Open Source Modular Powerwall

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maximedulude

New member
Joined
Oct 10, 2016
Messages
10
Hi all,
I would like to know if you would be interested to help me design a powerwall that would take in modular battery packs that you would swap in just like you swap a server into its server cabinet.

I have a couple of problems that I'm trying to solve :
1- BMS for the whole thing and for each module
2- How to design the pack to be able to have a low Peak Amp on each cell. ( So we can use cheap cells )
3- The Powerwall itself would be a Metal box a little bit like your phone provider in the local area box. Tall but not too much and not very large. I would like it to be outside the home and I understand that this would come with some problem regarding warm/cold outside temps.
4- How will it be charged and could we make it so we can in the long term just change the battery composition in a pack to upgrade our filled Powerwall? This would be the ultimate goal and being able to sell back your older module for people that still have space in theirs but dont have the money to buy the new cutting edge pack.

Thanks I think that this could be really really great for all of us.
 

MicahT

New member
Joined
Oct 16, 2016
Messages
13
I think this is an awesome idea. I have a lot of experience with BMS's (I come from the electric bicycle battery world) so I'd be happy to offer some support there if you need it. What voltage would you be designing this to run on?
 

maximedulude

New member
Joined
Oct 10, 2016
Messages
10
The voltage that I would like this powerwall to run on is quite high...
The thing is this is the cells specs :
100X Wholesale PKCELL ICR 18650 Battery Rechargeable Li-ion Battery 3.7V 2200mAh
Product Details
Brand: PKCELL
Voltage: 3.7V
Storage Voltage: 3.7-3.9V
Charging Cut-off Voltage: 4.2V
Discharge Cut-off Voltage: 3.0V
Capacity: 2200mAh (NOT HIGH DRAIN)
Norminal Capacity: 2200mAh
Size: 18.0*65.0mm
Weight: 46g
Protected: NO
Battery top: Flat top
Max Constant Charging Current: 2200mA(1C)
Max Constant Discharging Current: 4400mA(2C)
Material: Lithium Li-ion ICR
Recharging cycles: At least 500cycles
Appliations: Flashlight,headlamp,lantern,LED light,dive light,green laser,fan,headlight,torch,laser pointer,gun laser,weapon light,vape,mod,ecig,mechanical box mod and so on

As you can see their Peak AMP is quite low ( 2C ) so If I would like to be able to run some power hungry appliaces, I would need and inverter and a BMS that would be able to handle high Voltages and to ramp up the Voltage to make sure that the instant C on the cells isn't too high.
Currently 3D Printing the end of the battery block to have a better idea on how the + / - and the BMS In ( from the main bms of the powerTower itself ) would look like.
Thanks for you help really appreciate it! :)
 

maximedulude

New member
Joined
Oct 10, 2016
Messages
10
Can you people help me figure out if this is correct :


image_moagbc.jpg
 

hbpowerwall

Administrator
Joined
Oct 7, 2016
Messages
1,980
maximedulude said:
Can you people help me figure out if this is correct :


image_moagbc.jpg


Hell no looks like math :)
 

maximedulude

New member
Joined
Oct 10, 2016
Messages
10
Yeah... Got told that this isn't how it works lol

My friend told me that it supposed to work like this :

1- Whatever the load is on the AC household the thing that matters is : Watts * (Watts+lost (in AC-> DC) + lost in (DC High to DC Low) ---> this will be the load that the batteries need to give to the DC-DC inverter.
So..
2- If my packs need 13S XP, then the Nominal Voltage will be 3.7 * 13 -> 48.1V
3- If the load is 1000 Watts in AC, I will need to calculate the loss in DC to AC and DC to DC and add that to the total P that my batteries must provide to make it works.
3- So lets say that we have a 10% lost in this process that goes into heat... 1100Watts is what we need to provide 1000Watts.
4- We then have to say that this 1100W on batteries will be /48.1V -> 22.869Amp total on the cells... To split that load if my cells are only capable of arround 4A each i will need arround 6-7P or will the Amps be splitted even if the cells are in series? I do not think so... but let me know ;) Trying to figure out how batteries works before I work out how the electronics will work. I do a lot of java and web so when I will understand really good batteries & electronics the GUI will be very very detailed for this project.

The more I get help to understand the better this project will be at the end. Thanks everybody :)
 

s9Josh

New member
Joined
Nov 4, 2016
Messages
9
Hi there. For detailed planning you really need to pop over to <!-- m --><a class="postlink" href="http://forum.solar-electric.com/">http://forum.solar-electric.com/</a><!-- m --> Just create a new topic. Usually the moderator BB will take your specs and reply with the math and answers you need. He is quite good and very responsive last time I was active on the forum. He loves being helpful and knows all the efficiency numbers.
 
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