dumbass
100 kW
I think in some form this question has been answered but I didn't find anything on it. I use GBS or ThunderSky lifepo4 20ah cells. I dismantle them from the 4 pack they come in and reassemble them into my own configurations of 8 cells per pack (24v 20ah) In this way I can use them on my wife's bike (24v) or my own bikes that are 48v.
I do not use an "off the shelf" BMS per say. What I do is build a Cellog8 wired to a 90db alarm into each pack. So weather charging or discharging if a cell or the complete pack goes out of the set peramitors I get an alarm.
Here's the problem; this cells are a PITA to keep properly balanced even with a string of single cell chargers. So I did a test using just 4 cells that were sitting all winter without being charged. I charged 2 of them (actually over charged them to 3.80v. And left the other 2 at 3.33v. I then connected all 4 cells in parallel. I took a quick reading and all cells were reading 3.34v. Not sure why that was but that's what they were. I then connected together 8 single cell chargers (2a per charger or 16a total). I then connected them to the first cell in the string of 4. Powered them up and within 2 hours each of them started turing off one by one. The longest one took 2 1/2 hours all the chargers to be turned off. The final voltage was 3.62v on every cell.
So this is no different them Ping building a 20ah pack from 5ah cells. What I did is for charging purpose is create a single 3.2v 80ah cell. My thought is to purchase larger 3.65v chargers. I have ordered 3.65v x 10a and a 3.65v x 20a. Charger.
My plan is to build my pack using Anderson connector (!6, 8 - and 8+). When charging I will have a mating Anderson connector that will parallel the cells. But when discharging I will remove the parallel connector and replace it with a series connector. Wiring this connector in a way so as to have the final neg. and pos. (giving 24v) available for connecting to the bike through a fuse.
OK, I invite someone to shoot holes in the idea so I can improve upon it. Please understand I DO NOT want an off the shelf BMS.
Bob
I do not use an "off the shelf" BMS per say. What I do is build a Cellog8 wired to a 90db alarm into each pack. So weather charging or discharging if a cell or the complete pack goes out of the set peramitors I get an alarm.
Here's the problem; this cells are a PITA to keep properly balanced even with a string of single cell chargers. So I did a test using just 4 cells that were sitting all winter without being charged. I charged 2 of them (actually over charged them to 3.80v. And left the other 2 at 3.33v. I then connected all 4 cells in parallel. I took a quick reading and all cells were reading 3.34v. Not sure why that was but that's what they were. I then connected together 8 single cell chargers (2a per charger or 16a total). I then connected them to the first cell in the string of 4. Powered them up and within 2 hours each of them started turing off one by one. The longest one took 2 1/2 hours all the chargers to be turned off. The final voltage was 3.62v on every cell.
So this is no different them Ping building a 20ah pack from 5ah cells. What I did is for charging purpose is create a single 3.2v 80ah cell. My thought is to purchase larger 3.65v chargers. I have ordered 3.65v x 10a and a 3.65v x 20a. Charger.
My plan is to build my pack using Anderson connector (!6, 8 - and 8+). When charging I will have a mating Anderson connector that will parallel the cells. But when discharging I will remove the parallel connector and replace it with a series connector. Wiring this connector in a way so as to have the final neg. and pos. (giving 24v) available for connecting to the bike through a fuse.
OK, I invite someone to shoot holes in the idea so I can improve upon it. Please understand I DO NOT want an off the shelf BMS.
Bob
