using multiple 4s/12v BMS in series for 48V battery

sparklehunt

New Member
QUESTION: Anyone know/try if the ubiquitous 4s/12v BMS (from JiaBaiDa brand, xiaoxiang, china mfg, etc) can handle being placed (4x) SERIES to 48V battery bank?

MORE INFO:
I would be using (3x) VICTRON BATTERY BALANCER ($65 ea) to go in between each pair of 12V batteries I make.

+ lead ---- 12V batt w/ 4s BMS --victron-- 12V batt w/ 4s BMS --victron-- 12V batt w/ 4s BMS --victron-- 12V batt w/ 4s BMS ---- minus lead

POSTULATION: it works

POTENTIAL ISSUE: when any bms DISCONNECT triggers (last failsafe, the charger and loads will have limits configured within the BMS limits), it would see a full VOLTAGE of 48V across it's mosfet/whatever method of disconnecting it utilizes (by the way is this really true? does the voltage travel through the load when the current stops). Please note this is similar to putting all-in-one/drop-in 12V packs (like BattleBorn) in series which is COMMONLY done and even suggested by them. Of course they use the BATTERY BALANCER too.

PRIOR / RELATED THREADS

WHY? My THOUGHT PROCESS....
Sourcing good, affordable 16S BMS is hard; either expensive, bad reviews, or OOS/sketch ordering.
Overkill Solar backordered
REC/Orion/Batrium/ $500+ minimum.
Affordable Chargery/Daly/Ant are from China (I get anxious about shipping from China). Chargery has threads about their issues like accurate SoC, etc a couple months ago, not sure if fixed. Daly has threads about smoking when not approaching their limits.

For the 4s bms though, seems WIDELY AVAILABLE and RELIABLE (bigger market perhaps?). Also they are PROGRAMMABLE. Oh and I forgot AFFORDABLE. and many youtube vids prove they function as advertised. For example Battery Hookup says theirs are in medical equipment and COSTS $40 in their package. So I THOUGHT: how can I use this BMS for my purposes. Btw COST wise is 4*$40 (4s bms) + 3*$65 (battery balancer) = $340 vs $500+.

Also this is my FIRST battery bank, it would be ADVANTAGEOUS to be able to RECONFIGURE with 12V and 24V system if I want. Of course I will balance them before reconstructing.

EXTRA QUESTIONS if you are feeling generous
what BMS does Battleborn use? In Will Prowse's teardown, the bms looks very similar. Could it possibly come from same manufacturer?


thank you for your assistance in advance.

edit: updated some links and grammar
 
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MisterSandals

Participation Medalist
when any bms DISCONNECT triggers (last failsafe, the charger and loads will have limits configured within the BMS limits),
When any of the BMSs disconnect, the series is broken and the battery bank voltage is (theoretically) zero.
I think that discharge will be stopped but some BMSs allow charging on LVD.
 

sparklehunt

New Member
You could just use a 48v BMS. The Orion will work fine. It handles cells as pairs.

.
I don't understand 'handling cells as pairs'? I don't know their algorithm exactly but as 16s configured would handles all 16 cells at the same time. I'm not aware of any extra 'pairwise' functions.

Also yes, any of the expensive BMS would work. The point was to figure out if this alternate method would work too.
 

MisterSandals

Participation Medalist
Also this is my FIRST battery bank, it would be ADVANTAGEOUS to be able to RECONFIGURE with 12V and 24V system if I want.
This is a good thought but in reality wouldn't you be heavily invested in a 48V inverter, 48V capable charger(s) though possibly 12V and 24V capable as well, step down converter for low power devices (everybody needs 12V for something, right?).

Taking a step back, have you done an energy audit? What are the results of that and what does your audit suggest as the best size battery for YOUR situation?

I think that getting your system sized to a realistic audit, the first time, will provide the most cost effective system.
 

sparklehunt

New Member
When any of the BMSs disconnect, the series is broken and the battery bank voltage is (theoretically) zero.
I've heard this description before and don't fully agree that the voltage is zero when the path is open circuit. There is still an OC voltage. That's what a DMM does, is measure that open circuit voltage without actually having a load (ideally infinite Z)
I think that discharge will be stopped but some BMSs allow charging on LVD.
Can you specify if you are talking about COMMON PORT or SEPARATE PORT bms? Separate can definitely disable charging and discharging circuits separately. I've heard of some common port ones that can do the same (with diodes inside perhaps). Is this BMS capable of that? No idea. But it doesn't answer my question? Plus I don't believe a good system should expect to operate with BMS disconnects triggering on a normal basis.
 
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sparklehunt

New Member
I have 32 cells, and I'm using the Orion with 16 leads.
What is your config for 32 cells? If 2p16s, then of course the Orion would work. I assume you have the Orion Jr? version 1 or 2?
It's your alternative method, go for it.
I asked the question as a practical matter for $$$ and also for a technical curiosity to crowdsource experienced people's knowledge. Though I do appreciate the advice...I predict most people would do well by your advice to just get the Orion. By the way how much was your system total and where did you buy? I can't seem to get it direct from the mfg.

edit: this convo has no relevance to original question
 
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sparklehunt

New Member
This is a good thought but in reality wouldn't you be heavily invested in a 48V inverter, 48V capable charger(s) though possibly 12V and 24V capable as well, step down converter for low power devices (everybody needs 12V for something, right?).
Very true.
Taking a step back, have you done an energy audit? What are the results of that and what does your audit suggest as the best size battery for YOUR situation?

I think that getting your system sized to a realistic audit, the first time, will provide the most cost effective system.
I don't know what an 'energy audit' is, but I have this. My biggest potential draw would be a 700W AC on for 6hours = 4.2kWh. The voltage (12, 24, 48) I choose will impact the chargers, inverters, electrical connection sizes. However I can achieve this kWh needed with any voltage can't I? Let's say 12V 1280Wh batteries (standard size). I could do 4p1s for 5.12kWh or 1p16s for the same 5.12kWh. I do agree that cost effectiveness is important, but my calculations are telling me there aren't huge differences. Except in a BMS, hence my original question.

Please let me know if I am missing something. I tried to be thorough, but I accept I am noob.
 

MisterSandals

Participation Medalist
My biggest potential draw would be a 700W AC on for 6hours = 4.2kWh.
700W AC is 700W DC plus the 15% (YMMV) loss from conversion. = 824W DC

On a 12.8V system that is 824W / 12.8V = 64A which is very reasonable for wires and breakers.
On a 25.6V system that is 32A. Routine.
On a 51.2V system that is 16A. Childs play.

Usually here the numbers bandied about for when to use which voltage (as i understand):
<2000W-3000W 12.8V battery is fine though ragged over 2000W, requiring huge wires and fuses.
<4000W 25.6V is fine.

So MY thoughts are why you are even considering 51.2V system. Thats just me.
 

sparklehunt

New Member
700W AC is 700W DC plus the 15% (YMMV) loss from conversion. = 824W DC

On a 12.8V system that is 824W / 12.8V = 64A which is very reasonable for wires and breakers.
On a 25.6V system that is 32A. Routine.
On a 51.2V system that is 16A. Childs play.
Thanks for walking me through that! I like those rule of thumbs, very useful. I guess I should go and price out some wire based on a 5% (from Victron) loss goal and see the difference.

I'm sorry I may have misled. My mention of 700W AC was focused on battery capacity.

Focusing on losses in wire I'm thinking of a 3000W inverter (which would only do ~1800W at 60 degree Celsius). Biggest actual appliance would be an 1800W induction cooktop. So should I be doing these wire calcs assuming worst case 3000W?
Next question, should I be going even safer and calculating with surge power (6000W)? My understanding from Wiring Unlimited by Victron is that this 5% rule prolongs the life of components and ensures their reliability, like MTBF (mean time before failure). Protection capacitors shorten their life the more they are thrashed.

Usually here the numbers bandied about for when to use which voltage (as i understand):
<2000W-3000W 12.8V battery is fine though ragged over 2000W, requiring huge wires and fuses.
<4000W 25.6V is fine.
Hmmm I see....I need to run some numbers with some copper wires again with the 5% rule. Suggestions on what type of wire? I'm thinking marine-grade tinned copper. Also where to buy?
So MY thoughts are why you are even considering 51.2V system. Thats just me.
So if we establish from above that more than 12v nominal is better for a 3kW inverter, I have found that 24V seems to be like an ugly middle child in terms of availability? I may not have looked hard enough. The Victron inverters for 120V AC either seem to be for 12V or 48V. Not too much for 24V.

Also, here's a question to you sir, why NOT 48V?

And also do you have any leads as to my original question? Still very curious. And even if we did decide on 24V, I would love to be able to use the 'trick'.
 

MisterSandals

Participation Medalist
I'm sorry I may have misled. My mention of 700W AC was focused on battery capacity.

Focusing on losses in wire I'm thinking of a 3000W inverter (which would only do ~1800W at 60 degree Celsius). Biggest actual appliance would be an 1800W induction cooktop. So should I be doing these wire calcs assuming worst case 3000W?
This is what the energy audit is for. Determine how many watt hours you use per day (we need to make sure we can harvest this much AND recharge from yesterday). And determine your max loads, which are often based on inverter size.
If you have a 3000W inverter and intend on using it at near capacity, the THAT is likely your max load.

So using the guidelines, a 12.8V system is too small. 25.6V seems about the right size to me. Others may chime in and say go as big as possible. When you get over 25.6V, you're dealing with deadly voltages for sure. I'd say if this is your first system, consider the risk reward. If in doubt, start a new thread asking for advice whether 25.6V of 51.2V makes the most sense for YOUR system and YOUR use. Don't forget to mention what your level of expertise and experience is because that matters quite a bit too.

There is an energy audit worksheet in my signature. You will learn a LOT with this simple exercise. Perhaps more while doing the audit than any other step. Its REALLY important... i usually tell folks that solar is not for them if they are not interested or able to do a simple energy audit.
 

sparklehunt

New Member
This is what the energy audit is for. Determine how many watt hours you use per day (we need to make sure we can harvest this much AND recharge from yesterday). And determine your max loads, which are often based on inverter size.
If you have a 3000W inverter and intend on using it at near capacity, the THAT is likely your max load.

So using the guidelines, a 12.8V system is too small. 25.6V seems about the right size to me. Others may chime in and say go as big as possible. When you get over 25.6V, you're dealing with deadly voltages for sure. I'd say if this is your first system, consider the risk reward. If in doubt, start a new thread asking for advice whether 25.6V of 51.2V makes the most sense for YOUR system and YOUR use. Don't forget to mention what your level of expertise and experience is because that matters quite a bit too.

There is an energy audit worksheet in my signature. You will learn a LOT with this simple exercise. Perhaps more while doing the audit than any other step. Its REALLY important... i usually tell folks that solar is not for them if they are not interested or able to do a simple energy audit.
Thank you, will do. We do digress...

Still no progress as to the ORIGINAL question posed. No one else is curious about it? For those who do need a 48v (aka 51.2v) system, I think it is valuable information. Correct me if I'm mistaken.
 

sparklehunt

New Member
I am going to do a little reading. I know this has been asked and likely answered many times. I can't say i paid much attention to many BMS in series.
Hey thanks. I did do PRIOR RESEARCH and link two threads in original post. Here is another one I missed that touches a similar topic. I did not notice any supporting evidence for answers or new considerations in that thread. Also, it does not address the new feature of using battery balancers between the pairs of 12V batteries being series connected to higher total voltages.
 

MisterSandals

Participation Medalist
Lets see if an expert @OverkillSolar has an answer to running 4x 4S BMSs in series.
Hopefully this incantation will summon him or his likeness.

My understanding from comments that I read here is that there aren't any restrictions to running BMSs in series. I think the overall amperage of the individual BMSs needs to be respected but not sure what else would prevent doing it.

How about @BiduleOhm? Any insights?
 

BiduleOhm

Electronics Sorcerer
Running them in parallel isn't a problem but running them in series might fry them if they can't handle that configuration and/or you have to many of them in series because of the higher voltage.

You'll need the technical specs of the BMS to know exactly what you can and can't do with them. But if I had to guess I'd say 4 is far too much, usually they can handle 2 but not more.

My recommendation would be to use a 16S BMS (NB: I didn't read the rest of the thread, but just the last post for now).
 

BiduleOhm

Electronics Sorcerer
POTENTIAL ISSUE: when any bms DISCONNECT triggers (last failsafe, the charger and loads will have limits configured within the BMS limits), it would see a full VOLTAGE of 48V across it's mosfet/whatever method of disconnecting it utilizes (by the way is this really true? does the voltage travel through the load when the current stops).

Yes that's correct. The open BMS will see the full voltage if the others are closed.


When any of the BMSs disconnect, the series is broken and the battery bank voltage is (theoretically) zero.

That's not correct. Current will be 0 but voltage will be 48 V (well actually up to 58 V for standard LFP cells) across the open BMS if any load is connected. The voltage across the load will be 0 tho.


So my new recommendation after reading the rest of thread: given the power level I recommend a 24 V system. 48 V is nice for reducing the current and so the wire sizes, losses, etc... but you're not at a crazy high power level and 24 V will basically have the same advantages while being cheaper and have easier to source devices. A 12 V system would be even easier to make but it would be pushing it of course, hence my 24 V recommendation ;)
 

Tecnodave

Solar Addict
I agree that a 24 volt system is best for your use, Ive been 24 volt off grid for over 20 years now and have found no limitations in that, I am using a MagnaSine MS4024AE 120/240 volt inverter as my larger inverter and run a small household with it including a 2 h.p. 240 volt deep well pump pumping from -350 feet sometimes of the year and a 180 amp Miller mig welder, not at the same time, but normally I use a much smaller Inverter, a Exeltech XP 1100 watt 120 volt inverter , more efficient, and super quiet EMI/RFI, never felt I needed to upgrade to 48 volts, but then again Ive done electricity for my entire career, long since retired. Im super efficient so have no energy hogs except for the water system.
 
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