EPEver BN 40a MPPT Battery is 3S5P

ProfitBroseph

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I have 6x 250w SanTan panels on the roof of my bus.
I have 2x EPEver BN 40a 150v MPPT.
I have 3S2P setup on panels, with 3 on each side of my bus that I can tilt, thus 2 MPPTs for voltage/sunlight differential, which I believe is necessary.
I have 15x 3.2v 400ah cells connected 3P5S for an 18v battery.
I am hoping to charge my battery bank with these EPEvers to ~18v.
Will I have to put the MPPTs into 24v charging mode?
Epever Manual shows 9-17v parameter -says “please use double value in 24v” charging, but will the MPPT recognize my battery as a 24v version if voltage runs from 15.5v-18v?)
OR in custom battery mode can I set these parameters to whatever I want between 8v-32v as stated elsewhere in manual without worrying abt “24v mode?”

What do y’all think of this setup anyway?
I’m wondering if I’m actually oversized on panels; I believe this 150v unit is rated for 780W of panels on 12v systems or 1560W on a 24v system, just wondering what this means for my setup.
Am I correct that the MPPT’s rated charge power of 520W (for 12v) is much lower than MPPT max PV rating of 780W, meaning I’m potentially leaving some current at the panels, but not leaving much bc panels are 5+ years old?
Can I safely assume these MPPTs will charge my batteries in full sun to 18v at 28.8a? Or is my math inaccurate?

Final question: is my 150v MPPT at risk of over-voltage from 3x ~40v panels wired in series? I count just 120v max input but I can’t find precise values for how high the input might get in cold+sunny conditions.
Panel sticker shown below for anyone interested.
 

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NVS

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Why do you have your batteries in a 3p5s configuration? Lifepo4 cells should be in multiples of 4 for correct voltages, A 4s would be for 12v, 8s for 24v and so on.
 

DerpsyDoodler

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I had a bad experience with a Chargery and 500a Daly BMS, and now I own 10 overdischarged 3.2v, <400ah cells.
I’ve capacity tested via charge/discharge cycles and matched them 1/10, 2/9, 3/8, 4/7, 5/6 with a cumulative capacity for these paired cells of ~700ah.
I have 5 new (3.2v 400ah) cells arriving from Guangdong in the next 30 days (I hope.)
I glazed over this because a lot of these numbers seemed like nonsense when I first read them.

Am I to understand you still have 15 good cells and have 5 more on the way? For a total of 20 good cells?

If so, and assuming your xantrex inverter is a 12v inverter, then all you need is 5 reliable BMS to put together 5x 12v nominal batteries.

5x jbd (or overkill solar) BMS will do the trick. They are fet based, but with 5 in parallel and properly fused you will have nothing to worry about. Get the ones rated for 100A. As for fusing, Your inverter should be your largest load. Refer to manual for its fuse size, then divide by 4 and round up to get fuse size for each battery. size your wires to the fuses. With this configuration, you'll have full capacity even if you have to take one of your batteries offline for any reason. Assuming 350a inverter fuse, you'll want a total of 7x class t fuses. 1x 350a (assuming this is the fuse size your inverter recommends, again, refer to the manual and work back from there), 5x 100a, and you'll need to make a determination of your DC loads, so you can size a fuse and wire to your DC distribution block.

If you're on board with this, start making your materials list and we can move forward with wire sizes and making determinations for the rest of your system. Don't purchase anything else until we've fleshed out a plan and its been looked over by others on the forum.
 

ProfitBroseph

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I glazed over this because a lot of these numbers seemed like nonsense when I first read them.

Am I to understand you still have 15 good cells and have 5 more on the way? For a total of 20 good cells?

If so, and assuming your xantrex inverter is a 12v inverter, then all you need is 5 reliable BMS to put together 5x 12v nominal batteries.

5x jbd (or overkill solar) BMS will do the trick. They are fet based, but with 5 in parallel and properly fused you will have nothing to worry about. Get the ones rated for 100A. As for fusing, Your inverter should be your largest load. Refer to manual for its fuse size, then divide by 4 and round up to get fuse size for each battery. size your wires to the fuses. With this configuration, you'll have full capacity even if you have to take one of your batteries offline for any reason. Assuming 350a inverter fuse, you'll want a total of 7x class t fuses. 1x 350a (assuming this is the fuse size your inverter recommends, again, refer to the manual and work back from there), 5x 100a, and you'll need to make a determination of your DC loads, so you can size a fuse and wire to your DC distribution block.

If you're on board with this, start making your materials list and we can move forward with wire sizes and making determinations for the rest of your system. Don't purchase anything else until we've fleshed out a plan and its been looked over by others on the forum.
I have 10 damaged 3.2v 400ah LiFePO4 cells.
5 cells have capacity >350ah
5 cells have capacity <350ah
I have paired the damaged cells 10/1, 9/2, 8/3…etc
I also have 5 new cells en route from china which bring me to a total of 15 cells.
I’m not sure there’s a “perfect” way to use my 15 cells together, which is sort of why I came here.
I am boondocking/off grid in a converted school bus 90% of the year and I have no interest in having spare cells on my bus.
I cannot imagine wanting to upsize my system if I can use 12 cells get a 12v 1100ah battery.
To go further, I really really can’t imagine wanting to upsize my system if I can use my 15 cells to make a ~15v battery.
But this is a mobile array mounted on a mobile battery bank. If I have another system failure I may build a different battery, but I am sort of hoping this is the last battery I hafta build in this bus.

I wasn’t trying to argue with anyone abt their input.
On the other thread a fella was saying I’d hafta charge my cells up to 19v+ and he had experience burning out both cheap/expensive components.

I’m a new solar person and fairly new to electrical work entirely. My brother is an electrical engineer, and I am a pharmacist.
Looking at the specs for my system components thus far, they are all rated at or above 18v so I was asking if any of them can be used at that value and you (and the 19v fella) said not to attempt it.

That’s fine if I shouldn’t do it but I would like to better understand what the limits are.
Xantrex assured me their charger doesn’t mind working up to rated specs.
I sure hope the EPEver can charge a battery to 18v if desired.
Why would either charger care what kind of battery is attached? I don’t understand but I am here to learn.

It is easy advice to just get rid of my damaged cells and build a 12v battery.
Or to couple my old cells to my new cells in a 12v setup.
I was really hoping for some different advice, allowing me to use my damaged cells and maximize my battery voltage due to my large-ish solar array in a 16v arrangement.
 
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rickst29

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Your Tracer BN controllers can be configured for "custom batteries" with bulk charging at 18.0v (3.6V per cell) and float charging at about 17.0 volts. But what about your loads? Nominal battery Voltage of 16 Volts is much too low for most "24v" inverters, and much too high for most "12v" inverters. And non-inverter "12v" devices, other than heaters, will die young (perhaps immediately) if subjected to such high voltage.
 

ProfitBroseph

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Why do you have your batteries in a 3p5s configuration? Lifepo4 cells should be in multiples of 4 for correct voltages, A 4s would be for 12v, 8s for 24v and so on.
I have had a 12v battery for several years.
Now I have some used/damaged cells and new cells and the best way to combine them is in this orientation, as far as I know.

I had a bad experience with a Chargery and 500a Daly BMS, and now I own 10 overdischarged 3.2v, <400ah cells.
I’ve capacity tested via charge/discharge cycles and matched them 1/10, 2/9, 3/8, 4/7, 5/6 with a cumulative capacity for these paired cells of ~700ah.
I have 5 new (3.2v 400ah) cells arriving from Guangdong in the next 30 days (I hope.)
 

ProfitBroseph

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Your Tracer BN controllers can be configured for "custom batteries" with bulk charging at 18.0v (3.6V per cell) and float charging at about 17.0 volts. But what about your loads? Nominal battery Voltage of 16 Volts is much too low for most "24v" inverters, and much too high for most "12v" inverters. And non-inverter "12v" devices, other than heaters, will die young (perhaps immediately) if subjected to such high voltage.
This is the info I was wondering about.
My inverter I can set to use whatever voltage I like within 9-18v.
But on 12v lights and water pump and diesel heater etc you’re saying I should not attempt it. I don’t want to shorten the life of my extensively 12v wired system.
 

MisterSandals

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Can I safely assume these MPPTs will charge my batteries in full sun to 18v at 28.8a? Or is my math inaccurate?
This sounds pretty sketchy. What exactly are you hoping to power with your battery(s)?
If you have 12V appliances/tools, you should build a 4S (12.8V) battery(s).

Putting cells together willy-nilly is not a solution, especially when a BMS, possibly built for a specific number of cells is involved.
Which BMS(s) do you have or are expecting to use?

I had a bad experience with a Chargery and 500a Daly BMS, and now I own 10 overdischarged 3.2v, <400ah cells.
I strongly recommend fixing whatever caused your "bad experience". Was it failed equipment? User error? Incorrect wiring?
Throwing new equipment into a known bad process/mechanism isn't a solution likely to result in success.
 

NVS

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I would capacity test each cell and find out their capacity. Then make 4 parallel strings 3 cells out of them, buy using the 12 best capacity batteries. Each string capacity should be very close in average capacity.
 

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MisterSandals

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Then make 4 parallel strings 3 cells out of them, buy using the 12 best capacity batteries.
I would also consider 2P4S x2 if you have 16 or more usable cells. This would require 2 BMSs.
You have 2x SCCs so its also possible to make 2 distinct systems, each with its own battery. But without any idea what you are trying to accomplish its hard to do more that bring up the idea.

Each string capacity should be very close in average capacity.
This is the key to making a 2P or 3P battery work in my opinion.
 

ProfitBroseph

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I would capacity test each cell and find out their capacity. Then make 4 parallel strings 3 cells out of them, buy using the 12 best capacity batteries. Each string capacity should be very close in average capacity.
You’ve just described the 12v set up I’ve been using for the past 15mo, except with only 8 (of 10) cells 2P4S.
I have 10 damaged 3.2v 400ah LiFePO4 cells.
5 cells have capacity >350ah
5 cells have capacity <350ah
I have paired the damaged cells 10/1, 9/2, 8/3, 7/4… to make a 4S2P battery.

I also have 5 new cells en route from china which bring me to a total of 15 cells.
I’m not sure there’s a “perfect” way to use my 15 cells together, which is part of why I came here.
I understand that using only 12 cells (or any multiple of 4) would work for a 12v battery. I have been using my cells like this for the past 15mo.
I would like to use the full capacity of my 5 new cells and as much of the capacity of my remaining cells (many of them have >300ah) as possible.

I do not have 16 cells and it’s not possible to get an additional cell or use the cells I have without pairing them due to the aforementioned damage from over-discharge. -So any plans that don’t involve paralleling my damaged cell with a new cell isn’t possible as far as I know.
 

ProfitBroseph

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This sounds pretty sketchy. What exactly are you hoping to power with your battery(s)?
If you have 12V appliances/tools, you should build a 4S (12.8V) battery(s).

Putting cells together willy-nilly is not a solution, especially when a BMS, possibly built for a specific number of cells is involved.
Which BMS(s) do you have or are expecting to use?


I strongly recommend fixing whatever caused your "bad experience". Was it failed equipment? User error? Incorrect wiring?
Throwing new equipment into a known bad process/mechanism isn't a solution likely to result in success.
You asked me this on another thread.

My Chargery BMS did not accurately report ICV and my vendor checked his inventory and none of his new stock was accurate either. While I was waiting for him to contact me via eBay messenger again, he sent me an additional BMS and my return/dispute window closed so we couldn’t talk anymore.
I used new Nissan Leaf relays with the Chargery but my load was not disconnected and my 16S 48v battery was damaged with 4 cells totally unusable and 10 cells capacity tested >300ah. You like Chargery’s and I’m happy to send you one just bc you’ve asked me about it twice now. Hell, you can have the Daly AND a Chargery if you can make a Chargery work for me.
My “500a” Daly BMS never supported >150a and I am unable to turn it on or connect via BT or via PC SinoWealth software. Sales from China helped me diagnose it as “toast” after I used it with a hair dryer. I can only assume it was never safe to use with >100a and while I’m happy to continue trying to diagnose it, I am not in a garage or a shop and I live off-grid full time (using this battery) with my family of 5.
I don’t know anything about BMS’ except that what should be a fairly simple device has given me hell, for no good reasons that I can discern.
My current plan is to get an electrodacus (when production resumes in April) but I’m happy to use any BMS. A friend has an electrodacus, and I’d rather not try and figure out how to turn my BMS on (Daly did this) or why values don’t read within 5% of my Fluke (Chargery did this.)
 

NVS

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Its just not possible to put 5 cells in series for a battery for 12v appliances.

Thinking outside the box a little here but have never tried it. Buy another solar charger that is user programable . Make a 5s2p battery, and have your new scc charge the 5s2p battery to its 18v capacity. Then, connect battery to the pv terminals on the second scc, which would be connected to your 4s1p battery from your new cells.
 

MisterSandals

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You asked me this on another thread.
Sorry, there are dozens of threads. Glad to hear I am consistent.

In regards to getting a high amp BMS solution, I am working on a high amp disconnect using a remote throw breaker. Waiting for greenhouse season to be over to proceed with installing.

I gotta leave now, summoning @BentleyJ to pass on his RT breaker solution.
Will do more when I get back home (sorry).

I cannot recommend anything outside 3P4S or 4S3P (with 3 BMSs).
I have not tried either of those so take that into consideration.
 

ProfitBroseph

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Its just not possible to put 5 cells in series for a battery for 12v appliances.

Thinking outside the box a little here but have never tried it. Buy another solar charger that is user programable . Make a 5s2p battery, and have your new scc charge the 5s2p battery to its 18v capacity. Then, connect battery to the pv terminals on the second scc, which would be connected to your 4s1p battery from your new cells.
I’m a solar noob and apparently, a battery boob.

Sorry, there are dozens of threads. Glad to hear I am consistent.

In regards to getting a high amp BMS solution, I am working on a high amp disconnect using a remote throw breaker. Waiting for greenhouse season to be over to proceed with installing.

I gotta leave now, summoning @BentleyJ to pass on his RT breaker solution.
Will do more when I get back home (sorry).

I cannot recommend anything outside 3P4S or 4S3P (with 3 BMSs).
I have not tried either of those so take that into consideration.

Let’s go ahead and agree that I’m not going to be able to use all of my damaged cells.
Say I’m gonna build a 3P4S battery consistent with feedback I’ve received here.

What BMS solution do you recommend?
I’ve seen 16s BMS’s that allow fewer than 16 cells by bundling wires, so I figure there are options.
 

DerpsyDoodler

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I’m a solar noob and apparently, a battery boob.



Let’s go ahead and agree that I’m not going to be able to use all of my damaged cells.
Say I’m gonna build a 3P4S battery consistent with feedback I’ve received here.

What BMS solution do you recommend?
I’ve seen 16s BMS’s that allow fewer than 16 cells by bundling wires, so I figure there are options.
3p4s means you'll have only 1 BMS and will be limited to its discharge capacity. Given a 3kw inverter, you'll either need to use one of those chargerys (assuming they are operable and in good condition) with a 500a rated contactor or figure out how to make it control the inverter directly (i think it may be possible). In lieu of this, you'll need multiple BMS to build 3 separate 12v batterys in a 4s3p arrangment. You'll need this because of current sharing for your monstrous 12v inverter, with the upside of redundancy. If one of your 12v battery packs should fail, you can disconnect it and still have a working system. Do you understand the difference between 4s3p and 3p4s?

All of that said, this arrangement will leave you with 3 spare cells. If you don't want spares, invest in 1 more cell for a 4p4s or 4s4p arrangement.

As for the pairing of the damaged cells, have you checked the internal resistance (IR) of all the cells? I would label them all with that information. You want series'd cells to closely match in IR, and you want to configure "usuable capacity" as the lowest capacity cell in the pack. So if the most damaged cell is only 325AH and you are doing a 3p4s arrangement, multiply 325 by 3 (3p), and this will need to be the set capacity of the entire pack.

Furthermore, you will need to play a number juggling game to determine which cells to parallel based on IR. You will want the total IR of each 3p bundle to closely match each other 3p bundle. Someone may be able to better assist. I do not remember, off the top of my head, how how to calculate resistance in parallel.

With all of that said, pairing damaged cells with new cells in the same pack under the same BMS isnt the greatest idea, because if one of those damaged cells decides to short, they may damage the good batteries and destroy them as well.

Perhaps use the damaged cells in their own pack with their own BMS arranged as described above, then build a separate pack with its own BMS out of all new cells. Given that youre using damaged cells, you may end up being very happy that you have a spare or 2 hanging around.
 

ProfitBroseph

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3p4s means you'll have only 1 BMS and will be limited to its discharge capacity. Given a 3kw inverter, you'll either need to use one of those chargerys (assuming they are operable and in good condition) with a 500a rated contactor or figure out how to make it control the inverter directly (i think it may be possible). In lieu of this, you'll need multiple BMS to build 3 separate 12v batterys in a 4s3p arrangment. You'll need this because of current sharing for your monstrous 12v inverter, with the upside of redundancy. If one of your 12v battery packs should fail, you can disconnect it and still have a working system. Do you understand the difference between 4s3p and 3p4s?

All of that said, this arrangement will leave you with 3 spare cells. If you don't want spares, invest in 1 more cell for a 4p4s or 4s4p arrangement.

As for the pairing of the damaged cells, have you checked the internal resistance (IR) of all the cells? I would label them all with that information. You want series'd cells to closely match in IR, and you want to configure "usuable capacity" as the lowest capacity cell in the pack. So if the most damaged cell is only 325AH and you are doing a 3p4s arrangement, multiply 325 by 3 (3p), and this will need to be the set capacity of the entire pack.

Furthermore, you will need to play a number juggling game to determine which cells to parallel based on IR. You will want the total IR of each 3p bundle to closely match each other 3p bundle. Someone may be able to better assist. I do not remember, off the top of my head, how how to calculate resistance in parallel.

With all of that said, pairing damaged cells with new cells in the same pack under the same BMS isnt the greatest idea, because if one of those damaged cells decides to short, they may damage the good batteries and destroy them as well.

Perhaps use the damaged cells in their own pack with their own BMS arranged as described above, then build a separate pack with its own BMS out of all new cells. Given that youre using damaged cells, you may end up being very happy that you have a spare or 2 hanging around.
3P4S is my ideal setup bc I’ve been using my batteries 2P4S for the last 15mo and the capacity is matched high/low as I mentioned above.
I’ve seen no degradation, I’ve done no research on internal resistance, and I just charged/discharged to determine capacity and pair them.

The internal resistance is not great on any of them, I suspect. The voltage drops substantially under heavy load and some distant items in my 40’ bus can’t pull enough amps off the battery to run (diesel heater requires 10a so now I run it on a 120v power supply.)
As they are paired now (2P4S) I would love to keep them, I have space constraints and I built into a custom space behind a trap door in my bedroom floor (see photo), but I’ve consistently discharged 700ah from 2P ~350ah cells for the 4S battery I use currently. Batteries will run microwave/instapot thru inverter no problem, but as mentioned above my Daly BMS is shot, and we would hafta bypass it to run microwave off batteries. Easier to just start generator.

My understanding is that I can add 4 more cells to make my battery 3P4S, and my battery should measure 1100ah.
Is this incorrect?
Can you explain more the absolute risk of an internal short?
 

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DerpsyDoodler

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3P4S is my ideal setup bc I’ve been using my batteries 2P4S for the last 15mo and the capacity is matched high/low as I mentioned above.
I’ve seen no degradation, I’ve done no research on internal resistance, and I just charged/discharged to determine capacity and pair them.
And you've not had a problem with them staying balanced or BMS cutting out in the process of normal use?
The internal resistance is not great on any of them, I suspect. The voltage drops substantially under heavy load and some distant items in my 40’ bus can’t pull enough amps off the battery to run (diesel heater requires 10a so now I run it on a 120v power supply.)
Are you properly sizing your wire for the length of the run and the amps needed?

As they are paired now (2P4S) I would love to keep them, I have space constraints and I built into a custom space behind a trap door in my bedroom floor (see photo), but I’ve consistently discharged 700ah from 2P ~350ah cells for the 4S battery I use currently. Batteries will run microwave/instapot thru inverter no problem, but as mentioned above my Daly BMS is shot, and we would hafta bypass it to run microwave off batteries. Easier to just start generator.
Do you plan on running multiple devices/appliances at the same time?
My understanding is that I can add 4 more cells to make my battery 3P4S, and my battery should measure 1100ah.
Is this incorrect?
Depends on the capacity of the 4 more cells. Ideally you'd set your capacity to the AH of the lowest parallel bank, so add another 350 for 1050AH.
Can you explain more the absolute risk of an internal short?
An internal short would discharge a cell and any cells connected to it quickly, turning that energy into heat, causing the cell (or cells) to vent, and ultimately destroying them (potentially causing a fire).
 
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