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Double Capacity MintyBoost with 4-AA Battery Holder Modification

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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
 
 

 
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jono4564 years ago
 I made a 4 AA-cell USB charger also but used a slightly different approach.

I used 4 NiMH AA cells 2700mAh which are actually higher capacity than Alkaline cells and cost only peanuts to recharge and can be recharged 500 times. This is much greener than using throw away Alkalines.

Then, since they are slightly lower voltage (nominal 1.2v), all that needs to be done is to connect the 4 cells in series. No voltage regulation is required. This makes it very simple to construct, comparatively and there are zero losses as no heat is produced in the regulator components. The voltage stays well within the USB specification limits.

Advantages: MUCH cheaper to operate.  MUCH greener. MUCH simpler to build. As much or more runtime than alkalines.

I have used mine to power my Palm TX PDA for a few years. Still using my first set of Panasonic 2700mAh AA cells.


pkunze jono4564 months ago
How exactly did you do this? I have been trying to build one to charge my iPhone 4S with four AA rechargeable wired in series and cannot get it to charge! How many solar panels do you have?
This is great for Disposable Batteries, that are 1.5v which if hooked up in series would give 6v way to much for USB, but Rechargeable's like you said only have 1.2v so that gives you 4.8v - 5v perfect for USB. 

Lets' see...  4 batteries in series gives you 2450mAh and 2 in series gives you 4900mAh. The minty boost is only 85%-60% depending on how much juice you pull out of it.  4900*.6=2940mAh  So at it's lowest efficiency we be actually gaining 2940-2450=490mAh by using the Minty Boost Circuit.  Not bad might give an extra charge or two on certain things.  Then you gotta take off how inefficient it is actually charging batteries from another battery so that lowers the eff. even more. 
I have done the experimentation and charging Li-Ion batteries like those in most all PDA, cell phones, computers etc. is quite efficient. Charging NiMH or NiCd is not, but you charge your NiMH from the wall socket so it still only costs a very few pennies for a complete charge.

I cannot imagine anyone would want to use AA alkaline, or any alkaline primary (non-rechargable) cells for any routine use as that would be quite expensive. That is why the MP3 players etc. come with rechargables in the first place.

Personally, I have tried using 4 AA alkaline cells in series for the higher 6 volts and have found it does not hurt my Palm TX at all. I suspect that would be true of most any if not all USB devices in reality. I am not advocating the reader to risk it but I have done so and the margins built into electronics will allow for that much voltage deviation easily.

I would be more concerned about high voltage spikes put out by the minyboost chip, particularly if the caps and inductor used were not correct. I would certainly want to put it on a scope before I put it on my $300 iPod!
Well Think of it in terms of capacity.  1 AA Rechargeable has about 2450mAh. 2 In series only has 2450 mAh, but 4 batteries in sets of two, two stringed together then the sets are hooked up in parallel it will give you 4900mAh.  50% more current, then if it was all hooked up in series.  If all you was getting was 50% eff out of the Minty Boost then It would be exactly the same has hooking them up in series.  But you'll probably get a minimum of 60% at 200mAh and 85% at lower current draw. If it's operating at 85% then the capacity of your cell's will be 4165mAh at 5v, and the rest of the 4900mAh will be wasted in the conversion. Now compare that to the Capacity of the series cells 2450mAh at 5v.
 I am afraid you are applying some magic there. Try changing all of your values to watt hours and it may be easier to see.

Yes, you get twice the current capacity with two sets of 2 AA paralleled But you only have half the voltage.

When your mini boost nearly doubles your voltage as it must, it does that at the cost of halving the current capacity.

You can see this clearly if you think in terms of power i.e. watts = volts X amps.

Now If you apply your 65% efficiency you have shown that you will only get 65% as many watt hours out of the 4 AA-cell parallel/series miniboost setup as you will out of the 4 AA cell series setup.

Just remember, if the mini boost, or any circuit, increases the voltage of a source it has to decrease the amp/hours available. If that were NOT true we could just keep adding miniboost type circuits to increase our voltage indefinitely and with no loss in current available (amp hours) we could power our homes on 4 AA-cells.
jono456 jono4564 years ago
 The reason for the miniboost chip is if you need 5 volts but only have 3. You don't use a miniboost circuit if you already have 5 or more volts from your battery supply.

If using the mini boost was somehow more efficient, when you already have 5 volts or more of battery power, they would be in existence in all battery powered devices to get the 'free energy'. They are not.

My Bad, I completely forgot about converting it to watt hours, Makes more sense now. Thanks.
You are also adding mAh incorrectly. The addition of battery capacity is the same regardless of parallel or series configuration. 2 sets of 2 in parallel gives 3V with an output capacity of double. 2 sets in series gives 6V with the same output current as a single config. As far as battery capacity, in either case there are still 4 batteries. 4 batteries at say 2500 mAh = 10Ah total. The difference comes in when you use the parallel config and draw twice as much current.
 I have seen this circuit and/or something very similar posted in many places on the internet. It always gathers a great following of enthusiasts but I have never been able to understand why.

IF you only have 3 volts of battery power then it is a USB solution but IF you have 5 volts or more of battery power then it is a waste of money and energy to build or to use. But even when you show the waste, most people still want to build it, looking for any excuse possible to try to justify the inefficiency

IF you want to use 4 AA alkaline cells instead of NiMH  all you need do is insert a 1n400x series diode in series with the batteries to drop the voltage to a safe level. This is far simpler and less loss then stringing 2  sets of 2cells in series then paralleling them  for 3 volts and then driving the miniboost circuit.

I am starting to think it is somehow a fascination with the Altoid tin. But whenever you are paying for batteries to power a device, efficiency is paramount in my way of thinking. Electrical efficiency means for a cheaper device to operate as well as a smaller and lighter package to carry around with you, not to mention more environmentally friendly.
B_Wolfe jono4564 years ago
It'd be cool if you made an instructable for a usb recharger without the minty boost circuit.
 I am confused. I do not see where you are gaining anything using the Minty Boost Circuit. It always operates at a loss compared to just battery cells in series with no minty boost or voltage regulation at all which do not have any added loss other than the cells themselves heating, and of course the minty boost device also has that loss just the same.

Maybe I am misunderstanding your comments?
jsaen33 jono4564 years ago
This is the same setup (4 aa-cell @1.2V) I have been using for years to power my Dell Axim PDA. Very simple setup just be sure and use a blocking diode.
Kasm279 jono4564 years ago
Palm ftw! I have a USB cahrger that i use for my Palm m515, comes in handy for the phone and DS too... 
jbrown1208 months ago
couldn't you just run 2 2 battery clips in parallel to one another for same effect without modding the 4 clip?
RoysterBot (author)  jbrown1208 months ago
Yes you could. I preferred to use the 4 AA battery holder because of the way it fit in the Altoid tin.
jlomax1 year ago
Will this work with the Samsung Galaxy Note?
RikSmith1 year ago
Thinking about trying this with 3 lithium rechargeable 18650s wired in parallel - as a first project. Will it work and what should I be worried about? Thanks in advance!
what happens when the cathode is not ended with silver stripes and why did you use red and black wires and not any other.pls reply me
RoysterBot (author)  Caleb Yankey1 year ago
If you reverse the diodes then you will not get current to flow from the batteries. Red and black are standard colors associated with + and - DC power connections. But you can use any color.
is it compulsory to use a silver stripe.pls reply me
RoysterBot (author)  Caleb Yankey1 year ago
I do not understand your question.
heyboer1 year ago
Instead of the mintyboost usb configuration could an ac charger (as shown below) be hacked to accomplish the same thing?
4-9-2013 11-35-55 PM.jpg
RoysterBot (author)  heyboer1 year ago
If you mean hacked to be able to provide USB power from AA batteries then no.
Thanks yhanks for this project.Hope to be experting more from you
sarju72 years ago
Does anyone know if this will work on the playstation vita?
If it charges with 5.5v DC, then technically it should. The only way to find out for certain is to try it. (At your own risk)
jsilvers12 years ago
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 (author)  jsilvers12 years ago
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.
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 (author)  jsilvers12 years ago
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.
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
JerryBYong2 years ago
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 (author)  JerryBYong2 years ago
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/

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 (author)  JerryBYong2 years ago
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.
Ryutso2 years ago
So by "double capacity" you mean, if 2 AA's charge your phone for 4 hours, this will charge it for 8 hours?
RoysterBot (author)  Ryutso2 years ago
I'm referring to the fact that if you use identical batteries then the charging capacity in this configuration is about double.
jman123242 years ago
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.
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?
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