48vdc telco battery converted to 12vdc for TAB

Kasism

Hi all, work in the telco industry and picked up a 'faulty' backup battery for a cell site.

The battery is a 48vdc LiPo unit.   It was not working up to spec so it was sent for recycle.   I retrieved it, opened it up, and find that it has 14 cells at 3.7v cells.   Upon checking, I found one cell was 0.5v so that is why the whole string was considered dead.  So I removed that cell...   That leaves me with 13 x 3.7v cells.  

The specs on the battery in question - http://www.giant-eng.com.tw/files/Evolion_en_2012.pdf

The specs show that the battery is a 52vdc nominal no load delivering 77-74AH power, and 3900WH.

So just make sure I understand some basics.  From the specs, the 14 batteries in series delivers 77ah at 52vdc. 

Using this reference site -   ( https://www.se.com/us/en/faqs/FA229757/) 

Each battery in series adds the voltage and averages the AH. 

So if the entire 14 cell pack gives 52v @ 77AH then each cell must be (52/14) 3.7v @ 77ah.

I went in and reconnected 4 cells in series giving me 14.7v, and did that so that I now have 3 strands of 14.7v each. 

So if I understand, then this gives me 14.7v @ 77AH (again, in series add voltage, average AH)

I will now combine them via parallel, to still deliver 14.7v.  (This should be ok for a 12v system before load)

So from the same reference, in parallel, average the voltage and add the AH to give me 14.7v and (77x3) 231AH?

I am sure there are some 'losses' when combining these, but even 200AH would be a nice keep.

Did I get this right?   That makes the 65lb battery pack very useful if so!

Thanks for any review!
keith

Cbusguy

Lipo's are the most dangerous lithium chemistry you could put in a camper.   This is the chemistry that starts fires and explodes.   RV applications typically use Lithium Iron 

Your math looks good and does the idea.   The biggy here is you need to get a battery management system to manage the batterys.   If you simply hook it up to the trailers 12 volt system and go for it you will run a high risk of a fire.  will prowess on youtube has done many DIY lithium battery builds and has some recommendations for BMS's.   

I looked into using some tesla power module,  but the battery management system was expensive and the diy option was complicated enough I simply didnt want to run the risk.

Interested in following your progress.

Kasism

Thanks for the warning, yes Lithium seem to have high risk for sure.   Guess i will keep this bank for my telescope control system outside at night, as the mount, computers and the cameras will be away from the trailer.  I had planned to use it and recharge it with solar panels, and a Victron MPPT.    Thanks again, will advise on the next steps and if any failures happen.
keith

Cbusguy

@Kasism I don't believe you understand.   Beyond a simple victron battery charger.  Lipo batterys need a much more aggressive battery charging/management system.   The big vendors such as Renogy, Lion and Battleborn build them directly into the battery.    Here is a link to a DIY build

I am sure the device the battery was originally housed in had the system built into it.  Here is a link to an example   This probably isn't the right one for you but gives you an idea of what I am talking about.

These battery packs are fantastic,  but can be dangerous if not handled properly.