Glubux's Powerwall

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Glubux

Member
Joined
Nov 9, 2016
Messages
124
A quick presentation of my project.

I already produce a part of the electricity that I need. I have 1.4 kw of solar panel on the roof, an old 24v 460AH forklift battery, a Victron MPPT 100/50 charge controler, an 24v to 12v Victron voltage lowerer, and a 3KVA Victron inverter.

The plan is to build a shed to put all the batteries and the charge controler/inverters.

I started to collect laptop batteries a few months ago, I have around 650 for now, I started sorting and making my packs:

image_fvwftp.jpg


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Ideas are :

-100 Ah for each pack by matching the number of cells, possibilty to add or remove cells if needed
-maximum use of copper wire, easy to find and easy to solder
-same bus bar lenght for each cell
 

Sean

Member
Joined
Oct 8, 2016
Messages
946
Your neatness is to be applauded.

Have you tried testing the same cell in each of your dischargers and comparing the results ?
 

Glubux

Member
Joined
Nov 9, 2016
Messages
124
Sean said:
Your neatness is to be applauded.

Have you tried testing the same cell in each of your dischargers and comparing the results ?


Thank you.

I tested it indirectly by testing a freshly separated pair of cells and capacity was only a few mah different, this happened a couple of time on different chargers so I would say they are not perfect but precise enough.
 

Glubux

Member
Joined
Nov 9, 2016
Messages
124
Glubux said:
Sean said:
Your neatness is to be applauded.

Have you tried testing the same cell in each of your dischargers and comparing the results ?


Thank you.

I tested it indirectly by testing a freshly separated pair of cells and capacity was only a few mah different, this happened a couple of time on different chargers so I would say they are not perfect but precise enough.
 

miwall

New member
Joined
Oct 26, 2016
Messages
18
Hi like you Idea of using copper wire for busbars what Size cable is this looks like it could be 1.5mm or 2.5mm cable striped from Twin and Earth cable used for house wiring ?
Also what with missing out Batteries in your pack!
 

Lux_Gamer

Member
Joined
Oct 11, 2016
Messages
65
Hello,

I really like your pack design and your fuses.
One question is all that copper not a bit over kill.
Correct me if i am wrong but if it is 2,5mm cable it could handle 16-25 amps.
On the other hand i dont know how much you will pull form that pack.

Lux,
 

Glubux

Member
Joined
Nov 9, 2016
Messages
124
The copper wire is a 1,5 mm, easy to find, I'm not sure it's overkill, I ll see when I'll put them to the test, anyway it is better to have too thick than too thin.
 

station240

Member
Joined
Oct 9, 2016
Messages
185
That size wire is probably about right, as you also have to consider resistance.
I worked out what the resistance of the longest length of wire there is.
0.0022789 Ohm => 2.2789mOhm
So the internal resistance of a cell is higher than the resistance of the wire.
 

miwall

New member
Joined
Oct 26, 2016
Messages
18
Hi Looking good i like you idea of using copper wire for he busbars i have copied you design within slight modification will up load pic soon, also how are you capacity rated your packs i see some of the have cells missing???
good work keep it up....! :mrgreen:
 

Glubux

Member
Joined
Nov 9, 2016
Messages
124
I decided to make 100Ah packs with a maximum size of 80 cells, the lowest cells I used are between 1200 and 1300 mah ( 1250 X 80 = 100)

I'm building 7 packs, running some test and if everything is ok I'll build bigger packs this time, 160 cells, minimum 1500mah, 250 Ah

Looking forward to your build!
 

hbpowerwall

Administrator
Joined
Oct 7, 2016
Messages
1,998
Love the effort into making them look smart. Don't look anything like used laptop parts any more :) good work.
 

Glubux

Member
Joined
Nov 9, 2016
Messages
124
I think they will be on a shelf at first, in a garden shed, with one shelf per string but this is not completely clear in my mind, I ll post some pictures later.
 

Lux_Gamer

Member
Joined
Oct 11, 2016
Messages
65
Hi Glubux

Nice pictures they look very good.
Which camera are you using?
Really looking forward to new updates

Lux,
 

Glubux

Member
Joined
Nov 9, 2016
Messages
124
Thanks.

I'm using a Nikon D7200 with a 17-55 F2.8 and a 85mm F1.8, great lenses!
 

Glubux

Member
Joined
Nov 9, 2016
Messages
124
A little update here after one week of lithium power!

First thing, I really like how the cells react compared to lead acid, the charge efficiency seems a lot better, no waste in absorption.

They hold the load very well too, the voltage goes down very slowly and predictably.

I didn't try big loads yet, the biggest was the hoover, a bit above 1200W and absolutely no sign of warming, I'll try to drain more power in a few days and watch with the thermal camera, but first I need some sun to charge.

I had an issue though, I let everything plugged during the night to see how well it hold the charge (2 fridges, the inverter, the 18650 process...).
During the 5 first nights all was ok, there was remaining around 20% energy in the morning, but in the 6th night the voltage dropped dramatically, 4 packs were still at 3.30v, the next one was 3v, the next one slightly above 2v and the last one slightly bellow 2v...

That's the goal of testing I guess, so I unplugged every packs, recharged to 3 volts the lowest and then went to work thinking about what happened.

And the interesting learning that comes out of this is than the biggest voltage drop was in the pack with the less cells. Just a reminder, I decided to make 100 Ah packs by matching the number of cells, 80x 1250 cells for the full pack and 51x 1950 for the more empty. I knew this wasn't going to be perfectly accurate and now I can see clearer. Those simple math are done with the capacity mesured with a 1C discharge rate, but we now that if you discharge at a lower C rating, the capacity raises, my guess is than it raises more on a 80 cell pack than on a 51.

So I add a few cells in the packs (very easy to do BTW), re-balanced them and I'm looking forward to see how it goes.

One last thing about balancing, the first time I blanced them (at 3.8v), I noticed than they were drifting a bit while reaching full charge (4v) and same thing with low voltage (3.3v) but everytime they were around 3.8v, the balance was still perfect. Two conclusion : first, this was a clue that some packs were a bit weaker, the ones I noticed then were the ones which fell around 2v. Second thing, I think as long as you don't reach the top or the bottom of your packs, they can be slightly uneven without unbalancing.
 
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