diy solar

diy solar

Building a 24 V battery bank: Using 12V batteries is much cheaper, but is it worth it over using 24V batteries?

Steve_S said:
The JKbms with 2A Active Balancing is fine for the 280's, my packs all use those BMS'.
The B cells are Voltage & IR Matched and still quite reasonable at that price point. They are fine if you build a straight 8S Battery Pack with it's own BMS.
I have A Cells, B Cells, Used EV Cells in my bank. I have done numerous tests including extreme Thrash tests because of my situation, reliability is critical, especially when it's -35 outside. The A Cells certainly do perform better, with slightly faster charge because the cells are IR matched so very little balancing is required, they do give me the 280AH. My B cells are more finicky when finishing charge but it is not significant enough to be a problem. The Used EV cells are actually pretty darn good after I tweaked them. In "MY CASE" having 6 packs in a bank irons all that out and I do get 100% of my capacity... Yes, I've drained the entire bank to Low Volt Disconnect in tests.

I built my own boxes, I cannot ever recommend having the cells/terminals etc in "open air" - that's just begging for trouble! Even a Covered shelf with a clear cover in front... be safe !

I use MRBF Fuses because they are perfectly fine for <36V. These are cheaper than Class-T (as good) and make for a much cleaner install (depending on the individual of course LOL) You can see below, that the (+) Busbar is offset to allow the MRBF fuse to clear over it's (-)

Blue Sea MRBF fuses made by Eaton/Bussman (for 200A BMS, use 250A fuse)

MRBF Terminal Fuse Block - 30 to 300A - Blue Sea Systems

Easily and economically satisfies ABYC 7 circuit protection rule by mounting on a 3/8 battery post, battery switch or bus bar.
www.bluesea.com www.bluesea.com

! WARNING ! There has been a LOT of Horse Pucks tossed about Binding/Compressing cells. It's been bad enough that people could have gotten to Physical Fistacuffs over it. The cells are to be BOUND snugly to prevent their expansion from twisting the terminal blocks. Do NOT put them under pressure !!! In fact, if you build the boxes below they fit the cells "snugly" and that's enough... Alternately Amy sells the Steel Cases for a more Pro finish, she also has Stackables that sit one ontop of the other... Not shown yet I think.

H4454fb0b4ae044059f1b227cda4f87afN.jpg_720x720q50.jpg


<--- Box Link:

Luyuan Diy Battery Box/case Set/kit For 8s 4s2p 24v 280ah 304ah 320ah Battery Pack With With Compression Battery/cell Device - Buy Larger Box For Men,Seed Storage Metal Box,Car Waterproof 12v Battery Box Product on Alibaba.com

Luyuan Diy Battery Box/case Set/kit For 8s 4s2p 24v 280ah 304ah 320ah Battery Pack With With Compression Battery/cell Device - Buy Larger Box For Men,Seed Storage Metal Box,Car Waterproof 12v Battery Box Product on Alibaba.com
www.alibaba.com

I built all my own boxes out of 3/4" - 19mm Plywood with a clear polycarbonate cover. See attached below. I am using Pike Industries BusBars shown below. https://pikeind.com/industries-busbars/

24v-280ah-jpg.120043

280ah-battery_box-jpg.30611
Click to expand...
Thanks, lots of good info.

Yes my packs will be protected on all sides, but not tightly wrapped in a case. The inter-cell busbars are of the flexible type, so I don't think the terminals will be affected at all from cell swelling.

How did you pack the cells together before inserting into the boxes, tape? How is the BMS mounted?

Re cell compression, I'll follow your guide Luyuan_Tech_Basic_LiFePO4_guide_1a.pdf on page 8, and try to make a snug package to keep parts from moving around.

Re fuses, a 3.2V cell with 0.25 mOhm IR could in theory release a 12.8kA current. But the 0.5 m AWG0 cable I will use to connect to the main busbars (1m in cable total) will up the resistance to maybe 0.60 mOhm. Then the current would be 5,3kA. Looks like the Blue Sea MRBF can handle 5kA @ 32 VDC and even more as voltage drops, so it should be fine.

I'm on a tight budget. If I had more money, I'd double the capacity, get BMS displays for monitoring and proper boxes, but I think my current setup will work. This is my first version. I suspect I'll be learning and experimenting as I go along.
 
Steve_S said:
The JKbms with 2A Active Balancing is fine for the 280's, my packs all use those BMS'.
The B cells are Voltage & IR Matched and still quite reasonable at that price point. They are fine if you build a straight 8S Battery Pack with it's own BMS.
I have A Cells, B Cells, Used EV Cells in my bank. I have done numerous tests including extreme Thrash tests because of my situation, reliability is critical, especially when it's -35 outside. The A Cells certainly do perform better, with slightly faster charge because the cells are IR matched so very little balancing is required, they do give me the 280AH. My B cells are more finicky when finishing charge but it is not significant enough to be a problem. The Used EV cells are actually pretty darn good after I tweaked them. In "MY CASE" having 6 packs in a bank irons all that out and I do get 100% of my capacity... Yes, I've drained the entire bank to Low Volt Disconnect in tests.

I built my own boxes, I cannot ever recommend having the cells/terminals etc in "open air" - that's just begging for trouble! Even a Covered shelf with a clear cover in front... be safe !

I use MRBF Fuses because they are perfectly fine for <36V. These are cheaper than Class-T (as good) and make for a much cleaner install (depending on the individual of course LOL) You can see below, that the (+) Busbar is offset to allow the MRBF fuse to clear over it's (-)

Blue Sea MRBF fuses made by Eaton/Bussman (for 200A BMS, use 250A fuse)

MRBF Terminal Fuse Block - 30 to 300A - Blue Sea Systems

Easily and economically satisfies ABYC 7 circuit protection rule by mounting on a 3/8 battery post, battery switch or bus bar.
www.bluesea.com www.bluesea.com

! WARNING ! There has been a LOT of Horse Pucks tossed about Binding/Compressing cells. It's been bad enough that people could have gotten to Physical Fistacuffs over it. The cells are to be BOUND snugly to prevent their expansion from twisting the terminal blocks. Do NOT put them under pressure !!! In fact, if you build the boxes below they fit the cells "snugly" and that's enough... Alternately Amy sells the Steel Cases for a more Pro finish, she also has Stackables that sit one ontop of the other... Not shown yet I think.

H4454fb0b4ae044059f1b227cda4f87afN.jpg_720x720q50.jpg


<--- Box Link:

Luyuan Diy Battery Box/case Set/kit For 8s 4s2p 24v 280ah 304ah 320ah Battery Pack With With Compression Battery/cell Device - Buy Larger Box For Men,Seed Storage Metal Box,Car Waterproof 12v Battery Box Product on Alibaba.com

Luyuan Diy Battery Box/case Set/kit For 8s 4s2p 24v 280ah 304ah 320ah Battery Pack With With Compression Battery/cell Device - Buy Larger Box For Men,Seed Storage Metal Box,Car Waterproof 12v Battery Box Product on Alibaba.com
www.alibaba.com

I built all my own boxes out of 3/4" - 19mm Plywood with a clear polycarbonate cover. See attached below. I am using Pike Industries BusBars shown below. https://pikeind.com/industries-busbars/

24v-280ah-jpg.120043

280ah-battery_box-jpg.30611
Click to expand...
I just watched this video (link below), and it got me a bit worried about grade B cells. In my discussion with Amy I got the impression that grade B only had slightly lower/higher capacity, voltage and/or internal resistance. But there seems to be something more fundamental wrong with some of the grade B cells. All it takes is to draw 100W from a cell and it starts showing weird behavior, which in my case is 1,6kW total. I will easily hit that threshold when I run power tools etc, and I don't want the BMS to cut out from detecting a low cell voltage. Do you know if Luyuan does a stress test of the cells before they are shipped?

 
I used Fibratape (Fiberglass reinforced tape) and taped the cells into 4 cell blocks, I also included a pull string, in case I had to pull them out. That was a Boo Boo, it made them a tad too snug and made that really hard to do.
30609-c0da85ea3c4dc174035846b0935c794a.jpg


Note that the BMS' come with 10cm 7AWG Ultrafine wire silicone wire. I found the leads to be too short for what I needed for my setup, so I extended them using a Crimped Butt Connector an 4AWG Silicone wire. 2x 7AWG = 4AWG.

Battery Cables are something that folks do trip over a little. I'll keep this simple, there are different grades of wire, from Coarse to Ultra Fine wire, there is Pure Copper, Tinned (for marine & $$) and then the "dubious". You can purchase any kind, premade to specific lengths but if that is the case then be cautious and stick with Top Quality Manufacturers & Vendors... STAY AWAY from Auto supply houses ! You can't imagine the crap they do flog ! Fine for an old Diesel Truck but NOT solar !

I use Ultra Fine Wire "Welding Cable" which has the most strands per square mm. When sizing your wire, you have to account for the worse case scenario. That means 1 Battery Pack pushing the absolute Max Amps that your Inverter could conceivably pull. For example, my Samlex EVO can deliver up to 12,000W pulling just under 500A to do so. Now my BMS' will prevent that BUT as we all know "shit happens" and only a fool does not take such into account... hence fuses, breakers & all that goodness to keep our butts safe. I myself use only Royal Excelene 4/0 (120 mm2) Ultra Fine Welding with from Southwire, see the link below for ampacity & thread count info etc... http://cabletechsupport.southwire.com/en/tile/10/spec/70305/?country=International I am sure you can get this in EU or very similar, it is not all that unique.
 
BjornM said:
I just watched this video (link below), and it got me a bit worried about grade B cells. In my discussion with Amy I got the impression that grade B only had slightly lower/higher capacity, voltage and/or internal resistance. But there seems to be something more fundamental wrong with some of the grade B cells. All it takes is to draw 100W from a cell and it starts showing weird behavior, which in my case is 1,6kW total. I will easily hit that threshold when I run power tools etc, and I don't want the BMS to cut out from detecting a low cell voltage. Do you know if Luyuan does a stress test of the cells before they are shipped?
Click to expand...
Heads Up, SFK has a Rancid Reputation around here... Most of us have NOTHING good to say about them. I'll leave that there.

Using 280AH cells as example;
A-Cells will always deliver the specified Amp Hours from the Working Voltage Range (3.000-3.400). These are Factory Validated & can be matched to other A Cells. When these cells are further tested by outsiders, from 2.500-3,650 they usually test out around 290AH +/- a bit.

B-Cells DO NOT deliver the specified AH from the working range, they are typically under by a few percent. That is Factory Tested and then classed as such. They will typically deliver between 270-280. When tested from 2.500-3.650 they may test up to 285AH - You can expect at least 5% to 10% (max) less capacity.

IF less the cells test lower than 10%, most manufacturers will recycle or at worse debadge and go to "grey market". For example CATL will Recycle the cells - they learned a long time ago...

The Factory Testing involves some stress tests... I do not know any vendor Stress Testing cells... that's a labour nightmare and more...

I have only had 1 Battery Pack cutout when under heavy load (Mig Welder actually) when it was down to 2.700Vpc and one cell dropped to 2.500 when my cutoff was 2.600. A Mig hits hard ! There's a spike to see. If your bank is that low, then you better charge before plugging tools in.

Something else which is obvious but not... When you have multiple packs in one bank, they do divide & share the loads/charge proportionately
and that really reduces the chances of an LVD. If your inverter demands 100A and that's split with 4 packs, they only have to deliver 25A ea, which barely would wake them up.

Note when I say proportionately.. If you have a bank of LFP batteries, they can be different AH without issue ! "Simple Description" Say you have a 100AH, 200AH & 300AH in a bank and you are pulling 60A, the 100 will deliver 10A, the 200 will deliver 20A and the 300 will deliver 30A. This is generally how it works and if observed during operation you will see this happening and the Amperage will float a small bit but stays pretty consistent. The same thing happens in reverse when Charging.

Hope that helps.
 
Steve_S said:
Heads Up, SFK has a Rancid Reputation around here... Most of us have NOTHING good to say about them. I'll leave that there.

Using 280AH cells as example;
A-Cells will always deliver the specified Amp Hours from the Working Voltage Range (3.000-3.400). These are Factory Validated & can be matched to other A Cells. When these cells are further tested by outsiders, from 2.500-3,650 they usually test out around 290AH +/- a bit.

B-Cells DO NOT deliver the specified AH from the working range, they are typically under by a few percent. That is Factory Tested and then classed as such. They will typically deliver between 270-280. When tested from 2.500-3.650 they may test up to 285AH - You can expect at least 5% to 10% (max) less capacity.

IF less the cells test lower than 10%, most manufacturers will recycle or at worse debadge and go to "grey market". For example CATL will Recycle the cells - they learned a long time ago...

The Factory Testing involves some stress tests... I do not know any vendor Stress Testing cells... that's a labour nightmare and more...

I have only had 1 Battery Pack cutout when under heavy load (Mig Welder actually) when it was down to 2.700Vpc and one cell dropped to 2.500 when my cutoff was 2.600. A Mig hits hard ! There's a spike to see. If your bank is that low, then you better charge before plugging tools in.

Something else which is obvious but not... When you have multiple packs in one bank, they do divide & share the loads/charge proportionately
and that really reduces the chances of an LVD. If your inverter demands 100A and that's split with 4 packs, they only have to deliver 25A ea, which barely would wake them up.

Note when I say proportionately.. If you have a bank of LFP batteries, they can be different AH without issue ! "Simple Description" Say you have a 100AH, 200AH & 300AH in a bank and you are pulling 60A, the 100 will deliver 10A, the 200 will deliver 20A and the 300 will deliver 30A. This is generally how it works and if observed during operation you will see this happening and the Amperage will float a small bit but stays pretty consistent. The same thing happens in reverse when Charging.

Hope that helps.
Click to expand...
Good to know about SFK. I don't mind if a cell is 10% under in capacity or has a bit higher IR, I can live with that. But a cell that takes a nose dive in voltage at 100W (as shown in the video) would ruin the whole pack. I really hope that it is a rare abnormality, and that he is making it seem more common than it really is. It is inconvenient to have to wait another two months of shipping for a replacement of a faulty cell.

I agree that if you have many cells in your bank, then stuff like that doesn't matter as much. I'm more exposed, because right now 16 x 280Ah is all I can afford.

Interesting to see your cell assembly method and selection of cables, good info. No more questions at the moment. Thanks for the support. I'll keep you updated on my project.

Oh yes, one more question. A few competitors of Luyuan surfaced on Alibaba when I searched for "LF280K EU stock", for example QSO. What other sources besides Luyuan would you recommend? Always good to compare before you make a deal.

qsolifepo4cell.en.alibaba.com

Lifepo4 230Ah, Lifepo4 230Ah direct from Shenzhen Qishou Technology Limited in CN

Lifepo4 230Ah from Shenzhen Qishou Technology Limited. Search High Quality Lifepo4 230Ah Manufacturing and Exporting supplier on Alibaba.com.
qsolifepo4cell.en.alibaba.com qsolifepo4cell.en.alibaba.com
 
There are a few vendors with EU warehouses but I don't know much about them. There are quite a few European members here with direct experience that would be able to answer those questions. Search this forum (see top right of the page) for "EU Warehouse" "Europe Warehouse" etc. It comes up quite a lot !

On the 1 cranky Cell in a pack issue... I did have 1 pack where 1 cell would not charge over 3.2V no matter what, active balancing etc was no help... all the other cells would go higher to compensate for the "pack level voltage". As soon as the charging stopped, the higher cells kept dumping into that one low cell, over a short period of time this actually "dragged" the pack down. I had to swap out that one cell because ultimately it even affected the entire bank (but only slightly). This particular battery pack I built (yrs ago) used "bulk" grey market cells and there were no tests or reports other than shipped at X.XXX volts.
 
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Steve_S said:
CHARGE PROFILE:
Absorb/Bulk: 27.6 for 45 minutes (3.45vpc) (some call this boost)
Equalize: OFF
Float 27.5V (3.437vpc)
MIn Volts: 21.2 (2.650vpc) (Also a good cutoff for Inverter)
Max Volts: 28.6 (3.575vpc)
Rebulk Voltage: 25.6 (3.200vpc)
End Amps: (Allows for full Saturation at set Float Voltage, then as A drops to this point to trigger the transition to FLOAT mode.)
(*1): End Amps is calculated from the LOWEST AH Battery Pack in a Bank. IE: (100AH X 0.05 = 5A 280AH X 0.05 = 14A.)
NB: EndAmps = TailCurrent. Different manufacturers use different terms for the same thing.
Click to expand...

Just have a question for you Steve - why do you float at 27.5V (3.437vpc)?
Looking at the charts you've posted that would be about 99-99.5% which seems pretty high in a working system that would be under load. Just curious as most of the info I've read shows others floating in the 26.8-27.2 range.

BTW thanks very much for all the info you provide in your posts and resources...I am a long time Midnite Classic user who is just switching over to Lifepo4 and it's very much appreciated.
 
googdot said:
Just have a question for you Steve - why do you float at 27.5V (3.437vpc)?
Looking at the charts you've posted that would be about 99-99.5% which seems pretty high in a working system that would be under load. Just curious as most of the info I've read shows others floating in the 26.8-27.2 range.

BTW thanks very much for all the info you provide in your posts and resources...I am a long time Midnite Classic user who is just switching over to Lifepo4 and it's very much appreciated.
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The moment that the incoming charge stops the battery cells immediately start to settle which is expected with LFP. Float can continue to service loads once the batteries are no longer taking a charge, until solar input can no longer satisfy demand. The batteries never stay at that SOC as loads start the discharge process and usually by the time that starts the cells have already settled down to 3.390 +/-. Simply put, they don't get to stay @ 3.400 for very long at all and when they first reach "100%" and start to float, the internal balancing is still going on to a point for an hour or so, which is what I observe with my bank, across all the packs.

check this out, you may not see signatures.
Steve_S-Tech: My Final Config for Midnite Classic SCC & JKBMS' w/ Large Bank (works amazingly well) Includes Charge Profile & BMS Config

Hope it helps, Good Luck
 
BjornM said:
I'm building a 24V 400 Ah LiFePo4 battery bank. My first choice would be to get 2 x 24V 200 Ah and do 2p. I've found a unit that looks good at LiTime.

Then I saw that 4 x 12V 200 Ah in a 2s2p config is a lot cheaper. But is it worth the savings? Then I will have the potential risk of getting unbalanced batteries over time. Not sure about how much of a problem this is in real life. LiTime make it seem like a non issue. They even have examples of 4s4p configs without using any external battery balancers.

If I make sure to do some battery maintenance once a year, will that take care of it? I'd fully charge each of the four batteries separately.

Separate question: if you do 2s2p, what are the pros and cons of connecting the two midpoints together? What I mean is you first do two pairs of 2p that you then connect in series, so technically I guess you call it 2p2s.
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I'm gathering 12 volt, 100 AH Redodo batteries right now for a battery bank. Redodo supports up to 4P4S for 20+ KWHR of storage with off the shelf batteries. I'm just getting started so I may limit myself to 2P4S for right now as I have a lot of work to do. Plus battery prices seem to be dropping like a rock. If you take advantage of their periodic deals you can get a 12 volt, 100 AH battery for about $205 plus tax with free shipping. A month ago it was about 10% higher. Its hard for me to justify trying to source cells and BMS systems (which seem to be hard to source) for that kind of $$. I've got solar frames to fabricate and house rewiring to accomplish to make all of this work. Battery cost seems to be about 30% of the project. I'm going to try and setup a hybrid setup. I have very reliable grid power but its getting expensive, rising in cost a lot faster than inflation. Plus I have space and can get cheap used solar panels for a ground mount system. I have been studying the various battery sellers and it sure looks like Litime and Redodo and perhaps Power queen are all the same manufacturer. My dealings with Redodo so far have been superb. They are very responsive.
 
Dave911 said:
I'm gathering 12 volt, 100 AH Redodo batteries right now for a battery bank. Redodo supports up to 4P4S for 20+ KWHR of storage with off the shelf batteries. I'm just getting started so I may limit myself to 2P4S for right now as I have a lot of work to do. Plus battery prices seem to be dropping like a rock. If you take advantage of their periodic deals you can get a 12 volt, 100 AH battery for about $205 plus tax with free shipping. A month ago it was about 10% higher. Its hard for me to justify trying to source cells and BMS systems (which seem to be hard to source) for that kind of $$. I've got solar frames to fabricate and house rewiring to accomplish to make all of this work. Battery cost seems to be about 30% of the project. I'm going to try and setup a hybrid setup. I have very reliable grid power but its getting expensive, rising in cost a lot faster than inflation. Plus I have space and can get cheap used solar panels for a ground mount system. I have been studying the various battery sellers and it sure looks like Litime and Redodo and perhaps Power queen are all the same manufacturer. My dealings with Redodo so far have been superb. They are very responsive.
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I'm strongly leaning towards the DIY side, but not completely won over yet. Trust in the sellers is the biggest issue with doing DIY from China.

Here in Europe my cheapest off shelf alternative would be the LiTime 12V 200 Ah. I can get a set of four for $2125 USD including VAT and shipping. If I go the DIY route I would get 40% higher capacity and at the same time 15% cheaper. But of course I have to build them myself with the risk that entails. Depends on the mindset I guess. I'm a DIYer at heart, so I don't mind. And then it will be natively 24V (not 2 x 12 V), meaning that each BMS makes sure all the 8 cells of the 24V are in balance. With two 12V packs in series, there is no such guarantee and a risk that the two packs drift apart in voltage over time and become unbalanced. This is not optimal, but to be honest I'm not sure how big of a problem this really is in real life. I felt that I got some evasive answers from LiTime when I chatted about this, as if they are not sure themselves.
 
Be aware that DIY may present some difficulties, namely when components get a bit stubborn (like a BMS, for example).
 
Looks like you got lots of answers to this question!

This is a snag with using multiple LIFEPO4 in series or parallel as unlike flooded or AGM they have their own BMS that can sometimes throw a battery out of balance and messes with the entire bank.

To prevent that I suggest using fewer batteries and a larger battery capacity. May be more expensive but less headaches.

I recently replaced three 125AH AGM and considered using two 200AH LIFEPO4 but considering I live off grid full time and can't have my system go down I decided to go with a single Enjoybot 400Ah LIFEPO4 for that reason and I get more than double the amp output for a bigger inverter.

Good luck!
 
Solarcabin Channel said:
Looks like you got lots of answers to this question!

This is a snag with using multiple LIFEPO4 in series or parallel as unlike flooded or AGM they have their own BMS that can sometimes throw a battery out of balance and messes with the entire bank.

To prevent that I suggest using fewer batteries and a larger battery capacity. May be more expensive but less headaches.

I recently replaced three 125AH AGM and considered using two 200AH LIFEPO4 but considering I live off grid full time and can't have my system go down I decided to go with a single Enjoybot 400Ah LIFEPO4 for that reason and I get more than double the amp output for a bigger inverter.

Good luck!
Click to expand...
Why did you choose that over having redundancy?
 
SolaroSsaurius said:
Why did you choose that over having redundancy?
Click to expand...
I have three systems for redundancy. My main system is 400 watts solar and 400Ah LIFEPO4 and I have 400 watts solar on a 200Ah power station and a 200 watt recharging station with a 200Ah Lifepo4.

I prefer that set up to one large battery bank because if one system fails for any reason I still have power to get by on until I find the problem or replace the failed component.

I also have several portable solar panels and power stations I keep charged in the event I need more power on low sun days and to take camping.
 
Steve_S said:
There are a few vendors with EU warehouses but I don't know much about them. There are quite a few European members here with direct experience that would be able to answer those questions. Search this forum (see top right of the page) for "EU Warehouse" "Europe Warehouse" etc. It comes up quite a lot !

On the 1 cranky Cell in a pack issue... I did have 1 pack where 1 cell would not charge over 3.2V no matter what, active balancing etc was no help... all the other cells would go higher to compensate for the "pack level voltage". As soon as the charging stopped, the higher cells kept dumping into that one low cell, over a short period of time this actually "dragged" the pack down. I had to swap out that one cell because ultimately it even affected the entire bank (but only slightly). This particular battery pack I built (yrs ago) used "bulk" grey market cells and there were no tests or reports other than shipped at X.XXX volts.
Click to expand...

I've officially joined LiFePO4 nerd club. Made the order today from Luyuan in China. 16 x EVE 280Ah grade B and 2 x JKBMS JK-B2A8S20P. Building two 24 V units.

Thanks for all the support and tips, you are great asset here on the forum.

Will keep you updated with how it goes, once the stuff arrives approx two months from now. I suspect I will have some questions about the BMS. :cool:
 
Solarcabin Channel said:
Looks like you got lots of answers to this question!

This is a snag with using multiple LIFEPO4 in series or parallel as unlike flooded or AGM they have their own BMS that can sometimes throw a battery out of balance and messes with the entire bank.

To prevent that I suggest using fewer batteries and a larger battery capacity. May be more expensive but less headaches.

I recently replaced three 125AH AGM and considered using two 200AH LIFEPO4 but considering I live off grid full time and can't have my system go down I decided to go with a single Enjoybot 400Ah LIFEPO4 for that reason and I get more than double the amp output for a bigger inverter.

Good luck!
Click to expand...

I live alone off-grid and very remote. Absolutely wonderful in the summer, pretty stressful in the winter. I've been there for 8 years now and feel very exposed if something should fail. Winters in Sweden can be harsh. So I'm slowly building up several systems for redundancy. One thing I decided this year was to invest in an over capacity in solar panels. I went from 1.9kW to 5.5 kW of panels on my roof. I can easily manage on 1kW, if the sun shines all the time. So the idea is that they will give me enough power even when it is over cast or raining. Unlike batteries, solar panels never wear out (30+ year life span). That way I can have lower capacity batteries, because they don't need to cover my use for more than a day or two.

My lead acid battery system (8x 12V 100Ah = 9.6 kWh) is starting to fail now after 8 years of use. Two batteries already dead. So now I'm investing in LiFePO4 instead. I decided to go the DIY route. I know, it might sound stupid for something I need to rely on, but I have an electronics engineering background, so I think I can pull it off. Plus I'm low on savings. Today I ordered 16 x EVE 280 Ah grade B cells and two BMS though Luyuan on Alibaba. I will build two 24 V units of 8 cells each, so in total 13 kWh. If play nice with those units and not top charge or bottom discharge I might have 10 kWh of useful capacity, which is HUGE improvement over my current system where I rarely go below 80% SOC to extend lifetime, so that's only a useful capacity of 2 kWh. I understand your reasoning with having few batteries so that fewer things can fail. But I prefer to have two parallel units. If one fails hopefully the other will still work.

Multiple units in parallel is normally not problem, and will not make the batteries unbalanced. But multiple units in series without a BMS between them might lead to imbalances. In theory. I have no practical experience of how common that problem is though for LiFePO4. But I can tell that my lead acid system (2s4p) have batteries that are seriously out of balance, even though lead acid is said to balance itself if you equalize charge every now and then. But then my batteries is way past their due date, so maybe that's not strange.

I have looked at A LOT of energy storage systems. At one point I decide to learn how to make my own lead acid batteries, but eventually gave it up. Toxic mess. I was into compressed air for a while. And cogen (combining heating and electric generation) through a Stirling engine or Peltier modules. Pumped storage. Fly wheel. But in the end it is hard to beat batteries.

I also keep two petrol generators for worst case scenarios. I heat my home with firewood, so that part is no stress at all. Cold inside? Light a fire!

Good luck to you too! Hope to stay in touch and share ideas.
 
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Just when I thought I would end up manually balancing my 4S2P 12 volt battery setup, I find this:

An automatic balancer for assembled 48 volt battery packs using 12 volt batteries. $54 for each set of 4S string of batteries.


This is by PowMr which I believe is another brand of Growatt. PowMr is also selling 12 volt batteries with prismatic cells and a built in BMS.
Sure this all takes up a little more space to obtain 5 KWHR of storage, but still its all packaged and it doesn't cost a bunch of $$ like rack batteries.

A PowMR 100 ah battery for $219.

Now I really don't see a downside to assembling 12 volt batteries. Plus I get to have cool names on my batteries like Redodo, PowMr, and LiTime. Who makes up these names! :)
 
Dave911 said:
Just when I thought I would end up manually balancing my 4S2P 12 volt battery setup, I find this:

An automatic balancer for assembled 48 volt battery packs using 12 volt batteries. $54 for each set of 4S string of batteries.


This is by PowMr which I believe is another brand of Growatt. PowMr is also selling 12 volt batteries with prismatic cells and a built in BMS.
Sure this all takes up a little more space to obtain 5 KWHR of storage, but still its all packaged and it doesn't cost a bunch of $$ like rack batteries.

A PowMR 100 ah battery for $219.

Now I really don't see a downside to assembling 12 volt batteries. Plus I get to have cool names on my batteries like Redodo, PowMr, and LiTime. Who makes up these names! :)
Click to expand...
Just be aware some of these balancers are known to emit a high pitched whine, if your battery is going to be in your living space.
 
Brucey said:
Just be aware some of these balancers are known to emit a high pitched whine, if your battery is going to be in your living space.
Click to expand...
I have multiples, they do. Don't sleep next to it.
 
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