Batteries Batteries!!

I can see the virtue of making linkable cells so they can be individually serviced/charged. If I do another pack will go that route. For now the pack seems ok. I know its not balanced so it will be a good test of a used cell pack at perhaps its worst. Made a set of charge cables that allow me to use my Fluke meter to monitor the charge. Am close o finishing the E bike so soon be able to really see how well it works.

Still think theres something I might have missed on the BMS or the rather simple instructions(a page or so back in the thread) may have omitted. Most BMS units I have read about have 3 inputs, B-, P-, and C-. C- being the dedicated charger input. This one only has B- and P- with an N- it indicates not to use. Who knows.

Ok the mystery is solved with the BMS! According to the wiring diagram sent with the unit the N- terminal is not to be used. Being as I had nothing to loose since it didn't work as was, I made a harness to input the charger into the N- terminal, cut the pack open to get and hook up the balance plug and hoped for the best. Yeah! It worked. When charging without the BMS the voltage was 2v higher since its a bulk charge. Im guessing the lower voltage was because it was balancing/regulating. Wont know for sure how well the BMS will works until I discharge the pack when the bike is finished. Current thought is to use the BMS only for charging, and remove when done. Easy enough to hook up. Plan to run a digital volt/ammeter so I believe I can handle the current regulation, plus I believe operation will be more linear. It seems the design of the BMS is to reduce current loading by ground regulation. Makes since seeing as it is only connected to the ground side of the battery.

Ignore the red wiring in the pics on the jumper harness(plugs are black) ran out of black.

Hope this helps others that may wind up with this type BMS.

Finally got the bike up and running and tested the battery. Only got 2 loops around my 5mi circuit before the rain started so its not a complete test of ultimate range. The battery supplied plenty of power. Freshly charged it topped the bike at 29mph on my Garmin, as soon as the voltage from the topping charge dropped it settled into a steady top of 25mph with a nice cruise in the 20 range. I stopped the charger when the voltage reached 52v which is 4.0v/cell so its not a full charge which is 54.6v. Probably stay with the 4.0/4.1v/cell range. The BMS did in fact balance the cells some what. Will probably take a few charges to accomplish balance. After the 10mi run the rest voltage was 48.6v or 3.73/cell. Have a volt/ammeter to install so I can tell more precisely what is going on under load. I ran a mix of pure motoring and assistance. I also always pedaled to around 5mph before hitting the throttle saving pull away amperage. Also I ride totally in flat land so it doesn't get much better on battery conservation.

I have to say Im pleased maybe more surprised at the success of a home built battery from used cells. Running with out a BMS seems real doable and would keep the pack build cost around $100 depending on current cell cost. Btw the battery weighs in at 10lbs, 40lbs less than comparable SLAs!!

More info. Found a chart indicating % of charge. 4.05v=83%, 4.1v=89%, 4.15=94% and 4.2v is 100%. Rate of capacity(amp hours) is about 2% greater that the percentage charge number. Cycles diminish with higher charge voltage. You have to charge above a certain voltage to basically get the cells chemistry to function, but in the e bike world charge rates are well above that threshold.

Put 12 more miles on the same charge for a total of 22. Top speed down to 18-20mph and voltage is 3.64/cell. will ride more tomorrow.

Made 9 more miles on the original charge for a total of 31 before my speed control cut the battery out. It is apparently set at 3v., rest voltage was 41v when I got home, Im sure reaching 39v or 3v/cell under load. I found I could still milk it the last 1/2 home pedaling a bit to let the voltage rise then motoring a bit. Not bad considering when I pulled the charger it was at 4v/cell or 83% charge at the beginning.

Strangely I was still making around 20mph when it cut. I purchased this as a 36v system, then discovered it could do 36/48v. So at around 39v(cut out for the 48v system) It would have been like recently charged battery for a 36v system. That explains the decent cruise speed til the cut out. The bike had ok power at the end needing pedal assist to get it quickly to 20. Was a whole different story on 48v pretty snappy for a kit E bike.

Moral of the story get as much voltage as you can afford!

Yep your right! This build was all about efficiency, and practicality. Next ones for fun! Pretty impressed with the homebuilt battery considering the cells are recycled. Will charge up the new 15ah battery and do a range check on it. Would love to milk 50mi from it!

Would love to get 50mi from the bigger pack and think its real doable with my riding style and the flats I ride in. The home built pack is hanging in there real well. I only use the BMS for charging and I did a cell read today on each of the 13 cells individually. They were all with in a tenth or two of a volt. The BMS has pretty well balanced the pack, glad I dug it out of the trash!

Doing great, on the third charge cycle. Have added a speedo that I calibrated with my Garmin to keep up with mileage. The range runs from the low 20s with no assistance to the mid 30s with assistance. Assisted take offs and cruising will use sometimes less than half the amps of just riding. An ammeter is a real necessity for battery management. All in all I am very pleased with the build and amazed that so small a pack can have so much power. Am building another pack that will have 14cells(51.8v), and will run no BMS. Will be arranged a bit differently and be of more refined construction.

I will do that SB, waiting on stuff to come in. This battery will be 13.2ah and 51.8v nominal. Will consist of 84 cells!!

In the mean time I modded the original home built pack to a 14 cell 51.8v pack by adding 4 additional cells. Was more trouble to carefully cut through all the tape on the pack than to mod it. Kinda scary cutting into all those cells with a metal knife blade. If the weather improves tomorrow hope to give it a try.

Got a chance to try the modded battery. Am very pleased with the results. Charged it to 4.15v/cell or 58.1v. Of course performance is a bit better. Will hit 29mph for a short while on a freshly hot battery. Will settle into a 27mph top speed vs. the previous 25. Acceleration is slightly better with the increased voltage. Cruise amperages dropped slightly for a given speed and at previous cruise amperages the speed increased 1/2mph.

My take away from this is if one is buying an all in one box kit minus the battery, buy 48v. They are usually the same kit with different chargers and usually cost the same(they did from my seller). Open the controller and check the capacitor voltage, if its 63v , then by all means build or buy a 51v battery if you can do so. This would also be true for a 36v system, build a higher voltage battery. A 12 cell with a nominal voltage of 44.4 would work nicely.