Instructables

Hack that battery pack! ( also, a small lesson in series, parallel, and series-parallel)

Picture of hack that battery pack! ( also, a small lesson in series, parallel, and series-parallel)
(be sure to check out the last step for some updated info and a how to for this method using 4 batteries, using four would increase the life span. i had to use three for the sake of saving space.)

hack that battery pack!! we have all seen those 4 double a battery holders sold at radioshack, online, etc. the following involves modifying that same battery pack. But what can you do to it? first before I answer that i would like to say that I needed to make this to meet a few needs in a small 8vdc booster circuit i made. The circuit can use a voltage input as small as 1.2 volts and amp it up to 8. So i needed a power supply, I was planning on using just one double a battery but the run time on that would be so short, also once the battery voltage drops lower than 1.2 it would quit working. It would last maybe two hours if I used one battery. SO after some thinking I decided to use a battery pack, but all 4 double a battery packs are designed for series wich would give me a higher voltage output but not a longer runtime, so I hacked my pack! with a few simple modifications I turned it into a series parallel battery pack. Whats this and why? If you havent heard of series or parallel before then I will explain the terms now. batteries that run in series outputs a higher voltage while maintaining the same mah as one of the batteries, some devices that use this set up are tv remotes, radios, flash lights etc. its where batteries are set up in a way where the positive terminal of one battery runs into the negative terminal of the next battery. Parallel however, now when you set up batteries in parallel you will have the same voltage output as one battery but a longer run time. So the batteries used in parallel would be setup with all the positive terminals and negative terminals connected. I know this can be confusing thats why I included a few pictures to show you what series and parallel look like(see next step for a look at the pics). Now this battery pack hack is modified to use series parallel. (you will notice I cut off one of the battery holders, turning the 4pack into a 3 pack) If you have a good understanding of parallel and series then you can probably figure out what both combined does. If not I shall explain!  I hacked my pack to use two batteries in parallel then in series with one battery, so I am using two double a batteries in parallel while using another in series of the two parallel. this way I can have the voltage output of two batteries but the run time of three.

 Update! Its been brought to my attention, if you use two batteries in parallel in series with two more batteries in parallel the performance would be better! see last step for a picture.



in short. Series creates a higher voltage output. (4 double a batteries would be 6volts. 1.5x4)
parallel creates a higher mah. longer run time (2000 mah per battery, 4 double a batteries is 8000 mah)
 
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Kokoska4 months ago

Hello there! I am making bike lamp ( headlight ) and i have eneloop 1.2V 1900 mAh battery. 8 of them. I would like to make 4 battery holder ( 2 batteries series and 2 parallel ). My calculation says it would be 2.4 V and 3800 mAh per holder, is that correct? And second holder with 4 batteries would be connected parallel with first so i get double capacity right?

hashmaster11 months ago
be careful running the 3 batteries. with the 2 in parallel, and the 1 in series. once the single battery is discharged you run the risk of over discharging the battery, this can create a short, which can overheat the battery real quick. not a big problem with the once use aa, but li-ion can explode if discharged like that. always use caution with batteries.
out-of-the-box (author)  hashmaster11 months ago
the batteries I am using for this are nickel based. I always take extreme caution when dealing with any type of power source. For lithium ions I buy or build cahrge controllers.
nbenson111 months ago
Having this setup. Wouldn't the single battery run dry before the two in parallel? Given its mah is smaller than the banked together section. Like putting a D battery and an A battery in series would result in the A dying but the D being fine.
out-of-the-box (author)  nbenson111 months ago
I just updated it. I added a last step showing how to use two batteries in parallel in series with two batteries in parallel, that way all batteries have the same life span, while still multiplying the voltage by two and increasing the mah. I still however will be using my 3 setup. Thanks a lot for your comment! I gave you the credit in the last step.
Cool. With the 3 setup if the single battery goes you will still have power but most likely a voltage drop (however still just over 1.2)

Glad I can help in some way :)
out-of-the-box (author)  nbenson111 months ago
good question. The run time is what i was aiming for, the doubled voltage was a plus. I only added the double voltage for one reason, to prevent voltage drop beyond 1.2 volts. If the single battery does die before the rest it still should work. I haven't noticed anything yet, but if something does occur I will be sure to update this. the only way to prevent it from happening would be to set it up with two batteries in parallel in serries with two batteries in series or just the two batteries in parallel before the single in series. Hmm. I will deffinetly have to check into your thought. thanks for posting!
crazyg11 months ago
Also handy if your using a pack on a device that is preferring lithium battery's higher amp output .so a 4 aa pack set up as 2x2aa works great as a lithium 3v replacement , great for saving money when you just need to test something that requires a special battery