DIY Tesla UPS
Some months back, I mentioned I was going to build a UPS out of old Tesla battery modules.
There's been some significant delays but it looks like my DIY UPS will be ready within the next few days. It's working well under testing on my bench, so it just needs to get packaged into a nice box.
Specs are as follows:
6KW Inverter (Output)
21.2KwH Capacity (17KwH usable)
I'm using 4 Tesla modules for this first version. Should be enough for almost 3 hours run time under FULL load.
I have a BMS monitoring the voltage of each cell. It balances the cell voltages if the delta is too high. There is a contactor which is disengaged if the overall voltage, current or temperature exceeds spec. This is for safety.
In order to reduce risk further, and increase battery longevity, the charger will only charge upto 24.2v (85%). And it cuts off at 18v (5%), hense the 17KwH usable capacity of the nominal 24v.
The inverter is for 24v, so we're using some chunky cables! 70mm2.
This thing is going to replace our ageing lead acid based UPS, where batteries need to replaced every 3 years. And even when replacing them, they still have shit capacity (45 mins when new, and seemingly halving every year). Hopefully this Li-Ion setup will last a decade or longer.