Project Planning

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Doc3G

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Figured I'd start a new thread since I have shifted focus from my initial plan to build a Golf Cart battery to building a small power wall. I'd like to have a clear game plan from the beginning and hopefully, a few members can offer some guidance.

My plan is to first build a ~ 13kWh power wall and then add solar, then hopefully expand the powerwall. Why that rating? Because that is about equivalent to a Tesla powerwall and I want to see how much a DIY version costs.

Here's what I'm thinking, so please feel free to comment on where I'm off track or whatever.

Cells: Planning on harvesting ~ 1400 cells from the ring packs from battery clearinghouse. These are ~3000 mAh each. I've harvested about 100 so far and only managed to destroy one cell in the process and the 33 that I've run through my opus and liitokala testers have all tested better than advertised. I haven't done a real IR check yet, as I'm waiting on my YR1035 to arrive still.

Inverter: I really like the review David Poz did on the Growatt SPF5000ES.

Sun: I live on the Texas Gulf coast and get 4.5+ avg hrs of direct sun daily. I've got two massive rooflines, one that faces south and the other facing west, so I have plenty of options for good sun.

What I don't quite understand at this point is what size to build the packs, especially to make the system scalable, as well as what to do about the BMS solution. For the golf cart battery I was originally planning, the big, expensive BMS setups didn't make sense, but it may make more sense for a power wall. I want safety to be the top concern so I want to use the cell level fusing strips that battery hookup sells.

I guess the packs need to be in 14s configuration but how many should be in parallel per pack is something I have no idea about the best approach. At the end of the day, I'm doing this because it's interesting to me so I want to learn along the way, I just don't want to make a bunch of expensive mistakes in the process :D
 

floydR

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One thing is to test consistently which means using one tester either the opus or the liitokala not both. I have 4 opus 3400, an icharger x8 and various other meters. 14s80p @3000mAh per cell would give you ~12kWh 14s100p would be around ~15kWh.
Need to check the building codes to find out if using a Growatt SPF5000ES with auto transformer would be legal to install.

later floyd
 

OffGridInTheCity

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>What I don't quite understand at this point is what size to build the packs, especially to make the system scalable,
No 1 issue is off-grid vs sending power to grid (hybrid). When off-grid, you have to store excess power in your battery bank and then use it thru the night. If you're grid-tie, you can just send excess to grid so battery is more of a UPS (simple backup when power goes out).
Not 2 issue - When off-grid, are you OK loosing PV power or do you insist on using it all. If you don't want to loose any power, the battery must have a minimum size.

I'm off-grid, and I insist on using all the PV power I create. Assuming you're thinking similarly... let me share some key things to think about from my own operations.

The key variables are PV in, consumption out, and battery size. In my case....
- The13kw PV array generates 18,000kwh/year - max of 80kwh/day in spring/summer - which is the max the house can consume.
- Average consumption is 2,500w/hour - with max typically <= 14,000w.
- 81kwh battery bank averages 40% DOD with high of 55% in spring/summer and low of 16% in winter.

From the above we could try to estimate / extrapolate some things to help you get into the ballpark of design.

==== SPECIFICS FOR YOUR SITUATION =====
>I guess the packs need to be in 14s configuration but how many should be in parallel per pack is
14s = 'most mainstream' 48v nominal... highly recommend you go this route.
14s100p (of 3000mah/cell) would be 14,400kwh battery @ 48v (I use this https://milliamps-watts.appspot.com/ so I don't have to multiply by hand :) )

Operationally:
- By extrapolating from my experience - at a 60% average DOD on a 14.4kwh battery - you could support up to a 4kw PV array.
- Per pvwatts ( https://pvwatts.nrel.gov/pvwatts.php ) at Dallas Tx - a 4kw PV array would be 20kwh/day max in summer. That's 833w/hour * 24hrs.

Per cell....
- A PV array of 4000watts / 48v = 83a of charging input. 83a / 100cells = 830ma/cell charging. [OK]
- At 833w average consumption that's 833w/48v = 17.4a = 174ma/cell discharge. [GOOD]
- At max 5000w - 5000w/48v = 104a / 100cells = 1.04a/cell discharge. [1a / cell is hefty]
 
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Doc3G

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One thing is to test consistently which means using one tester either the opus or the liitokala not both. I have 4 opus 3400, an icharger x8 and various other meters. 14s80p @3000mAh per cell would give you ~12kWh 14s100p would be around ~15kWh.
Need to check the building codes to find out if using a Growatt SPF5000ES with auto transformer would be legal to install.

later floyd

I have noticed that the liito and opus have differences in what the final battery voltages are and typically how much power they recharge. I currently have 3 Liito's and 3 Opus's. From my POV I see the pro's of the Liito that it consistently charges to 4.2.V vs 4.14V for the Opus, the Liito interface is easier for me to read and I really like that I can see a green light when a battery is done. The only thing I like about the Opus more is that b/c it has a 1000 mAh discharge test setting, it is a little faster per round than the Liito. Is there anything I'm missing about the Opus that should make it preferable? They are all from Amazon/Ebay and all still within the return window so I can choose to send one set or the other back at this point.
 

Doc3G

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>What I don't quite understand at this point is what size to build the packs, especially to make the system scalable,
No 1 issue is off-grid vs sending power to grid (hybrid). When off-grid, you have to store excess power in your battery bank and then use it thru the night. If you're grid-tie, you can just send excess to grid so battery is more of a UPS (simple backup when power goes out).
Not 2 issue - When off-grid, are you OK loosing PV power or do you insist on using it all. If you don't want to loose any power, the battery must have a minimum size.

I'm off-grid, and I insist on using all the PV power I create. Assuming you're thinking similarly... let me share some key things to think about from my own operations.

The key variables are PV in, consumption out, and battery size. In my case....
- The13kw PV array generates 18,000kwh/year - max of 80kwh/day in spring/summer - which is the max the house can consume.
- Average consumption is 2,500w/hour - with max typically <= 14,000w.
- 81kwh battery bank averages 40% DOD with high of 55% in spring/summer and low of 16% in winter.

From the above we could try to estimate / extrapolate some things to help you get into the ballpark of design.

==== SPECIFICS FOR YOUR SITUATION =====
>I guess the packs need to be in 14s configuration but how many should be in parallel per pack is
14s = 'most mainstream' 48v nominal... highly recommend you go this route.
14s100p (of 3000mah/cell) would be 14,400kwh battery @ 48v (I use this https://milliamps-watts.appspot.com/ so I don't have to multiply by hand :) )

Operationally:
- By extrapolating from my experience - at a 60% average DOD on a 14.4kwh battery - you could support up to a 4kw PV array.
- Per pvwatts ( https://pvwatts.nrel.gov/pvwatts.php ) at Dallas Tx - a 4kw PV array would be 20kwh/day max in summer. That's 833w/hour * 24hrs.

Per cell....
- A PV array of 4000watts / 48v = 83a of charging input. 83a / 100cells = 830ma/cell charging. [OK]
- At 833w average consumption that's 833w/48v = 17.4a = 174ma/cell discharge. [GOOD]
- At max 5000w - 5000w/48v = 104a / 100cells = 1.04a/cell discharge. [1a / cell is hefty]

Thanks, I'll have to do some number crunching. I know our avg consumption was around 100 kWh per day, but ranges anywhere from 2100 per month to 3600.

Some of these terms I'm still not entirely familiar with, but my thought was:

Stage 1 Proof of concept: My central dehumidifier is on a dedicated circuit and accessible thanks to the holes still in my garage wall from the install. I planned to build a battery, add a few solar panels, use something like the growatt, and then run just the dehumidifier off this system. The PV would generate whatever it generated and would be used up and whatever it fell short of, the Growatt would pull from the battery and when the battery fell too low it would pull from the grid.

Stage 2 Would be to increase the battery size to the point that pulling from the grid would be a rare occurrence.

Stage 3: Tie my whole house into the system, and just as in stage one, the house would pull what it could from the PV and battery and then pull whatever else it needed from the grid until the system finally scaled up to the point that it rarely dipped into the grid.

I do remember reading something about how the cheap all-in-ones weren't certified to feed power back into the grid, but it almost sounds like Floyd is saying that maybe they can't draw power from the grid at all?

If that is the case, then I guess I would really be limited to stage 1 and need to build the initial battery large enough that the dehumidifier would never need to dip into the grid and that system would be what you are describing as "off grid." ?
 

OffGridInTheCity

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>but it almost sounds like Floyd is saying that maybe they can't draw power from the grid at all?
Off-grid includes *Drawing power from the grid*. This is perfectly OK and no different than wiring up an extra light or a new appliance. Regular electrical rules / inspections apply. Equipment choices don't matter except UL or ETL certification is likely required for inspections.

Hybrid includes *Pushing power to the grid*. This can result in energizing the power lines down your street and potentially electricuting workmen when the grid goes down and the work on things. This requires cooperation with your power company - and they will have specific rules, equipment lists, and inspections you'd be wise to follow.

Middle approach - There is a middle approach that uses limiters to 'sense' incoming power from the grid at your main panel and will only feed power to your home circuits 'up to' the amount coming in. Not sure that Growatt does this. Here's a thread on a typical 'limiter inverter' https://secondlifestorage.com/index.php?threads/limiter-inverter-with-rs485-load-setting.7631/



All-in-one can mean off-grid or hybrid. In off-grid case, all-in-one means PV input (charge controller built-in), Battery input, and Inverter output (inverter built in) and in Growatt case ATS/UPS as well. In the hybrid case, all-in-one means PV input, optional battery input, inverter output, and grid-tie (push excess back out to the grid) and implies ATS/UPS. So all-in-one means different things depending on off-grid vs hybrid... its good to be clear on this when purchasing/designing your system.

----------------------
Off-grid. When you do off-grid in cooperation with grid there's typically a daily cycle. Sun rises, PV charges battery, inverter turns on and takes over providing power. When the Sun goes down, PV stops, the inverter will run down the battery and shut-off, and the grid takes over. Typically this cycle repeats each day. In other words, the power energizing these circuits will switch back and forth each day.

PV power is quite variable by time of year and weather - so off-grid power may be capable of running your circuits 3hrs (winter/cloudy day) or 10hrs (winter/sunny day) or up to 24hrs (summer time) for each cycle. ATSs (automatic transfer switches) and UPSs (uninterruptible power supplies) facilitate daily transitions between off-grid power and grid power so it can be seamless - I don't even notice when mine switches over.

I believe the off-grid Growatt (all-in-one) has ATS and UPS built-in. So you simply wire the Growatt AC output to multiple circuits (enough to consume the power you generate/store in the battery) and it will automatically use battery/inverter power while it can and switch to grid power when the battery runs down.

------------------
At the risk of going on and on... but from your tone I think you're thinking this way... so let me give you a vision of how to integrate Growatt AC output into your home.

Each home will have a Main Panel. You can buy an Manual Transfer Switch and hook it to circuits in the main panel. For example, I use a 10 circuit MTS - https://www.electricgeneratorsdirect.com/Reliance-Controls-A510C/p50933.html that can handle 240v@50a (12,000w). They make smaller ones. You would feed the Growatt AC output into the MTS and then hook the MTS into your main panel and then you can choose up to 10 circuits to be 100% Grid-only or Off-Grid by simply flipping switches. The grid input to the Growatt would come from the main panel. Here's a quick visual:


1619626397941.png


You could skip the MTS and just hook the Growatt AC output to power a sub-panel and move circuits from the main panel to the sub-panel... but I find the MTS 'elegant' :) and I can choose the amount of load on the off-grid system.
 
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floydR

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From my POV I see the pro's of the Liito that it consistently charges to 4.2.V vs 4.14V for the Opus, the Liito interface is easier for me to read and I really like that I can see a green light when a battery is done. The only thing I like about the Opus more is that b/c it has a 1000 mAh discharge test setting, it is a little faster per round than the Liito.
It comes down to personal preference, since I have never used the Litto charger/tester Basically I chose the Opus BT-C3400 because I could get it quicker (seller is local). Although now i see that Amazon can get the Opus3400/3100 as fast as the next day.

Later floyd
 

Doc3G

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----------------------
Off-grid. When you do off-grid in cooperation with grid there's typically a daily cycle. Sun rises, PV charges battery, inverter turns on and takes over providing power. When the Sun goes down, PV stops, the inverter will run down the battery and shut-off, and the grid takes over. Typically this cycle repeats each day. In other words, the power energizing these circuits will switch back and forth each day.

PV power is quite variable by time of year and weather - so off-grid power may be capable of running your circuits 3hrs (winter/cloudy day) or 10hrs (winter/sunny day) or up to 24hrs (summer time) for each cycle. ATSs (automatic transfer switches) and UPSs (uninterruptible power supplies) facilitate daily transitions between off-grid power and grid power so it can be seamless - I don't even notice when mine switches over.

I believe the off-grid Growatt (all-in-one) has ATS and UPS built-in. So you simply wire the Growatt AC output to multiple circuits (enough to consume the power you generate/store in the battery) and it will automatically use battery/inverter power while it can and switch to grid power when the battery runs down.

This is what I was hoping to do.
------------------
At the risk of going on and on... but from your tone I think you're thinking this way... so let me give you a vision of how to integrate Growatt AC output into your home.

Each home will have a Main Panel. You can buy an Manual Transfer Switch and hook it to circuits in the main panel. For example, I use a 10 circuit MTS - https://www.electricgeneratorsdirect.com/Reliance-Controls-A510C/p50933.html that can handle 240v@50a (12,000w). They make smaller ones. You would feed the Growatt AC output into the MTS and then hook the MTS into your main panel and then you can choose up to 10 circuits to be 100% Grid-only or Off-Grid by simply flipping switches. The grid input to the Growatt would come from the main panel. Here's a quick visual:


View attachment 24852

You could skip the MTS and just hook the Growatt AC output to power a sub-panel and move circuits from the main panel to the sub-panel... but I find the MTS 'elegant' :) and I can choose the amount of load on the off-grid system.

This type of setup looks great and I've seen something similar in the past when I've considered a panel for an emergency generator (where you can energize just a few circuits that your genset can handle, such as the refrigerator circuit, main lights, etc).

Thanks for all the info. You've really helped me visualize that I need to further delve into how many and when I'm going to add the PV to the system design.

The main reason I want to make this scaleable is because I don't know for sure how long I'm going to live in this house. I graduate from med school in 2 years and have almost no control over where I go for residency other than ranking my current location as my top pick (it's sort of an automated dating game, they match you with whoever you like most but also which program likes you the most). Ultimately, I don't plan to sell the house if I have to move for residency, but rather I would rent it out until I finished, and then we would come back to the area. However, I'm leary of dumping a bunch of money into something that might be untenable for a property management company to maintain. If I don't have a ton of $$ invested, in a worst-case scenario I could just shut the whole thing off so the renters didn't deal with it.

Thus, TLDR, it's a bit of a hobby/experiment now, but, if things start looking like I'm going to get to stay here for residency, then I would invest the money to scale it up and enjoy some financial return on the hobby.
 

Doc3G

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It comes down to personal preference, since I have never used the Litto charger/tester Basically I chose the Opus BT-C3400 because I could get it quicker (seller is local). Although now i see that Amazon can get the Opus3400/3100 as fast as the next day.

Later floyd

I already know the answer to this but I'm going to ask it anyway :D

Whichever charger I decide to use, I'm going to need to go back and retest/recharge the cells I previously charged/tested on the unit that I chose to send back? Otherwise, there won't be a consistency in the rating and that will skew the repacker?

Luckily, I labeled the cells with L or O to indicate which charger I used.
 

OffGridInTheCity

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----------------------
This type of setup looks great and I've seen something similar in the past when I've considered a panel for an emergency generator (where you can energize just a few circuits that your genset can handle, such as the refrigerator circuit, main lights, etc).
Yes - you got it. IF you did a manual transfer switch with a 'generator plug' instead of hard wired... you could plug in the Growatt then unplug and take it with you when you sell and charge a bit more for 'generator enabled' main panel. :)
 
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floydR

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Whichever charger I decide to use, I'm going to need to go back and retest/recharge the cells I previously charged/tested on the unit that I chose to send back? Otherwise, there won't be a consistency in the rating and that will skew the repacker?
Yes :)
 

Doc3G

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Yes - you got it. IF you did a manual transfer switch with a 'generator plug' instead of hard wired... you could plug in the Growatt then unplug and take it with you when you sell and charge a bit more for 'generator enabled' main panel. :)
Solid idea, that actually would add some value to the home since we live in a hurricane-prone area.
 

Wolf

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Whichever charger I decide to use, I'm going to need to go back and retest/recharge the cells I previously charged/tested on the unit that I chose to send back? Otherwise, there won't be a consistency in the rating and that will skew the repacker?
I somewhat agree with @floydR and that using the same charger/analyzers will give you the most consistent results.
That being said I built my Frankenstein pack using 6 different Charger/Analyzers. Foxnovo, OPUS, LiitoKala, SKYRC, Zanflare and XTAR.
I was at that time also testing the accuracy of these testers. The LiitoKala and Zanflare I gave away. https://secondlifestorage.com/index.php?threads/free-liitokala-lii500-and-zanflair.9004/
Nevertheless I used all of their results in building my first 14s80p battery. The Zanflare results were heavily questioned and when possible a cell of the same mAh results from another tester was substituted.
Tight IR was observed as mentioned many times in my posts. You see when you sort your cells it really doesn't matter if the charger analyzer is off by ±100 or so mAh as when you mix them all together the odds of you building 1 pack with the cells of only 1 make charger is next to nil.
This doesn't mean I condone this practice, and for simplicity and less "second guessing" I would certainly recommend using 1 style of tester exclusively.
But as I said my frankenstein battery with cells tested from 6 different testers and very carefully selected cells actually came out quite well.
I recorded the tester used in my 6000+ cells tested spreadsheet here is a snip.
Wolf
1619667694005.png
 
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Doc3G

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I somewhat agree with @floydR and that using the same charger/analyzers will give you the most consistent results.
That being said I built my Frankenstein pack using 6 different Charger/Analyzers. Foxnovo, OPUS, LiitoKala, SKYRC, Zanflare and XTAR.
I was at that time also testing the accuracy of these testers. The LiitoKala and Zanflare I gave away. https://secondlifestorage.com/index.php?threads/free-liitokala-lii500-and-zanflair.9004/
Nevertheless I used all of their results in building my first 14s80p battery. The Zanflare results were heavily questioned and when possible a cell of the same mAh results from another tester was substituted.
Tight IR was observer as mentioned many times in my posts. You see when you sort your cells it really doesn't matter if the charger analyzer is off by ±100 or so mAh as when you mix them all together the odds of you building 1 pack with the cells of only 1 make charger is next to nil.
This doesn't mean I condone this practice, and for simplicity and less "second guessing" I would certainly recommend using 1 style of tester exclusively.
But as I said my frankenstein battery with cells tested from 6 different testers and very carefully selected cells actually came out quite well.
I recorded the tester used in my 6000+ cells tested spreadsheet here is a snip.
Wolf
View attachment 24855

Nice, thanks for the insight. I've already redone all the cells I charge on the opus now, but it's good to know for future projects.
 

Doc3G

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OK, so I think I'm more than halfway through recovering the batteries at this point so I'm trying to plan for the next steps. I saw y'all mention 14s100P but is that one giant pack? :oops: As I've been perusing youtube I think I would like to use HBpowerwall's rack and a similar system to what he has so that if I want to swap a pack in the future that it would be pretty straight forward. I also want to use the battery hookup cell-level fusing, as in this video:

The pack he is building is 4 wide by 20 long though, and the whole P + S and how to arrange the packs is still a bit confusing for me.

Another question that I have is scalability. So, for example, if I build this setup with ~ 12-14kWh's, what happens if I want to expand my storage capacity. For example, if I got a great deal on a different type of cell (such as a 21700) could I build another 48 volt pack and add it to the system or am I stuck using 18650 cells? I'm still a bit green on how the whole system works.

Finally, if I set my system to a very conservative parameter such as 40-70%, and assuming I'm meticulous in my cell selection (and the cells I'm using are essentially new, all @ > 100% of original capacity), how many cycles is a realistic expectation? I'm planning on keeping the powerwall inside, so it won't be exposed to extreme temperature.

Updated harvest picture attached.
 

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floydR

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Inside your house or a separate outbuilding? Keeping a DIY powerwall in your house is not a wise idea.
Later floyd
 

OffGridInTheCity

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OK, so I think I'm more than halfway through recovering the batteries at this point so I'm trying to plan for the next steps. I saw y'all mention 14s100P but is that one giant pack? :oops: As I've been perusing youtube I think I would like to use HBpowerwall's rack and a similar system to what he has so that if I want to swap a pack in the future that it would be pretty straight forward. I also want to use the battery hookup cell-level fusing, as in this video:

The pack he is building is 4 wide by 20 long though, and the whole P + S and how to arrange the packs is still a bit confusing for me.
I use 260ah / pack as my 'base design'. Some packs have more cells to achieve 260ah and some have less. Some of my packs have 120cells (2170mah each) and some have 88cells (2950mah each) and some have aprox 100cells (2600mah each). However, each pack (120 or 100 or 88) is the same physical size / hookup. So some packs are more sparse in terms of the number of cells.

I have 84 if these packs in the powerwall ( 6 x 14s). The packs are interchangeable both in ah and physical design - but I built them in groups of 14s.
Another question that I have is scalability. So, for example, if I build this setup with ~ 12-14kWh's, what happens if I want to expand my storage capacity. For example, if I got a great deal on a different type of cell (such as a 21700) could I build another 48 volt pack and add it to the system or am I stuck using 18650 cells? I'm still a bit green on how the whole system works.
Key topics:
1) Chemistry. A different form factor of the same chemistry - e.g. 21700 lithium-ion, 18650 lithium-ion, Leaf cells are lithium-ion and some pouch cells are lithium-ion - will have the same voltage range. A 16s LifePo4 battery (different chemistry) can successfully be paralleled with a 14s Lithium-ion battery but you need to pay close attention to the different voltage ranges and align min/max voltages. If you tinker with the 's' you can list out the voltage ranges and see where they overlap. LTO's can be made to overlap with 48v nominal as well.
2) Power (ah): Is the new battery the same ah. If the 1st battery = 100ah @ 48v, then it would be good that all expansion/parallel battery(s) have the same overall power - e.g. 100ah in each one regardless of chemistry.
3) If you want all packs to be interchangeable... then you need a physical pack design that will be the same dimensions/hookup but accept a variety of cell counts (at least) and perhaps different form factors.
4) BMS considerations. Batrium can handle many packs of different form factors if they are all the same chemistry (voltage range) and power (ah).
If you were to do a 16s (48v nominal) LifePo4 - it would be a different chemistry / voltage range and need a separate BMS from the lithium-ion packs.

**I'm 18650 and Batrium. In my case I plan to stay (and kind of feel locked in a bit) with Lithium-ion because I like having single BMS to manage the overall battery. But this is a choice, not a box canyon :)

Finally, if I set my system to a very conservative parameter such as 40-70%, and assuming I'm meticulous in my cell selection (and the cells I'm using are essentially new, all @ > 100% of original capacity), how many cycles is a realistic expectation? I'm planning on keeping the powerwall inside, so it won't be exposed to extreme temperature.
I just hit 1000 cycles on my 1st 18650 lithium-ion 14s120p battery with no detectable issues or loss of capability. It averaged 40% DOD over the 2.7yrs (1000 cycles) within the voltage range of 3.5v low and 4.0v high. Its 1 of 6 that make up an 81kwh battery bank. The charge/discharge amp range is 150-300ma/cell - which is below 'standard' ratings of the cells.
This 40% DOD 3.5v low -> 4.0v hi aligns with the 75-25% SoC range from Figure 6 on the famous Battery University page - https://batteryuniversity.com/index.php/learn/article/how_to_prolong_lithium_based_batteries/ . I'm actually hoping for 7000 more cycles - but who knows! :)
1622161412172.png

I may continue to build more batteries and try to get to the 75-45% SoC level in the next couple of years.
 
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Doc3G

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I use 260ah / pack as my 'base design'. Some packs have more cells to achieve 260ah and some have less. Some of my packs have 120cells (2170mah each) and some have 88cells (2950mah each) and some have aprox 100cells (2600mah each). However, each pack (120 or 100 or 88) is the same physical size / hookup. So some packs are more sparse in terms of the number of cells.

I have 84 if these packs in the powerwall ( 6 x 14s). The packs are interchangeable both in ah and physical design - but I built them in groups of 14s.

Key topics:
1) Chemistry. A different form factor of the same chemistry - e.g. 21700 lithium-ion, 18650 lithium-ion, Leaf cells are lithium-ion and some pouch cells are lithium-ion - will have the same voltage range. A 16s LifePo4 battery (different chemistry) can successfully be paralleled with a 14s Lithium-ion battery but you need to pay close attention to the different voltage ranges and align min/max voltages. If you tinker with the 's' you can list out the voltage ranges and see where they overlap. LTO's can be made to overlap with 48v nominal as well.
2) Power (ah): Is the new battery the same ah. If the 1st battery = 100ah @ 48v, then it would be good that all expansion/parallel battery(s) have the same overall power - e.g. 100ah in each one regardless of chemistry.
3) If you want all packs to be interchangeable... then you need a physical pack design that will be the same dimensions/hookup but accept a variety of cell counts (at least) and perhaps different form factors.
4) BMS considerations. Batrium can handle many packs of different form factors if they are all the same chemistry (voltage range) and power (ah).
If you were to do a 16s (48v nominal) LifePo4 - it would be a different chemistry / voltage range and need a separate BMS from the lithium-ion packs.

**I'm 18650 and Batrium. In my case I plan to stay (and kind of feel locked in a bit) with Lithium-ion because I like having single BMS to manage the overall battery. But this is a choice, not a box canyon :)


I just hit 1000 cycles on my 1st 18650 lithium-ion 14s120p battery with no detectable issues or loss of capability. It averaged 40% DOD over the 2.7yrs (1000 cycles) within the voltage range of 3.5v low and 4.0v high. Its 1 of 6 that make up an 81kwh battery bank. The charge/discharge amp range is 150-300ma/cell - which is below 'standard' ratings of the cells.
This 40% DOD 3.5v low -> 4.0v hi aligns with the 75-25% SoC range from Figure 6 on the famous Battery University page - https://batteryuniversity.com/index.php/learn/article/how_to_prolong_lithium_based_batteries/ . I'm actually hoping for 7000 more cycles - but who knows! :)
View attachment 25173
I may continue to build more batteries and try to get to the 75-45% SoC level in the next couple of years.

Cool, thanks for the detailed info. So, if I build a pack in 14s configuration then I can technically continue to add packs b/c essentially I'm just adding more packs in parallel?

I like the idea of planning ahead so I think I would like to follow your lead and make all of my packs the same size. That said, from browsing the market, it seems that there are a lot of ~2100 mah cells so I should probably make the standard size bigger.

For the ring batteries, I could do something like 14 in series by 6 which should be around 252 ah. For the standard modem 18650's I could do 14s by 9 which should be around 264 ah. Would those be close enough in capacity to work as a scalable system?

If yes, then if I built all the packs as 14x9, what do I use as filler for the empty spaces on the ring battery packs since 3 rows would be unfilled? Just junk cells or something else? I've seen HBpowerwall use junk cells in some of his packs where he wanted fillers to prevent short-circuiting.

Then, for the BMS, I would need the watchmon plus enough longmons for however many 14s packs I build?

Sometimes I feel like this rabbit hole just keeps getting deeper, lol.
 

OffGridInTheCity

Well-known member
Joined
Dec 15, 2018
Messages
1,658
Cool, thanks for the detailed info. So, if I build a pack in 14s configuration then I can technically continue to add packs b/c essentially I'm just adding more packs in parallel?
Well... If you build a battery that is 14s, then build a 2nd battery of 14s of the same ah, then you can hook the 2nd battery's +/- to the 1st battery to parallel them. You could also parallel individual packs if you do it in groups of 14 at a time - but that would be 28 large wires instead of just paralleling the overall 14s battery which is 2 large wires.

I like the idea of planning ahead so I think I would like to follow your lead and make all of my packs the same size. That said, from browsing the market, it seems that there are a lot of ~2100 mah cells so I should probably make the standard size bigger.
It was an 'accident' in my case - but that's what I did. I started with 2200mah cells (which tested on average 2150mah) and built my packs to hold 120p + a few extra which got me the 260ah base pack. Then, later it was easy to keep the same physical size / layout of pack structure but do less cells. For example - this 260ah pack is from RING NCR18650A cells... and I only needed 89 of them to make 260ah.
1622646203302.png


*Cells tend to come in at 2200mah (or higher) when new. If you accept 80% or better of 2200mah - that's 1760mah (1800mah) as you bottom out - probably a mix of 1800, 1900, 2000, 2100, 2200. That puts you in 130p range (for 260ah) as the 'most cells' I'd ever use in 1 physical pack. Knowing all this - I can choose to buy 2200mah or larger cells and have tended to 2600mah or 3000mah lately.

For the ring batteries, I could do something like 14 in series by 6 which should be around 252 ah. For the standard modem 18650's I could do 14s by 9 which should be around 264 ah. Would those be close enough in capacity to work as a scalable system?
264ah per pack works for me - but that's a question of you. The pic above is 89 cells @ 260ah.. and weighs enough that I don't want to be man-handling any more than 130 cells... but maybe you're OK with physically larger packs. Also I use Batrium as BMS which has no trouble balancing 2 or 3 times the size shown in the pick.


If yes, then if I built all the packs as 14x9, what do I use as filler for the empty spaces on the ring battery packs since 3 rows would be unfilled? Just junk cells or something else? I've seen HBpowerwall use junk cells in some of his packs where he wanted fillers to prevent short-circuiting.
I just leave them empty - and you can push in cells later on and solder them up to the bus-bar. If you're spot welding, it can be a bit trickier.


Then, for the BMS, I would need the watchmon plus enough longmons for however many 14s packs I build?

Sometimes I feel like this rabbit hole just keeps getting deeper, lol.
You need 1 watchmon 4 for up to 250 packs - https://support.batrium.com/article...l-monitors-can-be-installed-with-one-watchmon. You need 1 longmon for each 3.7v (nominal) pack.
 
Last edited:

Doc3G

Member
Joined
Apr 18, 2021
Messages
56
Well... If you build a battery that is 14s, then build a 2nd battery of 14s of the same ah, then you can hook the 2nd battery's +/- to the 1st battery to parallel them. You could also parallel individual packs if you do it in groups of 14 at a time - but that would be 28 large wires instead of just paralleling the overall 14s battery which is 2 large wires.

View attachment 25213

You need 1 watchmon 4 for up to 250 packs - https://support.batrium.com/article...l-monitors-can-be-installed-with-one-watchmon. You need 1 longmon for each 3.7v (nominal) pack.

OK, so the assembly of the packs is what I'm still having a hard time wrapping my head around. I understand the 1st statement as indicating that each of my 14s9p packs would essentially function like a 48v battery that I could string together in parallel x however many packs I end up with.

The second statement then is basically saying that I could build a pack that was all in parallel (so that the nominal voltage of the pack was 3.7v) and then string 14 of those packs together in series to get up to 48v, correct?

Of the two options, I prefer option 1 since, in theory, I could add a new pack here and there whenever I had free time to expand the system without needing to build 14 new packs. However, the last statement, that I need 1 longmon for each 3.7 pack is where I'm confused.

Does that mean that the longmon's won't support a pack that is 14s9p (48v), thus forcing me to build 3.7v packs?

The BMS still has me a bit perplexed. For example, I was watching some videos on installing the longmons yesterday and it looks like it just hooks to the positive and negative of a pack? So, does that mean the individual cells aren't monitored? My understanding is that in a theoretically ideal system the BMS would monitor each individual cell?
 
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