylic rod and have the entire length of the rod glow, then the 3mm round LEDs are likely woefully inadequate. I would start with 1 Watt LEDs, and that may not be enough. You also should be aware of the viewing angle of the LED. A typical 1W LED spreads the light over 120 degrees, so most of it would not even enter your rod. You would want LEDs with a narrow angle.
 

Thread Starter

THRobinson

Joined Jun 7, 2018
55
I keep forgetting to link the LED lights.

I have no thin wire, so figured easier to just get prewired. I wanted 5mm, but, given the shape of the lightsaber hilts and being under 3 inches long, 3mm might be even too big. I played with the 3D models a bit and I think 3mm will work but almost no wiggle room for space.

Lightsaber... um... beam? blade? No idea what you call it.... is 6 inches long. I plan to stick it in the drill and while it's spinning go over it with steel wool to frost it so the light has something to reflect off.

Light angle is a bit wider than wanted but being inside the hilt the light will only have a small hole in front of it to shine out so hoped it would be enough. Trial and error, and well, no LEDs yet, ETA is Nov 4th.

Go figure... now they're back in stock. Not pre-wired but this was my first choice.
AMAZON CANADA LINK

Those say 3v and 30 degree... maybe should grab those?
 

djsfantasi

Joined Apr 11, 2010
8,565
The LED die is a few mm from the external dome giving you some room to play. I’ve filed the tops of the LEDs to concentrate the light straight. I’ve also machined the top and drilled a mounting hole for acrylic rods. You’ve got to be careful not to hit the actual LED.
 

Thread Starter

THRobinson

Joined Jun 7, 2018
55
so, just file the top flat and CA glue direct to the rod then? I was debating that, minus the filing part.

Would the 3v 30 degree bulbs be better? then no need for the step-up.
 

djsfantasi

Joined Apr 11, 2010
8,565
so, just file the top flat and CA glue direct to the rod then? I was debating that, minus the filing part.

Would the 3v 30 degree bulbs be better? then no need for the step-up.
Maybe. What do you think expect when the batteries run down? I’d expect weak light sabers. I’d go for 4.5V and a buck converter to step down.
 

Thread Starter

THRobinson

Joined Jun 7, 2018
55
There was some math in post #3 that said 3.7v 500mAh would be maybe 25h. I was looking at a 3.7v 1000mAh lithium battery with a recharger... plus an on/off switch so not running 24/7.

I do have an extra buck converter on the way, bought 2 (one for another project that I might not use anyways).

I am open to ideas and suggestions for sure... needed for Christmas so have some time. Starting now simply because we're keeping it on the cheap and eBay/AliXpress from China, not only slow but 50/50 if ever arrives. Giving ourselves time for backup plans.

The 2 main conditions are that the space for batteries is small, which is why leaning towards the lithium packs and a charger, but could I suppose cut a hole in the back for AA battery holder... or 9v battery. Whatever fits and is bright and lasts longer.

And of course the lightsabers are small, and 2 are questionable if thick enough for the wires. Like in THIS PHOTO you can see the end has a very very narrow part before the "blade" comes out. 5mm LED is just too big.

Also, no mention of resistors or series/parallel...
 

djsfantasi

Joined Apr 11, 2010
8,565
You may need to compromise on the lightsaber hilt. Creative painting will hide any discrepancies BTW, you can chuck the LED in a drill and file off the hat-like projection at its base. Plus, you might be able to thin the diameter as well.
 

Thread Starter

THRobinson

Joined Jun 7, 2018
55
That ridge at the base affects the projection? always assumed just part of the mold or for mounting.

So, what route would you go? If this was your project. My issue is I don't have parts laying around to test/play with, so everything I I have to order now and wait. Except some caps/pots which I have tonnes of and aren't used in this project at all. :D

AA batteries? 9v battery? the 3.4v lithium? step-up, buck or resistors? NiMh or Lithium?
 

eetech00

Joined Jun 8, 2013
3,418
Hey guys... niece is wanting to build a shadow box with mini light sabers in it.

I got the STL files for Vader/Luke/Obi/Yoda's sabers and got acrylic rods we plan to "frost" so the light shows up. Just a small project.

I am gambling with AliExpress, fingers cross, not had much luck with them. Ordered from places with a 4 week ETA instead of an 8 week. Found 1 seller with pre-wired LEDs, and because of size, grabbed the 3mm ones (blue, red, green). Says 5-12v. I also bought a Type-C usb 5v1A charging module with safety for Lithium batteries. I also have a small switch, and a buck-converter that I can use from another order. Tonne of resistors, I think all 1/4w.

Plan is to make a box/frame for the wall with no wires that can be recharged.

I was looking at something like THIS BATTERY, 3.7v 1000mah, small and rechargeable, cheap and fast shipping. But, 3.7v not 5-12v.

Would I be better off with something bigger? or will the buck-converter set at 5-12v work or do I need this DC-DC BOOSTER? How long would 4 LED's last off that battery? Should I grab other lights? (was trying to find 3v ones pre-wired but didn't see any with 4 week ETA's cheap).

I "think" the plan is to wire the 4x3mm LEDS in parallel, run the wires to the booster, booster to the type-c charger, from the charger to the 3.7v 1000mah battery.

The switch I have on hand, I guess between lights and booster?
Can you post the STL file so we can have a look?
 

Tonyr1084

Joined Sep 24, 2015
7,088
Grab yourself a super-bright white LED, 5mm and touch it to a coin cell. Then see if the saber effect is adequate for your project. You won't need a resistor with a CR2032 coin cell. If you have enough room for it you can use the next size up coin cell, a CR2354. Packs a lot of energy and will last a long time. I had some old coin cells and wanted to deplete them before tossing them into a collection bin. Took some LED's and clothes pins and pinned them together with the 2032 cell. Those super-bright LED's burned continuously for weeks. And they were fairly bright for much of the time. For a cost of around $2.50 a cell those large coin cells can give you a lot of bang for the purpose you propose. It's cheap experimentation and you'll get fast results. Otherwise if you go with larger lithium based batteries you'll need current limiting (resistors). The hilt isn't likely going to be large enough to accommodate a buck-boost converter. If I'm wrong about the space - then maybe a buck will work. But you'll still have to adjust the current down to somewhere around 5 to 20mA. Even at 5mA a SB-LED is pretty darn bright.
 

Thread Starter

THRobinson

Joined Jun 7, 2018
55
@Tonyr1084 Well, the box frame is almost like this frame. The white border has a 1/2" gap behind it before it hits the masonite board/backing. The middle part where the sabers go is 1/2" deep.

Plan is to grab foamcore with a black surface and replace the white border with it and lay a piece down in the middle as well. I'll add mounting blocks to the back side of the hilts to epoxy to the foamcore, and on the back of the foamcore cut v-grooves with a knife for the wiring to fit.

Then behind the border, in the gap I'll fit all the batteries and such. On the right side of the frame I was going to file out 2 holes, 1one for the USB-C port and one for the small on/off switch I salvaged from an old router years ago. Basically attach everything with hot glue to the masonite board so when the back is removed everything comes out with it.

So, with foamcore thickness and the small gap, AA batteries with a holder I don't think will fit. Coin cells definitely would, as would the Lithium battery I was linking to earlier. The small buck converters/step-ups/battery charger will have plenty of space.

Ideally though, I don't want the person to have to open the frame ever for swapping batteries. That's why I was looking at the Lith battery and USB charger option. But that all said, I don't understand a lot about electronics. Basic skills and I get ideas, but I need help with the parts because again, I don't have a bucket of parts to play with. That's why when I order stuff lately, I get extras to play with. :D
 

Thread Starter

THRobinson

Joined Jun 7, 2018
55
Aliexpress still hadn't shipped my order after almost a week and said will ship within 1-7 more days, so cancelled.

Grabbed the ones in stock again at Amazon Canada, 5mm 3v-3.2v 30 degree angle, blah blah blah.

Will grab 2xAA rechargeable NiMH batteries and a holder. Plus my on/off switch. Gonna forget about chargers, lithium batteries, etc.

5mm might be too big but will try filing to fit them in. For wires to run through the hilts, my 18awg is too thick so grabbing an old Ethernet cable I was about to toss and will use the wiring from that, which is very thin.

Since using 2 x 1.5v batteries, wired in series I shouldn't need any resistors I assume or buck converters etc.

4 x LED lights though... In series correct?

Hopefully this setup is simple and bright enough? Should I go 3xAA and use the buck converter after all?
 

jiggermole

Joined Jul 29, 2016
63
in parallell. Two AA batteries at 3v total might have issue turning on an led with a forward voltage of 3.1v. I personally wouldn't trust the internal current limiting of the 2032 cells, but for testing purposes they're right. The internal resistance of the cell limits the output current so you don't blow up the led. The internal resistance of the AA batteries may be too high for the leds. However, I have opened up several cheapo work lights and thats how some of them have been. Alkaline batteries just wired directly to the leds. Its shady, but it does function and light up.
I've found those little blue and green indicator leds to be quite bright at 20ma.
I should have included this in my last post, sorry. There are a number of good calculators on line for choosing your resistor for an led. This is the one I use at digikey. https://www.digikey.com/en/resource...ors/conversion-calculator-led-series-resistor . I know the math is simple, I won't turn away a ready built calculator.
And my calculation in #3 was a rough estimate based on one single led at 20ma. Your mileage may vary. just as a guess with the nimh batteries, 1.5v apiece, 1600mAh capacity and 4 20mA leds in parallell. My guestimate is 20ish hours. the 2032 battery would last in the 6-8 hour range. I guessed at 500mAh capacity.
If you're using leds in the 20mA range than the 26 or 28 awg wire in ethernet is sufficient for current carrying capacity. The NFPA 79 goes all the way down to 30awg with a current carrying capacity of 500mA.
As far as you're power situation. NiMH is a solid choice. They're pretty robust. And
 

BobTPH

Joined Jun 5, 2013
5,748
NIMH batteries are 1.2V, so two are 2.4V , which will probably not light your 3V LEDs at all, or maybe light them very dimly.
 
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