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Old 11-29-19, 08:55 AM   #1
Robaroni
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Default A 10Kw LiFeP04 battery bank

About 2 years ago, before LIFEP04 batteries became the backup standard, I scored 640 new Tenergy 32700 LiFeP04 batteries for about $900 USD including shipping. These were purchased to replace my 13 year old L/A bank.

A little background:
I have two systems here, in 2006 I installed my first PV array with backup. I went to backup, as opposed to off-grid, because I have ready access to grid power and running batteries everyday is an expensive battery solution. I knew as I built my system I would install an intertie down the line and selling my excess to the grid was a better option. This way the grid keeps my batteries charged for when I need them and I still sell my excess after all my needs are met.
In 2011 I installed my intertie system which just sells back to the grid. So I have two systems, the intertie sells back to the grid and the intertie/off grid sells back after my needs are met.

First and foremost was safety - I wanted the bank to be bullet proof safe
and I wanted at least 2 to 2-1/2 days of power in complete darkness - which should never occur.

______________________________________

The build:

Because these batteries are stationary I built them in 4 groups of 4S36P (4 series and 36 parallel).
The batteries are rated at 3.2V, 5.5A, this meant that 16S (4x4S) would give me 51.2V for my 48V system.

I used one piece of finished plywood (~$25 at Home Depot) cut into 4 equal pieces (see pictures)
I machined jigs to cut and form each battery holder in the system. I wanted access to each battery and I wanted to be able to remove each battery. I also wanted each battery fused - just in case one went south. I did test a battery with a dead short to see how it would react. No fire no flames, just got warm and died. LiFeP04's are ideal for backup.

For fusing I used bare 24AWG wire on each battery and for the bus bars I used 1/2" copper pipe (the heavier pipe, L?) I connected the four 12V modules using AWG 2/0 battery cable.

The clips were made from surplus 316 SS 3/4" x .020" 100 foot rolls of banding and the battery wooden rails from hard maple. Because you can't solder directly to 316SS I spot welded nickel tabs to the SS when running fuse wires.

________________________

As it stands now I have a little over 10Kw of PV. My energy supplier owes me several hundred dollars and I have driven my EV for the last 2-1/2 years at a total cost of less than $75 for maintenance, inspections and charging. If the grid fails I expect to run easily for several weeks, even at my 42 latitude in the winter, without issues. I tested the system this winter accidentally leaving a space heater on during the test. It ran about 24 hours and the system recharged the next day which was partially overcast.

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