The Italian Job

Hello Guys,
I'm new member of the forum, my name is Daniele and i'm from Italy. My house is powered by my home made powerwall with 18650 battery pack and 18x 260w solar modules. Here some pics of my job:



At the moment i have 14 packs 48p made with Panasonic NCR18650B and Batrium BMS:




I'm working to improve capacity of my system and i'm currently doing new 80p packs with Samsung INR18650-29E, here some details:






When i will add new packs to my system i've planned to install a shunt trip + 125A circuit braker in order to keep it safe.

I hope you like my job and you will help me to make it even better.

Welcome ... Realy like the color of the packs
Looking gooooood...

Nice clean setup.

Very nice setup. Welcome to the world of recycled power

very nice and clean installation, really like it . What's the overall capacity?

Welcome and have sun!

At the moment is 8Kwh with Panasonic. Soon i will add 12Kwh with Samsung, so i will have 20Kwh total

Italians do it better
;-)

Even though I am using different types of non 18650 cells, I think the best looking powerwalls are ones like this with exposed 18650 cells with a uniform colors.

Nice work, looks great.

Work in Progress!!

Finally i made all the new packs! ready to be installed!!

Hi Onizuka, looks like you are using new cells so what I mention below may not be an issue in your case. But am curious to hear what thoughts you and others have around it.

Recently some people have been talking about disadvantages of connecting both positive and negative terminals from the same cells (as is in your design as well). Think it came out from a live test by Peter in which he found that cells on the top were heating a lot more compared to cells at the bottom. Wonder if you and others here have any thoughts on the conclusions?

Hi, yes, i knew about that issue and i'm curious to check it on my system too, but i would need a thermal camera and i don't have it at the moment! But yes, probably cells on the top of the pack should get more stressed...main problem for me was that i need flat bottom of the pack in order that it can stand up by himself on the shelf, but my initial idea was to put POS and NEG on the opposite of the pack. I will try to do a test on my system and we will see.

The heating (if a problem) is probably because the voltage drop in the wires is letting the cells at the other end from the connection do less work. The easiest solution (especially in your case) is to make the connections to the middle of the pack. This will do the same good as using 4 times as much thickness of copper, better than opposite ends connection which makes much less difference, and you still get to stand your packs up.

My design is front loaded (and stacked row), so like yours it needs to be on the front. I brought my cable from the rear to the front.Does waste copper.

this is very good layout, the only problem is that you need almost double copper to do it.

Onizuka said:

this is very good layout, the only problem is that you need almost double copper to do it.

Click to expand...

14swg house wire is fairly cheap. And get the 3/1 wire if possible. It costs just a little bit more, and you get a 4th wire (red, black, white or yellow, and bare or green)
You can get a lot of cable from recycling centers. Here in the Florida, US there is shop called The RePurpose Project. There are loads of people who donate the items to them. It's amazing what they have there. Ceiling fans, electrical conduit, plumbing parts, wood planks, pianos at times, cloth, etc, etc. It's a non-profit company and most of the time you can haggle a price. I usually get stuff there they ask "me" how much I wanna pay.

Korishan said:

Onizuka said:

this is very good layout, the only problem is that you need almost double copper to do it.

Click to expand...

14swg house wire is fairly cheap. And get the 3/1 wire if possible. It costs just a little bit more, and you get a 4th wire (red, black, white or yellow, and bare or green)

Click to expand...

I am also in Italy for 10 years now and have not seen this kind of solid copper house wire since I got here (and I've been looking...). I was used to this kiind of stuff being everywhere in UK too, but here not. The recycling situation here is also quite different from UK/US. There aren't even thrift stores (charity shops). The largest solid wire I could find was 1mm, new from a Bennet supermarket, and copper roofing sheet.

Needless to say when building my packs (currently up to 7s144p) I needed to be very frugal with copper and did a lot of analysis of current flows. Along the way to the design I used in the end I realised that connecting the packs at the ends was very ineffective, the only benefit being that they could lie in narrow drawers or be stacked and still accessible.





the diagram above is calculations for the voltage drops on one side of a pack calculated with 314swg wire (9.73mm total) and 1 amp per cell flowing. Same end connection is obviously the worst, minimum drop is 12.4mV, maximum drop is 39.4mV, a difference of 27mV. with opposite ends connction the maximum drop is in the centre and is 32mV and minimum is at the end: 25.9mV, a difference of 6.1mV. With central connection the largest current flows are minimised in length. Max drop is 11.4 at the end, min. drop is 5.2mV in the middle. Difference is 6.2mV (actualy the differences are the same, just rounding errors make it look slight diference).

with an 80p pack the figures double but the proportions stay similar. Same end: max 74mV min 18mV diff 56mV. Opposite end: max 59mV min 45mV diff 13.3mV. Middle: max 20mV min 7mV diff 13.3mV.

With a pack as long as an 80p (420 cells) there could be 2 mid-pack connections at row 5-6 and row 15-16, dividing the current further and reducing the drops and differences by 4 times again to: max 5mV, min 2mV, diff 3mV.

But I guess you could also look at my math and say that with such small differences even at these high currents, what does it really matter...?

Good luck, it's all looking good so far.

Then what do they use for house electrical wire over there!?!?! :huh:

Korishan said:

Then what do they use for house electrical wire over there!?!?! :huh:

Click to expand...

Country that running on 240V do not require thick wire for home.

The current is running half of the 120V.

That cause the thick wire become expensive.

While 1.5mm (Awg16), 2.5mm(Awg14) smaller wire is cheaper.

Hello Guys, for my busbars I used 1.5mm copper wire that i found in Brico shop in my area, is quite cheap, a couple of euros for around 4-4.5m rolls.
Jeremy, you made very nice analyse, what is your opinion regarding best design of busbars in order to have as much as same current drawn from each cell?