Hi all!

I've started flying fpv with 3s batteries, but for about 10 months or so i'm now flying with 4s batteries. So i have a bunch of 3s batteries on a box without giving them any use.

So i decided to "recycle" them into a "big" battery for field charging. 
This is the process that if followed (please, manipulating lipo batteries can be dangerous, only do it if you are sure of what you are doing

this is only the process that i followed (please, do not take it as a tutorial).

The batteries i've used for this are cheap zop power 1.500mah 40C:




First of all, i've checked  that all batteries where in storage voltage (all cells) and then i've de-solder all the cells and separated them carefully. Then, with a multimeter you have to find wich side is positive and wich is negative, and mark it on each cell. Its very imporant not to make mistakes in this step!! (i've checked it twice)






i had 16 good cells of 1.500mah (i had to discard someones that were damaged) so i decided to make a 4s 6.000mah pack, making 4 packs of 4 cells in series each, and conecting this 4 packs in paralel to each other. (i dont know if explaining myself well...) 

But i foundend a website with a good diagram for making this. (sorry the web is in Spanish, but the pictures are quite explanatory...)

this is the link: http://tallerdedalo.es/web/ConexionLipos

as you can see on the diagrams of that website, it only shows how to make a 3 parallel conection, but it can be extrapolated for more parallel connections:



First i've made the packs of 4 cells conected in parallel, so i have four 1s batteries of 1.500mah each one (following this diagram






(remember that the website where i got the diagrams only shows how to make 3 paralle conections, just add one more cell)

this is how i made each pack:





Here are my four packs:



For soldering each cells i've used a thick wire without the jacket and fully tinned.

Next place the 4 packs in order  and solder them as shown in the first diagram:






Then solder the xt60 with the wires:



and the balance conector:



now you have a functional 4s battery of 6.000 mah. it only remains to protect everything well and isolate it. I've used some "foam" to protect the bottom and top of the battery and isolate all with electrical tape and heat-shrink







although the resulting battery is in theory of 6,000mah, it gives me to charge 2 or 3 batteries 4s of 1500mah.

It's not too much, but when i go out for flying i can carge and fly 2 more batteries due to a lot of old batteries that I did not use at all....

Please, as i said before... lipo batteries are dangerous... treat them carefully. 

Always be aware of the polarity, and be carful no to short-circuit them... When i was making one of the parallel packs (mi idea was to make a 4s/5p to get 7.500mah) i accidentaly shorted negative with positive with the tip of the welder and although it was only a moment and apparently nothing happened  when I realized, that package was starting to swell more and more  and getting very hot....so i quickly putted it on a safe place. Finaly it dosnt burn or explode but it was close to it.....

PS. if someone sees something that is mistaken, please advice to correct it

As you charge your flight packs with the 6000mAh pack, the voltage of the charge pack will drop, which is (I think) why you are only able to charge 2 packs with it. Ideally you would have a 5S or 6S 6000mAh pack so that it can still charge your flight packs to 16.8V. You would then be able to charge up to 3 x 1300mAh or 5 x 1050mAh packs.

Good use of old cells though.

(Disclaimer - This is not a suggestion that anyone SHOULD do this, as Pablo says, LiPo's are volatile and can explode and/or leak toxic gas when mistreated, always be aware when doing anything with LiPo's that they can be hazardous!)

Good work Pablo! I've built a lot of A123 packs (LiFePO4) in my life and it was always fairly nerve-wracking - it takes a lot of extra guts doing it with lipos!

Nice effort and it looks like a good way to re-purpose unused batteries, although I'm paranoid enough as it is about normal off-the-shelf LiPos so I'm not sure hacking any about is something I would try to be honest  It certainly looks like you did a good job with the solid bridging wires across each of the banks 

The one issue I do see with this setup however is no ability to monitor the voltage on each of the individual cells. You can monitor each "bank" of cells but not the individual cells in a bank. So no way of knowing if an individual cell has gone bad and with everything completely wrapped in black tape you won't be able to see if one of the cells in the middle of the pack is starting to puff up.

(12-Aug-2018, 12:21 PM)SnowLeopardFPV Wrote: The one issue I do see with this setup however is no ability to monitor the voltage on each of the individual cells. You can monitor each "bank" of cells but not the individual cells in a bank. So no way of knowing if an individual cell has gone bad and with everything completely wrapped in black tape you won't be able to see if one of the cells in the middle of the pack is starting to puff up.

This issue would not be any different than for a lot of commercially produced packs.  Many larger packs are manufactured as 3S2P or 4S2P, but only have monitoring for each bank of cells.  You may not be able to tell about an individual cell (but you will know if there is a problem in a bank of cells).  As for puffing, same thing - it would be pretty obvious which bank is a problem.  [Fortunately I never had to worry about "puffing" with the metal-canned A123s... ]

Nice work Pablo!  Thank you for taking the time and effort to point out the potential dangers in doing this.  Hopefully it'll stop someone who does not realize what they're dealing with from finishing there "home grown" pack when they return from the ER.

(12-Aug-2018, 06:33 AM)Tom BD Bad Wrote: As you charge your flight packs with the 6000mAh pack, the voltage of the charge pack will drop, which is (I think) why you are only able to charge 2 packs with it. Ideally you would have a 5S or 6S 6000mAh pack so that it can still charge your flight packs to 16.8V. You would then be able to charge up to 3 x 1300mAh or 5 x 1050mAh packs.  

Good use of old cells though.

(Disclaimer - This is not a suggestion that anyone SHOULD do this, as Pablo says, LiPo's are volatile and can explode and/or leak toxic gas when mistreated, always be aware when doing anything with LiPo's that they can be hazardous!)

thanks tom!
yes, it would have  been better to make bigger pack, but I did not have any more good cells.
I also have to  discarded someones  that were too damaged. When I started in the FPV I was really crashing many times.....  now i also crash a lot jajaj   

Now i have 6 1500mah 4s batteries and 3 1300mah4s, so when i go out to fly i can fly 11-12 packs. For the moment its a good fligth time for my

(12-Aug-2018, 12:21 PM)SnowLeopardFPV Wrote: Nice effort and it looks like a good way to re-purpose unused batteries, although I'm paranoid enough as it is about normal off-the-shelf LiPos so I'm not sure hacking any about is something I would try to be honest  It certainly looks like you did a good job with the solid bridging wires across each of the banks 

The one issue I do see with this setup however is no ability to monitor the voltage on each of the individual cells. You can monitor each "bank" of cells but not the individual cells in a bank. So no way of knowing if an individual cell has gone bad and with everything completely wrapped in black tape you won't be able to see if one of the cells in the middle of the pack is starting to puff up.

thanks snow leopard,  i also prefer not to have been hacking so much with lipos, just in case.... time ago any battery with some problem I discarded it, but little by little if I have been daring to fix them, for example, repairing the balance cables etc...   always very carefully

Regarding what you comment on the voltage of each cell in each "bank", i think that as each cells of one "bank" are conected on parallel, all of them have the same voltage, so you can monitor the voltage of each cell (should be the same that the bank of cells) by the balance conector.  For example, if one individual cell get damaged and and it stays with a very low voltage, the whole bank of cells will be left with that low voltage.

you are rigth, its dificult to see if some cell its puffing up...

i have to say that i storage my normal batteries on an ammo box inside home, this one i have it on another ammo box but in the yard... so I sleep more calm

(12-Aug-2018, 02:34 PM)sirdude Wrote: Nice work Pablo!  Thank you for taking the time and effort to point out the potential dangers in doing this.  Hopefully it'll stop someone who does not realize what they're dealing with from finishing there "home grown" pack when they return from the ER.

thanks sirdude!

yes, it never hurts to warn of the risk, especially for people who may be starting in the hobby and do not know the risks of lipo batteries