Alright, I think I've explained how this thing works in bits and pieces but I am going to break it down now that it is all together.
The charging side consists of an five AC power supplies that each put out 12V. Each 12V power supply is wired to a DC-DC buck converter which puts out 4V at a max of 4A. This will charge each parallel string to 4V which is roughly 85% of its capacity or ~2.2Ah. Keeping the charge lower than 100% improves battery life. I've edited the charge curve chart to estimate this below. Charging in this manner should give roughly 320Wh (2.2Ah x 8 parallel cells * 3.6V * 5 series cells).
Now lets take a look at the discharging side of things. Lets start with the power switch. It physically cuts off power to the low voltage disconnect. This eliminates any phantom draw, because the low voltage disconnect powers up an LED display as soon as it is connected. This voltage display is great for checking the state of charge as the max pack voltage is 20V (5s x 4V). However, it does draw something like 200mA when its on and powering the relay.
When you flip the switch on, the low voltage disconnect controls an 80A relay. If the voltage is above its set point, that relay is enabled and power is sent to the output DC-DC converter. As the pack is drained, it eventually hits the low voltage setting and the power to the DC-DC output converter is severed. The low voltage disconnect also has a hysteresis setting which stop the relay from turning on/off as the voltage recovers after the load is removed.
