I finished my build of a 12s 36v 20ah A123 battery pack back in February but I am still running some load tests. I’m happy so far with the results and had fun with the build process. Thanks again to all the posters on this forum for all their valuable contributions. I knew little about lithium batteries prior to coming across this forum. The NiMH batteries on my e-bike died a while ago and I needed a replacement battery system. Anyway, what follows is the recap of my battery pack build process.
I originally considered buying a Headway 36v15ah battery kit using 40152 cells including charger for $414 with free shipping. But then I came across this forum and all the talk about A123 20ah cells. I liked the idea that I could get 5ah more for about the same weight with the A123 cells. After viewing packs built by other ES members, I decided to go with the A123 cells. Then came the tough decision of where to get the A123 cells. I finally decided to take a chance with Victpower at the end of last year purchasing 13 cells at $14.70 each plus $114 shipping and $12.30 processing fee for a total of $317.30. I got “salvaged” short tab A123 cells from Victpower. I have since determined that one cell’s capacity is weak at 16,746ah when discharged down to 2.5v and another cell has developed a tiny black “leak”. The other cells appear to be within specs. However, I now wish I had ordered at least 2 spares instead of 1.
There still seems to be a lot of confusion over where to buy these cells. I consider myself lucky with my Victpower purchase. However, it now seems that Victpower is running low or out of the short tab cells and cell quality seems to be getting worse. If I had to get cells now, I would probably buy from OSN Power and get new full tab matched cells made in the USA or Korea since other ES members seem to have had reasonable results with them.
I spent about another $70 for parts from HobbyKing. That included 2 Celllog-8M voltage monitors and miscellaneous wiring and connectors. I also picked up a used Thunder 1220 smart charger for $50 and two 575 watt HP power supplies for $25. Add about another $30 in hardware from McMaster-Carr and Home Depot which included bolts, washers, nuts, ring terminals, vinyl tubing, aluminum strips and polycarbonate side pieces. So my total costs for the pack build ran about $500.
I tried to keep the pack costs down while building a safe setup that could easily be taken apart for repair. I also wanted to have compression on the cells to minimize cell puffing. This build is fine for my recreational e-bike usage drawing 30a max. After I began my build process, OSN Power came out with their 2 build kits which I would have considered using had I known about them earlier. However, they require the 12mm short tab Korean cells or full tab cells to work with their kits. They can be used with 10mm short tab A123 cells but only with “careful” cutting into the cell which I did not want to do.
Interestingly, OSN is now selling their 36v 20ah modular pack with BMS and 5a charger for $546 including shipping. So, it’s almost not worth doing your own build assuming you get good matched cells, their 1 year warranty is honored and you don’t get “killed” in return shipping costs. However, I prefer the use of voltage monitors for my pack rather than a BMS and OSN only builds the packs with a BMS. So if you don't want the BMS, it's easier to just order the cells and build kit parts rather than the assembled pack from them. I would stay away from the Victpower pre-assembled packs due to their soldered tab connections making for a tough time to repair the pack. Also, the quality of Victpower's assembled packs leave a lot to be desired.
I have included some photos of the build below. I'll post my load tests results and findings later.
View attachment 1
I originally considered buying a Headway 36v15ah battery kit using 40152 cells including charger for $414 with free shipping. But then I came across this forum and all the talk about A123 20ah cells. I liked the idea that I could get 5ah more for about the same weight with the A123 cells. After viewing packs built by other ES members, I decided to go with the A123 cells. Then came the tough decision of where to get the A123 cells. I finally decided to take a chance with Victpower at the end of last year purchasing 13 cells at $14.70 each plus $114 shipping and $12.30 processing fee for a total of $317.30. I got “salvaged” short tab A123 cells from Victpower. I have since determined that one cell’s capacity is weak at 16,746ah when discharged down to 2.5v and another cell has developed a tiny black “leak”. The other cells appear to be within specs. However, I now wish I had ordered at least 2 spares instead of 1.
There still seems to be a lot of confusion over where to buy these cells. I consider myself lucky with my Victpower purchase. However, it now seems that Victpower is running low or out of the short tab cells and cell quality seems to be getting worse. If I had to get cells now, I would probably buy from OSN Power and get new full tab matched cells made in the USA or Korea since other ES members seem to have had reasonable results with them.
I spent about another $70 for parts from HobbyKing. That included 2 Celllog-8M voltage monitors and miscellaneous wiring and connectors. I also picked up a used Thunder 1220 smart charger for $50 and two 575 watt HP power supplies for $25. Add about another $30 in hardware from McMaster-Carr and Home Depot which included bolts, washers, nuts, ring terminals, vinyl tubing, aluminum strips and polycarbonate side pieces. So my total costs for the pack build ran about $500.
I tried to keep the pack costs down while building a safe setup that could easily be taken apart for repair. I also wanted to have compression on the cells to minimize cell puffing. This build is fine for my recreational e-bike usage drawing 30a max. After I began my build process, OSN Power came out with their 2 build kits which I would have considered using had I known about them earlier. However, they require the 12mm short tab Korean cells or full tab cells to work with their kits. They can be used with 10mm short tab A123 cells but only with “careful” cutting into the cell which I did not want to do.
Interestingly, OSN is now selling their 36v 20ah modular pack with BMS and 5a charger for $546 including shipping. So, it’s almost not worth doing your own build assuming you get good matched cells, their 1 year warranty is honored and you don’t get “killed” in return shipping costs. However, I prefer the use of voltage monitors for my pack rather than a BMS and OSN only builds the packs with a BMS. So if you don't want the BMS, it's easier to just order the cells and build kit parts rather than the assembled pack from them. I would stay away from the Victpower pre-assembled packs due to their soldered tab connections making for a tough time to repair the pack. Also, the quality of Victpower's assembled packs leave a lot to be desired.
I have included some photos of the build below. I'll post my load tests results and findings later.
View attachment 1
