Make your own “Powerwall” (Big LiFePO4 Battery Pack!)

As you might know the electrical energy in
my garage is created by solar energy which on the other hand is getting stored in a big
and heavy lead acid battery. Only problem is that the original capacity
of this battery decreased noticeable over time. That is why I have been searching for more
modern alternatives to this energy storage problem. And what I found was the Tesla Powerwall,
which is basically a container filled up with batteries, an inverter to supply mains voltage
and a cooling system. But honestly speaking, I don’t need the
inverter, nor a capacity of 13.5kWh and I especially do not want to pay $7600 for it. So in this video I will be showing you how
I created my more or less crude but still functional DIY Powerwall. Let’s get started! This video is sponsored by JLCPCB, whose offices
were visited by more than 100 customers in the past year.

And you can meet them as well at the Maker
Faire in Rome this year, where they will be giving out gifts. The three main ingredients for a DIY Powerwall
are of course the batteries which will form the battery pack, a decent BMS to protect
them from all kinds of mishandling and of course a suitable enclosure. So, let’s start off with the battery pack. According to Wikipedia, the Tesla Powerwall
consists of Lithium Ion cells.

Out of such batteries I already created several
battery packs in the past, so this should be an easy job, right? Well, to do this I firstly calculated the
capacity of my original lead acid battery which was around 1.2kWh. For the battery cell itself I went with the
Samsung INR 18650-25R whose capacity should be around 9Wh. That means I would need around 134 off those
cells which would set me back around 448€. Now that is of course pretty expensive in
comparison to the cheap lead acid battery, but then again Li-Ion batteries offer a way
better volumetric and gravimetric energy density which means the final battery pack will be
much smaller and lighter. But as I was about to order, I noticed that
the cells do not perform well in cold conditions which is a problem because temperatures in
Germany can go down to -20 degree Celsius in winter. That is why I started searching for a more
durable battery type alternative and found LiFePO4 batteries or Lithium iron phosphate
batteries.

This battery chemistry is known for not only
being able to handle lower temperatures but also for being safer which you can easily
see for yourself by just searching for them on YouTube. Another difference is that LiFePO4 offers
a slightly different nominal voltage which actually makes it more suitable to be a lead
acid replacement and also the charging voltage is a bit different, but a constant current,
constant voltage method is still recommended for charging. However the only reasonable LiFePO4 cells
I found were these, with a capacity of 19.2Wh at a price of 9.19€ if I order 63 of them,
which I would require. That would equal around 580€, which was
a bit too pricey for my taste. Thankfully though I found those 100Ah LiFeYPO4
cells at a price of 114€. The Y by the way stands for Yttrium that is
added to the cathode to allow this battery to work down to -45 degree Celsius.

4 of those cells in series should not only
give me a voltage range between 14 and 11.2V but also a capacity of 1.28kWh at a price
of 457€, which seems acceptable. Once again this battery technology is not
as cheap as lead acid, but lies with its better gravimetric and volumetric energy density
right between lead acid and li ion. So naturally, I ordered 4 of those cells along
with suitable terminal connectors and a fuse. After receiving them, I inspected them to
make sure that they were not damaged and then continued by connecting the cells with the
terminal connectors according to this diagram in order to create the 12V battery pack. As soon as I was sure that all the voltages
at the battery pack were correct, it was time to choose a suitable BMS which should at least
feature an overvoltage, undervoltage and over current protection along with a balancing
feature to keep all the batteries at the same energy level.

Now of course I could have used one of those
4S Chinese BMS which you can find all over EBay. But it just didn’t feel quite right and
safe for such a big amount of stored energy. So luckily after I searched the web for quite
a while and only found pretty expensive BMS, I finally discovered the company Energus Power
Solutions which offer the Tiny BMS for a more reasonable price. It works with 4 cells of LiFePO4 and basically
offers all the features that I have been looking for and even more by for example offering
temperature measurements, Analog and Digital Inputs and partly Outputs and also logging
of the battery activities.

So after receiving my board along with all
the required wires and temperature probes, I added a fuse to the plus terminal and another
terminal connector to the minus terminal which I then used to connect the BMS B+ and B- solder
pad to the battery pack through thick 12AWG wire. Next I removed all the wires from the BMS
balance connector expect the 5 upper ones which I then either soldered to the terminals
or locked them in place with the used screws according to this scheme. Afterwards I plugged the balance connector
into the BMS and continued by preparing the two temperature sensors, securing them in
place at the right and left side of the pack and then hocking them up to the BMS as well. And as soon as I was done securing the BMS
in place and tidying up the wiring, the hardware of the battery pack was basically complete. So I hooked up the included USB UART converter
to the BMS and a computer and started the given Battery Insider software. There I am able to define all the max and
minimum voltage, current and temperature values and whether I want to use the dual port or
single port mode.

Dual Port basically means that my charger
and load circuit are not the same and thus I want to cut them off separately. But since I am using an MPPT Charge controller,
which offers a load output on its own, I have charger and load circuit combined and thus
I need the Single Port Mode which therefore means I have to connect the charge controller
to the B+ and C- solder pad. Of course you can also find all those information
in the 76 pages long manual of the BMS which was actually quite an interesting read. To finish the software part however, I set
the voltage and current values according to the LiFePO4 profile that my MPPT charge controller
came with. And with that being done the battery pack
was ready for installation inside a housing.

So after measuring the dimensions of the battery
pack, I chose a slightly oversized electrical cabinet. As you can see it is not only made out of
tough steel sheet and thus weighs a ton but it also fulfills all kinds of safety standards
which is always nice to have. And of course the battery pack fits effortlessly
inside it, which means it was time to drill a big hole in the bottom lid of it in order
to mount a cable feedthrough and then I continued by drilling 4 holes for the cabinet into my
garage wall and then securing it through the help of plastic anchors and big screws. Next I prepared two conduit pipes which through
the help of pipe clamps I then secured to the wall. Last but not least I guided thick wire into
the electrical cabinet, placed the battery pack inside it, and hooked the B+ and C- pads
up to the wire which I then connected to the charge controller.

And with that being done my rather crude Powerwall
was complete. According to the appliances used in my garage,
it also seems to work without a problem which was also confirmed by my solar charge controller
app as well as the BMS software. Now granted, my solution is a tiny bit more
expensive in comparison to the tesla Powerwall when we look at the kWh per €. But then again I can easily modify it by adding
more batteries to not only increase the capacity but also change voltage up to 51.2V. And with that being said, I hope you enjoyed
watching my unique take on the DIY Powerwall project. If so don’t forget to like, share, subscribe
and hitting the notification bell. Stay creative and I will see you next time..

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