Batteries Batteries!!

Finally got my SLAs (4) 15ah for my 48v system. V Max Charge Tanks. Supposed to be superior to most SLAs, built to MIL specs with better plates for deepcycle etc- blah blah blah. Have a good warranty though. Waiting on tires to begin the build. Dropping the 700c fixie to 26x1.5 high pressure tires for less rolling resistance.

Next project is to build a Li-Ion battery pack, a 48v 10ah. I bought a lot of 60 Sanyo 18650 2600mah cells still tabbed in pairs. These are supposed to be unprotected. I need 52 for the build. They are used but checked out. Hoping out of 60 I will get what I need. Will assemble them into 13 4cell 10ah packs in parallel then series them together. Going to manage them with a 48v 30amp 13s BMS for Li-Ion. The bike will be built to run with either pack and charge with the same 48v charger so I can swap out as needed.

Any insights, advice and pointing out any brain fades in my thinking would be appreciated!

Sounds like a great idea Deacon! Sorry about the nimh pack. Hope Im able to come up with a decent pack out of this parade of batteries. Read all the rest voltages and really only 3 are suspect. Am cycling them now. Took longer to clean them from original packaging than to build the pack probably.

Started assembling the packs of 4. There will be 6) 7.4v packs in series for 44.4v@ 10.2ah and 1) 3.7v pack@10ah for 48.1v@10ah. The pics represent the 7.4v/10ah cells. They are sitting in parallel in the pic, but will be in series. Somebody correct me if I am wrong before I get these things soldered!

OK- first lesson learned. These batteries are tabbed in pairs. with proper salvaging the original tabs can be soldered together. However if one does this be sure the tabs on the positive end are humped up off the heat shrink of the battery. The entire outer case is negative. If you have a tab against the heat shrink and burn through it while soldering youre in for quite a light show! Probably best to solder wire jumpers on the positive end to the middle of the tab bridges.

Well hopefully my general science learning will prevail. One really has to be careful to keep things in order. Assembling the batteries is fairly elementary. You just have to be familiar with the batteries chemistry/characteristics your are working with. I am trying to match cells. Ideally one would cycle all the cells to know their actual capacity, a huge job with this many cells. I am going to match cells based on their rest voltages, and cycle(charge/discharge) representative cells from each group. Sorta of an educated crap shoot. The BMS will balance the cells as much as their capacities will allow. One cant expect a perfect battery from used cells but for the money invested(less than $150 including the BMS) Im willing to gamble.

Thanks for the links Motortriker. I separated the cells that were paired by cutting the - tab. I could then read the cells individually. Cells with voltages 3.75 or over I assumed good(not best to assume I know) and soldered the tabs back together. Cells with lower voltages were charged then load tested on my charger noting the mah in the charge discharge cycle. I found all the cells to be of good capacity. I found one @ 3.15v that I figured done for. It actually charged up to 4.2v and returned better than 2500mah on the load test. Hoping for the best!
You are right it would be best to test each cell.

Hey SB Thanks for the kudos but folks been building these packs for years. My E bike kit was a 36v that was actually a 48v with a 36v charger, so I opted for 48v because of increased performance at a lower amp draw. Bought a 48v charger of course.
These cells were from reclaimed laptop batteries, they are genuine Sanyo. Still not super cheap around $75 and a possible crap shoot. They do read the voltages. Some sellers actually load test but at higher $$.
If using a BMS the SLA charger will work, as well as the controller. The BMS will also balance the cell groups. I bought a new set of SLAs which I want to be able to use so am making this bike able to easily accept both types.
Building the pack is kinda fun, you have to be able to solder well and keep up with what you are doing, but its not demanding.

What I have built is a 13 cell pack with 12s and 1p for 48v. It is a 10.2ah pack which is pretty good capacity. The BMS will limit the surge draw to 30amps with a constant max of 15amps. for 720w constant max and 1440w surge--if my figures are right, think so.

Hers a pic, it aint no thing of beauty, but its well assembled. Weighs just over 5.5 lbs and is 9.5x2.5x2.85 in. I will find a secure case for it. Am leaving the +/- wiring off until I assemble the Ebike which is next.

See what I mean about keeping up with things! The cell in the middle of the pack closest to the ruler needs to be bridged and one in the next row right near the back as well as the next row front. Didn't affect the voltage of the pack, but it would have lost a good bit of capacity!! Long day with too many cells and a lot of soldering. All fixed now.

The pack is made of parallel 4cell sub packs that are [email protected]. These are then joined in series to make a [email protected] "brick". I then assembled the 7.4 bricks into the main battery jumping 7.4v at a time til I reached 44.4v. I then added a 3.7v parallel 10.2ah pack to the last series cell to get 48.1v. When assembling 52 cell you get a little bug eyed and I neglected to join some of the + ends of the primary 4cell sub packs taking that pair out of the circuit. I got the voltage but not all the capacity.

I would think not SB, the packs will come off the charger @ close to 4.2v which is well over the 36v rating. The controller has a margin built in to allow for a fresh charged battery. Open the controller and look at the capacitor. I bet its a 60v. Which will allow either 36/48v use.

Didn't see the first question. A BMS is a battery management system. It regulates the battery with in certain parameters on charging/discharging. Sets amp draw levels, cut off voltages, charge voltages etc. You could operate with out one but the batteries wouldn't get properly balanced on charging, could be overloaded and over charged/discharged. @ $40 it a deal!