DIY Powerwall
 

The wife recently came across some blog with people who use huge banks of old 18650 batteries (hundreds or thousands) from old equipment and appliances for energy storage, like a DIY Tesla Powerwall, but for a fraction of the price.

The ones I've seen claim that the more batteries you use, the lower the current running through them, which extends their useable life. This supposedly makes any safety risks negligible.

I admit that adding 10-20 kWh of storage to our PV system for the price of 3-5 kWh is tempting, but...

Just skimming through search results showed that some experimented with AGM batteries (instead of 18650's), but with worse results.

I haven't found anyone trying this with cellphone batteries, of which there are more and more in the waste stream.

Anyone here tried this, or came across anything interesting?

A friend was building up a 24V power wall using old laptop battery cells, don't think he ever finished it, needed hundreds of cells, having to sort them out first to even up capacity, then join them into a bank with individual battery fuses. Can understand doing this for something like a push bike power pack, but for a stand alone "Power Wall" its a huge amount of effort.

I currently require a portable inverter device to replace an old petrol AC generator; decided to use the small 50 AH Lifepo4 cells as a power source, these will be safer and much easier to build.

See link here where I have started on the project. http://www.thebackshed.com/forum/Vie...ID=4&TID=14660

Cheers
Mike

Hi Guys, haven't been around for quite awhile, but ...

I've built a few hundred (it seems) powerwalls for off grid use. I've used a variety of batteries. Mostly repurposed crashed electric car modules. Really like the Chevy Volt modules. Toyota Prius Prime used to be fairly inexpensive and obviously good quality. The Volts were quirky with charge discharge voltages. Buy an inverter with a wider voltage range for sure.

Lifepo4 bus cells. Mmmmm. Be ready to do a lot of testing and try to match capacity.

Honestly, new good quality Lifepo4 would be my recommendation. The new cost is so low in kit form now. Jeez. The only trick is the BMS and in the past few years those have also improved. Some nice bluetooth models out there apparently. I can't recommend any as I haven't tested any.

DiY powerwalls are great. One thing to think about. Its not if the cells catch on fire. Its what happens if the fire gets to the cells. I continue to recommend batteries of any kind have a separate outdoor location. Or build a nice steel box. See the new code 9450 is it?

Cheers

Long time since I posted but I have a power wall set up. I used commercial lfp ul listed battery’s and a Schnider xw inverter (built like a tank :)). I looked into the diy option and if you can put the battery’s outside in a dog house that’s insulated, cooled and heated it’s ok but I would not put a diy battery in or near a structure. A nice battery shed could work but I rather keep my home insurance :) ul and electrical inspected and your good to go.

My 48v back-up bank
 

To replace my old LA battery bank, I used three 48v packs from Big Battery. Kinda like these.
https://bigbattery.com/products/kit-...-120ah-6-3kwh/
In nice steel boxes.

The system is intended for short term back-up in the event of grid failure.
The normal inverter(Xijia 3000W) load is only about 300 watts.
If it's sunny, the 600w PV runs cool, and the bank isn't used much.
The bank does discharge a little when it clouds over, but charges right back up.
Sooner or later, the sun always comes around..
I did get a new (modern) FIOS box installed, and it seems to use less power.
That means slightly longer run times will be possible at night, and take less recharge time.

Most of the sunny days, 99% of the PV available output isn't used. Since the goal was to be able to power sump-pumps to keep the basement dry when the grid was down, I never expected to use the back-up power for things like the upstairs refrigerator & TV etc.

I did it with a score of LiFePo4 batteries (see photo). I'm pretty good at this but the problem was balancing. I tried several systems and even commercial ones but could never get the batteries at high enough voltage for decent run times.
As you approach 3.6v on LFP batts the internal resistance rises and when that happens you start getting unbalanced cells.

I'm using the batteries in my electric tractor this summer and went with EG4 batteries from Signature Solar. They run 7k cycles with deep discharges and are much better in my system.

I went with three of these:
https://signaturesolar.com/eg4-lifep...ery-48v-100ah/

I can monitor each cell, the charge level, battery life and health and battery cell differentials. (see photo)

The state of charge is after three days of overcast weather running off grid.