LIFEPO4 cells

[scott jewell]

I am looking to build my own battery but know little about LIFEPO4 cells.

I do see that they sell a lot of cells for a reasonable price. I had three 22 Ah SLAs but were VERY heavy and weighed the bike down.

I also found out that people like to run the cells in series and use a BMS. I do not want any BMS and running cells in series the pack is only as good as the weakest cell. NOT what I want.

For one thing I almost got run over by a city bus when I started across a busy intersection the light was green and then turned red. My pedal chain was broke and the light turned red and the 36 volt controller had an LVC
or low voltage cut off which happened in the center of traffic. I came within inches of dying that day.

I changed controllers but heard that a BMS has the same feature. Therefore I want to run ten packs of ten in parallel. I was told that these batteries are only 1/3 what they are rated for. That is false advertising which should be considered a crime or a scam.

However I do not wish to order LiPo as a fire hazard. My cousin almost burned his house down with one of those self balancing skateboards. Therefore LIFEPO4 cells are my last hope as do not have $500 or more for a factory 20Ah LIFEPO4 pack.

Please someone let me know if the following diagrams will work and reccomend a charger for that please.

 

[indianajo]

I've taken a LiPO4 battery apart to examine the battery management system. It was 11 stacks of cells for 15 AH and 48 v. The BMS disconnected stacks as they charged up to max so that the other stacks could continue to receive charge until all were charged.
Cell charge voltages do vary. A cell is one electrochemical device and a battery is an assembly or holder of more than one. So your device on the right with lots of parallel cells, each stage will only charge until the lowest capacitory cell reaches cutoff voltage. This is bad design.
Also I'm personally not sure my welding quality would be good enough to ensure all cells actually stay connected as the battery was shaken by road bumps. The first battery I bought, only one of the eleven stacks was actually connected when I bought it, and the last one opened up eleven miles into my first trip. The connection problem was under the solder joints on the BMS board. I suspect the argon feed was off when that battery was welded, and the amazon vendor was selling me rejects the scooter company had flogged off. He had a great website, but **** batteries. I paid a premium for full information on that battery, but amazon did give my money back. The vendor did not want the old battery back before refund.
18650 cells apparently come in several rated discharge currents. I downloaded a datasheet previously for a "flashlight" variety, and 11 stacks would not have made 30 amps safe discharge current for a 1000 W controller (26.4 A), The cells I bought in the first battery were allegedly sanyo. The batttery was rated at 60 A discharge according to the vendor, but I can't find a sanyo datasheet online to confirm.
The second LiPO4 battery was from a LA warehouser of sun-ebike.com and performed okay until my power wheel or controller quit after 60 miles. Check out the prices on e-bay; you pay a little more for an e-bay warrenty and shipping from LA instead of china.
I too am suspicious of LiIon due to various fires, and notice on wikipedia that LiPO4 allegedly has more discharge-recharge cycles. LiPO4 is allegedly heavier, but with me carrying a 30 lb basket and 50 lb supplies on the back, I find 18 lb battery + rack on the front fork balances the bike out nicely. Before electrification my front tire would weigh as low as 15 lb on the foot scale, with the rear reading 110, with the bike loaded but without me on it. This lead to skidding when dodging vicious dogs.
If you're worried about battery dropout, invest in a voltmeter to bolt to the handlebar. I don't see any convenient ones online, but I could build a 42 v (or 30 v) warning system out of a LED, a transistor, and a stack of zener diodes 1 v less than the warning voltage.
The charger I got from the first battery vendor was generic and seem similar to the ones on amazon & ebay. Check the charge voltages, apparently it goes up as time goes on. The first battery was dated 1548 internally, or 48th week of 2015, and it had a 58.4 v charger on a nominal 48 v battery. It was bought September, 2016. The second battery from sun-ebike had a 61 v charger on a 48 v battery. The sun-ebike charger was proprietary.
And for safety sake don't ride around without your foot propulsion system working.