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BMS Basics 4 100AH 200AH 4 & 8 Battery Setups

Davetv1423

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Dec 29, 2019
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Hello
Cany anyone chime in here on the (short answer:) for a BMS Setup...

-Does it matter that i have 100 amp hr batteries vs. 200 amp hr batteries?
-The Numbers on the BMS stand for how many batteries the BMS can handle correct? (4s - means 4 "terminals/4 batteries) - right?

I haven't seen any of Will's videoes either that cover the difference or benefit of the Amp Hour of Battery you select.
EG: with most battery DIY's and off-the-shelf Lifo4's are completed/sold in a 100AH setup - why is this?

I'm Looking at Goal of a 120 or 200ah setup with two sets of 4 batteries (8 total) end-of-day / but / will start by purchasing only 1 set (4) of these same adding the other 4 later.
Q - Do i buy a different BMS to handle all 8 or two BMS's that handle 4 each and does it matter if they are 120 ah vs. 200 ah?

Q - Not looking to run an AC or anything but a small skillet or hotplate in my RV from the setup...

Any info appreciated -
Thx
RV Dave
 
OK, short answers:

Does it matter that i have 100 amp hr batteries vs. 200 amp hr batteries?
No.
The Numbers on the BMS stand for how many batteries the BMS can handle correct? (4s - means 4 "terminals/4 batteries) - right?
No. A BMS is required to balance the individual cells within a battery (a battery being a container for one or more cells). 4S means that within the battery there are four LiFePO4 cells connected in series or that the BMS supports up to four cells. An 8-cell BMS supports up to 8 cells within a battery.
EG: with most battery DIY's and off-the-shelf Lifo4's are completed/sold in a 100AH setup - why is this?
Such capacities are equivalent to common lead-acid batteries and, therefore, marketed as 'drop-in replacements'. A DIY LiFePO4 battery can be designed/built for any capacity and any terminal voltage you require.
Q - Do i buy a different BMS to handle all 8 or two BMS's that handle 4 each and does it matter if they are 120 ah vs. 200 ah?
Generally a BMS is contained within the battery container, so if your battery container has eight cells, choose an 8-cell BMS. It doesn't matter what the capacity of the individual cells are, only that they are the same.
Q - Not looking to run an AC or anything but a small skillet or hotplate in my RV from the setup...
OK.

Let's take an example to illustrate this.

You want a 200AH 12V (nominal) LiFePO4 battery. Each LiFePO4 cell has a nominal terminal voltage of 3.2V, so connecting four in series would give you 12.8V (nominal). Each cell in the battery must have the same capacity (else one cell in the series string would become fully discharged before the others) so you would buy 4 x 200AH LiFePO4 cells. Note: the capacity rating in AH depends on the voltage, a 200AH cell will provide 200 Amps for one hour at 3.2V (nominal), connect four of these in series and you have a 200AH battery at 12.8V (nominal). Your battery contains four cells so buy a 4-cell BMS.

If you wanted a 400AH 12V (nominal) LiFePO4 battery you would connect 8 x 200AH LiFePO4 cells in a 4S2P configuration (two series strings of 4 cells in parallel) and use an 8-cell BMS.

If you wanted a 200AH 24V (nominal) LiFePO4 battery you would connect 8 x 200AH LiFePO4 cells is a 8S configuration (one series string of 8 cells) and use an 8-cell BMS.

Clear as mud?
 
OK, short answers:


No.

No. A BMS is required to balance the individual cells within a battery (a battery being a container for one or more cells). 4S means that within the battery there are four LiFePO4 cells connected in series or that the BMS supports up to four cells. An 8-cell BMS supports up to 8 cells within a battery.

Such capacities are equivalent to common lead-acid batteries and, therefore, marketed as 'drop-in replacements'. A DIY LiFePO4 battery can be designed/built for any capacity and any terminal voltage you require.

Generally a BMS is contained within the battery container, so if your battery container has eight cells, choose an 8-cell BMS. It doesn't matter what the capacity of the individual cells are, only that they are the same.

OK.

Let's take an example to illustrate this.

You want a 200AH 12V (nominal) LiFePO4 battery. Each LiFePO4 cell has a nominal terminal voltage of 3.2V, so connecting four in series would give you 12.8V (nominal). Each cell in the battery must have the same capacity (else one cell in the series string would become fully discharged before the others) so you would buy 4 x 200AH LiFePO4 cells. Note: the capacity rating in AH depends on the voltage, a 200AH cell will provide 200 Amps for one hour at 3.2V (nominal), connect four of these in series and you have a 200AH battery at 12.8V (nominal). Your battery contains four cells so buy a 4-cell BMS.

If you wanted a 400AH 12V (nominal) LiFePO4 battery you would connect 8 x 200AH LiFePO4 cells in a 4S2P configuration (two series strings of 4 cells in parallel) and use an 8-cell BMS.

If you wanted a 200AH 24V (nominal) LiFePO4 battery you would connect 8 x 200AH LiFePO4 cells is a 8S configuration (one series string of 8 cells) and use an 8-cell BMS.

Clear as mud?

forgot to mention "Cells" not batteries above - looking at the aluminum (blue) cells on Aliexpress -
So i need a BMS of 8s - if i'm running the 400 ah example above
Or a 4s BMS with only 4 "cells" at 200ah each..
:)
Thanks!
 
What voltage do you plan to use? 12-24-48 volts? 12 volts = 4s bms ( 4 cells ) / 24 volts = 8s bms ( 8 cells ) / 48 volts= 16s bms ( 16 cells ).
 
Since i have a system im adding too I'm thinking its better to stick with 12 volts...
However, reading more - i see it's not suggested to tie more than 6 Lipo4 batteries together in parallel...?
Considering weight, battery area, and its outside (will build a custom HDPE box to hold them/sealed as i'm in FL not up north) maybe i do 200 ah batteries/cells..
 
OK, you are suffering from a bit of what I call alphabet soup confusions which happens to many.... the jargon get's folks mixed up.
Cells are rated for their AMP HOUR capacity, which is different than the Amps they put out.
A 280AH cell for example has exactly that, 280 Amp Hours @ 3.6 Volts, when assembled into a 12V pack (4 cells), that pack or battery is considered as 12VDC / 280AH.
Most LFP cells are capable of a 1C discharge rate. If using the 280AH example, that means max 280A out. If .5C rate discharge that means 140A out.

When looking at a BMS, they are rated for the amount of amperage they can handle. So a 4S/100A BMS will handle a maximum of 100A @ X voltage, be it 12,24 or higher. The BMS' that do not use external relays, use FETS for internal handling of the power, FETS work well but are not tolerant of working beyond spec. So if you know you will be pulling 100A on a regular basis but may have a surge that could double it, you best to go with a 200A BMS. If you stick to a 100A BMS (FET based) and all of a sudden have a demand of 120 / 130 amps, the BMS will more than fail / burn out.

Common-Port means it uses the same wiring to charge & discharge the battery pack.
Separate Port means there is a separate wire for discharging and another or charging, each can be separately disconnected by the BMS as needed.

The load you are going to pull, including Inverter, Devices/appliances have to be figured into to determine the amperage potential to select the proper BMS. 1000W @ 12V = 83A. 1500W @ 12V = 125A

You can parallel Packs to make a larger battery bank. Each pack is a separate & independent entity managed by it's own BMS. If properly wired in a parallel bus method, you will get the most balanced charge & discharge to/from the bank of packs and there really is no limit like there was with Lead Acid batteries. Have a look at pages 9-12 especially in this excellent document by Victron: https://www.victronenergy.com/upload/documents/Wiring-Unlimited-EN.pdf

Some gotcha's that may seem wise but aren't. It sort of falls into Penny Wise, Dollar foolish thinking.
There are LFP cells from 10AH to 1000AH available on the market, of course the price climbs as the size/capacity does naturally. YES there are 1000AH cells and they are crazy pricey and not that common !

There are different ways to build packs, most suitable is to have each cell managed and preferably balanced by the BMS because that offers the most management possible. Another method is to parallel cells in packs to double the pack capacity, so instead of using 4 100AH cells to make 12V/100AH pack, you use 8 100AH Cells to make a 12V/200AH pack. The parallel pack in essence "ghosts" the cells and your not getting the best management possible and there is potential for problems going unnoticed till it's too late. The "proper" way would be to use 4x 200AH cells to make a 12v/200AH pack, or 4x 400AH cells to make 12V/400AH.

The economy factor (dollar foolish part)
Doubling cells and losing 1/2 the managing capability is foolish and a false economy on saving on BMS cost (it's not that big to pinch pennies).
Often times buying 8 100AH cells to build two 12V/100AH packs ea with 4S BMS will actually cost more than just buying 4x200AH cells and one BMS. Remember there is a Shipping Cost and it's NOT CHEAP as LFP cells are heavy and it adds on top of the cell cost ! When you crunch the numbers up and compare it as cost per Amp Hour including shipping & handling plus BMS, it becomes more obvious.

At present the XUBA 280AH cells made by EVE seem to be the best price point but sales & specials come up regularly. Many of us here have bought these over the past couple of months and folks are testing & beating on them and using them, I have 16 arriving on Wednesday. See link in my signature for XUBA deal for a long thread on these as well there is a link to another long running detailed thread on them in there too.

!!! CHARGING !!!
Please be aware, the bigger the battery bank in Amp Hours the more Amperage will be needed to charge the batteries. At a charge rate of 0.5C on a 100AH pack, means 50A, a charge rate of 1C is 100A. You cannot exceed the cells limits and those vary by brand & size/capacity of cell. So however you intend to charge the batteries, you have to ensure you have enough amperage to do the job. So the Solar Charge Controller (SCC) needs to be sized accordingly and supplied with enough panel to be able to deliver that amount of amperage. An AC Charger if used, running from your AC power source also has to have enough amperage to do the job. Many Inverter/ Charger units are designed to be able to charge their attached battery banks based on their design / wattage ratings. These vary quite a bit when looking at product lines and quality / tier level.

** Some folks have built massive LFP packs 500AH+ and then think that a small 12V/30A SCC with a pair of 12V 100W panels will do the job.... NOT ! It would take forever to "trickle" charge because that will never even get 30A charge from the SCC going out. This is surprisingly quite common (hence a PLAN is a MUST before buying anything) with new to solar people. Also NEVER EVER make assumptions, 99% of the time that ends up making an ass out of oneself. Everything has to work together in cooperation to achieve the goals you have. Properly sizing a battery bank to meet your needs and wants, having enough charging capability to recharge your battery bank and to maintain it in good health a all times.

Hope that helps,
good luck.
Steve
 
Some folks have built massive LFP packs 500AH+ and then think that a small 12V/30A SCC with a pair of 12V 100W panels will do the job

I think the issue is that many people start with solar panels, and then decide on a battery. This is the wrong way around - one should start with the battery choice and then design the rest of the system around that. The size of the battery gets decided by the amount of autonomy you need. Naturally, design it all first before buying anything.
 
Most newbies goes for Common port ... If you do go for SEPARATE port LOOK at the CHARGE RATE to your battery ... There will normally be 2 numbers -- discharge and charge printed on the BMS ...

SO for for Separate Port BMS's you may see it listed as a 40A BMS but it can only do 10A charge to your BATTERIES .. maybe 20 or 40 .. it all depends on the BMS ... so before you get a SEPARATE PORT one CHECK closely the CHARGE RATE ....

That's why i normally recommend common port for newbies ...
 
Since i have a system im adding too I'm thinking its better to stick with 12 volts...
However, reading more - i see it's not suggested to tie more than 6 Lipo4 batteries together in parallel...?
Considering weight, battery area, and its outside (will build a custom HDPE box to hold them/sealed as i'm in FL not up north) maybe i do 200 ah batteries/cells..

LOL - In the last 24 hours I have seen 1 person say more than 2 in parallel is bad .. another 4 ... and now six ... actually as long as you are pushing current through the batteries you will be fine regardless of length ... heck i got some battery strings that look like little trains all hooked up with no issues ... and YES -- you can even mix amp hours (aH) on batteries in parallel ... :cool:
 
@Steve_S, whilst your post is exquisite, I would respectfully challenge your point:
Please be aware, the bigger the battery bank in Amp Hours the more Amperage will be needed to charge the batteries.
I do agree that a larger capacity battery bank can accept a higher rate of charge, but I don't agree that it has to have a higher rate of charge. For example, if one only consumed 1,000Wh per day, but wanted say 10 days' autonomy with a 10,000Wh battery bank, it is perfectly reasonable to have a 200W PV array and charge at 17A ... whilst the bank could accept 833A, it would still be fully charged at the end of the day with just 17A.

Edit: Corrected typo.
 
@Steve_S, whilst your post is exquisite, I would respectfully challenge your point:

I do agree that a larger capacity battery bank can accept a higher rate of charge, but I don't agree that it has to have a higher rate of charge. For example, if one only consumed 1,000Wh per day, but wanted say 10 days' autonomy with a 10,000Wh battery bank, it is perfectly reasonable to have a 200W PV array and charge at 17A ... whilst the bank could accept 833A, it would still be fully charged at the end of the day with just 17A.

Edit: Corrected typo.
Well, yes & no... how much can yo charge on Max Sun Hour Days and how much can you charge on Low Sun Hour Days
My Hi avg is 4.63 hrs a day, in December lo avg is 2.35 hrs per day. That is a factor very few use in the common calculations, one must plan for worst case.... it's why we also have gensets because the sun is not always willing to come out & ply when we want. Also we never see full max output from a solar array in the real world, remember the 20% toss way for real world use on the wattage ratings. Better with a tracker but there is still loss. The point is to put back the amps you take out in a reasonable time and being able to generate enough to do so in a timely fashion, which is the window of available sun hours.
 
Well, yes & no... how much can yo charge on Max Sun Hour Days and how much can you charge on Low Sun Hour Days
My Hi avg is 4.63 hrs a day, in December lo avg is 2.35 hrs per day. That is a factor very few use in the common calculations, one must plan for worst case.... it's why we also have gensets because the sun is not always willing to come out & ply when we want. Also we never see full max output from a solar array in the real world, remember the 20% toss way for real world use on the wattage ratings. Better with a tracker but there is still loss. The point is to put back the amps you take out in a reasonable time and being able to generate enough to do so in a timely fashion, which is the window of available sun hours.

I am still amazed every time you mention how little sun you get ... yet still have such a phenomenal system that produces so much ... here in South Texas we are sort of opposite -- literally all of my remote stations are completely FULL by 1000 in the morning after working full up all night so we don't even remotely deal with the same nuances that you do trying to suck up every ray ... BUT thats why i love to read your stuff ...
 
I am still amazed every time you mention how little sun you get ... yet still have such a phenomenal system that produces so much ... here in South Texas we are sort of opposite -- literally all of my remote stations are completely FULL by 1000 in the morning after working full up all night so we don't even remotely deal with the same nuances that you do trying to suck up every ray ... BUT thats why i love to read your stuff ...
I can summarize that in one way. Type A personality, A Pure Virgo to boot (Sep 5), 3 Eng degrees, Many years in Military & Federal Service and to top it off a Partially Eidetic Memory (Yes it's good BUT it is also a curse), never forget a damned thing, wish I had known that before joining up to the SSF ! (Special Service Forces).
 
I can summarize that in one way. Type A personality, A Pure Virgo to boot (Sep 5), 3 Eng degrees, Many years in Military & Federal Service and to top it off a Partially Eidetic Memory (Yes it's good BUT it is also a curse), never forget a damned thing, wish I had known that before joining up to the SSF ! (Special Service Forces).

HOLY COW -- we have the same birthday .... but i only have 1 EE degree (but thats enough for me - LOL)
 
What voltage do you plan to use? 12-24-48 volts? 12 volts = 4s bms ( 4 cells ) / 24 volts = 8s bms ( 8 cells ) / 48 volts= 16s bms ( 16 cells ).
12v since i have an older system / smaller system but most is being replaced but 2 solar panels on the RV - dont know what they are...
 
OK, you are suffering from a bit of what I call alphabet soup confusions which happens to many.... the jargon get's folks mixed up.
Cells are rated for their AMP HOUR capacity, which is different than the Amps they put out.
A 280AH cell for example has exactly that, 280 Amp Hours @ 3.6 Volts, when assembled into a 12V pack (4 cells), that pack or battery is considered as 12VDC / 280AH.
Most LFP cells are capable of a 1C discharge rate. If using the 280AH example, that means max 280A out. If .5C rate discharge that means 140A out.

When looking at a BMS, they are rated for the amount of amperage they can handle. So a 4S/100A BMS will handle a maximum of 100A @ X voltage, be it 12,24 or higher. The BMS' that do not use external relays, use FETS for internal handling of the power, FETS work well but are not tolerant of working beyond spec. So if you know you will be pulling 100A on a regular basis but may have a surge that could double it, you best to go with a 200A BMS. If you stick to a 100A BMS (FET based) and all of a sudden have a demand of 120 / 130 amps, the BMS will more than fail / burn out.

Common-Port means it uses the same wiring to charge & discharge the battery pack.
Separate Port means there is a separate wire for discharging and another or charging, each can be separately disconnected by the BMS as needed.

The load you are going to pull, including Inverter, Devices/appliances have to be figured into to determine the amperage potential to select the proper BMS. 1000W @ 12V = 83A. 1500W @ 12V = 125A

You can parallel Packs to make a larger battery bank. Each pack is a separate & independent entity managed by it's own BMS. If properly wired in a parallel bus method, you will get the most balanced charge & discharge to/from the bank of packs and there really is no limit like there was with Lead Acid batteries. Have a look at pages 9-12 especially in this excellent document by Victron: https://www.victronenergy.com/upload/documents/Wiring-Unlimited-EN.pdf

Some gotcha's that may seem wise but aren't. It sort of falls into Penny Wise, Dollar foolish thinking.
There are LFP cells from 10AH to 1000AH available on the market, of course the price climbs as the size/capacity does naturally. YES there are 1000AH cells and they are crazy pricey and not that common !

There are different ways to build packs, most suitable is to have each cell managed and preferably balanced by the BMS because that offers the most management possible. Another method is to parallel cells in packs to double the pack capacity, so instead of using 4 100AH cells to make 12V/100AH pack, you use 8 100AH Cells to make a 12V/200AH pack. The parallel pack in essence "ghosts" the cells and your not getting the best management possible and there is potential for problems going unnoticed till it's too late. The "proper" way would be to use 4x 200AH cells to make a 12v/200AH pack, or 4x 400AH cells to make 12V/400AH.

The economy factor (dollar foolish part)
Doubling cells and losing 1/2 the managing capability is foolish and a false economy on saving on BMS cost (it's not that big to pinch pennies).
Often times buying 8 100AH cells to build two 12V/100AH packs ea with 4S BMS will actually cost more than just buying 4x200AH cells and one BMS. Remember there is a Shipping Cost and it's NOT CHEAP as LFP cells are heavy and it adds on top of the cell cost ! When you crunch the numbers up and compare it as cost per Amp Hour including shipping & handling plus BMS, it becomes more obvious.

At present the XUBA 280AH cells made by EVE seem to be the best price point but sales & specials come up regularly. Many of us here have bought these over the past couple of months and folks are testing & beating on them and using them, I have 16 arriving on Wednesday. See link in my signature for XUBA deal for a long thread on these as well there is a link to another long running detailed thread on them in there too.

!!! CHARGING !!!
Please be aware, the bigger the battery bank in Amp Hours the more Amperage will be needed to charge the batteries. At a charge rate of 0.5C on a 100AH pack, means 50A, a charge rate of 1C is 100A. You cannot exceed the cells limits and those vary by brand & size/capacity of cell. So however you intend to charge the batteries, you have to ensure you have enough amperage to do the job. So the Solar Charge Controller (SCC) needs to be sized accordingly and supplied with enough panel to be able to deliver that amount of amperage. An AC Charger if used, running from your AC power source also has to have enough amperage to do the job. Many Inverter/ Charger units are designed to be able to charge their attached battery banks based on their design / wattage ratings. These vary quite a bit when looking at product lines and quality / tier level.

** Some folks have built massive LFP packs 500AH+ and then think that a small 12V/30A SCC with a pair of 12V 100W panels will do the job.... NOT ! It would take forever to "trickle" charge because that will never even get 30A charge from the SCC going out. This is surprisingly quite common (hence a PLAN is a MUST before buying anything) with new to solar people. Also NEVER EVER make assumptions, 99% of the time that ends up making an ass out of oneself. Everything has to work together in cooperation to achieve the goals you have. Properly sizing a battery bank to meet your needs and wants, having enough charging capability to recharge your battery bank and to maintain it in good health a all times.

Hope that helps,
good luck.
Steve
Hello,
Thank you for the great information included in your response.
Sincerely,
Scott
 
Wow, looks like I may have tripped over my own ignorance, ya'll should feel free to let me have it. Hope it's cool to ask some ignorant questions, because it looks like ya'll know much better:

So I'm poor and searching for reasonably priced portable battery power to handle lights, music, and a trolling motor on a tiny 10’ inflatable boat I carry on my motorcycle.

I already travel about as heavy as I safely can, so lead didn't seem like the answer. Google led me to China, so I purchased 8 100ah cells in hopes of building a 200 ah battery. The seller offered to throw in a "bms", which he said I'll need, so I pulled the trigger. The 8 batteries look like what I ordered, and include the "jumpers" to connect them... but the bms is tiny, has 5 colored wires to plug in, and that seems pretty odd to me. After trying to read up on what to do with it, I arrived here, and now I'm not even sure how to link the 8 batteries, let alone the bms. Any and all help would be greatly appreciated. Attaching picture of what I received... hopefully. (Not very good with my crappy phone either.)
 

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Download this resource: https://diysolarforum.com/resources/luyuan-tech-basic-lifepo4-guide.151/

That will explain assembly and more.

The BMS's vary depending on manufacturer & type of BMS. The wiring is simple enough, the black is (-) and the rest are the battery sense leads, each one goes onto the appropriate (+) side of each cell. Ring Terminals have to be installed onto the Harness and then attached to the battery BEFORE plugging the harness into the BMS. WARNING, One tiny BooBoo and the BMS goes POOF, it is very sensitive electronics and no margin for error. Best to review the Manual for that specific BMS.
 
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