Parallel Battery Strings - worst solution ever? 

Having that modularity and ability to add/remove capacity or perform series battery set maintenance as needed without taking your entire system down is key. Sounds like you have a great plan and your videos going deep in the weeds on most subjects have taught me a ton. Thank you.

Thank you SO much Andy. You keep answering technical questions i have. Awesome effort dude! Dave from Zimbabwe!

Love your channel Andy!!! I will be starting a channel soon as well! I have 3 strings of 16- 200ah LiFePo4's and 3 JK BMS I am putting together for my 16x7 tiny house on wheels I have a MPP LV 6548 im hooking up to the 27KW bank, its all replacing an AIMS 24v 14KW system I currently have run for nearly 3 years un interrupted! 2 deep freezers and a full electric kitchen with a bunch of big appliances!, Air conditioning, electric heat, 50 inch TV and many fans! all running off 8-260 watt solar panels! we have been all over the south and western US 2 years now without a hiccup!! Lovin it!! Keep up the great work Andy!!!

I like your 2 separate battery approach for a couple of reasons. #1 With 2 BMSes you will double the balancing current. #2 If there is a problem with a cell and the BMS shuts the battery down, you will still have power from the 2nd pack, eliminating a Blackout situation.

I find you sharing very helpful and thought provoking. I have just received 32 310Ah cells from China and am waiting for the lithium battery tester to arrive to check them. After seeing this video it has made me change my mind back and forth between two 1P16S and one 2P16S layouts. As both seem to work and you have opted for the former I will go for the latter and report back if I come across any issues. It will save me having to buy and therefore wait for a second BMS. Keep up the excellent work. We are all learning lots care of your efforts.

Hi Andy, your channel gave me the courage to purchase cells (only 4) for RV installation. I got them,finally, a couple of weeks ago, & now have an operational system. Thanks

Awesome exactly my thoughts on the subject and what I am going to try

I have 16S2P and two sets of 16S1P. Both configurations have pros and cons. Just to note some advantages of the 2p system: - easier to match individual cell capacities (combine the strongest+the weakest, then 2nd strongest and 2nd weakest etc...), this way you can evenly distribute differences in capacities. - You just need one BMS - cons: you need more busbars

Thanks very much for your efforts to explain so much about the different types of arrangements for batteries. I have just bought sixteen batteries and two BMS's to build two 24v banks and parallel them. I am replacing an old set of GM batteries in my boat with LifePO4 batteries I bought on eBay. I am not really very advanced in my understanding of these systems but luckily I have found your channel and have now discovered how to build up my battery. Your vid on programming the Victron controller was also useful as I have a Victron controller on my boat's 1500 watt solar system. I have a very cheap inverter on my system , 24v to 240v 1500 w and am wondering if I would make any significant gains in efficiency by replacing it with a better quality inverter. The original controller was also a cheapy and it frizzed out after about six months which is when I replaced it with the Victron which I love because of the bluetooth connection , the original controller had no bluetooth . So thanks again I will watch a lot more of your vids as they are a great source of knowledge for me.

You have made your decision, great. Just as a side note Pylontech use the parallel string method in there battery systems. Each of the us3000 battery frames I am using is operating at 15S and parallel connections are made at the front of each frame. Each frame has its own BMS, shunt and internal cut off. The only difference is each frame's BMS is connected via an RS485 data cable so BMS data is shared to each frame as well as the MPP inverter charger I am using, so I assume each us3000 frame knows what the parallel frames are doing. I have been toying going your direction but as I have already invested in the Pylontech solution its far easier for me to add a few more Pylontech frames to increase the storage capacity.

Brilliant... Very cogent arguments for either potential setup. It just goes to show, that there is no actual Right or Wrong answer, it's all dependant on the individuals needs and priorities.

I love that you've done the research and have decided to begin doing your own experiment. I'm looking forward to seeing what the results are. I'm betting that it will work perfectly!!!

Following this with great interest. I have recently built my 8s 24 v battery and am also now thinking of doubling in size. Learning a great deal and love the format

Andy, I’ve had 2 1p16s 280ah packs connected in parallel for several months and they stay perfectly balance. They both charge and discharge at the same rate. I’ve turn off one pack for several hours to manual unbalance them and by the next day they are again perfectly balanced . I’m using Daly smart bms and all the cells are balance to within a few millvolts

Both approaches are valid and have positive and negative aspects. Do what you want to do. I went with parallel banks, and each individual bank can handle the full load. No regrets, and easy to increase run time by adding another battery. But don't worry, either one will work well, but since BMSs have a tendency to fail, more redundancy was my choice.

Andy, This is really great information and well presented. I live on a boat - 1850 w array 8X 6 volt 330 AH wet cells 48 volt . When they die I am going to LIP and you are getting me up to speed. Thanks

The one advantage in parallel is if you have some cells that always tend to run a bit high (happy) and another that’s a bit low(sad) you may be able to pair them up so you get a better average. That way the BMS’s balancer doesn’t have to work as hard and you get a better finishing voltage.

👍 thank you! i also stick on separate banks, because a bad bms can not Kick me out of buisness. best wishes from Germany.

061021/1838h PST 🇺🇸 061121/1138 Brisbane. Thank you immensely for discussing such an intelligent subject on paralleling LiFePo4 batteries. There has been no such discussion on YT, or may be some peripherally, skimming on this, very important issue. But no one knew what was being discussed. After downloading the ORION BMS, going through it and listening to your lecture; it became crystal clear as to how to Parallel LiFePo4 batteries, correctly and safely. Imagine 33 batteries being paralleled with its own dedicated BMS! Flabbergasting, indeed, but logical. Thank you for your lecture on this subject, you have opened up and cleared my doubts. Stay safe and 73s…

Good stuff, I think that will work well for you. Although my 24 cells are 6P4S from new and I've never had an issue if i got a new batch I would build a second battery. I've even thought of splitting my pack into smaller packs and buying more BMS's

Thanks Andy, very well explained - looking forward for your upcoming battery V2.0. Cheers

Thanks

Thank you for using my comment in this video. I don't remember what BMS manufacturer said it, but they said I could not parallel BMS units. Maybe another topic.

This was simply an excellent analytical discussion, I applaud your thinking. Also kudos to your many followers on your channel, it seems you have a very sophisticated, intelligent following. Need to send you a few beers, I often join you when studying you videos.

I agree on your logic of paralleling strings. It's pretty much what people have been doing with car batteries !! They can't access each cell, and so they parallel 2 strings ! Great videos .

A further advantage to smaller paralleled strings vs. one huge paralleled cell bank: Physically moving them. Say I have a bunch of whatever cells, I can move them from one application to another if they're paralleled each with own BMS. JBD bms with UART is a good choice for this. I have a front and rear paralleled 10s packs from Leaf modules, in a 1970's GE Electrak garden tractor. A lesson I've proved from the tractor: keep the main +- cables identical lengths. I did not with with layout of the tractor and I do see eddy currents, a couple of amps? for some 15 min? after charging and discharging, since one bank has less cable resistance (I might redo it to improve). I plan to do 4 paralleled 14s (7 modules) for a house battery bank, and these will also be able to be moved to an RV as needed. Downsides are extra complexity of multiple bms's and disconnects (all smaller and cheaper though), but the flexibility and redundancy I think could be worth it.

Another consideration: many of these "discussions" revolve around cylindrical cells... Like 18650s with a limited capacity (in comparison to these big 280Ah cells) and thus limited charge/discharge rates. If you have 3p 280Ah cells, where will you find a BMS capable of 900+ amps charge/discharge? How many solar charge controllers can pump 200+ amps into your battery (0.25c)? Once you move away from small cylindrical cells, it just makes sense to build 1p banks with discrete BMS boards per bank. I don't know that you could even find a BMS capable of matching a 2p, 3p, 4p.... pack with such huge capacities. Of course, if you're building a pack from 3400mAh cells, can you imagine the number of BMS boards you'd need to power a house if you used 1p banks? Phew! Economics is the real deciding factor in both scenarios. Either method works.

That is super interesting that you’re going this route. I will be watching for your results :)

Deseando ver el final. Gracias por tus enseñanzas

Sir can you explain me the searis connected lithium phosphate battery is imbalance cells how can we balance it ?

Hey Andy, please number your videos, so it is easier to find the previous video you often mention. Thanks for the great show, and manny amps to you!

This is also how the software industry evolved from single large systems to multiple instances/containers running in parallel. I think this parallel string idea is for sure the right way to go in the future as it makes things much more modularized (easier to service and adding or reducing cells) and as long as the BMS is cheaper then it will be perfect. For now I think the BMS world hasn't evolved in to this modularized mind set yet, because what they could make is there is a simple/cheaper submodule (voltage current sensor + relay) for each string then have a central management unit that can wire multiple sub modules. Maybe the demand of personal home/RV battery system never has the need to frequently changing capacity or servicing cells so perhaps there is no market pressure on to this "distributed" architecture so it might never hit the market 😁

This topic is very interesting, i have the same question in mind. How to parallel. I'm in proces of building a small house for vacation, and i will start with a 48V 100Ah batery pack, but in time i will grow up the capacity and numbers op solar panels. Waiting for next results. You're doing great jov, thanks for this channel. Sorry for bad English I'm from România

Nice video, one minor critique on your comments around 5:30. You are correct in that there won't be much current going between the banks if the voltages are similar and the banks are just connected to each other. And you are correct in that the voltage of a bank with a higher SOC will want to rise more quickly than one with a lower SOC while charging. But current will still not flow from the higher SOC bank to the lower one while charging is still active. That isn't where the problem is. The bank with the lower SOC will receive most of the current from the charger simply because the bank with the higher SOC will have lower current acceptance (it takes a higher voltage to make it accept more current, but since the banks are tied together it can't get that higher voltage). The problem occurs when the charger turns off or the change rate changes. That is when you will start getting currents going from one bank to the other. There is an easy way to describe this (it also describes the micro current cycling you talk about later). Lets say you have two banks with mismatched SOCs. What will happen when you charge the banks up is that the charger will eventually manage to push the voltage up, but then when the charger turns off or the charge rate changes significantly, the settling rate for the two banks will be different and will cause current to flow from one bank to the other as they settle down. Similarly, if discharging the ganged banks with a load, and your load then turns off (or changes significantly), the cells in both banks will 'recover' some voltage... but if the banks are mismatched, they will recover at different rates and again will push some current from bank to another. And this happens EVEN IF the banks are fairly well matched. Thus you wind up with micro-cycling between the banks. -- Also, if you didn't see it... with the number of strings you have, blocking diodes are now MANDATORY. They are not optional any more. You absolutely need them for safety and shouldn't depend on your circuit breakers and fuses for that function. Long-term reverse voltage stress on the panels is just not good for them. Even though a solar cell is basically a diode, it is one designed to generate electricity and not designed to have good reverse-breakdown-voltage characteristics. Also the voltages coming off of the panels are fairly high and an inductive spike can spike the voltage high enough to hit the break-down voltage of the panel cells, causing a fire in a short-circuit situation. While unlikely, it is even possible for the inductance to cause the voltage spike high enough to arc the breaker and/or fuse, turn into plasma, and not break the connection. Hence why blocking diodes are now mandatory. -Matt

Perhaps the best "Andy" solution is to just have a shunt on each battery in addition to the system-wide shunt you have out in front of the busbars. You could even wire the shunts into a battery monitor display with the polarities reversed so it acts more like a "tachometer" for the battery banks, telling you which direction the flow of energy is biased. Even better would be having the pi or an arduino independently monitoring the shunts and recording data and packaging it up for VRM to consume. Thank you so much for your videos. I love the way that you present the information, and the topic is something that I'm very much into. Cheers!

Boat builders use parallel strings (see Mastervolt, Victron). Best to split the DC bus into load and charge. Overloading switches off the charge bus, but your load will continue. Undervoltage will switch off the load DC bus, but keeps the charging up/connected. If you use parallel strings, split DC bus probably makes not much sense (as one of more other strings are always connected, when only one string disconnects).

Mal wieder sehr informativ! Danke!

Nice Story to Come, thanks for letting us join the adventure.

Good job as always 🙏🏾👏🏾🇬🇧🇯🇲

Hi, can you still charge the battery to full cap. & how long would it take?

Another great video Andy thank you

I connected 26 14s10p (18650 cells) packs in parallel. No problems with that. Each pack has its own BMS and active balancer.

I'm running a 3 x 1P18S system, with one Batrium BMS (blockmon). It sure makes for some nice graphs but I concluded this week that I will need active balancers on each of the strings to help out on the higher and lower end of the charge cycle. It Has more to do with the used cells the alibaba rip off has send me then the setup itself. Im looking forward on your experience with the cheap balancers while charging, mine are still in the mail :)

Thank you. I am looking at 8 (500ah 3.2v) cells making a 1000ah 12v bank but could not find a bms to fit a single bank, so I was going to make two banks of 500ah with 2 bms's and connect them to a common busbar. I was not sure if I should fit 2 shunts before making the connection to the busbar. The reason for the set up is infrequent charging and drawing higher loads over short periods (230a for 3 minutes) as well as a small load continuous. The only thing I was definately advised to do was make all the leads before the common connection to the busbar identical lengths. I look forward to your next video, theory is fine, but practical is better.!

What could go wrong, I like it

I have a 500w 12v wind turbine... marsrock mppt hybrid controller 1500w wind and 1500w solar. This mppt controller came with a battery balancer but it seems to only be used for 24v application (series wiring). Can having a 12v battery wired in parallel effect the mppt controller?

I'm running 6 byd battery strings in paralell each has its own bms no problems . really no other way to do it when you connect premade batterys.

Congrats with the 10000 subscribers. As an afterthought on your video about parallel batteries I thought of the following. On my boat I have a LiFePo bat. Parallel to a LA battery. To avoid current flowing between the batteries I installs two blocking diodes between the batteries. One at each batterie. At least this avoids current flowing from ones batterie to the other. Best regards, Tom

I had a 4s4p and had a problem and 8 cells died together and 8 cells lived to be used another day. Now I have a 5s4p pack, higher voltage, higher energy, same peak current (1300A) and it should survive as it won't be overcharged at the voltage the first try was experiencing (18.2V). I had a full-time capacitor balance board, and no bms, no fuses, hard to fuse for over 1000A anyway :-D Aside from the over charging, the balance board got salty and wet and failed or possibly got cooked by the overly high voltage, and that's what lead to two banks staying at an acceptable voltage and 2 banks being absolutely fried/boiled to death :-D So from that extreme torture test, I would conclude that the paralleled cells do indeed walk in step and fight in unison and die side by side, or live together through strength in numbers. Having said all of that, My other comment stands, I'll seriously consider having 4 independent banks, however I can't think of a valid use case beyond a 2-way split, so there's that.

I have run the 280ah 16s 2 strings in parallel using the daly bms. I would be curious if the JK bms can also work in parallel mode

Same as parallel drop in style lithium batteries (e.g. battleborn). Each has built in BMS.

I think it is very unfortunate that all of the engineering advice of the problems, complexities, and dangers of paralleling strings provided by the ORION BMS writeup, was "thrown out the window" because of some anecdotal evidence of success with parallel strings. A single or even multiple examples of success with parallel strings simply does not negate sound engineering warning of that practice.

Lithium batteries have a bms built in--.is it a problem paralleling two or three batteries with a bms in each.

Glad you found the right solution for your system. If you are curious about the stray charging currents between the individual banks, just have two shunts, one per bank and that way it's easy to monitor. This will satisfying your thirst for knowledge And Beer lol.

Andy, I already have a double battery setup as you describe and I have split the charge controllers between the batteries, so there is little current flow between the batteries or you are using up their cycle life just moving power back and forth between them. Keep up the good work. Love your channel.

i have similar build requirements for a go cart. as proper weight distribution is needed i seek a setup that will allow the use of multiple individually bms protected 16s3p packs in parallel going to a fused buss bar and then controller. i fear that when charging or discharging if one pack disconnects due to a voltage fault then the rest of the packs will operate and become out of balance from the pack thats disconnected. my fear is that the bms may at some point will clear the flault when im unaware of it, reconnect parallel and experience extreme balancing currents. i feel as though i need a bms that can communicate with the others to prevent this? please what is your opinion?

All parallel banks could be at different voltages but as long as each series string has its own bms the bms’s will limit the current to safe levels in both charging and discharging between each bank.

I'm getting ready to build a 2P16S using 280Ah LifePo4 cells. I will use a 100Amp BMS (all from battery hookup). This will replace a DIY 18Kwh pack (48v) that I made from 18650 cells a couple years back. I figure that if I was able to run 120 cels (LiPo 18650 = 120P14S) in parallel for 2.5 years without ANY issues at all, then a 2P configuration using LifePo4 should have no issues at all.

Consider creating a dual of your entire system down to the inverter. Hopefully your inverter can take a synch input so that the inverters can be paralleled to the load. That way you never have to worry about taking one down for maintenance - you just might have to shed some loads. In fact you might want to routinely take them off line in low demand periods to balance the individual strings.

👍 great Andy, I think you are right, parallelling cells will never reveal bad cells. If you look at your fellow aussie HBPowerwall he is using al lot of parallel cells and now and then needs to dig into issues with them (thermal camera, fuses etc). So a parallel crate with BMS will cover that, and your power will not easilly switch off while the cells are massive, small cells will be overloaded much easier, the 280Ah is huge. If you use the right fuse and size of wire it will be a good solution and never forget a maintanable one. So good thinking Andy and thanks again for sharing. I was wrong with the huge Amperes which flow when parallel the cells as also the BMS will monitor the progress and will kill the connection when something goes wrong. Also paralleling cells will give you 3.2V with ~600A in 1C, that's huge when you make mistakes, that will easier burn than a closed box in series. Have fun building the new one!

I’m looking forward to seeing the results of parallel batteries. I haven’t seen this topic covered by other RU-vidrs. I plan to do the same using (8) 280 ah EVE cells and (2) BMSs to create (2) 280 ah 12v batteries down the road for an RV build.

I have a question: I have two battery packs. Each pack is 48volts 16s 272ah. I want to connect both banks in parallel using two 200 amp Daly BMS with parallel modules on both.

Hi, what is the best way to connect 5 or 6 gel batteries of 100AH for a 12v system? They do not give me warranties if I connect them in paralel... Thanks!

Orion's claims are misleading. If parallel anything you always will have balancing between them. Between 2 cells (in 1 pack) or between 2 packs. But with 2 packs you monitor all cells and with 1 pack you monitor only the two cells average. Also you can buy cheap Renogy shunt with display to monitor each pack's power consumption (no need to buy an expensive Victron). I always tell people to test the 20-80% and 30-70% balance of 2 cells and measure the current flowing. Because of the flat discharge curve only minimal. So if you put 2 cells parallel it will take a long time for them to balance out. Luckily you use lower charging V, so you will not float one pack full when the other is still charging. This helps balance out the 2 packs easily. Only one thing you have to pay attention and that is the current. If 2 packs online you have 2C charging and discharging rate. If one stops (like BMS stops it) then you have to get it lower to 1C max. Or you use only 1C and there is no problem :)

I have a 14s144p, and you don't need one BMS per 1p. You figure out how much you need based on how much difference you have between the 1s and the maximum charge rate. If you don't have enough and see the cells are not balancing fast enough, then you just throw on one more BMS parallel to the existing BMSs.

Andy, I think you have made the right decision to build two separate banks with their own separate BMS and fusing protection before paralleling them. If you parallel the cells first, then you are creating a battery with a humongous amount of short circuit current potential which makes it very difficult to provide adequate fault interrupting capability. The individual 280ah cells are already capable of producing very high amounts of short circuit current. Paralleling the individual cells makes it even worse. If you parallel the individual cells you had better use at least Class T fuses with high interrupting capability to protect the bank from a catastrophic fault. In my opinion, fault current interrupting ratings of protective devices is a subject that seems to be overlooked or ignored in most DIY battery builds that I've seen on the internet and it is a serious safety consideration that needs to be addressed. All too often, I've seen cheap fuses or circuit breakers used to protect these lithium battery banks. There can be serious consequences with these batteries if the catastrophic protection devices are not capable of breaking the maximum fault current available when called upon.

How would two banks of different capacities behave? I have 4 202ah and 4 85ah lifepo4 cells on their way, each with their own bms (intended for different purposes). But could they theoretically be banked together? Are there any tests you can show with your 100ah cell with the 280ah to show why it would or would not work?

062021/0422h PST 🇺🇸 062021/2122h Brisbane 🇦🇺 Addendum to my below comments. I went through the OrionBMS supplement on paralleling LiFePo4 batteries. The more I read, the more I get confused. Then again your comments, contradicting the Orion statements. Now, I’m like, should I stick to “Classic” paralleling of 8 Prismatic cells? Or should I wait for your test results in few weeks? I’d rather wait for it. My simple question is why the publicity from Orion about the “dangers” of Paralleling the cells? Orion also emphasize the use of a Qualified EE to perform paralleling the cells. I incorporate every safety measures, redundant safety measures even, like CBs, ANL fuse blocks and switches (on single 4S my system) Paralleling the same configuration with similar safety measures, will cause safety issues? I’m flabbergasted. I ask, (Orion) why such fuss? The Battery assembler from Nevada 🇺🇸 has JBD BMS built-into their batteries and has no objection to paralleling them. A family in Idaho 🇺🇸 has installed 8 of those batteries in 24V configuration in parallel and running with no issues for over a year. I think, your approach to seek the truth about paralleling is much appreciated and is looking forward to the results. Please let’s know. 73s…

your the man, cant wait😎😎😎

Andy, since you go trough that path, is it possible to measure the energy swap between the packs along the day? the idea is to have a graph/map of internal exchanges and calculate the losses (if possible). Perhaps it will give you one or two fantastic videos... Thank you again for all the remote experience and explanations you provide.

How do I get ahold of you? I went to your website, and tried finding an email or something? Had some cool stuff to share with you I know you’d love!

I hope to see more videos, they are always good, even without the pyrotechnics ... hahaha. More SPAT parts. Thx for the fun.

I was just downloaded and read that Orion BMS - Strings, Parallel Cells, and Parallel Strings, particularly pg 15 "Parallel strings with 1 charger per string and single discharge DC bus." As I'm sitting here I got to thinking what if you had 2x discrete off grid systems instead since if you had say 800ah in 2x strings you probably need 2x 4000w inverters paralleled? Why not have 2x discrete systems each with their own solar panels, charger, inverters, BMS, and inverter? The cost will undoubtedly be more but only one extra charger, more wiring and higher installation time/cost is needed. Thing is I don't know much about off grid but I will because I'm building an off grid house soon on my 52ac bush block that has no power. What I don't know is if 2x inverters can combine synchronized AC output but since many 48v inverters are designed to be paralleled maybe they can - maybe they can't, I dunno? Even if they can't, then you could wire the house with two independent systems. One for the lights, one for the power points (or however you want to divide it). Generator autostart may need a diode or possible just 2x relays to isolate the start inputs but that seems comparatively simple to do.

Wisdom ! Thank you 😏 !

As always with high energy, if it goes sideways....it will do so spectacularly.

Ahahah Good executive call. 👍 That's the way mate! And a correct and possible one also. Already seen three LFP battery banks in parallel each one with individual BMS, and no worries. Even saw Battery banks of LFPs being paralleled with different chemistry NCAs and working like a charm for years now... So... Go for it! 1p 16s and don't forget 1b..(one beer) 🍺🐸

where do you get your circuit breakers?

I don't mean to be the nervous Nancy here but looking at that table with those cells on it makes me think of the dog coming in and bumping against the table, those cells are going to hit the floor. 🤔🤨🧐

Andy, I don't want to waste your time, but I have a technical question, like everyone. In this very useful video you connect the 2 battery banks in parallel. How many Amp's you can use in total? Is it like BMS 1 + BMS 2 = total please? Regards. Willy

Hola , saludos desde Panamá, siempre me pregunte porque UD no armó un sola batería grande e vez de 3 pequeñas ya que UD tiene un Tesla y este solo tiene una gran batería hecha de muchas baterías en paralelo-serie y no pasa nada .

I have one 4p16s for each breaker panel but would like to have two 4p16s on the breaker with the higher loads.

Here in the U.S we have available a number of "drop in", 12-volt-nominal LiFeP04 batteries which are designed to replace lead acid batteries, primarily in mobile applications (RVs of various flavors, boats, etc.). Battleborn is probably the most well known of these. The individual drop-in batteries vary in construction and type of cells but are always internally in some form of series string to get the 12 volt nominal voltage (there are also 24-volt "drop-ins"). The "drop-ins" also always have an internal BMS (if they don't have an internal BMS they can't really be considered "drop-in"). When more than one of these batteries are used in an installation (which is usually, based on my observations) these batteries are paralleled (which, when using a battery with internal prismatic cells, exactly duplicates the setup described in the video, albeit at 12v) and, sometimes, put in series strings and then paralleled. E.g., in my caravan (travel trailer in U.S.-dialect) I have six 105Ah, 12-volt-nominal batteries (each with 4 prismatic cells internally). The six batteries are arranged in 3 series strings which are paralleled for a 315Ah, 24-volt-nominal bank. These sorts of installations have been going on in the U.S. for several years and I've yet to see any real complaints nor have I observed more than the usual number of smoking holes in the roads around here :-)

if the inrush current is too high , the BMS will cut or the breaker will trip

I put 4× 80 amp diodes on each battery and supply them from there own mppt charger , no circulating currents

Hi Andy, I have not built anything yet, but I would go for multiple strings of 1p16s, its more scalable! Anyways its a pleasure watching your videos and learning things. Should I say things or stuff?

In before the hate messages, please try it and get a good sense of the paralleled current transfer. I have found that my 1p6s batteries paralleled to 9 strings passes significant amounts of current at times. As you said, it is the top and bottom end that matters. Every battery passing current to the one low string can hit 6-7 amps on a battery that is otherwise passing near no current as it tries to keep the voltages up or opposite when it is trying to keep the voltages down. To do it again I would group the batteries by resistance and match high resistance batteries one per parallel string to do 9p6s. You need a lot of shunts. :-) Thank you for what you do. There is probably no perfect solution.

what about integrating an arduino to read the strings voltages. if the voltage difference between the strings is higher than a defined value, trigger a relay to cut off the string or send you a notification.

Hello very informative I want an suggetion I have bank of two batteries 24 v 300 amp made in series. Can I take 12 volt from one bettery for my other solor power controller

I have a Victron SmartShunt is it suppose to draw 41 watt continuous?

I've worked with dual parallel batteries my entire life. One isolated one night while the other gets consumed, and the opposite the next night. That way there's always at least 50% available the next morning in the worst case scenario. That exact system is in need of a LiFePO4 upgrade and I've been planning it for a while. However depending on which cell sizes are available when the time comes to order, I was thinking of ordering 16 cells instead of 8 for 2 banks. I guess that's still on my mind, but now I'm thinking about 4 banks instead of 2 :-)

Andy i love the way you tell us whats going on,,,, I am going to buy cells for my motorhome so is it best 12v , 24v , 48v , as i live full time in the van so want a good system, I am in the uk ,,,

to be safe you can set a little voltmeter module on each battery bank to be sure you connect battery with equal voltage.

where is part 2 ?

the problem is with more cells in parallel the more hassle the bms will have keeping the cells balanced now while they new i doubt this is much of a problem but as the cells start to age i think they will need to be balanced more often with only a low dump load capacity to discharge the other voltage bank it will struggle to bring that bank down to that of the others

What do you think - my inverter is 48v so my battery bank is 3.2v individualized batteries are 280A need 15 pcs 48 divided by 3.2v I’m sure you know I’ve got 13 batteries at 280A what’s you’re thoughts on using 3.2v but 200A putting 2 of the 3.2v 200A in series still 3.2v but 400A twice because I’m short 2 batteries and would you put the 2 3.2v 400A batteries on the main positive & negative or in the middle of the 48v bank ? I will post when I do & I’m creating a wheeled crate battery bank , inverter alternator charging to be self-sufficient & looking into solar ! Thank you for all you’re work in helping others ! 😉

I'd be curious to see if the capacity is affected in any way. Maybe you could run 5 or so charge and discharge cycles and then do a combined capacity check with atleast 0.5C to see if it you get the expected combined capacity.

I agree with your decision to run multiple BMS's... I am running 5 BMS's. Also, I would suggest stripping the insulation from the BMS wires after moving them on top of the bus bars. LOL

Thanks for your videos. For people who are reluctant to mount batteries in parallel (obviously LifePo4 do not have the problems of lead-acid ones) say that Batrium has a system of connected BMSs that can control different batteries at the same time (I think up to 7) and connect them in parallel. It is quite an expensive system, but it is one of the most advanced that I know of; although the technical advice is with subscription (something that I dislike and I decided not to buy them). If I decided to increase the capacity of my battery (it is exactly the same as yours, but with a 200A JBD BMS) I would also choose the option of making a whole battery and connecting them in parallel. Although the rest of the components are not of the quality of yours (I did not put Vitrom) Sorry if it is not understood correctly, my English is very limited and this is a machine translation.

Would this be a good time to talk about diodes, again? :D I know, I know... But those would disable inter-string current but then charging is more difficult. Just make sure those breakers are bi-polar, can break the in-rush current and have a suitable rating as to not damage the cells.

Here is another comment. 😄 You don't need a 2 pole breaker per battery. You can just put it on the positive side. When you said "it counters the BMS when one bank charges to the other bank" is not correct. You are actually assisting the BMS and that is how some of the more efficient BMS work instead of bleeding current out as heat through a resistor, they use the power to charge up other parts of the battery. The BMS is concerned about equalizing the voltages across the different cells so you don't overcharge any individual parallel bank which causes fires. Also the current from one bank to the other bank is OK as long as your bus bar can handle all the currents combined so where you put the charger will be part of that equation. Currents going from left to right will cancel currents going right to left, but currents going left to right plus having a charger going left to right will add the two currents in a small section of your bus bar and will heat up if your bar is not sized properly to handle the current. Even if the charger was on the left side, that would first start charging the left bank then the right bank. Think of current as water, and the physical height as the voltage and when you open the gates, wherever the water flows is how the current would have acted. I'd be interested in seeing your prior video, but I don't know which one it is. I do parallelize my banks. The only concern is if you are bottom balancing and so how much difference the cells are would become a concern, but you just have to make sure your BMS can handle the difference. If you top balance, and make sure the low cutoff voltage is set higher than the lowest capacity cell, you're good. But most cells bought around the same time will mostly degrade at the same rate and after years, they will most likely still be very close to each other. Mine still are after years. and LiPoFe batteries have even more cycles before they degrade than other Lithium chemistries. My memory says somewhere around 1000-4000 cycles for LiPoFe