Looking for driver (or emitter) to run from a 5V, 2A USB power bank

Tried searching, but didn’t find anything helpful…
I have a project in mind where I’d like to run a light from a USB power bank. I’d like to keep the power bank stock if possible (rather than cutting into it to run directly from cells), so the output would be standard USB, 5V, ~2A. The light will ideally have a ~2ft power cord ending in a USB plug, so it could theoretically be run from a computer or other USB power source as well. Tint should be warm or neutral, floody more than throwy, hopefully >300 lumens on high (though more is better, especially if there are useful lower modes). 2-3 brightness modes would be nice, more wouldn’t be a problem, and I don’t need an ultra-low moonlight mode. Diameter of emitter & driver should be less than ~25mm, but there’s a little flexibility here. There might also be a little bit of room for a small heat sink if that matters, but not enough for a fan etc. Finally, if necessary I can dissemble the power bank and drill an extra hole for wiring, so I can run wires straight from the cells, and use the power bank simply as a battery holder. That would simplify things in terms of using familiar drivers, but I’d like to explore possibilities of using USB power first.

I’m making a few assumptions here: First, that an XM-L2, Nichia, etc. run by common drivers won’t happily handle 5V, and that they’ll do better with the ~3.7-4.2V we typically see off an 18650. Most of the regulated drivers I’ve seen specify 4.5V max input, but maybe I’m missing something obvious?

Is there a good driver that would take the 5V from USB and output a regulated ~4V to an emitter?

Or maybe I don’t need a regulated driver, if the USB power bank is already regulating current? If I’m overthinking this, is there another useful means of stepping down 5V to ~4V (if necessary), and allowing some sort of brightness control? Maybe switching to alternate resistors (I’d rather not build something like this from scratch) or adding a potentiometer (dial-able brightness control would be cool).

As you can probably tell, I know a little about electronics, but not enough to be really useful in this case… TIA for any advice or suggestions!

http://www.ebay.com/itm/121919016505

They are adjustable-output-voltage only, but LEDs will only pass X amount of current at Y voltage, so there you go. Set the voltage to get the desired light output. That version is about half the size of a postage stamp.

available from many different sellers all over, you don't have to buy direct from China. Search ebay for something like 'dc converter -boost' and restrict it to US sellers, scroll and check the pictures until you find a match. There are larger versions that use the same basic circuit as well, if size doesn't matter.

I’ve tried running XML2 on copper with copper heatsink with 5V 500mA and it’s one of the brightest beast I’ve ever done.

but the output of the powerbank always never reach more than 1A no matter how thick the wires are. It just somehow regulated to 500mA even when plugged to 2.1A out

if you are considering driving this through your pc USB out the XML2 are pretty safe as long as there’s heatsinking even with ordinary aluminum board as they never go more than 300-500mA

with modes any nanjg boards will do the trick regulating if you needed modes. Note that you only use it for modes as I find it quite unnecessary with USB outs.
I’ve tried with a 10400 xiaomi powerbank direct drive to a single xml2 u2 1a and it only draws max 400mA

though I’m still curious how phones or tablets can draw up to 2.1A while all we know XML2 can be driven more than 3A

Thanks for the replies!
Comfy - that DC converter definitely looks like it would do the trick.
power - thanks for the firsthand report of giving 5V to an XM-L2! Definitely sounds like the simplest option.

To either of you: If I used either 5V or 4V coming off the USB power source, how might I adjust brightness (or just add a low mode)? power, you mentioned a Nanjg board for modes only - does that require modification to the driver? The Nanjg drivers I see at mtnelectronics specify an input voltage of 2.8V-4.5V, but would 5V work in this case?

Thanks again!
Andy

On those little DC-DC converters, you can remove the tiny little adjustment pot and use wires to connect to a normal size externally adjustable pot and you have 0-100% dimming. This may be simple, or a little difficult. It'll depend on whether the current draw is acceptable with the pot turned wide open or not. If it's OK wide open (due to limited current as power911 describes), then you're done. If you need the max to be less than that, you'll have to trial-and-error a fixed resistor inline with the pot, so that turning the knob to 100% doesn't let the module go to actual 100%. If that makes any sense.

I think it makes sense - thanks!
If I’m basically going to be trying the voltage regulator wide open, I may as well bypass it altogether and just use a pot, right? Most of the pots I see on ebay are 1/4watt, which would be too small.
Does it look like this one should work? http://www.ebay.com/itm/281068417718 I like the idea of integrating the switch and brightness control.

No, a pot big enough to use as a dimmer all by itself would be huge and expensive and would only work by dumping whatever doesn't go to the LED straight to ground which is something you don't want to do to whatever device you have the USB plugged into. It just needs a little adjustable power supply. Like a flashlight with an e-switch, none of the output current goes through the little pot, the pot just tells the controller chip how much voltage it should put out. It doesn't really need an on/off switch, dimmed all the way down is zero output, and switching converters like this don't draw any power (or such a small amount it's not worth bothering with) when they aren't outputting anything.

Got it! (I think)
Thanks yet again.

So I’d take the DC-DC converter, solder off the tiny philips-head pot, and wire in a pot more like this:

(Bigger than stock, large enough to add a knob, but still compact, doesn’t need to handle significant current) Also includes an off switch, so I wouldn’t need to integrate that elsewhere in my design.

I’d still appreciate any other opinions or suggestions, but I think this is enough to get me started! (Well, started on ordering parts from China, at least… :wink: )

If you guys make a good design that snaps / slides onto a powerbank, someone can get xiomi to make it cheap for a group buy.

Interesting project, what do you want to use this for?

Plugging USB 5v to nanjg directly will do. No need for modifications as the board won’t even heat up

There are US sellers, at least for the DC converters. Scroll until you find a pic that matches what I linked earlier.

http://www.ebay.com/sch/i.html?_from=R40&_sacat=0&_nkw=adjustable+dc+module+-boost&rt=nc&LH_PrefLoc=1

The larger LM2596 boards will work too, but I don't know how much space you have available (the 'big' ones are still tiny, see pic):

Have you seen this product from Banggood? Looks similar to what you’re describing. Probably wouldn’t be too hard to swap in the emitter of your choice.

This XTAR UL1 is also quite a good product.

Maybe not quite what you are asking for as it is only about 500mA draw and quoted at only 180 lumens but I have a couple and have been very happy with them.

EDIT: and apologies to cmflippen but Banggood are quoting 2000lm from that XP-G R5 flashlight head you linked to above. They should be shot - not gonna happen! Simply more of the worst kind of exaggeration we’ve come to expect.

Thanks again for all the tips and links! A few specific replies:

Let’s not get ahead of ourselves! :wink: We’ll see if this works as well in reality as it does in my head.

I’m not exactly sure what to call the product I have in mind - I guess it’s most like a battery-powered desk light, or portable task light. More like a lantern than a flashlight. I’ll definitely post here if/when I complete it!

Thanks! I’m going to try the voltage converter + potentiometer first (I like the idea of dial-able brightness), but if that doesn’t pan out, I’ll start my driver search with a nanjg.

Yeah, I saw some of the US sellers, and decided I’d rather pay ~1/3 price and wait a few weeks. Since I was ordering 3 similarly cheap products (DC converter, pot, heatsinks) the total from China was about $5, and getting exactly the same products shipped domestically would have been at least an additional $10. Not in a hurry.

cmflippen & gadabout : The products you linked are somewhat similar to what I have in mind, especially with the gooseneck in gadabout’s link. I’m hoping for slightly brighter and a slightly longer/stiffer gooseneck, but I’m not too surprised that someone already markets a product with the same general ‘bauplan’ .

General update : Parts are on order from China. So after I receive them, and after I get a chance to play around with this, I’ll post back with a progress report. Thanks again!

I found this the other day: http://www.lck-led.com/7135-350ma-700ma-1000ma-dimming-driver-p-1330.html?cPath=135