Sats Nkamoto

Hi all, long-time lurker, first post in a long while.
My current setup: 2× Sunsynk 8kW in parallel, 2× Solar MD SS4144 (14.4kWh each, CAN comms to the master Sunsynk). System works well but I'm hitting minimum SOC most nights and the grid is kicking in. I want to add roughly 30kWh of storage without replacing what I have.
The plan: Build a 16S2P pack using 32× EVE LF280K (or MB31 314Ah) cells in a DIY steel frame, with 2× JK 200A active balancer BMS. Wired in dumb parallel at the DC busbar alongside the Solar MD batteries — no CAN comms to the Sunsynk, just the JK BMS protecting the cells independently. Only change on the inverter side is updating battery capacity from ~555Ah to ~1,120Ah and turning off BMS_Err_Stop so it doesn't fault when the DIY pack doesn't respond on CAN.
Questions:
Any gotchas with running a DIY pack alongside Solar MD batteries in dumb parallel on a Sunsynk? Happy with the Solar MD being the CAN "master."
The Solar MD datasheet shows an operational voltage of 44.8–55.6V. I'm planning to set absorption to 55.6V on the Sunsynk to respect that ceiling — does that sound right to those of you running mixed banks?
Has anyone sourced cells from Cell Supply SA (cellsupplysa.co.za)? Looking at their EVE MB31 314Ah packs. Their Judge.me reviews look solid but would love to hear from someone who's actually received cells from them, especially for a larger order.
Cape Town based if anyone local has done something similar.
Cheers

Thanks for the reference. Sold to Solo and successfully delivered today. 👍

We are seeing a number of inverters with bypass exceeding the actual inverter rating. It was actually normal for those with trip switches to trip when going over the inverter rating. It is for this and other reasons why 5kW inverters are just more popular than 3-4kW units. 

1mm2 cabtyre is rated for 10A or about 2.2KVA  So if you have a 3KVA inverter that gauge will be too thin.  Use 1.5mm2 cabtyre which is rated for 16A.   Your electrician can later use 2.5mm2 house wire to do the permanent installation.

The link I sent was actually the wrong one - it shows the 20A version. The one I intended to share was this one: https://www.livestainable.co.za/product/victron-energy-blue-smart-ip22-12-301-230v-cee-7-7-battery-charger/ which is the IP22 30A (with a single set of output terminals) model.  I've placed my order and will update this thread with the result. Thanks for all the input, guys - much appreciated.  

Thanks, @TaliaB but do I really need the IP65 "waterproofness" when I'm installing the system inside? Maybe I'm missing something, but the IP22 model is cheaper and has a higher charging capacity (30A vs 25A)

Great company good service. I got this one from them better choice for your application
https://www.livestainable.co.za/product/victron-energy-blue-smart-ip65-12-251-230v-cee-7-16-retail-battery-charger/

the left hand side is the correct way of connecting the batteries/inverter/charger...
yes, but as @DouglasBray wrote, higher charge currents would be better, to shorten the charging time, I'd say 30A in total for C/10, in other words, 10A current for each of the three 100Ah batteries...

Download Victrons guide called "Wiring Unlimited". Its a good read. I think many people on this forum would benefit from it. In there they cover your question with diagrams.

Your Typical 100A Deep Cycle Battery has a Maximum Charge Rate of 25A. For each Battery you place in Parallel you add the Charge rate (This is Roughly accurate and there are a number of factors that could influence this). So Effectively you are charging 300Ah Battery with 5A Charger (about 30 Hours to Charge from 50% or 15Hours to charge from 25% - again roughly and depending on so many factors). You really want to charge at around 50-80% of the Maximum of the Battery, so in your case 30-40A Charger.
These are just basic figures to help you understand, there are a number of Engineering Factors that still need to come into play, but if you look at it from this perspective: the amount of power you take out during load shedding is the same amount of power you must put back in while the power is on as long as it does not exceed the Battery or Charger Specifications (I like to use 50% of the Specified Maximum Values to be safe - Yes I know, I Over Engineer Everything, But is lasts...)

Pity i am in Gauteng i fix a lot of inverters up to 12kva

It can safely handle 18

I confirmed with the supplier that the 8kW Sunsynk should safely handle 14 x 660W panels split across the two MPPT's.

I think if there are two MPPT's and there is a specification -(MPPT Range – 125~425V) the inverter can take max 425V per MPPT.

That's high. Well... depending on how many people are living on the property. But it is often the advice given on this forum that you need to reduce your consumption first, and then your solar dream gets easier to realise. So consider full gas stoves, keep an eye on geyser temperatures, put LED lighting throughout the new house.

I wouldn't trust myself to give good sums, but it might be a good idea to leave the final solar design until you know what your consumption is.

Here's some good tips on reducing electricity consumption
https://ltcelectricalservices.co.za/electrician-in-edenvale-and-bedfordview-boksburg-benoni-germiston-bruma-alberton/how-to-save-electricity/

It starts with the architecture that allows the house to use the winter sun to warm the walls(and keep the summer sun out), insulation that prevents heat loss(and ventilation to cool the house in summer). Then underfloor heating, geothermal heat pumps are better in places where the air reaches below zero celcius, the normal ones are fine for south africa.
50kwh storage is only 10-12 pylontech up5000 or BYD like in this system 
I would go with a similar system when starting from scratch and budget allowed.

Yes EV's have huge lithium batteries, charging them from pv directly rather then storage will save on storage costs.

Hi all,
I'm building a 450sqm house in Stellenbosch soon and have the opportunity to adopt proper renewable tech from scratch.  Your input would be invaluable.
So far I'm thinking double glazing, isoboard under slab,  PV and heat pumps.  Even considering geothermal (i.e. ground sourced energy input to heat pumps) 
Some more info:
My current consumption is ±70kWh per day in winter - conventional HWCs, cooking, pumps, minimal heating
The electric vehicle I'm considering will require an additional ±30-40kWh per day to cover my daily average travel.
I'd prefer an ROI of ±10-12% on the capital employed.
The system must be able to cope with stage 3-4 load shedding.
I never want to have to wear ski clothes in my home in winter.
I will have ±90sqm 30deg North facing roof surface (2 sections) and would prefer to use a panel that covers the whole of the roof section for aesthetical reasons.
My back of the cigarette box calculation - please rip it apart.
Peak winter 120kWh per day / 10hrs of sunlight = 12kW per hr generated
50kWh discharged during 14 non-sunlight hrs (charging elec vehicle and others) = ±50kWh battery capacity!!?
I look forward to engaging with the smart people here