Upgrade second guessing

[Offgridiot]

Hello all. I’m in the process of upgrading my off grid system, starting with the replacement of my old FLA battery bank. I have a MagnaSine 4024 at the heart of the system, so I’m committed to 24 volt configuration. I’ve bought 8 Power Queen 12.8V 300AH LiFePo4 units (for some admittedly questionable reasons but here we are) and am planning to set them up as two parallel strings of 4 each, and series those together for 25.6 Volts, based on advice from someone on another forum. I tend to torture myself with overthinking these things, and this time is no different. So, I was led to the website smartgauge.co.uk where I found that the best way to wire multiple batteries together in parallel is with the ‘cross diagonal’ method. I took that as gospel and proceeded with my plan. I bought a length of 2/0 cable, and cut it into equal length pieces for the interconnects. All good. Now, I’m looking at buying a balancer to go between the series connected strings, and here’s where the overthinking/second-guessing starts. Every balancer setup I’ve found pictures of has the batteries wired differently than my plan (they either have all 4 parallel units bonded with a bussbar or post (as opposed to cross diagonal) or they have four sets of 2 units in series to get the 25.6V ), and this has me wondering if I’ve been led astray.

1. After having cut and crimped and heat-shrinked all the interconnects for my cross diagonal setup plan, I’m not sure I’d be able to use them in a different setup. If there are strong opinions from you experts about this, I’m open. Should I have my bank set up the way I’m seeing on the Victron balancer diagrams?
2. I’m seeing diagrams where the balancer wiring has the common terminal wired to the midpoint of the series connector. Is that literally where this should be tied in? Should I have two cables end to end for this so that I can tie in that ‘common’ balancer wire equidistant from each parallel string? Or is it fine to have it right at the one battery terminal?
3. Victron seems to be a solid brand choice for any electronic component. Their balancer though, seems relatively simplistic and underpowered (only 1 amp balancing power, and no voltage display)compared to a few others I’ve seen (5 amps balancing power, and voltage display for both sides). Opinions/recommendations?
4. The BMSs in my batteries are 200 amp. I bought 200 amp MRBF fuses for each positive terminal. Am I good there?
5. My batteries don’t have any Bluetooth capability but I’ve been looking at trying to add that functionality. I’m eyeing the Victron SmartShunt 500A smart battery monitor. There’s already one non-Bluetooth shunt in place in my system for the MagnaSine battery monitor (which I kinda hate), but it’s installed inside an e-panel metal enclosure, and if I was to replace it with the new Bluetooth shunt, the signal would likely have a hard time getting in and out of the enclosure). Would there be any problems adding a second shunt to the system?
6. I was thinking of installing a voltage meter on each battery. I understand that all of the batteries hooked together in parallel will automatically equalize, and the whole purpose of the balancer is to work to do the same but I was thinking that it might be possible for the BMS in any unit to shut down that battery, and it might not be immediately obvious something was wrong. I like the idea of being able to glance at all the individual battery voltages for peace of mind. Or is that a scenario that the alarm on the Victron balancer would let you know about, when one of the parallel strings all of a sudden has a different capacity?

I’ve attached a picture of my proposed bank setup plan. The plan also includes stacking one parallel string above the other for a smaller footprint.
Thank you in advance for any and all help

 

[MisterSandals]

I wrote a bunch but decided to just point you to this thread. Read the first 4 posts.

Calculation of parallel string battery currents

Hi, everybody! I'm a retired EE. I didn't want my EE skills to fade away after retirment, so I exercise them when I can. Whenever I see a non-trivial circuit analysis problem on one of various forums I frequent, I challenge myself to solve it. Recently I watched Will's video about current...

diysolarforum.com

 

[Offgridiot]

Hi MisterSandals. Thanks for the reply and link to the thread. I read the first 4 posts (and then some). A lot of good info to absorb. In the first post, there was a link to the same article that informed my decision to connect my bank the way I’m planning to. That’s where I got the terminology ’cross diagonal’ which I might have misused. I see that in post #25, the OP posted a picture of what he called the ’halfway’ method. That’s what I meant by ‘cross diagonal’, as opposed to diagonal, which seems to be yet another connecting method. Does that clarification make sense or change how you might have replied?
I could go the bus bar route if it’s a better option than the halfway method. It would mean having to buy a few more items but that’s not a huge deal if the end result means longer battery life.

 

[Offgridiot]

I wrote a bunch but decided to just point you to this thread. Read the first 4 posts.

Calculation of parallel string battery currents

Hi, everybody! I'm a retired EE. I didn't want my EE skills to fade away after retirment, so I exercise them when I can. Whenever I see a non-trivial circuit analysis problem on one of various forums I frequent, I challenge myself to solve it. Recently I watched Will's video about current...

diysolarforum.com

Not too familiar with the forum game…. I may have originally gone about replying to you in a less than optimal way.

 

[MisterSandals]

Ok, it took a while but i am up to speed. Your reference to post #25 was the key to my understanding your diagram.

Solarod says its theoretically a perfect balance so I'm on board with how you propose.

Not too familiar with the forum game…. I may have originally gone about replying to you in a less than optimal way.

You did everything right. I should apologize and thank you for pointing me to post #25, i was way off.

Nice work. This is your thread so take it where you want or start a new one with a more descriptive title for your next question (that helps drag people in).

 

[OffGridForGood]

Are you planning any further expansion to the system in the future?

 

[Offgridiot]

Are you planning any further expansion to the system in the future?

Yes. I also have bought a pallet of panels, 3 Midnite solar controllers and all the accompanying hardware for that stage of the project.

 

[OffGridForGood]

I mean, are you planning any further expansion to the ESS ?
(Energy Storage System)
if so, it would be best to plan now for how the expansion will be connected.
Personally I prefer large bus bars, with each pack fused to the bus, and a disconnect installed for ease of removing one pack while the rest just run.
consider how you will expand system, how you will do maintenance or repairs, how the system will work if there is a problem with one component.

 

[Offgridiot]

I mean, are you planning any further expansion to the ESS ?
(Energy Storage System)
if so, it would be best to plan now for how the expansion will be connected.
Personally I prefer large bus bars, with each pack fused to the bus, and a disconnect installed for ease of removing one pack while the rest just run.
consider how you will expand system, how you will do maintenance or repairs, how the system will work if there is a problem with one component.

No. I’m thinking this battery bank should suit my needs. I could see buying a few more batteries in the future for a stand in if maintenance is needed for the main bank on a regular basis. But I figured I can run my generator for household needs if that maintenance is only required less often. How often do you find you’re taking your batteries off line for maintenance?

 

[OffGridForGood]

No. I’m thinking this battery bank should suit my needs. I could see buying a few more batteries in the future for a stand in if maintenance is needed for the main bank on a regular basis. But I figured I can run my generator for household needs if that maintenance is only required less often. How often do you find you’re taking your batteries off line for maintenance?

While I was working out the balance issues with some cells, I was removing a pack from the rack on a regular basis, but wanted the system to be able to just run (keep the lights on) while I was tinkering.
Admittedly, once the cell balance issues were all addrressed, I seem to never touch the cells or packs anymore - the only thing I do once in a while is confirm the top balance (the delta) remains small on each pack.

 

[Offgridiot]

While I was working out the balance issues with some cells, I was removing a pack from the rack on a regular basis, but wanted the system to be able to just run (keep the lights on) while I was tinkering.
Admittedly, once the cell balance issues were all addrressed, I seem to never touch the cells or packs anymore - the only thing I do once in a while is confirm the top balance (the delta) remains small on each pack.

Ahh. So it sounds like you’ve built your bank from raw cells (not sure of the vernacular here but I’m talking about the individual blue cells, as opposed to the ready-made units like I bought from Power Queen). That’s beyond my current level of confidence, although I plan to try to learn more about such things before my 5 year warranty expires, after which I would maybe dismantle the units to keep a closer eye on the individual cells.
In the meantime, I had vague ideas about being able to shut off the main disconnect, and tinker with individual units if needed (which also leads to one of the reasons I bought 12V units for my 24V system….. I thought I could take a few units with me on my sailboat from time to time. I know I would have to rebalance all units before reuniting them when I returned from my boat trip but….)
So I know I don’t have the level of control of my system like yourself but part of my original set of (too many?) questions had to do with voltage meters for monitoring individual units at a glance. I guess all it might do is tell me if any unit BMS has shut down but even that would give me some peace of mind. Do you have an opinion on that?

 

[OffGridForGood]

Ahh. So it sounds like you’ve built your bank from raw cells (not sure of the vernacular here but I’m talking about the individual blue cells, as opposed to the ready-made units like I bought from Power Queen). That’s beyond my current level of confidence, although I plan to try to learn more about such things before my 5 year warranty expires, after which I would maybe dismantle the units to keep a closer eye on the individual cells.
In the meantime, I had vague ideas about being able to shut off the main disconnect, and tinker with individual units if needed (which also leads to one of the reasons I bought 12V units for my 24V system….. I thought I could take a few units with me on my sailboat from time to time. I know I would have to rebalance all units before reuniting them when I returned from my boat trip but….)
So I know I don’t have the level of control of my system like yourself but part of my original set of (too many?) questions had to do with voltage meters for monitoring individual units at a glance. I guess all it might do is tell me if any unit BMS has shut down but even that would give me some peace of mind. Do you have an opinion on that?

quite true, but working with cells, does open up a world of control that some ready made stuff doesn't offer.
with series connected packs, there can be issues.
Do your Power Queen batteries have blue-tooth - can you see individual cell voltages and know the max delta between the highest and lowest with an app on your phone/or a display?

 

[Offgridiot]

quite true, but working with cells, does open up a world of control that some ready made stuff doesn't offer.
with series connected packs, there can be issues.
Do your Power Queen batteries have blue-tooth - can you see individual cell voltages and know the max delta between the highest and lowest with an app on your phone/or a display?

I wish. No Bluetooth. No individual cell monitoring. It was beyond my budget for that perk when I was shopping. I think the best I can hope for is installing a balancer between the parallel strings (hooked in series) and voltage meters on each battery to be able to see if any BMS shuts one down.

 

[OffGridForGood]

I am too much of a control freak to live without knowing the cell voltages, or being able to adjust the settings in the BMS's.

Not a fan of series connected packs, since each BMS is only working to balance it's own cells, oblivious to the cells in series that are on a separate BMS. You have the right idea though, monitor them so you can see if they drift.
I have seen some reviews of the Power Queen and seemed ok packs.
if they were 'the right price at the right time' all good!

 

[Offgridiot]

I am too much of a control freak to live without knowing the cell voltages, or being able to adjust the settings in the BMS's.

Not a fan of series connected packs, since each BMS is only working to balance it's own cells, oblivious to the cells in series that are on a separate BMS. You have the right idea though, monitor them so you can see if they drift.
I have seen some reviews of the Power Queen and seemed ok packs.
if they were 'the right price at the right time' all good!

I’m too much of a cheap, Scottish SOB to pay more than I absolutely have to for anything. The price for these was better than anywhere else I was seeing at the time (I’ve had them for a few months now, waiting for me to make my decisions. I’ve had them at half charge (although now I’m hearing they might be better off kept at full charge while sitting). I guess I’ll just have to see how they perform and hope I don’t have to make a warranty claim. Fingers crossed.

 

[OffGridForGood]

I have a lot of short-arms-deep-pockets ancestors in my family too, which lead to this whole solar power plant we have now, because I didn't like the climbing utility rates!
For LFP half-charge is the proper way to store them, actually the proper way to ship them too, you may have noticed they arrive about half charge level. Leaving them at full charge for long periods is not good for LFP.
With a whole pallet of PV and three midnights, you have lots of stuff to work on this Spring.

 

[littleharbor2]

Yes. I also have bought a pallet of panels, 3 Midnite solar controllers and all the accompanying hardware for that stage of the project.

With this much additional power you will certainly need to rethink your battery bank, and system voltage for that matter. I have a friend who bought 3 Midnite Solar controllers for his system because he was unclear how the whole solar array wiring configuration worked. Basically he spent $1400 usd more than h needed.

 

[OffGridForGood]

maybe,
unlike Baja, the PNW is not known for it's sunshine...generally.
batteries are the most expensive part of a system, but also the easiest to upgrade.

 

[littleharbor2]

maybe,
unlike Baja, the PNW is not known for it's sunshine...generally.
batteries are the most expensive part of a system, but also the easiest to upgrade.

With the price of DIY Lithium these days I would have to say the racking/structure is the most expensive now. I've been building DIY batteries for friends that are cheaper and have more usable capacity than lead acid.

 

[OffGridForGood]

I am happy to see the cell prices dropping - especially while I am expanding the ESS!
I guess it depends how big the ESS is compared to the PV and Inverters, but in my system the cost of the ESS is about x3 the cost of everything else.