18650 Cell Phone Charger

[SnowplowTortoise]

Alright, please keep the laughter to a minimum. This is not what I envisioned when I first began, but I guess it’s what you get when you cross inadequate tools with a superficial understanding of electricity and total lack of preparation or patience. Here is my first attempt at an 18650 cell phone charger.



The plastic box is from Radio Shack. As recommended by Balou, I used the LM7805, which is a linear voltage regulator. It must not be terribly efficient because it gets really hot in use. I had to attach it to a piece of aluminum angle to help dissipate the heat and keep it away from the cells. The cells are connected through some magnets. I’m sure an actual 18650 holder would work better, but as I wrote, lack of preparation, etc.

So, it’s not going to win any beauty pageants, but it works. I’ll probably slap a voltmeter on somewhere so I know when the 18650’s are tapped, but I have to find one first. I’m sure the $5 unit in Dom post is better in a dozen ways, but this was fun to make and satisfying to see working, so I’m happy.

[SnowplowTortoise]

I'm back on the LM22671 approach. I'm hoping I can get rid of the heatsink and improve efficiency. But this is going to pull me in way over my head now. Here's the circuit I got from Webench.



The bill of materials amounts to about $4, so I guess there's no harm in trying. I apologize in advance for all of the dumb questions I will probably ask as I try to put this together.

[dom]

I like the way this thread is going SnowPT.
Hopefully some electronic smarty will jump on the wagon :-) Would be great to have a nice efficient charger.

A short update on my unit.
1. Still very happy with it :-)
2. As expected it's pretty inefficient.
3 Does the job.

Have used it several times till the protected battery ran out (sorry battery).

Any future uses will be time limited to stop battery damage.(approx 5hrs -though will check this more thoroughly)

I was sick the other day so spent approx
5hrs reading ebooks on my phone -this is
where the charger comes in real handy.

My phone only had one bar left at the start of the day,and with all that reading
the phone was up to 2 bars at the end
of the charger life.

Cheers
Dom

[poormanq45]

his could be done with a pair of Li-Ions in series then use a buck regulator to drop down to 5v.

[sqchram]

Sanyo Eneloop Moblie Boost (the largest capacity model). 5000 mAh, Li-Ion, and they were at Costco being clearanced for $15!

Output is 500mah.

[Kremer]

Sanyo Eneloop Moblie Boost (the largest capacity model). 5000 mAh, Li-Ion, and they were at Costco being clearanced for $15!

Output is 500mah.

woa, awesome, get me one!

I think you mean 500ma output, no 'h'.

[sqchram]

woa, awesome, get me one!

I think you mean 500ma output, no 'h'.

right, of course, 5V 500 ma output, so suitable for most cellphones.

[Rod911]

i have the device mentioned by the OP..
..it'll charge my ipod from empty to ~80% on a 2200 cell..
NOTE: only unprotected cells fit

I got mine delivered today. Bought from DX.

It's able to charge my N95 8Gb mobile just fine using the included 2200mAh unprotected cell. Also, most DX protected cells do not fit on this thing. However, the blue 2500mAh TrustFire and black/red 2400mAh TrustFire cells fit ok in it.

[spencer]

I would suggest taking a look at the mintyboost. If you can solder then buying the kit might be the easiest DIY method. The mintyboost is designed to work from 2XAA Alky I believe so 3V. The site says that you can use a lithium ion battery. If you wish to use more than one battery then you can just put them in parallel. Check it out.

[SnowplowTortoise]

Thanks Spencer - that's a great lead. I was just about to order the parts for my circuit, but the minty kit will actually end up being cheaper, and it benefits from being designed by someone who knows what the hell they are doing.

One question - do you think efficiency continues to improve as the input voltage approaches 5V, or is it really optimized for 3V as he writes? I couldn't tell from the graphs.

[spencer]

I have no idea. Even if it does increase or decrease it will only be by a couple percent. I wouldn't worry about a couple percent and I definitely wouldn't use more than 1xLi-ion(4.2V)

[PurpleDrazi]

I'ver heard that the minty boost only charges at 200ma.

Can anyone confirm or deny?

PD

[spencer]

Its supposed to put out 450mA or something. Not quite USB spec but really close.

[balou]

SnowplowTortoise: yes, the 7805 is a linear regulator, and as such gets hot - it's very function is to convert excess voltage into heat.

So... 2x18650 have 4.2V each, 8.4V total. USB spec says 500mA max, but many cellphone chargers deliver up to 1A.

So.... 8.4 - 5 = 3.4V
3.4V * 1A = 3.4W.
A neat 3.4W heater. Shouldn't get all to hot (I've run a LM317, basically a 7805 with adjustable voltage, at 30V and 0.5-1A down to 5V USB. The heatsink gets so hot water instantly evaporates if you touch it with wet fingers)

edit:

Ah, too bad. 6-8 sub-C's is starting to get pretty bulky. I guess I will set them aside for some future project. Thanks for the info.

So, back to the 18650 approach. I had found this pre-built board:
http://www.batteryspace.com/dc-dcreg...dc1ampmax.aspx
Why does it appear to be so big and full of stuff, when the circuit you described is just a little IC and 1-2 capacitors?

switching regulators are a lot more complicated

now for some random thoughts that were floating in my head:

-about the mintyboost idea: it's a boost regulator, so if you want to use 2 18650 batteries, it's not running as efficient as it could if you run them in parallel.
a buck regulator generally runs more effective. but effective also means large inductors. the prebuilt board looks rather nice. the problem with switch regs are that the chips for them are a lot harder to find, and then you also need to find a inductor which is a good match of your size/price/efficiency requirements. using a LM317 or 78XX regulator (last two digits specify voltage) is in many ways much easier (even building a AC input with filtering and additions for more stability 317-based supply is simpler than the simplest switcher imho.)

-the one you mentioned states 85% efficiency at full load. that sounds like it's less efficient at 500mA. your current solution has an efficiency at the beginning of 5/8.4 = 60% and near the end of battery life 5/7 = 71%

-I guess you're using unprotected 18650? dealextreme has protection circuits available for a really low price. you could build them into the case

-linear regulators have something called a dropout voltage. for the normal linear regulators it is normally stated as 2.5V - meaning, in the case of the 5V 7805 you need at least 7.5V input for it to run stable under all conditions. in the real world, at room temperature, 1.6V or even 1V can be sufficient (tested myself), albeit with lower maximum current. that'll mean 6.6V, or 3.3V per 18650, which could be considered an overdischarge for li-ion cells. one idea is to add a diode - it gives you reverse polarity protection, and your cells won't go below 3.5V as easily. suitable diodes is the 1n4001 (up to 50V) or the 1n4004 (up to 400V). they cost approx the same, are same size (or almost, depending on distributor) and 4004 might be more available because it's used in 110/230V electrical stuff (ok it's used in 230V stuff - anybody knows if they use 1n4003 in 110V applications?)

edit2:
the new Mintyboost can deliver 400+ mA. Better than the 200+ mA of the old versions, but still not that good.
The old version had an efficiency of 68% with 1.2V cells at 250mA. Please also note the huge difference in efficiency comparing different inductors (using alkalines at 250mA: 70% vs 82%)
At 3.5V-4.2V efficiency should be in the 85%+

Another random thought: use a LM317 instead of a 7805 and adjust it to 5.25V - still in the USB spec, some devices only charge with rather high voltage, and less heat in the linear regulator.
Personally, I don't really like the mintyboost that much - to low output current for me, especially if using 18650 which could deliver quite some current. The other module you linked to looks much better imho. That thing could deliver a respectable 10Wh out of its usb plug using two 18650

edit3:
and the edits don't stop...
Yes, this whole post is quite ambiguous about what's the best solution. You must know, I only give pointers What I don't know... 1x18650 or 2x18650? One thing about the mintyboost that puts me off is, frankly, the price of 20$. I ordered this one http://www.dealextreme.com/details.dx/sku.17836 as a reserve gift for christmas. I didn't forget anyone while buying gifts, so it's mine now. Yep, only one battery, even less efficiency, but it's small and only $4.44 (and doubles as a flashlight - altough only in the 5-10 lumens range). Have to try it with a 14500...

Btw: if you want to charge iPods, you need 4 resistors to get the right voltage to the data lines, else it refuses to charge (of course this is for making sure the usb port really can provide enough power - nothing to do with the fact that only apple-built charges can be used. nowadays many usb chargers have the right resistors, but there's no guarantee and it often isn't mentioned on the packaging)

[SnowplowTortoise]

oof - an Alpine avalanche of information... Thanks Balou! I am intending to use unprotected cells (IMRs), however I'm not sure that one of those DX protection circuits would really protect my cells against over-discharge. The ones I found cut off the voltage at 2.5V, which is only a safe number at high drain rates - say 1C. I was under the impression I should be shooting for something more like 3.0-3.2V for more moderate drain rates.

With the LM22672, I was planning to use the EN pin as a low-voltage cutoff. I was going to use a 100k Ohm trimmer pot as a voltage divider and set it so that the unit shuts down when the cells drop below 3.0V-3.2V. Does that sound reasonable?

the new Mintyboost can deliver 400+ mA. Better than the 200+ mA of the old versions, but still not that good.

I was just reading about that - it does seem a little weak. And as tempted as I am by this one-stop shopping, pre-engineered system, I think I am going to give the LM22672 a whirl. Webench is quoting 90-95% efficiency between 6-8.4V and from 0.2-1A, so I'm hoping I can do much better than my last attempt. Anyway, this is for fun, so easier is not necessarily better! Thanks again.
Craig

[JollyRoger]

I'm looking for a device that charges the small lithium batteries in portable electronics from 18650 standard cells. I've searched high and low for such a thing, but never found one that does exactly that. There a AA-powered things that don't work very well, and large packs that cost $100+ and are intended for laptops and portable dvd players, but no simple thing that will charge a cell phone or iPod from an 18650.

This one comes close, but I don't get the impression the cells are removable - a fatal law for a flashaholic.

http://www.goldengadgets.com/1-watt-led-flashlight-2200mah-usb-power-charger.html

So has anybody found anything better? If not, can somebody build this? I know I'm not the only one who would purchase such a device.

This product is actually pretty decent for the money. You can use your own 18650, as the other posters have confirmed. Think of it as a combo 18650 charger AND USB power source. Plus it is pretty decent LED light. I took the front apart (unscrews very easily) and it looks like some high powered LED (looks a bit different from Cree or Lumileds, etc.) Fairly easy to mod. Plus the led has its own converter board. The USB power source side has its own converter, too. There is also a charge indicator, which is very handy.

As far as the inefficiencies of upconverting 3.7V to 5V (USB) and then using that to charge a 3.7V cell, I think this is how most of the li-ion USB power packs work these days. It's not super efficient, but it's ok...

Here is another great portable USB power source and AA/AAA battery charger:
http://www.amazon.com/Duracell-Charg...462024&sr=8-10

I bought a few when they were on sales and I love them. USB power is nice and clean and the charger has 4 independent channels, which is nice. There is a flip out AC prong on the back. Not the smallest, but if you consider it's a USB power source that uses the AA or AAA batteries as the source (4.8V), it should be fairly efficient. Great for traveling, since you have a power source and charger all in one.

Wow, this must be my first post in...YEARS! hehe...

[acruxksa]

I've been entertaining the idea of building a portable usb charger myself and have also looked at the LM7805. This seems to be the cheapest and most popular method. In my research I've also stumbled across a switching regulator that might be a better choice. I believe it's more efficient than the LM7805 which should mean less heat. The trade off however is that it's also more expensive.

http://www.rcworldofplanes.net/prodV...idproduct=1047 or an adjustable version http://www.rcworldofplanes.net/prodV...idProduct=1048

This one http://www.robotshop.us/Dimension-En...olt-Micro.html looks like it would give you the ability to use 1-3 14500 or 18650 cells (or pretty much anything else you've got). It takes an input voltage anywhere from 2.6v to 14v and converts it to anything from 2.6v to 14v. a bit more $$ though. This is probably the route I'm going to take except I'll use a 4 AA battery holder which should give me the ability to use either 4 AA alkalines or 4 AA rechargeables. Heck a 3 AA battery holder could give you the ability to use alkalines, NiMH or 14500's. Plenty of cheaper alternatives to this out there, but making it yourself is most of the reason for having it.

When i get some free time, I'm going to give it a shot. Just haven't had the time recently.

More info on switching regulators as opposed to linear regulators. *note* the efficiency numbers for linear regulators when compared to switching regulators.

http://www.dimensionengineering.com/...regulators.htm

[skaura88]

Well, since we're both DIYers, here's my two cents...

Ditch the charger altogether. The LiIon->USB->LiIon conversion is bound to waste a significant amount of power.

Crack open the gadget whose runtime you want to increase, get at its cell and put a tiny three-terminal switch across the cell output before it gets to the monitoring circuit. To the other pin of the switch attach one of the two wires leading to a suitable connector (I'm in love with JST ones available at DX for this sort of job - they are small, unobtrusive and easy to use). The other wire, you just connect in parallel to the existing cell.
This way you have a gadget that works fine off its own cell, but to which you can connect any other LiIon cell via JST connector, flip the switch and have it use the external cell directly - no power lost in conversion.

This obviously won't do if you don't want an external cell hanging from your device (or in a holder attached somehow to said device); on the other hand, you can attach any LiIon at all - 14500 from a flashlight, prismatic cell from any trashed gadget, big fat LiPo leftover from the RC plane that you nosedived on concrete...

Depending on the device, it might work fine off a 4xNiMH battery too (3xNiMH won't do for a LiIon-powered gadget; it'll think the cell phone battery is empty almost immediately due to voltage incompatibilities).

[download]

I am using this more than a year for iphone. Can accept bare (unprotected) 18650 only.

[Lightcrazycanuck]

[Milan]

I am using this more than a year for iphone. Can accept bare (unprotected) 18650 only.

Wow, that looks interesting, never saw it at DX/KD.... any tip where it can be acquired?

[Lightcrazycanuck]

[NutSAK]

Wow, that looks interesting, never saw it at DX/KD.... any tip where it can be acquired?

http://detail.china.alibaba.com/buye...589555313.html

[download]

Bought it directly from China at that time, PM me if you want.

[dope]

Bought it directly from China at that time, PM me if you want.

Hi! I want one or two )) what should I do?

[download]

I got a 3 chargers. ( sold )

No battery included.
Please PM me if you are interested.

[ama230]

I had first wanted to say that I have a 18650 charger/flashlight that's really handy as there in case of an emergency and was pretty cheap. It could help you with your design.

Here is the one from deal extreme i got, but it took like three weeks to get here but what are you going to do when there is free shipping involved?
http://www.dealextreme.com/details.dx/sku.18883

Then there is one on ebay and you could probably find it cheaper... Its exactly the same and is going to get there a little quicker. It comes with all the plugs and is very simple to use.
http://cgi.ebay.com/LED-Flashlight-c...item27b3a78829

Hope this helps...
Eric

[KiwiMark]

Here is the one from deal extreme i got, but it took like three weeks to get here but what are you going to do when there is free shipping involved?
http://www.dealextreme.com/details.dx/sku.18883

This looks like a not bad charger. Reasonable price and would be able to boost my cellphone battery way better than my 1 x AA cell phone charger (good way to drain a few AAs though). I use my Nokia N85 as an E-Book reader while camping or away for a few days and the more charging options the better. I have a reasonable number of 18650 cells (one of my lights runs from 8 x IMR 18650 cells) so I could take 4 spares for my 18650 lights and/or recharging my cellphone.

Does this charger put out enough oomph to charge a cell phone to full? Or at least to 80% or more? I'd like to be able to ram 1000mA into the phone and get a decent charge in a short time.

[ama230]

This looks like a not bad charger. Reasonable price and would be able to boost my cellphone battery way better than my 1 x AA cell phone charger (good way to drain a few AAs though). I use my Nokia N85 as an E-Book reader while camping or away for a few days and the more charging options the better. I have a reasonable number of 18650 cells (one of my lights runs from 8 x IMR 18650 cells) so I could take 4 spares for my 18650 lights and/or recharging my cellphone.

Does this charger put out enough oomph to charge a cell phone to full? Or at least to 80% or more? I'd like to be able to ram 1000mA into the phone and get a decent charge in a short time.

It depends ont eh capacity of the phone battery itself. Then again a typical iphone battery is 1200mah+/- and this phone charger is 2200mah+/-, then it should charge you phone at least once and then some. If you carry a couple of the 18650's then you should be fine as they definitely have some capacity but there is always transmission loss involved even though its dc/dc.

[dope]

I got a 3 chargers. ( 1 left only )

Charger & plugs $20
Pouch $5 (Tight fit the charger only, not the plugs)
Ship $4, additional $3 for tracking.

No battery included.
Please PM me if you are interested.

Yes I am interested!
Sorry for a dumb question but how can I PM you?
If I click on your Name I've got some "denied" message
I am in Skype my ID is seffka7. Could you drop me a contact there or EBay item number. Please )) Thank you