MrWizard wrote:
The plan for now is to build my own batteries however that could change if I can find an effective/reliable/quality battery at a non-crazy price point. Right now I believe I can build my own batteries with BMS at around $534 per battery, which means I could build 500-600 AH and stay within my budget given everything else I plan to do.
that would be real nice
i have been researching, and i have not found that to be the case
500ampHr at $500 for 3.7v yes, but thats $1500 at 12v
if you can to 12v 500ampHr for $500, i would be interested in this
it cost me $350 for 675ampHrs of surplus 'Telco/server' AGM batteries
they weigh more than Li, but easier to manage, and and way more cost effective for me, just over 8000wHrs total, 4000w to 50% SOC, typical daily use 25~30%
as far as discharge, a BMS won't let Li go to a real ZERO state,
BMS cut off is around 20% SOC ?
everything i've seen says 20% to 80% is the ideal operation range for max life and efficiency,
charge to 4.2v per cell is normal with BMS
doing manually and over ride to 4.4v can be achieved, but repeatedly doing this will cause accelerated cell degradation AKA LOSS
i know you said you will be using a BMS, and commercial retail setups come with BMS, some DIY are fusing the cells, but skipping the BMS
this lets them get more discharge from the cells, but shortens cell life
have fun and keep us posted
I should have been more clear: $534 per 120AH @ 12V. That would be an all in price (shipping, taxes, etc). IF I want to get to 500-600 AH I'd need 4-5 12V groups so I'd be right in the $2K - $2.5K range when all is said and done. I think your research jives with mine on price.
The BMS cutoff is usually 10V (2.5V for any cell) to keep it safe. When in use you can charge to 100% day after day, but if you're going to store the batteries, ~90% is better. Assuming you keep the charging rate within reason you can get a minimum of 2000 cycles.
