lead acid upgrade to powerwall

graham

Member
Joined
Jan 5, 2018
Messages
46
Hi All

I am looking to replace an existing 12 volt 200Ah c20 lead acid set up with a diy powerwall,

my existing system is

2 x 80wp 21 Voc solar panels

6.6 amp PWM stecca charge control

charging 2 x 125Ah rolls @ 12 volts

this runs my 12v central heating and hot water pumps and control gear for the wood burning range,

It uses between 10 and 20 Ah per day depending on how long we run it for, I could reduce the consumption a bit if I changed the wiring to get rid of a couple of auto relays,,

In the summer the same 12 volt system powers the control gear an pumps for the solar hot water collector,, I have way power more than I need in the summer an think its been a factor in the demise of the existing lead acid batteries, so I need to find a use for the extra in the summer,, anyway,,

I know 12volt is not good for Lithium cells (thanks to your site) so im looking at doing the following,

2 x panels in series to get 24v

MPPT suitable size

7s30p Lithium cell 18650

I have seen new cells at 5000mAh by Ultra fire dont know if anyone has any experience of these?

then into a dc/dc converter to 12v supplying the existing system,

It looks like I will need some sort of BMS some pointers would be appreciated on suitable set ups as well as any comments thoughts, suggestions on my plan,,

Thanks for reading

Graham
 

And then you skip those cells.

How much money do you want to spend on charger? BMS you can go with most common smaller BMS boards from china. I have also done some reviews on some.
 
Thanks for that you saved me from getting burnt,,, great video about the fake cells very informative,, thank you

Charger,, I was thinking about a victron MPPT 75/10 or something similar so under 100 $ , i had a brief look at the MPT Boost from the links on your site , looks good too,, would my choice of charger effect which BMS to use?
 
Not really no. But it also depends on what your goal is in terms of functionality.

Some BMS systems can interact and talk to the charger but they cost alot more. The Victron is an awesome charger! You pay for what you get kind of and Victron is a good known brand!
 
after a lot of reading and referencing this site i put together the following ; image_fxzvbz.jpg



210 samsung cells 2600 mAh
7S 30P


LLT smart BMS 7S 20amp


Victron 75/15 mppt solarblue charge controller


I have re configured my two solar panels from 12 v parallel to 24 v series
my next step is to read the BMS and the Victron MPPT from a local network Raspberry Pi and moving on to replace my existing hotwater and heating pump controls which consists of a box full of various automotive 12v relays , with a raspberry Pi program. im still on the lower slopes of the learning curve on that one though... any pointers on where to goan what to learn would be great,,,
 
Looks like a squid with blue eyes :p
 
Looks very nice. Its similar to a projet Im planning (small solar setup, moving from 12V SLA to 24V lithium 18650 cells).

Where did you get your cells from (are they new or recycled)?

Also did you adjust any of the charge settings (maximum/minim voltages) on the Victron charge controller? I also have a Victron 75/15 and think its great!
 
After some very good advice from daromer on duff cells i opted for new cells from Nkon, I live in a remote area an used cells dont come easy,,,

I haven't changed any settings on the victron mppt yet, but i have just this afternoon got the victron connected to my raspberry pi on my LAN, so now will have a look at making some adjustments,

How do you communicate with your 75/15?
 
I have to victron 100/30 and added the bluetooth dongle. I connect with their app on my smartphone. Very cool setup.
 
I agree;;; the victron and the cheap BMS are my first successful ventures into communicating with my chargers/controllers its a massive learning curve for me. I now need to learn more about what/how to set all the parameters to.
Thanks to Daromer for the review on the LLT BMS with my limited knowledge it seems to be doing what it should. I haven't changed any of the settings on either yet, but im searching for info...

Its all bought a whole new enthusiasm to my solar set ups I've had three independent setups on lead acid battaries with a grid charger a bit in the winter months, hassle to get accurate stats. now i can check it on me tablet ... im livin the dream....:eek:)
 
Thanks graham said:
How do you communicate with your 75/15?

I also use the Bluetooth dongle and the Victron app on my phone. This seems the most convenient for my use.

Which cells did you go for and how do you plan on connecting them together?

Ive ordered some cells from Liitokala on AliExpress and have a few different plans to connect mine:
- 18650 battery cases (the black ones with flat tabs on each end
- Vruzen connector caps
- a future purchase of a tab welder

EDIT - seems my choice of 18650 connector caps is censored. Although you can probably work out what I mean, as Im not aware of any alternative brands.
 
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