DeonBez

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 info - that's what I expected...
As I said in an earlier reply: "... a 200 liter geyser would require about 4.65kWh to heat the water from 40C to 60C, regardless of the element rating" Assuming a total system loss of 10% (it's probably more...) you would be drawing just over 5kWh (50% of the battery's total capacity) just to heat the water in the morning. Obviously every system is different, but if we (again...) assume your over-night load (fridge, freezer, late night hot chocolate, etc...) is on average 0.25kW, then over a 10 hour winter night this would be drawing another 2.5kWh from the battery, leaving you with only 25% SOC left, just as you've confirmed.
That certainly would be the best option for you. Regardless or this, however, I would still suggest that you downgrade your geyser's element. Even if you opt for a larger new system, allowing for a 4kW geyser element would certainly require a larger inverter, bigger battery, and possibly more solar panels than what would be necessary if you replace the element with a 2kW unit. In addition to just the additional costs, using the smaller element will also assist in obtaining an extended battery life, due to a shallower discharge of the battery (everything else being equal...)
Good luck with the new system - and choose your components wisely 😁

I respectfully beg to differ... I don't dispute that (say) a 200 liter geyser would require about 4.65kWh to heat the water from 40C to 60C, regardless of the element rating, and that the 4kWh element would do this in half the time that a 2kW element would...
My point is that the 2kW element will be able to start heating earlier, and stop later, than the 4kW unit if it only uses solar - and that would make a difference. In my experience, a geyser element (or a stove) wants to be fed it's full "load requirement", thus a 4kW element will pull 4 kW if that is available, regardless if this comes from solar panels, the grid, or a battery (unlike when an inverter charges a battery, that might only push 200W into a 10kWh battery if that is all that is available). So, a 2kW element will be able to start up much earlier in the day than a 4kW element, as the panels will be able to produce the 2kW much earlier than 4 kW, and the same goes for the afternoons.
Another advantage would be that the 2kW element would not likely "overload" the 5kW inverter when used during the day, whilst the 4kW element would only leave 1kW "spare" for the rest of the house loads when it is heating the water.
Regarding the "upgrading cost comparison"... Not knowing the OP's system (how many panels of what Wattage, etc.) we will have to make some assumptions (and I hate doing that... but lets bite the bullet...). @King_M stated in his first post that he has 3600Wp panel output and a 5kW inverter - Adding (say) 4 x Canadian Solar 108 cell 405W panels at R1 221.3 (current price VAT Inclusive from a reputable dealer in Bloemfontein) would only cost R4 885.20 (plus installation cost...) to increase his maximum yield from 3.6kWp to 5.2kWp. Obviously this is only an example, and if the panels mentioned are not compatible with the existing panels, or if the inverter/MPPT can not safely handle the Isc and Voc, then one would have to look at using different panels...
Obviously, your "do nothing and pay for grid power" is also a valid argument, and if the addition of a few extra solar panels is not an option, then your argument does make financial sense.

What I have done is simply built a plywood enclosure with plenty of ventilation ...... I painted on a resin to seal the wood completely ....... I live in an area where even plastic rusts 😂 so although everything was IP65 i wasn't going to take any chances, two years in and all good.

Since 2021 I used the voltage settings below (no comms between Inverters and Batteries):
55.6V (3.475V per cell): Absorption phase
55.2V (3.45V per cell): Equalization for 1 hour (and yes I know all the super intelligent says it is not for LifePo4 ... but trust me it is good for the slow cells to catch up again)
53.6V (3.35V per cell): Float

Over 4 packs (i.e. 64 cells) the voltage difference is normally below 10mV

Ok, thanks @stefan44 , @Greglsh and @Stefan Cornelissen
@Greglsh , I'm off grid, so it hardly ever does what yours seems to do, unless some clouds come in after the batteries are full and we run off those for a while before the sun returns, but even if we're down to 92% SoC before sunset, at this stage the lowest morning SoC I've seen is probably 45%, so not too panicked about the lower SoC late afternoon, unless the next day is supposed to be cloudy, then I try and minimise the consumption overnight, I guess I need to get off my lazy butt and add the other 2 batteries, to have a combined 60kWh and thus no more panicking :-)
Ok @stefan44 on your settings... 30mV for balance to cell max voltage seems a bit skraal, meaning it won't get much chance to balance before things drop out of range, just looked at yesterdays charge, 3.400V by 12:00, 55V by 12:22, and effectively if that was my setting, probably not 20 minutes later cells would be 3.400V or less and thus end of balancing... ok this was on my worst battery and there was 26mv delta between the cells once 55V was reached...
I'll do some more homework, maybe can start balancing earlier, say 3.400V and then bring cell max voltage down to, maybe 3.480V so 55.68V for the pack...

Only saw this reply now
It's entirely probable that it's a "pirate" cable with a blocked driver

Item: 14.3kWh DIY Battery Kit
Age: New
Price: R32500 per kit (collected)
Payment Method Accepted: Cash / Instant EFT
Warranty: 3 years on the cells - non-local supplier
Packaging: Original for most
Condition: New
Location: Strand, Western Cape
Reason: I built enough for myself - cells leftover after builds for my own use and friends/family
Shipping: Not preferred
Collection: Yes, please 
Links: Pictures, JK BMS, LCD, Terminal Set (almost like this one) EVE280K-Product-Specification-Sheet.pdf
14.3kWh DIY Kit includes:
16x EVE 280Ah LifePo4 cells (LF280K cells package in 4x padded boxes each with 4x cells)
Eva foam padding between cells
Yellow Fiberglass isolation sheets under cells
Vertical Aluminum Box with high density silicon feet, threaded rods with compression plates for securing/mounting of 2 rows of 8x cells
200A JK BMS with built-in 2A active balancer including switch, cables and 3.5” LCD screen
2x 200A DC terminal sets (Black/Orange and male/female for 50mm2 battery cables)
200A DC breaker and fuse holder with 400A fuse
Assembly optional: Will assemble and test on request – only for collection as don’t want to package and ship a heavy (>100 kg) battery

Just to elaborate further regarding the "fine" temperature ranges for LiFePO4 batteries - Summarized by my good friend ChatGPT:
True Electrochemical Optimum for LiFePO₄
Based on lab-tested data and peer-reviewed sources:
Parameter
Optimal Range
Notes
Charge Efficiency
15°C – 25°C
Peak coulombic and energy efficiency
Discharge Efficiency
10°C – 30°C
Capacity is near-maximal with low resistance
Degradation Minimization
15°C – 25°C
Lower electrolyte oxidation, minimal lithium plating
Internal Resistance (Low)
20°C – 25°C
IR is lowest in this band
Supporting Technical Sources
LiFePO₄ Cell Behavior at Different Temperatures – Detchko Pavlov et al.
“Degradation Mechanisms in LFP Batteries” – Journal of Power Sources (Elsevier, 2017)
Battery University & Victron Energy (practical integration guides)
EVE 280Ah LFP Cell Datasheet (widely used in Sunsynk and similar packs)

Living in the Free State (RSA), we regularly experience sub-zero temperatures over night during the winter. It is known that lithium batteries do not perform well when cold, and can be damaged if charged when below freezing temperature. My inverter and 2 x 10kWh LiFePO4 batteries are housed in my unheated garage, and I've been quite concerned that the batteries could become too cold to operate optimally. After some trawling of the internet, I concluded that it would be best to isolate them in a "box" of polystyrene sheeting, and to add two small (7W each) heating mats below the batteries to add a small amount of heat to this "box".
I initially used some duct tape to just stick the panels together as a "proof of concept" pilot project, and then added the heating pads, purchased from a local pet shop (sold as reptile heating pads...) after the first week of operation. After a second week of careful monitoring, being concerned now to not over-heat the batteries, I proceeded to properly build a box using 2x25mm thick polystyrene sheets as walls, and an insulating "floor" made from fibre-cement ceiling board mounted on a 6mm plywood sheet, and raised off the concrete floor with some 38mm x 38mm pine brandering for the two heating pads (placed in shallow wooden boxes and covered with a thick layer of kitty litter to act as a thermal mass below the batteries).
Here are some photos.
The un-insulated batteries, showing the insulating "floor" and heating pad boxes with kitty litter...

The duct taped temporary box...

...And the final enclosure before final fixing to the wall

So far, temperature variation during the last week ranged from about 14 degrees C minimum to 17 degrees C maximum, even though we experienced a few nights of zero degree C minimum air temperatures in the early mornings. We expect some typical -4 to -6 C lows in the next week or two, and I will report back on performance after the next cold fronts.
I am quite pleased with the outcome of this little project.
Your feedback, comments, and constructive criticism will be appreciated.

Cannot say for sure. Just noticed that one reviewer on that product page mentioned that the cable does not work on Windows 11...

I have primatic cellls. Lots of them.
EVE grade A 160AH 3.2V, if you need send me a message.

So I am and have been totally off grid for 3 Years already that includes all services electricity water sewage garbage etc.
Current system
7.3KW PV East West configuration JA Solar all Black panels.
2 x Solis S6 6KW advanced inverters
7 x Hubble AM-2 Batteries
1 x 2KW Odin Wind turbine.
My Summer off grid production and consumption hovers around 25 to 30 KWH per day
I run 6 Fridges and freezers air fryer microwave oven LED flood lights most are on 24 Hours per day 3 small hydroponics systems CCTV system with 8 cameras laptops wifi equipment laser printer (not useds a lot) Aircon always on in the day in summer and 1 hour at night 3 electric fans always on in the summer 1.8KW Borehole Pump once a day for 30 Minutes 350 Watt pressure pump for Irrigation runs 20 Minutes twice a day 2KW Geyser element always on Element kicks in 6 times over a 24 hour cycle for 10 minutes and 45 Minutes after a Shower I use a electric 1.2 KW lawn mower to mow around 3000 squares of grass once or twice a week I can use my Angle Grinder Welder electric drills skill saw etc almost any time of day.
I have a 3KVA petrol generator and in the 3 years that i have been off grid I have only run the generator for about 18 hours
Cooking is mostly done on the Gas Oven Stove. We cookc everyday no takeaways here.
In winter time my consumption goes down a little to 18 to 20 KWH using the aircon a lot less use gas heaters and a fire for heat in the winter.
Adding a Donkey to my system for this coming winter with a piggy back geyser with an 2KW element however the donkey will provide most of the hot water in winter I have tons of decent Black wattle firewood so reducing my need for electric elements will have a small 15 watt solar geyser hot water pump to circulate the hot water between the geysers.
The water tank that feeds the main house with water is on a 5 Meter Stand so I don't need pressure pumps to provide pressure on my taps in and around the house.
I have a water filtration system for drinking water etc.
All our toilet waste goes to a bio digester and we have a grey water system that feeds shower water and dishwashing water into my garden.
The reason for the large battery bank is as follows.
If you want to have off grid power when using solar only you will need a battery bank equal to your normal 24 hour consumption however this does not cater for overcast and rainy days.
Hence the reason I have 35 KWH Storage got this before I got the turbine installed.
Because my consumption goes down in winter and my production from the PV in winter is lower the storage is perfect and I never run out of power however if we do have rainy overcast days in winter I would switch the Geyser off to reduce night time consumption and only run it when we need it the Donkey will eliminate this need this coming winter.
Because I have the turbine it will help a lot with Winter energy production because my Windy season starts and maintains through winter so my turbine will produce anything between 15 and 25 KWH per day
During that time and would make my battery storage and solar power almost obsolete.
However in Summer time I rely very much on solar production because the wind power production in summer per day would only be about 1 to 2KW per day.
The short and long is if you go solar alone and want to be completely off grid I would say your battery storage needs to be about 150% of the Power Consumption for a 24 Hour cycle that is if you do not want to run a petrol generator for emergency power needs.
You can reduce your nightly consumption by adapting your heavy consumption times to when you have solar power available.
Certain things you cannot get away from is your 24 hour loads or base loads and you need to cater for those in battery capacity or alternative power generation.
My Base loads in winter is a lot lower because the fridges and freezers have lower ambient temperatures so I turn them all down in the winter reduces base load significantly.
I don't need the aircon or fans to run all the time and that reduces the base loads at night quite a bit 3 electric fans can run at about 250 watt.
Other factors to consider is redundancy for potential failure that is why I have 2 x 6KW inverters if one fails I still have power and all of my appliances can still work with a little management.
I hope this gives you some context each person will have varied loads and base loads however it is important to plan you system and size it correctly to suit your specific requirement.

*******UPDATE*******
Nive from Lithium Batteries South Africa (LBSA) made contact with me on this forum and offered to look into the matter.
She had the battery collected from my house. The battery then received a full service and they found a loose terminal to be the cause of the issue. My battery was returned to my house same day and is now working perfectly.
I cant tell you how impressed I am with LBSA after sales service. Their excellent reviews on Google reviews back this claim up.
Do yourselves a favour and check out LBSA products and support a local business with excellent products and after sales service.

Item: 14.3kWh DIY Battery Kit
Age: New
Price: R32500 per kit (collected)
Payment Method Accepted: Cash / Instant EFT
Warranty: 3 years on the cells - non-local supplier
Packaging: Original for most
Condition: New
Location: Strand, Western Cape
Reason: I built enough for myself - cells leftover after builds for my own use and friends/family
Shipping: Not preferred
Collection: Yes, please 
Links: Pictures, JK BMS, LCD, Terminal Set (almost like this one) EVE280K-Product-Specification-Sheet.pdf
14.3kWh DIY Kit includes:
16x EVE 280Ah LifePo4 cells (LF280K cells package in 4x padded boxes each with 4x cells)
Eva foam padding between cells
Yellow Fiberglass isolation sheets under cells
Vertical Aluminum Box with high density silicon feet, threaded rods with compression plates for securing/mounting of 2 rows of 8x cells
200A JK BMS with built-in 2A active balancer including switch, cables and 3.5” LCD screen
2x 200A DC terminal sets (Black/Orange and male/female for 50mm2 battery cables)
200A DC breaker and fuse holder with 400A fuse
Assembly optional: Will assemble and test on request – only for collection as don’t want to package and ship a heavy (>100 kg) battery

Hi everyone, so I had the need to get daily, weekly and monthly solar statistics emailed to me but after requesting this directly from the Solar-Assistant team for months, I decided to create it myself. I have made it available to all if you can find the use for it and can be found here - https://github.com/Stef1986/email_scheduler_solar_assistant
Once you have cloned the repo locally, you simply edit the .env file with your Solar Assistant's MQTT details as well as your reporting preferences and run the docker-compose up.
Just have a look at the README.md, it should be detailed enough to get you going.
As a quick overview, basically what will happen is on the host of your choosing, you will run the docker container that will subscribe to the MQTT topic created in Solar-Assistant and will ingest all the data. It will then (based on your choosing) schedule daily, weekly and/or monthly statistic reports to be emailed to your inbox.

The body of the email will contain a nice table with statistics (configurable in the .env file) with min/max/avg values as well as a csv attachment (also configurable) containing the totals for daily, weekly and monthly for stats like PV generated, Battery in, Battery out, etc etc

Hope you guys enjoy and if this helped you, consider supporting my efforts with a beer or two 😁🍻

You may need to be more aggressive with your pricing.
Right here on PowerForum Store you can get a Deyness 14.3 kWh LFP with 10 year warranty for R37 375.
Dyness PowerBrick 14.336kWh Lithium Battery
 

Hi IvanZah,
I have followed a more convenient way and used the M5Stack Core 1 and the Commu-Module. The CAN-Port is connected to the Deye PCS connector only. It is running for almost a year now.
I could deliver you the Arduino Code. And help you with the code and setup. 
best regards
Peter
 
 
 
 

Good Day @MrNj
 
Over Voltage for a prolonged period may have caused cell damage or BMS damage as explained above.
Recommended charge voltages for the 48v 5.09kwh battery is
Bulk : 54v
Float : 52.5v
Low Cutoff : 43.5v
 
Your battery would need to be sent in to us for cell and BMS diagnostic. 
OVP - Over Voltage Protection - 270 instances, does void warranty, but i will assist in a resolution, please pm me and i can assist you.  

This is very impressive. Well done and GLWS!
Jay

Nice @GJ Cronje. Which enclosure and BMS do you plan to use? 

This explains a lot...
 

Apologies for stepping in on a classified thread... 
@ZS1SCI look at this thread. If you are interested in a box let me know. I have a font panel that fits the JK BMS 3.2" LCD and the JBD BMS LCD.

Q10 looks like it has been hand re-soldered; possibly the wave soldering was found to be suspect by an inspector, or it didn't work and this was re-soldered to fix the problem.
But this is the main power supply. If the LC Display is on, then that would seem to be working fine. As you will probably find in the service manual, I think you should be directing your attention to the circuit with Q6 and TX2, the soft start power supply. In the top right hand corner of this partial schematic trace, you'll see the "transformer" and diode connect directly to the DC bus, to start it softly (with a few watts).

Hi @Coulomb , I think i founded the problem. So I Strip the motherboard out and check the underside, and i think i founded the problem. Q10 that is BSX53. You can see in the photos that it looks suspect. I check your drawing and thanks again for posting it. It really help. 



I think to replace Q9 to just for in case to.