DIY Powerwall 4 – Adding capacity do your current system
Last time, we selected cells to set up a new battery. The last few months I received many questions about this topic. How can I safely add capacity to an
existing setup.
Recently, I added 10kwh to my existing 20 kwh powerwall. Let me guide you step by step how I managed
to do this without error or sparks.
To add extra capacity, you need to use the same voltage as the existing pack. Adding a 24V battery pack
to a 48V system is not possible, the same way that adding a new 56V pack to an existing 48V is not done.
I recommend the use the same chemistry, mixed systems with lithium and lifepo4 are possible but always
with a compromise and added complications.
Starting point: existing powerwall in use 14S 160P, we want to add another 14S 80P.
When building packs I always charge my cells to 4.2V before welding & soldering them together. So
once all 14 packs are in series I have roughly 58,5V. Here’s the first challenge, in order to extend battery life, the powerwall never goes higher then 56V.
One more job to check before we grab for the monkey wrench….. Make sure you’re prepared well. Install
support where you gonna install the batteries, make sure you have cables and connectors to connect the
new pack.
I’m going to assume you have all hardware and you’re prepared to do the job.
Step 1
I changed my charger settings and charged cells to 57V so that the new and old packs are sitting at the same voltage. I prefer to charge the cells to a higher voltage
because when we add another pack there will be less current between packs because of higher internal
resistance of the packs.
Step 2 switch off charger/inverter
Step 3 disconnect BMS/balancer, if you have a battery switch, disconnect the batteries from
charger/inverter (*)
Step 4 disconnect existing batteries from your main busbars.
Step 5 connect new batteries to the busbars. (you might see some sparks here if you don’t have a
battery disconnect, don’t worry)
Step 6 switch on inverter and connect a load to decrease the voltage from the new pack.
Step 7 Switch off load and check voltage. Repeat till you hit the same voltage as the existing pack.(57V)
Step 8 connect the older battery pack, so now all packs are connected in parallell.
Step 9 connect balance wires from the new pack to the BMS/balancer
Step 10 connect BMS/balancer
Step 11 connect a load to the inverter and get the voltage below 56V
Step 12 Update charger settings and set charging voltage back to 56V
As you can see it’s not so difficult. Make sure you can finish the project the same day. If well prepared
you can perform this job in less then 2 hours.
(*) For the balancer just remove the most positive wire (yellow wire on the picture)
Franky goes green – http://www.easypowerwall.com
Note: Franky is a valued contributor, however, his advice and opinions are his own.