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New Powerwall [telephone cabinet size]
#1
Hi all,
I have been contemplating the idea to build a powerwall and so far all I did was buying a couple of 18650 or recycling some without doing anything with them really... Now I just jumped the gun and I bough :

QTY : 3
Type of cells : LiFePO
Manufacturer of the cells : A123
Maker of the pack ( yes i plan to use the pack as a whole ) : BAE Systems ( yes the military corp )
Max discharge current : 70A per cell ( crazy hein! )
Voltage of the pack 40V
Voltage of the cell : 2.3/3.3V

I am still missing a couple of infos but so far that is what I bough.


Here's the link :
https://www.ebay.ca/itm/3-used-tested-bl...2749.l2649

So I got a couple of questions :
1- Since I plan to use these pack as is, should i go and use the 3 of them in series to get 120v DC? I think that could be great to lower the cable gage and by doing so the overall cost of this system?
2- This summer I plan to test it and add packs later on...
3- I only have 1 solar panel that is rated at 160W ( Eventually the goal would be to have 10KWh+ solar panel + wind turbine )
4- I am quite good at programming so I am considering an exterior to the house powerwall in an aluminium enclosure with sensors to regulate the humidity and temp lvl of the pack and of the enclosure using pi + arduino.
5- I gonna need some advise regarding the charge controller.

Still in the planning phase, but I am quite excited Smile
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#2
If you go with 120VDC, you'd need an inverter that can handle that. That will probably outweigh the cost of the copper you saved going from 48V to 120V. However, if you plan on running lights and certain types of motors on 120VDC (as many of those that run on 120VAC will also do 120VDC) then you could keep it that way. Buuuuut, that voltage is kinda dangerous as it's worse than touching 120VAC. You'll get what's called latching. Your muscles will contract and hold unlike the with AC where your muscles will convulse.

For safety and cost reasons, it'd be better go with 48VDC. It should be relatively easy to convert those packs over to 48V from 40V
Proceed with caution. Knowledge is Power! Literally! Cool 
Knowledge is Power; Absolute Knowledge is Absolutely Shocking!
Dollar Shave Club. Best Razor I've ever used
Certified 18650 Cell Reclamation Technician
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#3
The thing is I would rather have to deal with an solar charge controler that can do 48V but that can also be user programmable to set specific charge paterns... I can code so I am not affraid to "hack" things to make them work... PS hack in the real term not in the holywood fashion.
So now the question become : is there any solar charge controler that can be programmed to a specific voltage rather than the 12v 24v 36v 48v + that I usually see as output options? Thank you very much.
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#4
It's not a programming logic that makes them able to handle a specific voltage input. It's the physical hardware on the PCB that determines the voltage. You can change the code all you want, but you won't be able to get any real performance out of it.
If you really wanna hack it, make your own MPPT charge controller and code it up using a custom mcu. Julian Ilett made the MUPPET which he's done several videos on. The parts are actually relatively cheap and the whole thing is easy to make.
Proceed with caution. Knowledge is Power! Literally! Cool 
Knowledge is Power; Absolute Knowledge is Absolutely Shocking!
Dollar Shave Club. Best Razor I've ever used
Certified 18650 Cell Reclamation Technician
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#5
Yes, that might be a good idea. The goal of this project is for me to understand better how battery technologies work and to build my own pack to do some testing before a finalized one.

Regarding hardware / software, yes I do understand that current Charge controller are defined by their hardware but what I am wondering is this : Since the input from solar panels vary ( the voltage ) and that an MPPT is able to track and use that power I beleive using something close to a gate ( ps new to electronics ) why is it not possible to implement a similar "gate" on the dc to dc side on things? This would allow user to set a default software value for the dc output no?

Thank you very much again, your help is really appreciated and I will be looking into that custom made MPPT Smile

And I have a 3D printer is that can be usefull in a custom project like this one Smile
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#6
It can be set that way, as long as the hardware can accommodate it. The higher the voltage, the more space that is needed between traces and contacts. You don't want sparks happening on the pcb. Quick way to kill the mcu. Then, depending on how much current you want, you need to adjust the gauge of the wire. So there are a lot of hardware variables that need to be figured out before the software ones are introduced Wink
Proceed with caution. Knowledge is Power! Literally! Cool 
Knowledge is Power; Absolute Knowledge is Absolutely Shocking!
Dollar Shave Club. Best Razor I've ever used
Certified 18650 Cell Reclamation Technician
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#7
100% agree... Fore wires size I will be able to make it to Code no problem on that side. Still learning, but getting better everyday of my formation Wink

Anyway I will read a bit more about inverters and how they work and I will come back here with plans and detailed Household Loads calculations.

PS planning to build a small home and having a dedicated small concreate building that would house the batteries & any inverter / charge controler subpanel etc. This building will also be used as a structural pilar for an outside roof filled with solar panel. Anyway would love to give you more details but I need to have a good talk with the municipal gov before I can do such thing Smile

Thank you for your help, I really appreciate it.
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