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Jun 04, 2013, 10:38 PM
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Help!

Need help with DIY 18650 powerbank


Hello guys ,

I'd first like to thank every one in this forum for the huge amount of info provided, it's really like a mine of useful information in here.

I've been thinking about building a powerbank with 18650 cells for mobile phones and I came across so many schematics that I intended to build my design around. The common thing with them all was that they all have a separate 18650 charger/Dc-Dc converter modules.

This was till I found this amazing board at Sparkfun: https://www.sparkfun.com/products/11231 with the schematic and all which seems to have both of the modules into the same circuit.

My idea is that I'll add a female usb connector to the output of the regulator and add the extra resistors to the D+ / D- pins like with the MintyBoost3.

My main concern is the output current which is 600mA and I was wondering if this will be sufficient for charging all the modern devices. I also thought I should get some advice from more experienced guys if I'm missing any thing with this Idea.

Thank you all and I'm very sorry for making this so long .
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Jun 08, 2013, 01:22 PM
Proud to eat Kraut ;-)
Julez's Avatar
Do it like this:

Buy as many LiIon cells as you like. Connect all in parallel.

To charge them, use this circuit:

http://www.ebay.de/itm/DC-Buck-Conve...item5af19a9142

It can be adjusted to the correct output voltage.

Input can ba anything from a 5V USB charger to a 12V laptop power supply.

Check if a Schottky diode is needed to prevent leaking current back into the circuit when the pack is not charged.

On the output, you need a discharge protection.

http://www.ebay.de/itm/10Pcs-Protect...item33816ba36d

And a booster to get 5V for your USB.

http://www.ebay.de/itm/Dual-USB-Sola...item4abb9fb9eb

Maybe protection and booster combined:

http://www.ebay.de/itm/Boost-and-Pro...item33638162a9

The specs suggest the charging circuit is already included...

Anyhow, yo're welcome.
Jun 12, 2013, 09:44 PM
Registered User
Thread OP
Hi Julez,

Thank you very much for your answer to my question. I've actually built a powerbank before based on separate charge/discharge boards. I just thought it would be fun and cheaper to build it using this all in one board from SparkFun.

I don't think I'll need a charging balance circuit as I'm actually planning to use a single 5000mah 18650 battery. Can you please take a look at the links I provided and tell me if there is any thing wrong with the whole concept.

Again thank you for your help, I appreciate it .
Jun 12, 2013, 11:53 PM
Registered User
I was contemplating building a USB based 'powerbank' but never got around to it, despite a need to own one. I recently threw in the towel and bought this one and have been blown away by the build quality, capacity, and usefulness. So much so that I was glad that I procrastinated and did not actually assemble one. Being an engineer who takes great satisfaction in building stuff, that rarely happens...

Mark
Jun 13, 2013, 09:40 AM
Registered User
600mA is pretty low I would say you are right to be concerned. While that's fine for cell phones, though slower, it won't do for tablets. Most cell phones come with a 1A to 1.5A adapter. Some of the tablets are up to 3A now I think. You'll notice the mintyboost states it can not charge an iPad.

Gotta say Sparkfun makes good money on those boards though, I would guess about $15 profit per board. Componets are dirt cheap, about 50 cents for the MCP73831 and around $1.25 for the TPS61200. Most people don't realize just how cheap those single cell lipo charging chips are.
Jun 13, 2013, 08:32 PM
Registered User
Thread OP
Quote:
Originally Posted by mrforsyth
I was contemplating building a USB based 'powerbank' but never got around to it, despite a need to own one. I recently threw in the towel and bought this one and have been blown away by the build quality, capacity, and usefulness. So much so that I was glad that I procrastinated and did not actually assemble one. Being an engineer who takes great satisfaction in building stuff, that rarely happens...

Mark
Hi Mark,

I can actually see your point here but there is always that thrill of building your own stuff if you know what I mean, and this is why I'm always doing DIY projects.

Plus when I checked the link for that product you provided, I find that it would cost you a fraction of the price if you build your own. Not to mention the misleading description and false capacities most online sellers provide and when you test it you're like . Thanks for your reply
Jun 14, 2013, 01:28 AM
Registered User
Right there with you. Fortunately, I was able to catch a sale on Amazon when the 13000mAh Astro E4 was 20% off so it was less than $40 shipped to my door. I did the math and building one of similar capacity would have set me back ~$50 for the shell+electronics and 4 decent quality 18650 cells.

The E4 has a 2A port and a 1A port so it'll easily charge my Android phone and Nexus 7 tablet concurrently. I recently took it on a 4 day trip and really wrung it out by using it exclusively to charge both devices after heavy usage each day and it made me a believer. The built-in LED light is a nice added bonus. With the great performance and 18 month warranty, I would buy it again in a heartbeat.
Jun 14, 2013, 06:41 AM
Proud to eat Kraut ;-)
Julez's Avatar
Quote:
Originally Posted by Degooo
Hi Julez,

Thank you very much for your answer to my question. I've actually built a powerbank before based on separate charge/discharge boards. I just thought it would be fun and cheaper to build it using this all in one board from SparkFun.

I don't think I'll need a charging balance circuit as I'm actually planning to use a single 5000mah 18650 battery. Can you please take a look at the links I provided and tell me if there is any thing wrong with the whole concept.

Again thank you for your help, I appreciate it .
Hi Degoo,

no problem with the sparkfun board. The last link in my previous posting is, I think, a board with similar functionality, but it has more power and is cheaper. So if you go for a single board, this might be the better choice.

Quote:
a single 5000mah 18650 battery
Is there such a thing? My 18650 cells have around 2000-2500mA, although they may be a bit outdated. I would be interested if the rated capacity of your cell is actially achieved.


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