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

[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.

[thatone1guy]

Hi, I like your project, but what version of Minty Boost were you using?

[RoysterBot]

I have build this 4AA gadget charger with both version 2 and 3 of the MintyBoost.

[thatone1guy]

Great! After I build Minty Boost,I will build this. Thanks :)

[p3ngwin]

some people here are saying that it would be more efficient to simply have the 4 AA batteries in serial to get your USB 5V.  (possible at least with non-rechargeables due to them being 1.2v)

my question is about the efficiency comparison of using the MintyBoost methods and the "serial" method suggested. 

what is the lowest voltage the mintyboost drops out before it no longer provides 5V, compared to the dropout of the AA's in serial ?

i think that would reveal the real best efficiency

[RoysterBot]

Depending on the characteristics of the batteries you are using and the demands of the device you are powering the batteries will be able to give up their stored energy to a certain point. This point would be variable based on your conditions. You could determine this drop out point with some experimentation.

The MintyBoost v2.0 device is using an LT1302 boost converter which has a minimum input voltage rating of 2V. So this can give you some extra usage from batteries that were considered dead by your device. The LT1302 (or any DC-DC boost converter) sacrifices current to provide a target voltage. So you are able to gain device usability at the expense of energy efficiency. The efficiency curve of the MintyBoost varies with the input voltage. I have seen claims of from 94% at 5V to 73% at 2V but I can’t confirm those numbers. One thing on my to do list is to get a data logger and determine what numbers I’m getting. I’ll share the results when I do.

If your main concern is the most efficient energy transfer configuration then I would suggest batteries arranged to provide 5V. Battery voltage will of course vary with usage so use care. Some USB powered devices are more tolerant than others and can handle an input voltage of slightly more or less than 5V but I don’t recommend swaying from the USB standard of 5V.

Usability was my main concern. The ability to get reliable 5V power from the MintyBoost while using different kinds of AA cells is a plus for me.

[ptsampoukas]

It is true that a MintyBoost or any other switching circuit based design helps you get the maximum energy out of your batteries. For this you pay ~20% of the energy you get.

Based on specs like this (http://data.energizer.com/PDFs/nh15-2300.pdf) though, and if you have a 4 AA battery setup, you would have to need close to 2A for the switching circuit to give you more energy for the same batteries. And 2A means a VERY power hungry device.

The reason is that for current needs of 1A or less, the battery will give us more than 1.175V (so 4*1.175V=4.7V which is often the threshold) until it has offered more than 90% of its stored energy. This makes a ~80% effective switching regulator a bad choice.


Personally, I find that a simple setup with a manual switch that enables or disables a 1N4001 diode most practical. If you use 4 AA alkalines then enable the diode, if you use rechargables disable the diode. For most practical applications you get more energy for the same batteries, which is what counts.

[p3ngwin]

also, while i'm here, slightly off topic, but do you know anything about how i can have multiple power sources combine to charge a single battery unit? 

i have a project that i'd like to have solar & magnetic induction combine to charge a single battery pack. the energy inputs will be stabalised and regulated using something like a mintyboost or anyvoltmicro, but i'm not sure about the differing currents. 

i understand that the battery would charge at the lowest current of the two even if the voltage is the same? any pointers would be greatly appreciated.

[RoysterBot]

SparkFun Electronics might have things that would interest you. Do a search for "solar" on their web site (www.sparkfun.com).

[p3ngwin]

excellent, thanks for the swift and informative response. 

i too prefer a stable and practical USB 5v output from my input, so will be using something like a mintyboost or this. 

cost is little concern for me as i want a good balance of assembly effort, and flexibility of parts for other projects.

[tobyscool]

i used this items and used 4 AA batteries and it works i tried it on my ipod nano 5th gen,iphone 3g,NDS Lite and they worked.But i haven't tried it charging for an hour or more but it works

MC 7805 +5VDC Voltage Regulator
Type-A Female USB Port
100 UF Electrolytic Capacitor 10-50v
0.1-0.5 UF Capacitor 6-50v
150-160 ohm Resistor
9V Battery clip
2.2V 20mA LED
4 AA battery holder

[bowmaster]

This is nice. How many times could it charge an iPhone 4?

[RoysterBot]

From my experience with my iPhone 4 using 4 rechargeable batteries it will fully charge the phone from 20% about once.