Hi all,
I am currently planning my DIY Powerwall. I am planning to build a 14s140p system using 1.5A cell fuses (the glass ones recommended by AveRage Joe). I will connect the pack to a Sunny Island 6.0H-11 (my existing PV system is all SMA)and incorporate a main 160A fuse. The bus bars will probably we twisted AWG 8 copper wire ormaybe copper tubing.
The packs will be monitored by a Batrium BMS, though I am unsure as of yet if I will get the WM4 or wait for the WM5 (should come out this month). The Batrium BMS will also control a 12V Kilovac EV200 relay to quickly disconnect the packs in case of emergency or maintenance. I know I will bleed about 1.5W of power on the relay continuously, but that is a penalty I am willing to take for added safety.
Now to the main question - cell testing.
I have opened up a couple of packs and the initial voltage measurement on most of the cells looks good, but I have yet to test them as I just started building my testbench.
I am using TP4056s to charge the cells andZB2L3s to discharge andcapacity test the cells. I know that these don't have a constant 1A discharge rate, but since the cells won't have that under normal operation either, I believe they will deliver good results. Right now I am setting up 25xTP4056 and 15x[size=medium]ZB2L3 as my test bench all powered by a 5V 40A LED PS. I will use some of the 1.5A fuses to protect each charger/tester on the testbench.[/size]
[size=medium]Once I get my results I will have to make a decision on which cells to use. I am currently inclined to set the cutoff based on SOH, probably around 80% or so instead of having a cutoff of some fixed mAh number. I believe acell at 1500mAh that was designed for 1600mAh will deliver for better and longer lasting performance than one that was originally designed for 3500mAh. After all, the cells are just current sources in a parallel and will all deliver a slightly different current based on their capacity and the pack's voltage, while the SOC of each cell in the pack should be the same. This also gives me more flexibility to build the closely matching packs required for series connection.[/size]
[size=medium]I am very interested to hear your thoughts.[/size]
I am currently planning my DIY Powerwall. I am planning to build a 14s140p system using 1.5A cell fuses (the glass ones recommended by AveRage Joe). I will connect the pack to a Sunny Island 6.0H-11 (my existing PV system is all SMA)and incorporate a main 160A fuse. The bus bars will probably we twisted AWG 8 copper wire ormaybe copper tubing.
The packs will be monitored by a Batrium BMS, though I am unsure as of yet if I will get the WM4 or wait for the WM5 (should come out this month). The Batrium BMS will also control a 12V Kilovac EV200 relay to quickly disconnect the packs in case of emergency or maintenance. I know I will bleed about 1.5W of power on the relay continuously, but that is a penalty I am willing to take for added safety.
Now to the main question - cell testing.
I have opened up a couple of packs and the initial voltage measurement on most of the cells looks good, but I have yet to test them as I just started building my testbench.
I am using TP4056s to charge the cells andZB2L3s to discharge andcapacity test the cells. I know that these don't have a constant 1A discharge rate, but since the cells won't have that under normal operation either, I believe they will deliver good results. Right now I am setting up 25xTP4056 and 15x[size=medium]ZB2L3 as my test bench all powered by a 5V 40A LED PS. I will use some of the 1.5A fuses to protect each charger/tester on the testbench.[/size]
[size=medium]Once I get my results I will have to make a decision on which cells to use. I am currently inclined to set the cutoff based on SOH, probably around 80% or so instead of having a cutoff of some fixed mAh number. I believe acell at 1500mAh that was designed for 1600mAh will deliver for better and longer lasting performance than one that was originally designed for 3500mAh. After all, the cells are just current sources in a parallel and will all deliver a slightly different current based on their capacity and the pack's voltage, while the SOC of each cell in the pack should be the same. This also gives me more flexibility to build the closely matching packs required for series connection.[/size]
[size=medium]I am very interested to hear your thoughts.[/size]