One Dollar AA cell Power Bank!

[Dashmellow]

The other day I was impatiently standing in the checkout line at the local "Dollar Store" waiting for some lady to pick put a bunch of party balloons for her kid's birthday. Of course, once a customer finally makes a choice in these weighty matters the badly underpaid and totally unmotivated checkout clerk needs to individually fill each balloon with helium and then make sure that she secures each filled balloon to a metal bar so it doesn't float away while she is ever so slowly filling the rest of the order and this can take, you know, like forever. So I killed time chatting with some of the other customers on the line while I glanced around at the all the crappy "impulse purchase" items they always keep within arm's reach just for such an occasion. That was when I noticed the one dollar power banks!

I've seen these AA cell powered USB chargers around here and there for quite some time now but they've never really interested me very much and all of them that I've seen before work with a minimum of four AA cells. I can't recall ever encountering a two cell version and logic would seem to dictate that two AA batteries wouldn't give you enough voltage to power a USB cell phone charger.

But I was intrigued and thought, "Hey, it's only a dollar, what the hell? They come in white or black, so I bought a black one and much to my surprise it has turned out to be the coolest, most bang-for-your-buck item I've purchased in a long time!

Of course, for only a dollar you don't get any batteries with this thing so when I got home I popped in two 1900 mAh 1.2 volt AA Eneloop NiMh cells. (BTW, I'm a big fan of good quality LSD NiMh AA and AAA cells as an alternative to alkalines and Panasonic's Eneloops are hands-down the absolute best available.)

So, I don't know exactly what circuitry they've got inside these little power banks but some testing showed that this thing takes the power from two 1.2 volt NiMh cells and outputs a solid 5.3 volts @ .4 Amps! The result being that I can run a super-capacitor powered Mobius or an SG9665GC for at least two full hours with excellent results. If I were to use lithium AA primary cells my guess is that the run time would probably be at least twice that, and perhaps more! To top the whole thing off, the power bank is built pretty well for such a cheap gadget and so I think it will last awhile.

This little thing is pretty handy and is an especially great match for a super-capacitored Mobius as it is a small external battery that will provide the same run time as the standard Mobius 840 mAh internal battery option. This AA USB Power Bank is almost the exact same size as a Mobius except that it is two centimeters longer being 8 centimeters in length compared with the Mobius case length of 6 centimeters. The power bank and the Mobius are both 3 and one half centimeters wide and they are nearly the same height with the Mobius measuring 18 millimeters tall vs 20 millimeters on the bank.

A very cool find! I may have to buy another!

 

[DT MI]

Cool gadget. I'm going to have to look around for a couple to keep in the car 'just in case'.

 

[jokiin]

it's the commercial equivalent of the old Minty Boost/Altoids charger http://www.instructables.com/id/MintyBoost!---Small-battery-powered-USB-charger/

 

[Dashmellow]

it's the commercial equivalent of the old Minty Boost/Altoids charger http://www.instructables.com/id/MintyBoost!---Small-battery-powered-USB-charger/

That's cool! Thanks for posting this as it's offered an explanation of the circuitry that makes this work.

 

[jokiin]

must be a good design if even the 1.2v rechargeables will give you 2 hours run time, that's a bargain for a $1 gadget

 

[Dashmellow]

must be a good design if even the 1.2v rechargeables will give you 2 hours run time, that's a bargain for a $1 gadget

Yeah, I'm amazed. And the SG9665GC works too! To be fair to this little gadget, the screen of the SG flickers a bit when first powered on but once the screen turns off it works as well as the Mobius for about the same length of time. I'm aware that the SG9665GC is very efficient in power consumption anyway, which is why I thought to try it. Not often one stumbles upon such a bargain.

 

[jokiin]

yeah the .4amps is a bit on the low side to run our camera, but quite impressive for $1 all the same

 

[Dashmellow]

Cool gadget. I'm going to have to look around for a couple to keep in the car 'just in case'.

I found this at a "Dollar Tree" store. If they have those near where you live that would be the first place to look.

Edit: Apparently you can buy these by the case!

So, yeah, as a back-up power supply kept in a vehicle, with two AA lithium primary cells installed this charger would last safely as long as ten years in storage. I may have to invest in the cost of two lithium cells just to see what kind of run time I can squeeze out of this thing. My guess is that it may go 4-5 hours with lithium cells.

 

[Dashmellow]

yeah the .4amps is a bit on the low side to run our camera, but quite impressive for $1 all the same

Running the Mobius it would dip down to .34 or even .3 but the camera didn't skip a beat right up until the batteries died. The Mobius really wants .5 amps minimum so go figure.

 

[flank]

Thats a good find. I bought something similar for $20 before.

http://www.adafruit.com/products/14

 

[niko]

Those who are lazy to drive to "Dollar Tree" ( to save time and money on fuel ), or don't have that shop around, Aliexpress sells them for about 1.50usd incl. shipping.

Black colour case click HERE
White colour case: click HERE

As a "bonus" it has an LED as well

 

[Dashmellow]

Earlier this week I wanted to keep a watchful eye on a particular section of my rural property while I was out working in a different area. I set up one of my Mobius cameras (with super-capacitor) in the crotch of a tree branch with one of these AA power banks connected via a short USB cable. Later, when I thought the batteries were close to wearing down I was simply able to swap the power bank for another one with fresh rechargeable batteries that I had in my pocket and was good to go for another two hours without having to touch or move the camera. Using the Mobius for short term stealthy video surveillance has become a favorite use for this camera and these power banks make it especially easy.

I've been finding these little AA power banks to be pretty handy and now that I own two of them I've become a big fan. I'm finding that I use them more than I expected to when I first bought one on a whim. They're cheap enough that you can always have one at the ready if you just want to run a camera for a few hours and not have to fumble around with individual batteries. Great for short term full time parking mode too.

 

[Dashmellow]

Several months ago I speculated in this thread that a couple of AA lithium primary batteries would probably provide power to a dash cam for many times longer than a pair of alkaline or NiMH batteries and I finally decided to give it a try. So, all I can say is DONT TRY THIS AT HOME, folks! The results were anything but what I was expecting.

I used a pair of 6X Energizer Advanced lithiums that have been siting around for several years and despite the fact that two of these batteries cost several times what the one dollar power bank goes for I was curious to know just how long I could run a Mobius on them.

Part of the idea was to see if it might be worthwhile to keep one of these power banks in my vehicle loaded with lithium batteries as a kind of durable long shelf-life back-up for running a dash cam in full time parking mode or any other charging need that might arise. I was also thinking this might be a good safe alternative to my lithium-ion power banks to use on a very hot day while I'm out shopping or whatever and they would also be fine being permanently stored, or used in sub freezing conditions.

Bad idea, it turns out.

So, I set up a Mobius (with super-capacitor) to run off the power bank on the kitchen table facing out a big picture window and left it running until the LED pilot lights on the camera stopped blinking. Every now and again I would check on the set-up to make sure it was still running. As luck would have it I happened to check on it just in time to see the last couple of blinks at the moment when the batteries crapped out at the two and a half hour mark. I was expecting these 6X lithium batteries would run a lot longer than that, but oh well, I wouldn't have known unless I tried this. Nothing ventured, nothing gained, as they say. It was then that I got the shock of my life when I went to pick up the power bank and it was so hot I dropped it! Almost burned my fingers. Yikes!

So, while it turns out these little power banks are quite happy to run for long periods of time with alkalines and NiMHs, they really DON'T get along too well with lithium primaries for reasons I don't quite understand. Probably a lot of resistance is building up in the cells for some reason.

Interestingly, the power bank remained undamaged and is happily back in service with my Panasonic Eneloops. The Mobius was fine too.

 

[kuoh]

It was likely just the batteries that were getting hot. For the circuit to output 5.3V @ .4A, it would need to draw at least .7A from 2 x 1.5V batteries, but probably closer to 1A due to efficiency losses. While alkalines will tend to self limit the current due to the high internal resistance, I wonder if lithium primaries lack that side effect and the continuous high current draw caused the overheating. They are generally advertised for limited duration high drain applications, like charging a camera flash, so this may be pushing them outside their design boundaries.

Also, the longer life claim generally applies to very low current applications, like in a remote control. Most batteries have much lower apparent capacity when used in high drain applications, check the link below.

http://www.powerstream.com/AA-tests.htm

KuoH

So, while it turns out these little power banks are quite happy to run for long periods of time with alkalines and NiMHs, they really DON'T get along too well with lithium primaries for reasons I don't quite understand. Probably a lot of resistance is building up in the cells for some reason.

Interestingly, the power bank remained undamaged and is happily back in service with my Panasonic Eneloops. The Mobius was fine too.

 

[Dashmellow]

It's always been my understanding that lithium primaries were suited for continuous high current drain as I've seen them advertised as being ideal for things such as kids motorized toy cars and trucks. The Battery Showdown Project states that, "Clearly, these batteries perform very well under high discharge current". - "Lithium cells really shine under high drain".

In any event, since the Mobius requires only 500 mAh to run, one might think two lithium primaries wouldn't be taxed all that much. Then again, perhaps you are correct? Thanks for your comments @kuoh.

To be clear, I was well aware that the cells were getting hot, not necessarily the circuitry. I was just describing what it felt like to pick the thing up. I'm not sure it's a distinction worth fussing over.

 

[jbinx]

@Dashmellow
Most likely it's the voltage of these lithium primaries that caused that problem. These cheap powerbanks were designed to handle regular AA cells or rechargeables but not lithium primaries. Add to that that the lithium primaries are more than capable of pushing out high current without too much voltage sag and you've got a thermal runway.

 

[Dashmellow]

@Dashmellow
Most likely it's the voltage of these lithium primaries that caused that problem. These cheap powerbanks were designed to handle regular AA cells or rechargeables but not lithium primaries. Add to that that the lithium primaries are more than capable of pushing out high current without too much voltage sag and you've got a thermal runway.

I remember thinking back then that the voltage output would have dropped significantly by the time those batteries crapped out after two hours when I went to pick up the hot charger from the table but I guess lithium primaries can discharge for quite a long time before the voltage sags all that much, so what you say sounds plausible. I just wonder why those lithium cells still only powered the camera for two hours just like the NiMh as one might expect them just to keep going longer. I assume different circuitry would run the cells longer at lower temperature.

 

[SawMaster]

Good "boost" drivers can reach 90%+ efficiency these days. Can't say why the lithium primaries warmed up and failed to give the expected runtime- were they past their "use by" date? I'll do some asking around later tonight.

Definitely going to Dollar Tree ASAP- thanks for the 'heads up" on the deal!

Phi