My PowerWall 18650s in this one though

(Buzz) #1

(Ian ) #2

What sort of batteries are they… Was gearing up to use18650’s myself. How many kw is the battery pack… @ 48 watts I presume?

(Jaimyn Mayer) #3

I think we worked it out to be nearly 8kWh just with those batteries. @buzz also has a 6kW solar system coming shortly. It will be cool to see a finished (local) powerwall project.

(Buzz) #4

HeadWay 38120L 10000mAh 3.2v nominal 3.7v peak LiFePO4 cells in 16x12 configuration. Each cell here is equivalent to about 5 normal 18650s … so there’s equivalent of about 1000 18650 cells there.

(Biki) #5

I’m keen to see the results in terms of kWh usage over the day, discharge and charge currents etc over a few weeks.

awesome project :slight_smile:

(Ian ) #6

We were talking about inverters at the Tuesday meeting and was wondering what you thought of this.

Seems to have grid connect add well

(Biki) #7

Hybrid from mppt solar in taiwan. Doeant have au approval. They do a 15kw 3 phase unit with 10kW charge too! Would perfect if it passed!

2 or 3 strings? It has quite a higj string requirement so it falla into high voltage. meaning caged off and not end user accessible.

I could be wrong tho.

(Biki) #8

I want to startup liquid redox cell design project. Could be cheap! Need mechanical, chemical, electrical engineers :slight_smile:

(Buzz) #9

my custom BMS - it’s monitoring cell voltages right now.

(Buzz) #10

(Buzz) #11

(Buzz) #12

… now with active top-balancing/discharging and error reporting! … as well as the other stuff mentioned earlier… cell voltages, logging , webpage etc.

(Buzz) #13

Yesterday i worked out enough of the circuit for the SM-004-5v (sanmim sm-plg06a) isolated 5 volt power module that I can now adjust the voltage to anywhere between 3v and 9v. It just required unsoldering two fixed resistors and soldering a 5k ohm pot in their place. Its now giving me a stable 4.2 volts.

So to spell it out, you can use a string of these to charge a series-connected string of LiPo cells in your battery because the DC side of each is 100% isolated.

Because these things are set to a fixed voltage, it means they they reduce the current to maintain stable voltage as a pack charges, so as the battery approaches 4.2v, then the current being put into the pack decreases toward zero… so you can ( in theory) leave it connected to a fully-charged cell and it won’t over-volt or over-current.