Mi powerwall Build

M

miwall

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Oct 26, 2016
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HI This is the start of my build first pack ready, i still need to Crimp Lugs on to copper Wire 2.5mm wire from T&E Cable.
All Cells 2000mA And Above but considering using 1950mA And Above!!!!


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:mrgreen:
 
Nice!! :D

This looks stronger than mine!

The only concern I have with your design might be the different lenght of bus bar : the first cells of the pack might have more job to do than the one at the bottom, that's why I didn't put positive and minus on the same side but I don't know how important is this.
 
Hmmm....!!! Not sure that it would make a Massive difference but i might put the Higher capacity cells furthest away i.e down the bottom also i have uses 2.5 mm diameter cable which offers less resistance and volt drop but the distances we are talking about are negligible.
The reason i put the lugs at one end is intend to make a frame to hang the packs from busbars with very little support at the bottom of the pack But.....But.....Hmmmmm i quite like your way for thinking with your design it could eliminate unnecessary connections from the design.
Thanks Miwall :mrgreen:
 
Ok loving this design - looks sexy!
 
From my old electrical engineering studies I recall that the optimum charging configuration for batteries in parallel is to feed the positive and negative bus bars from opposite ends of the cell string.
This action equalises voltage drop through resistances found in bus bar linkages and allows all the batteries to be subject to the same series resistance wherever they are in the string.
Most people on the 'powerwall' build bug have the positive and negative exiting at same end. This could be for aesthetics or ease of assembly but it causes the first cells to see zero bus resistance (virtually) and the last cells to see the maximum, as both charge and discharge current has to flow through two full lengths of bus bar. This will allow unequal charging currents to flow in the pack. As lithium cells appear to be charging to very small fractions of a volt I think that some of the imbalances and failures seen could be due in part to this. I do understand that these effects will equalise when the cells rest and the voltages stabilise but many of these units are either being charged or discharged with little time for balance recovery. Just my thoughts but it might help someone.
 
MikeyBoy58 said:
From my old electrical engineering studies I recall that the optimum charging configuration for batteries in parallel is to feed the positive and negative bus bars from opposite ends of the cell string.
This action equalises voltage drop through resistances found in bus bar linkages and allows all the batteries to be subject to the same series resistance wherever they are in the string.
Most people on the 'powerwall' build bug have the positive and negative exiting at same end.
Click to expand...


I've told many people this. Always ignored
 
Evening Guys, This is the first of 28 packs second now built, it is going to be used to power the house, last year i managed to get my usage down to 6/8 Kw per Day.
Now i have had time to think the design through and have already switched the bus bars round the other way and reduced the pack size to 70 cells all just above 2000mA as i have quite a few of cell's between 1700mA and 2000mA that will be a pack size of 80 cell's giving me a overall Amp pack size of 140A which should equate to 0.5 Kw per pack.
I am loving the BSM system by DIY Tesla Powerwall in fact i am waiting for my Arduino Mega, On order to build a similar setup any feed back is great. :mrgreen:
 
Hi all,

A few thoughts about the asymetry induced by the positive and negative bus bars (generally) placed on the same side of the modules by the makers (including myself :)).

Obviously it creates an unballance of current between the cells. The cells close to the top (near the input/output terminals) will be crossed by more current than the ones in the bottom of the module. That's a fact.

The question is: how important is this unballance and how to assess the loss of performance / life expectancy induced by this asymetry ? I really cannot give an answer to this question - currently.

To get a measurement of the amplitude of this unballance, I will perform the following experiment:

Connect my HP34401A (Lab grade 6 1/2 digit DMM) between the top and the bottom of one of the modules making up my battery pack - On the same terminal - of course.
Load the string with a current of 100 A (5 kW output of the inverter dissipated thanks to 3 electric heaters)
Measure the drop
Perform some calculations and give some feedback on the forum - in a dedicated thread.

What do you think about this ?

BTW, my project is described here: https://hackaday.io/project/12296-a-110-kwh-powerbucket

Regards
Michel
 
Nice! I see you've found a solution to make opposite busbars :)

I also notice some missing cells in the second pack, have you read my latest update about this?

Nice colours matching with the zip ties !
 
HI yea i have read your post, but my packs with missing cell's are 1950mA and above X 70 Cells giving me approximately 140A this is the least amount of cell's i am going to have, the packs with 80 Cells are going to be 1700mA and above so Hopefully the deviation between the cell packs hopefully want be massive.
Also i am working on a BMS similar to NIsmo Nick's which will give me some automated protection.
Just received my Arduino Mega and have been learning the programming language quite intense but enjoyable!
i will watch to see how you get on with your next update.............. :mrgreen:
 
HI Micheal love you project i have one question for you where do you get your 18650 cells from do you buy them new if what do you pay and from where??
All the best Miwall :mrgreen:
 
HI Bigjohn part of the reason for the Heavy duty wire is that it acts as the support for the whole pack and i have loads of it. the cable is from 2.5mm T&E domestic cable striped. :mrgreen:
 
How is this project progressing ?
 
hbpowerwall said:
How is this project progressing ?
Click to expand...
HI Pete is gone a bit Slow over Christmas But hopefully will take Delivery of 550 Laptop Batt in the next 2 weeks but have been Prototyping using Arduino will upload Pic Soon.
Cheers :)
 
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