I have a 48V off-grid solar system(ANENJI 6.2kW hybrid inverter).. and I use AGM batteries.. I have 8 pcs, 100Ah each, in a "4S2P" configuration.. so, 2 in parallel and 4 of these pairs in series .. so this should be 48V 200Ah or 9600Wh battery.

I should mention that now I have 14 PV panels .. 7 in series and 2 series in parallel .. one series on each side of the roof .. these are all used and most of them are the same brand and model, but I do have couple of different ones.. most of them are 350W and 2 or 3 are 450W.. first I had only 5, then 10 (5 for each side of the roof), then bought 2 more and recently 2 more.. I buy them when I find a good price and have enough money to afford it.. I know this is not perfect but it is what it is. I bought more panels because I though that I didn't get much sunlight to the charge batteries during winter.. but now I'm not so sure about that. (my location is around 44-45° latitude) 

Problem is that during the winter the batteries regularly go to 0% .. like, every night.. sometimes even before sun goes down.. during the summer, they can last whole night but get to 5-15% SOC

But during the winter, I only have connected 5 cameras and a wifi router, nothing else, not even light bulbs, because I'm not in this house during winter.. I just need the camera surveillance and wifi for them  .. this is around 50W load(the inverter app says its 25-27W, but let's say its 50W).. let's say the night lasts around 15h and the inverter needs another 100w just for being ON .. that should be around 150W * 15h = 2250Wh !!

Are my batteries so bad that they can have only 23% of their original charge !?

To me this seems ridiculous.. I have 200kg of batteries and they can't power 5 little cameras and a router for more than 6-8h !?!? Realistically that's 50W load, and I can't get one night with that?!?

I've never bought new batteries because they are so expensive.. I always bought them used.. but still, I would expect they would have at least 50%.

Few days ago I did the 'equalization' program that my system has.. for that to work I had to change the 'battery type' setting to 'flooded' or 'user' .. so I set it to 'user' .. then I can set the 'bulk voltage', 'floating voltage' and 'low DC cut-off' .. and I did set this correctly, as the battery specification says.. I also used an inverter gasoline generator for grid AC input because I was afraid there was not enough sun for this. The inverter user manual is very shy on information about this program.. user can only set the equalization time, timeout, interval and voltage.. it says it can go up to 64V but I could only go to 62V.. not sure if it is a typo in the manual or something else.. the time and timeout setting were left at default.. so, 60min and 120min, respectively

While it was 'equalizing', the first battery pair in the series got to 16.5V, second pair was lower, around 15V and 3rd and 4th pair were only around 14V.. also, first two pairs got a little bit warm, especially around first cell in the battery.. so I guess my first pair is the worst, then the second pair and then 3rd and 4th are the same and better than the first two.. but I remember that last year, also the first pair was the worst so I bought 2 more batteries and replaced them. Can it be that the first batteries in the series get used more or something, or is it just a coincidence?

I repeated this 'equalizing' program 3 or 4 times that day and the batteries did 'equalize', I guess.. last time I did it the batteries were closer in voltage than the first time and the following night they got to around 40% SOC.. but the next day only around 25% and now its the same as before

I was thinking about switching to liFePO4 batteries because my system supports it but when I realized that those batteries can't work around or below 0°C , so I gave up on that.. now I'm thinking about buying new AGM but lower capacity .. say, 50 or 80 Ah.. just because of the price .. but I'm worried they would also quickly go bad and warranty would not cover it.. I know that you should not use more than 50% because otherwise the battery quickly gets damaged .. but my inverter has an AGM battery type in the settings and I would expect it wouldn't discharge the batteries below 50%.. is this correct? Should I set 'user' battery type and set my parameters for cut-off and everything else in order to not let the batteries discharge below 50% ?

What about GEL batteries ? I read that they can get greater DOD without getting damaged

Forget about lead acid and go for LiPo.

1 hour ago, Skipbidipop said:

I was thinking about switching to liFePO4 batteries because my system supports it but when I realized that those batteries can't work around or below 0°C , so I gave up on that..

Do you really have temperatures below 0°C in the room where your equipment is located? Not sure where you are located, but I would expect that even if outside temps drop below 0°C, the temps inside would remain above that. Or do you really have ice formed inside the room where your equipment is?

Otherwise I fully agree with @Tinbum. Lead acid or GEL are absolutely the wrong investment for a solar system.

3 hours ago, Tinbum said:

Forget about lead acid and go for LiPo.

I did that and bought 2 Revov B100 batteries. The problem is I did not install them for more than a year. The batteries self discharged and some of the cells are now damaged. So lost R 50k+

18 minutes ago, DaveMM said:

I did that and bought 2 Revov B100 batteries. The problem is I did not install them for more than a year. The batteries self discharged and some of the cells are now damaged. So lost R 50k+

? not really relevant to his (OP) questions.

temperatures there can go around 0 sometimes.. not much below 0.. maybe -1 but usually only for few days through whole winter.. my system is in the basement

yes, when you put it like that.. I'm now considering putting isolation there

 

so.. you really think that lead acid should be avoided ? But why?

4 hours ago, Tinbum said:

Forget about lead acid and go for LiPo.

you mean lifepo4 or lithium polymer like the batteries in phones ? I don't know much about either but I don't trust lithium polymer batteries because of the fire danger.. I leave that house for months and don't want that in my house while I'm not there

29 minutes ago, Skipbidipop said:

you mean lifepo4 or lithium polymer like the batteries in phones ? 

I think @Tinbum meant LiFePo. I certainly did.

34 minutes ago, Skipbidipop said:

so.. you really think that lead acid should be avoided ? But why?

I switched from Lead Acid to Pylontech a number of years ago - and it was the much better investment. My Lead Acids did not see much usage, yet were also basically dead after 2 years. And if I remember correctly, discharging them below 50% even faster depletes their lifetime. LiFePo is the much better suited technology for solar systems as the batteries are designed for regular cycling (e.g. Pylontech US3000C has a design life of >6000 cycles, which means more than 15 years if you do 1 cycle per day). Even though the initial investment for LiFePo is significantly higher than for Lead Acids, see how long your last set lasted you and do the math how many replacement sets you would need to get to the same life as a LiFePo battery. And you get a much higher Depth of Discharge (DoD) on LiFePo, which means to provide the same amount of storage you would need a whole lot more Lead Acids.

49 minutes ago, Skipbidipop said:

I leave that house for months and don't want that in my house while I'm not there

Absolutely no problem with LiFePo - they are perfectly safe. Google a bit if you want more details.

58 minutes ago, Skipbidipop said:

temperatures there can go around 0 sometimes.. not much below 0.. maybe -1 but usually only for few days through whole winter.. my system is in the basement

yes, when you put it like that.. I'm now considering putting isolation there

I am not an expert, but I think those temps are on the boundaries of the working temps for most LiFePo batteries. They don't like freezing and you need to dramatically reduce the charging current when around those boundaries. So isolating the room to keep temperatures a bit higher would be a good idea. I did the same - but to keep the heat out and keep my batteries below 30°C as much as possible...

I've had lead acid for 12+ years and also have Pylontech and also banks of 280Ah prismatic cells.

I still use the LA but in the background.

I have the batteries in a barn and have seen outside temperatures well in to the negatives and have never had any problems. Batteries do generate their own heat in use and if insulated well will keep that heat. It's also possible to use external heat on a thermostat eg greenhouse heater mat, that needs very little power.

Modern types are very safe, yes LiFePo 😀, - probably more so than LA!

 

 

Edited December 9, 2024Dec 9 by Tinbum

okay.. thank you all for help.. I will probably buy LiFePO4 cells and make a battery instead of buying a commercial one.. I have built a battery for electric scooter before, but it was a LiIon (18650) battery.. so I know little bit about BMSs and such

This is the one I'm thinking about : https://eu.nkon.nl/rechargeable/lifepo4/prismatisch/rept-cb56-100ah-100a-lifepo4-3-2v-a-grade.html

492€ for 16 cells..30,75€ per cell.. that pretty cheap for grade A cells, right?

The description says this: "cycle life: min 6000 till 70% @ 0.5C" .. what exactly does that mean?.. minimum 6000 cycles with max 70% DOD at 0.5C discharge.. so, to 30% SOC at 50A ?

___

My inverter has a battery com-port (rs232).. do you recommend any specific make/model of BMS ? I'm thinking about Jiabaida .. they are cheap, come with bluetooth, rs232 UART, temp sensor, etc..

I would put it all in a plastic box with styrofoam for insulation..and probably insulate the whole basement with styrofoam .. the BMS and cells heath should keep temperature above 0.. right?

I would imagine it means until the battery gets to 70% SOH.

Go on recommendation in choosing a supplier, their are a lot of bad batteries out there.

JK BMS's seem ok.

Edited December 10, 2024Dec 10 by Tinbum

ah yes, that makes sense

I've seen some good comments on NKON batteries.. do you know another good supplier in europe/EU ?

4 hours ago, Skipbidipop said:

My inverter has a battery com-port (rs232)

According to the manufacturers website [https://anenji.com/nl/products/6200w-48v-hybrid-solar-inverter-on-grid-off-grid-with-wifi] the inverter has an RS232 and RS485 ports and the RS485 port is used for LiFePO4 communications and usually the RS232 is for firmware updates.

I had a look at the website where you saw the LiFePO4 battery and I see that they also stock EVE batteries also have a look at them, what I would also suggest is that you make an Excel spreadsheet where you compare a couple of the batteries listed on the website e.g. battery capacity divided by price and see which one is the most economical.

These are my thoughts and Reading through youre original question and situation.

You are buying 2nd batteries because of affordability and maybe availability - I know the feeling. My initial install started with a 24V Axpert inverter and 2 x Telco 2nd life batteries I picked up. And luckily they gave me a good 3 years +. {being totally off grid) When I started you could not buy panel combiners and battery isolators etc off the shelf, and Lithium were not even in SA

My 2nd replacement set made me realise why the original owner needed to sell them, forcing me to acquire a tester to show soh/soc. Being able to read the batteries abilty is really needed. ! Shorting the terminals is not the test !

Now being out of money and a system working partially into the evening -  I split my circuit. Added in a cheap PWM charger and ran in parallel with inverter, using my first set of batteries (in parallel) to give a 12V circuit. And this handled my security side and a bit more. Cameras / Router / 12V LED lights and now SV smart switches straight off the battery.         Now I could switch on and off the inverter and lights from remote location. And Ohms law 50W of devices on a good 100 Ahr battery should last 25 hrs.  BUT the rules change with batteries in unknown.

In Youre situation I think you can afford to take 1 panel off each series string and seperate youre circuit.  7 panels in series totals 280V maybe too much.

Then -  do you need 48V 6 KW system or could you swap youre inverter to 24V 3KW. With this you could now rotate batteries to find the most reliable ones. and really when desperate 24V of batteries is easier to get to when failing. 

Bottom line and lessons learnt, one bad cell pulls a battery down, and one bad battery pulls a string down. And when a bad battery is under charge or being equalised will read its voltage, as the other cells are over bubbling. But then off charge it idles - takes a load and collapses.

And at a temp of zero - it just collapses faster.

17 hours ago, GerhardK83 said:

usually the RS232 is for firmware updates

yes, you are correct, RS485 is for the battery and RS232 is used for 'PC' com.. I used it to connect the WiFi dongle that came with the inverter

17 hours ago, GerhardK83 said:

they also stock EVE batteries also have a look at them

what exactly 'EVE' means?.. I thought those are for 'electric vehicle' or something.. 😅 I am still new to batteries

______

4 hours ago, Colin Says said:

1. {being totally off grid) When I started you could not buy panel combiners and battery isolators etc off the shelf, and Lithium were not even in SA

2. forcing me to acquire a tester to show soh/soc. Being able to read the batteries abilty is really needed. ! Shorting the terminals is not the test !

3. Added in a cheap PWM charger and ran in parallel with inverter, using my first set of batteries (in parallel) to give a 12V circuit. ........ 50W of devices on a good 100 Ahr battery should last 25 hrs.  BUT the rules change with batteries in unknown.

4. take 1 panel off each series string and seperate youre circuit.  7 panels in series totals 280V maybe too much.

5. do you need 48V 6 KW system or could you swap youre inverter to 24V 3KW. With this you could now rotate batteries to find the most reliable ones. and really when desperate 24V of batteries is easier to get to when failing.

I've split your post into bullet-points just to make it easier to replay

1. Yes, I'm totally off grid .. I use gasoline inverter generator if I really need to. ... What does SA stand for ?

2. I do have a battery tester but it's for car batteries.. it requires a CCA parameter of at least 100A and is thus useless for most deep-cycle batteries.. at least I think it is ? deep-cycle lead-acid batteries are not designed for high current ?

3. (and 4.) when I think about this.. splitting the circuit doesn't give me more energy, because I would still have the same amount of PV panels and same amount of sun.. and PWM chargers are just less efficient than MPPT.. is that right..? I mean, why would I have two separate paths for storing the same amount of energy if I can have just one, more efficient path ?

How did you calculate 25h for 50W ?.. my thinking is like this: 48V with 100Ah is 4800Wh.. then 4800Wh / 50W = 96h .. that is 4 days.. which I think is reasonable for such a small load.. I mean, that would be 100kg of batteries .. in those cheap UPSs, one small 15Ah battery can power my 450W computer for 15-20min, with inefficient inverter

and I actually have 8 batteries in 4s2p configuration.. so double the capacity, 9600Wh .. that's 8 days for 50W load.. of course, when the batteries were new.. and again, seems reasonable for only 50W load.. that's 200kg battery

4. 280V is actually around the most efficient voltage for this kind of charger, I think.. the range for this system is 60-500V DC.. it can easily support 12 x 350W panels in series

5. I do not NEED 6.2kW per se.. but it is good to have it If I need it .. it is true that it's easier to get 2 new 12V batteries when old ones fail.. but I can't afford to change the inverter now.. in the summer when I use refrigerator, freezer and water pump (and girls using their hair dryer, hair-iron) it is good to have a little bit of 'reserve'

2 hours ago, Skipbidipop said:

what exactly 'EVE' means?.. I thought those are for 'electric vehicle' or something.. 😅 I am still new to batteries

EVE is the battery brand, the battery brand of link that you posted is REPT. EVE Cells are quite popular in South Africa I do not know REPT cells.

 

Electric vehicles also uses Lithium batteries but a different construction (NMC) which is Lithium Nickel Manganese Cobalt Oxide or similar construction.

2 hours ago, Skipbidipop said:

How did you calculate 25h for 50W ?.. my thinking is like this: 48V with 100Ah is 4800Wh.. then 4800Wh / 50W = 96h .. that is 4 days.. which I think is reasonable for such a small load

Yes that calculation is correct, if you have a clamp meter which can measure DC current and DC voltage then you can calculate the power used by the loads and calculate how long the LiFePO4 battery would last. P = I x V I is the current in Amps and V is the Voltage in Volts.

It does not need to be a Fluke but make sure that the clamp meter can measure DC current.

7 hours ago, Skipbidipop said:

yes, you are correct, RS485 is for the battery and RS232 is used for 'PC' com.. I used it to connect the WiFi dongle that came with the inverter

what exactly 'EVE' means?.. I thought those are for 'electric vehicle' or something.. 😅 I am still new to batteries

______

I've split your post into bullet-points just to make it easier to replay

1. Yes, I'm totally off grid .. I use gasoline inverter generator if I really need to. ... What does SA stand for ?

 - SA   South Africa

2. I do have a battery tester but it's for car batteries.. it requires a CCA parameter of at least 100A and is thus useless for most deep-cycle batteries.. at least I think it is ? deep-cycle lead-acid batteries are not designed for high current ?

 - So Agreed a meter is needed when you cant rotate the batteries to find longevity.

3. (and 4.) when I think about this.. splitting the circuit doesn't give me more energy, because I would still have the same amount of PV panels and same amount of sun.. and PWM chargers are just less efficient than MPPT.. is that right..? I mean, why would I have two separate paths for storing the same amount of energy if I can have just one, more efficient path ?

 - PWM although not efficient  for Lithium,  it has an ability to charge Lead acid batteries at a fraction of cost.

How did you calculate 25h for 50W ?.. my thinking is like this: 48V with 100Ah is 4800Wh.. then 4800Wh / 50W = 96h .. that is 4 days.. which I think is reasonable for such a small load.. I mean, that would be 100kg of batteries .. in those cheap UPSs, one small 15Ah battery can power my 450W computer for 15-20min, with inefficient inverter

 - Given 50W     Cameras work @ 12V       Watts divide by Volts = I (Amps)      so expected 4 A

 - A 12v 100 Ahr battery can run a 100Amp load for 1 Hr then its flat    -     So   100 Ahr(Rated Battery) / 4(Given Load) = 25 hrs

 - Im sure there are more explicited calculations , which im not qualified for

and I actually have 8 batteries in 4s2p configuration.. so double the capacity, 9600Wh .. that's 8 days for 50W load.. of course, when the batteries were new.. and again, seems reasonable for only 50W load.. that's 200kg battery

 - As you said it shuts off 20h00 to midnight and so goes youre , no lights, no internet.

 - The inverter itself,  on and just idling draws a current value

4. 280V is actually around the most efficient voltage for this kind of charger, I think.. the range for this system is 60-500V DC.. it can easily support 12 x 350W panels in series

 - ive done this -  Connect 2 panels  check amperage charging display on inverter   Lets say its 8 A 

                              Connect 3 panels in series    - it displays 8A       Connect 5 panels in series    - its still 8Amps   

 - Youre setting on inverter Solar first /  Battery / Utility order        and appliances being 220V I would think panels to total around 110/220.

5. I do not NEED 6.2kW per se.. but it is good to have it If I need it .. it is true that it's easier to get 2 new 12V batteries when old ones fail.. but I can't afford to change the inverter now.. in the summer when I use refrigerator, freezer and water pump (and girls using their hair dryer, hair-iron) it is good to have a little bit of 'reserve'

 - On a 24 V system I have the required essentials running and using 25-35%, then my pump runs randomly, After that its fight for the wife doing washing or me pulling out the table saw, so I give way for the 2 Hrs.

- I have recently switched over to Lithium 2xbanks of 100 AH from 2 x 12v200AHr Leads  , and now switching on the table saw, first switch on spins the blade and cuts out, (it does not trip inverter or batteries) The second switch on it holds.   With my Lead acids  on first time. 

- I have just bought a 48V inverter only because the price has come down so much, and will create a new circuit for that (Direct to the workshop) but I will not throw out the 12 or 24 Volt circuit.

 

 

 

I bought these batteries: https://eu.nkon.nl/rechargeable/lifepo4/prismatisch/rept-cb56-100ah-100a-lifepo4-3-2v-a-grade.html

REPT CB56 - 100Ah

I hope they will be good, we will see what I'll get.. should be here in 2 weeks

___

I also bought this JBD BMS: https://www.aliexpress.com/item/1005004862569135.html?spm=a2g0o.order_list.order_list_main.5.3e6b18025wSEX4

I used this BMS for an electric scooter before, and I used the Bluetooth com for setup on my android phone.. but is says here it has UART com too..

Did anybody use this UART before? Is it RS232 or 485 ?

I know I can do the settings setup over computer, just like over Bluetooth on android .. Can I somehow connect it to the internet and see the settings and information remotely ?

What can I do with it? Can It be used to connect to my inverter?

I know there are actual 'Inverter BMS's' from JK..  you get a com board with rj45 connectors, some LED signaling and optional LCD and what not.. but it is more than double the price of this one

What actually does the inverter get from this? What is this communication used for? Why does the inverter communicate with the battery at all it it only charges the full battery pack and not individual cells?

Good cells, good BMS but the jury is out on getting Comms with that Inverter. I have only come across it once and managed to obtain Pylontech Direct RS485 Comms established. The UART I doubt will work out of the box with the Inverter. On the plus side it does have a lot of different profiles to try on the inverter side but given that you are restricted to UART means won't be a lot to try. I'd just wing it on voltage settings. This will be a needle in a burning haystack...

there are TTL to RS485 converters available .. would that help?

My inverter supports PYLON US2000 Protocol 3.5 Version and Standard communication Protocol form inverter supplier. And also it supports Lithium battery without communication

I don't understand what would the inverter need from the battery BMS anyway .. can you explain?

Does it only get the battery BMS settings, like max charging current, float voltage, etc.. and then sets the inverter parameter to those settings? .. or does it do something else? If that is the only thing it does, than I guess I don't really want it.. I think it's safer to just set the parameters in the inverter and the BMS separately .. then the com between them won't be a possible source of error.. isn't that right? So for example, if the BMS fails to limit the current the inverter would still not take as much current.. and if the inverter would fail to limit the current, the BMS wouldn't supply it

_____

My inverter has a WiFi module and I can see the status and configure the device remotely.. this is great and works OK.. If I somehow manage to connect the BMS to the inverter, is it possible to view the BMS settings and status over the same WiFi ? It would be great If the inverter could request such data(eg. voltage of each cell, battery temperature, etc..) from the BMS and display it in the same app

8 hours ago, Skipbidipop said:

there are TTL to RS485 converters available .. would that help?

My inverter supports PYLON US2000 Protocol 3.5 Version and Standard communication Protocol form inverter supplier. And also it supports Lithium battery without communication

I don't understand what would the inverter need from the battery BMS anyway .. can you explain?

Does it only get the battery BMS settings, like max charging current, float voltage, etc.. and then sets the inverter parameter to those settings? .. or does it do something else? If that is the only thing it does, than I guess I don't really want it.. I think it's safer to just set the parameters in the inverter and the BMS separately .. then the com between them won't be a possible source of error.. isn't that right? So for example, if the BMS fails to limit the current the inverter would still not take as much current.. and if the inverter would fail to limit the current, the BMS wouldn't supply it

_____

My inverter has a WiFi module and I can see the status and configure the device remotely.. this is great and works OK.. If I somehow manage to connect the BMS to the inverter, is it possible to view the BMS settings and status over the same WiFi ? It would be great If the inverter could request such data(eg. voltage of each cell, battery temperature, etc..) from the BMS and display it in the same app

I always use battery to inverter communication. The bms is the best thing to control the charging. It knows exactly what is going on eg cell voltages, cell temperatures etc and can instruct the inverter what to do. The inverter is dumb when it comes to charging without it.

I finally got the cells..:

REPT CB56-100Ah ... from NKON (eu.nkon.nl) .. they look nice.. no swelling .. all within 0.003V .. so I guess no need for top/bottom balancing ??

here are some specs:

Typical Capacity:     100Ah 25±2℃，0.5C/0.5C
Typical Voltage:       3.2V 25±2℃，0.5C
Typical Energy:        320Wh 25±2℃，0.5C
Operating Voltage:  2.5-3.65V 0℃<T≤55℃  ||  2.0-3.65V -20℃≤T≤0℃
Standard Discharging Current:                       50A 25±2℃
Maximum Continuous Discharging Current:  100A 25±2℃
Maximum Discharging Current:                      250A 25±2℃@50%SOC，10s
Standard Charging Current:                            50A 25±2℃
Maximum Continuous Charging Current:      100A 25±2℃

Maximum Charging Current:  150A 25±2℃@50%SOC，10s
Operating Temperature:         0℃≤T≤55℃ Charge  ||  -20℃≤T≤55℃ Discharge

Also, I got nice plated busbars, with each battery 2pcs.. and I bought 4mm threaded bar for compressing the cells and I plan to use thin hard cardboard between the cells for insulation.. and I bought 5.3mm terminals for the BMS wires.

I will use 8mm plexiglass on top and bottom for compressing the battery

What do you think?

also, the BMS is here

its the Jiabaida SP17S005 V1.6 with bouetooth and UART .. its 100A

I've seen some open source projects with PYLON protocol on arduino.. I plan to make a converter from UART to RS485 for communication with my inverter.. we'll see what will be of that.. I'm still learning about that

I would definitely go the full way & Top balance, the voltage tells you absolutely nothing about the SoC of each cell. Will also save you a lot of hassles because it will be your Quality control that when you assemble your pack you know they all started at the same SoC...

Edited January 11Jan 11 by Steve87

yes.. that makes sense .. whats the best way to top balance ? I don't have grid power at the house where I will be installing this battery.. but here, I have grid and 48V hybrid inverter.. Can I just charge the battery whit this inverter and then connect all the cells in parallel to balance them?

Ideally you need a DC variable power supply. I have 2 different chargers. One is variable voltage up to 5V but high amperage & one that is variable to 60V at low amps 5amps. 

Just placing them in parallel without a charge will not do anything.