Double Capacity MintyBoost with 4-AA Battery Holder Modification

Need a highly portable USB power source that can be replenished with readily available, common batteries?

The MintyBoost from adafruit Industries is an awesome little kit that nets you a USB charger that runs on 2 AA batteries. This is a great thing because AA batteries are available anywhere and together with the MintyBoost can be used to power most USB devices when you find yourself in a situation with no other source of power. As a volunteer providing emergency communications for organizations that are deployed to disaster stricken areas I have been in this situation before. Keeping critical communications links operational in the field is a major mission success factor. Having a highly portable source of USB power to keep cell phones working is a valuable tool for the first responder. There are, of course, many other uses for portable USB power. One of my favorites is extending the play time of graphic intense iPhone games while traveling.

This charger does more then just provide the 5 volts required to charge USB powered devices. The circuit incorporates a DC to DC boost converter that is able to draw power from batteries that may otherwise be considered "dead". Also known as a "Joule thief" this means you get more output from your battery power investment.

After building my first MintyBoost kit I immediately looked for a way to increase the charging capacity of the device. I noticed that a commonly available 4 AA cell battery holder will fit perfectly into a regular (pack of cards) sized Altoids tin with the MintyBoost. And the tight fit made for a very sturdy device with easy access to the batteries; which is important since the batteries are constantly being replaced.

Since the cells in a 4 AA battery holder are connected in series this results in an output voltage that can vary from about 4.8 volts to about 6.75 volts (for fresh batteries) depending on the type of AA cells used. The input voltage range of the MintyBoost is about 2-5 volts. So modifying the 4 AA cell battery holder to connect the output of 2 serially connected AA batteries together in parallel would result in about 3 volts for the MintyBoost input voltage but at twice the power capacity. The extra power capacity comes in handle with the power-hungry USB devices of today.

This battery holder modification is the primary subject matter of this instructable. I will also show how the modified battery holder and the MintyBoost are installed into the Altoids tin. Actual construction of the MintyBoost kit is not covered.

Thank you for all the great comments and feedback!

If you're interested in buying one of these completed kits they are now available here...
bit.ly/dh15cJ
 
 

Step 1 Tools and Materials

1 - Minty Boost (Available here: bit.ly/bHPSKI)

2 - 1N5817 diodes (Available here: bit.ly/c56Ymv)

1 - Altoids mint tin (about 3.75 x 2.5 x .8)  any flavor

1 - 4 AA cell battery holder
There are a number of sources for 4 AA battery holders. I used one from Jameco Electronics and it's shown in the images below. It costs about a dollar and includes a square of foam tape that comes in handy when mounting the holder in the Altoids tin. (Available here: bit.ly/9eOZlI)

22 Gauge stranded hookup wire (red & black)

Solder and related tools

Fairly hefty diagonal cutters

Stuff to insulate wires (Heat shrink tubing and related tools / Electrical tape)

1 wide double sided foam tape

Tools to cut thin, soft metal (Rotary tool and bit, small metal files)
 

Comments

[jsilvers1]

hey i would like to make one just like this but i want to add a led and a switch so when im not using it i can turn it off and not waste the battery power how can i do that

[RoysterBot]

Hello,

You would need a switch, an LED, LED mounting hardware and a resistor that you can fit in the case. There is not much room available so you may have a hard time finding the right parts to meet your needs. There is no need to remove the battery power from the MintyBoost since it draws very little power in its' idle state. I believe it would take about 10 years to drain the batteries if you never used it. So your LED circuit can just simply tap into the positive and negative battery leads for power.

[jsilvers1]

i have a small rc car on/off switch an led with built in resistor all i really need is simple step by step instructions on how to put it in the project if u can do that i would really be greatful

[RoysterBot]

Hello,

Since I don't have the components that you want to use I would not be able to create step-by-step instructions. Part of the fun of making things is the experimentation. Why not play around with what you have and see if you can create something that works for you? Then you can create your own instructable and share what you've learned with others. If you don't know where to start then try searching the web for projects that do something similar to what you want. I seem to remember seeing a MintyBoost with an LED flashlight somewhere but I don't remember exactly. It may have been on Instructables.

[jsilvers1]

one thing maybe u can help im using a USB DC-DC Converter 3V to 5V 1A Adjustable Step-up Boost Power Supply Module to help charge what i want to do u thing i need an dioed so that when the batteries get to low the battery from the lets say ipod doesn't go into the chrger and start draining the ipod and charge the batteries

[JerryBYong]

Hey there, I'm really new to instructables and I wanted to try to make a solar iPhone charger. I bought a emergency charger for an iPhone which uses 2 SA batteries. My idea(or Joshua Zimmerman's) is to. connect the charging circuit to a battery holder and a solar cell. I tried the charger I bought and realised that it charged really slowly! I thought that if I doubled the voltage, from 2.4v(rechargeable batteries) to 4.8v it would charge faster. However, I understand that this kind of charger doubles the voltage from 3v(normal batteries) to 6v and then regulates it at 5v. So will this mean that it will make my 4.8v 9.6v and then regulate it at 5v? Also,I hear that iphones require 2v on both + and - ends. So will it still work? BTW I'm a noob at this so what's the easiest way to make a solar charger for an iPhone that is fast charging and uses a solar cell, a charging circuit from a aa emergency charger for iPhone and 4 rechargeable batteries? Sorry for long thing... Thnks!

[RoysterBot]

Hi Jerry,

I am not an expert on solar charging so I would feel uncomfortable advising you. But there is plenty of information on the web. A Google search will return lots of helpful information. To get you started, here is information on a cool solar MintyBoost that you can build from parts available from Adafruit Industries...

http://www.adafruit.com/blog/2010/07/09/how-to-make-a-solar-mintyboost-a-solar-power-charger-for-your-gadgets/

[JerryBYong]

Hi there RoysterBot,
Thanks so much for such a quick reply. I don't really want to purchase more parts(my wallet's slimming down) but I recently found out that I can connect a 12v battery supply to a car charging adapter and it should charge an Iphone. I was wondering if I can use a 4.5v solar cell to charge the 12v power supply in the form of 10 1.2v rechargeable batteries.
Please let me know if this is possible.
Thanks,
Jerry

[RoysterBot]

Be careful. Rechargeable batteries have different charging voltage and current requirements depending on the battery chemistry. I would not recommend attempting to charge 10 1.2v rechargeable batteries of any type with a 4.5V solar cell.

[Ryutso]

So by "double capacity" you mean, if 2 AA's charge your phone for 4 hours, this will charge it for 8 hours?

[RoysterBot]

I'm referring to the fact that if you use identical batteries then the charging capacity in this configuration is about double.

[jman12324]

i was thinking of making this with the two sets of rechargeable aas in parallel and also have a solar panel attached before the diodes to produce extra mah's and to charge the batteries when minty boost not in use.

[frisbeechamp1983]

Instead of a usb connector, I wat to put a 3.5mm jack to charge my chuffle, So I could make this like a dock. what would I need to change?

[RoysterBot]

Hello. I'm not familiar with the configuration and power requirements of that 3.5mm jack so I can't comment on that directly. The Minty Boost circuit can supply 5VDC at up to 500mA. If that meets the power requirements of your device then it may be possible to wire the 3.4mm jack to the output of the Minty Boost.

[frisbeechamp1983]

OK

[pep2798]

or you could just buy 2 2 aa holders and just lay them end to end

[RoysterBot]

Yes you could. I initially tried that but prefer the nice tight fit I get with the 4AA holder.

[RoysterBot]

Depending on the AA rechargables used you can close to 5AH of capacity. But the MintyBoost can only supply half an amp at 5V where that solar system can supply 1.2 amps at 5V.

[lookwhatjoeysmaking]

my minty boosts batterys get relly hot any sugestions

[RoysterBot]

What brand and model of batteries are you using?

[dragon_ch]

I have been trying to quit smoking and now trying electronic cigarette. I saw this article about battery mod using 4xAAA/AA . I wonder whether "Double Capacity MintyBoost with 4-AA Battery Holder" will be able to output 2-3amp current which is required for electronic cigarette. Any advice will be greatly appreciated.....

[RoysterBot]

Hello,

The good news is I have 2 co-workers who have been using the electronic cigarettes with great results for a few weeks.

The bad news is that the MintyBoost circuit will only output a max of one half of an amp.

Are you trying to create a charger for the battery in the electronic cigarette or an alternate power source?

RoysterBot

[dragon_ch]

Hi,

Thanks for your prompt reply. I am trying to make it as a power source. I have the idea from here http://www.e-cigarette-forum.com/forum/battery-mods/106016-how-build-puck.html

If I can make it 3 amp with variable voltage from 3-7 volts, it will be perfect!!
Do you know of someone who can make it and sell it to me?

Thanks

[lordgarion514]

I know it's been awhile since you posted this, but I just found this 'ible and was wondering if it would work equally well if instead of using the AA batteries a LI-Ion battery from another cell phone would work and what mods would be needed if so. The cell battery I have(2 actually) is 3.7 volts. Also do you know if they make holders for them or would I need to rig up something?

Thanks

[RoysterBot]

Hello,

The MintyBoost USB charger will work from any DC power source in the range of 2 - 5 volts. So your cell phone battery will probably work fine. I am not familiar with LI-ion charging so I recomment that you disconnect the battery from the MintyBoost before charging. I don't know a source for cell phone battery holders.

Best Regards,

RoysterBot

[lordgarion514]

Thanks for the reply. As for charging the battery, I have the phone they came out of and the wall charger so that will be my charging "stand".

Forgot to mention, This is a very nice and polished "ible, Excellent job.

[iasonas]

Hi,
I 've built the charger but after a while it gets real hot. However the iphone is charging.I used the 1N5818 diodes instead of the 1N5817, because I couldn't find them. Could this be the problem? Apart from that, I measured the voltage of the data pins of the usb port and found out that both give approximately 3 Volts instead of 2. Can you help me please?

Best regards

[RoysterBot]

Hello,

The Mintyboost does get very hot. If you are charging the iPhone successfully then things sound like they are working normally.

To help dissipate some of the heat I make a small solder connection between the top of the USB connector and the case. I would also like to add a heat sink directly to the 8 pin chip but have not done this yet.

I was originally concerned about how hot the device got while charging but this has never been a problem in the two years I have been using it.

Best Regards,

RoysterBot

[iasonas]

thanks a lot !

[awsomeegan]

can you tell me what version of the minty boost is for or if it matters which version as i would like to do this to the version 3 minty boost

[RoysterBot]

Hello.

I have used this with both version 2 and version 3 of the MintyBoost.

[iamahuman]

Hi, I built this however when I use rechargeable AA it makes a high pitched sound, (but not with Alkaline) and when I use any sort of batteries the circuit board becomes too hot to touch for a couple of seconds, and it is wasting a huge amount of energy. Is there any way to stop this?
Thanks

[RoysterBot]

It sounds like you may have a problem with a solder joint, a short between some components or some other issue. Make sure the MintyBoost kit is working properly before trying the double capacity mod. Then when you do make sure you have the diodes installed correctly and there are no shorts.

[iamahuman]

Well, I retested the minty boost working alone, and it works perfectly fine so I must have made a mistake putting in the diodes.

[joshnosh]

where is the Joule thief? and do you really need diodes on the batterys. they cant be helping

[RoysterBot]

The Minty Boost circuit works like a Joule Thief in that it trades current for voltage and is able to leach out power from the batteries. I added the diodes in this project for safety. Since I was building these for non-technical people I wanted to make sure the design could handle someone installing batteries that were in radically different states of charge or mixed battery types. If you could guarantee balanced batteries of the same type were always used then you could remove the diodes and get more efficiency. In my case the safety factor was worth the few tenths of a volt drop that results is isolating the two sets of batteries with the diodes.

[joshnosh]

ok so its not a jewel thief at all really its a dc-dc converter
a jewel thief would be able to keep running till acid started leaking from the battery's where as this will die when they battery's are about 1v so i little less then most electronics but still not a joule thief. i don't see a real jewel theft being any good though as the battery has already given up most off its power at this point and probably wouldn't charge a phone/ipod
"few tenths of a volt drop" you make it sound like a low number. forward dropping voltage off the ones you linked is 0.45v which is still a considerable amount.
personally iv never had a problem with mixing battery's and i wouldn't put them in
but you have a valid point so that's up to you
tell me why did you not wire the battery's in series?
you could also avoid the diode problem by just having 2 battery's running and 2 in storage.

[RoysterBot]

Each set of 2 batteries is wired in series. Then the sets are connected in parallel. I did this for convenience when charging devices with larger batteries. I also build these with one set of batteries which leaves space for a spare set of batteries or a charging cable.

[joshnosh]

interesting
i ment why not all the battery's together in series giving 6 or so volts
i cant find what chip its based on but iirc it can take 6v and would allow you to squeeze more out off your batts and would be more efficient

[RoysterBot]

The chip's manufacturer recommends limiting the max input voltage to 5. There is a danger of exceeding that with fresh alkaline cells. You could probably get away with that if you use rechargeable cells. Once again I was designing for safety.