Can you parallel battery banks after bottom balancing?

[@MiguelSilva-mb6mb]

I think the best is to keep top balancing. I personally for solar setup, i dont like bottom balancing. I think this is good for a golf cart, eletric veicules, but for a static setup.... I think top balancing is the way to go, unless you have a very mismatched pack. Will Prose as a very good video talking about top and bottom balancing.

[@martehoudesheldt5885]

golf cart and ele forklift top balance . it is called equalize button or the chargers.

[@MiguelSilva-mb6mb]

@@martehoudesheldt5885 they use lifepo4?

[@martehoudesheldt5885]

On the ones that I have seen they float charge for a longer time to do the same thing. But only once a week

[@mortendiysolarshinybilplei4646]

I have put 5 parallel battery banks together over 3 years and top balance them every time also the old banks ,they have now run with no problem over 1 year I have solar in my cabin and slow charge , settings pr cell is 3.55 and never under 40% Yes I do have BMS but only for protection 2.8-3.65 Never bottom balance them

[@OffGridGarageAustralia]

Thank you!

[@551moley]

I must confess, It's nice to hear the rain on your roof and not on mine, I grew up watching Jason and Kylie with seemingly endless summers while we only had "Cornish sunshine" aka 🌧

[@calvinflager4457]

There is a popular solar channel where the man recommends bottom balancing but only for cells which are not grade A, i.e. used grade B cells. For new grade A cells, his recommendation is top balancing and using a BMS. right now I'm trying to figure out how to keep two of the cells in one battery(16s) balanced at higher voltages. My other 16s is almost always within .006 to .009 no matter the charge voltage. THANKS FOR THE VIDEOS.

[@russkubes]

I think if you do bottom balancing when trying to combine two banks, you would first bottom balance each bank separately to get the "final" voltage of each bank. Then you would use the voltage of whichever bank has the lowest "full" voltage. This won't prevent current going between the banks during (dis)charging as voltages at different SOCs may differ, but it should ensure that no cell can ever go over the max. Then, if you add a third bank later on, you just separately bottom balance that new bank, if the new bank voltage ends up higher than your existing batteries, you just need to drain the new bank to match then add it on; else drain your existing battery to match the final voltage of the new bank and set that as the new charge voltage. No need to drain all to 2.5. All in all, your capacity is always going to be the product of the capacity of the weakest cell and the number of parallel banks; and the charging/target voltage is always going to be limited to whichever bank has the lowest bottom balanced bank voltage. You'll still have some losses from current running between the banks over time, because the voltage curves may not be the same (though they're mostly flat anyway), but there should be no opportunity for a single cell to overcharge.

[@OffGridGarageAustralia]

Thank you, great comment.

[@diyEVguy]

@@OffGridGarageAustralia agree, maybe you can visualize his explanation in a nice step-by-step diagram using different colors? (I like top balancing better for my use cases but I like the explanation)

[@DeVerm123]

Well, most people are wrong:-) You bottom balance when the cells spend most of their time at a low SOC and you top balance when they spend most of their time at a high SOC. Boats top balance because by noon their batteries must be fully charged and solar is powering the boat for the rest of the day. Also, after balancing, -stay-away-from-the-knees-. No balancing, just monitoring, regardless of which balancing method. When a cell starts being too low, you inline-charge it. Example: cell 6 is too low: psu negative on cell6 negative, psu positive on cell6 positive and charge at 3.60V or so, limiting amps to charger max or cell max and count Wh going in and stop when you think it is at the avg of the other cells. When one cell is high you can use an electronic load or even just a power resistor to discharge it a bit (inline, no breaking up of cells) For adding batteries: charge new one to same SOC and switch it online.

[@jforthewin8029]

Small system bottom balance. BMS to watch voltages. Large or expandable system top balance. Active balancing. Great video!

[@upnorthandpersonal]

You're going to give yourself a massive headache. What state of charge is your battery going to be in most of the time? That's where you balance. For vehicles you are mostly at the bottom, so bottom balance. No expansion there, just one battery. For solar, you're mostly at the top, and you want to have a flexible, expandable system - so top balance. You will never have a perfect balance of the cells with xx mV at 99% state of charge, especially with these cells (I've been running them for over a year now). Stay below the 90% or even 80%, and stop worrying. Add another battery and and when needed. Accept that your weakest cell will determine capacity, maybe replace it if it's really bad, but a couple Ah doesn't matter. Sit back, relax, have a bear, and watch your system perform without having to babysit the thing.

[@argorito]

completely agree with you. Andy, take a beer and relax. Forget these cells aint german soldiers, all strait and moving synchronously. Take care of them, of course, but do not become crazy. Awaiting the new battery setup. Don't send us to take a nap with this "unsmokable" videos...... don't forget the beers......

[@WillProwse]

Agreed

[@OffGridGarageAustralia]

Guys, I'm super relaxed with this. I'm just asking these questions because many have them and there are no answers to find...

[@WillProwse]

@@OffGridGarageAustralia I made some videos about this some time ago. Just top balance them all and put them in parallel. It's really not a big deal. Top balance manually if you wish, or let your bms top balance it over the course of a few weeks. I took most of my manual balancing videos down because it's a waste of time. Let the bms balance it. Here is a random video I made about active cell balancers and how pointless they are : kzbin.info/www/bejne/mZ69XpKph9N6oJo Bottom balancing was only done when we were running these packs without bms. Times have changed, and top balancing is standard with bms managed packs.

[@OffGridGarageAustralia]

Thanks Will, I remember this video from you: kzbin.info/www/bejne/fIPdo4JoiKakiaM

[@TheMoep87]

As for adding another pack to a bottom-balanced system: 1. I think using the lowest "charge-stop" voltage you measured for any battery will do as "charge-stop" voltage for the overall system 2. When adding a new battery pack: after balancing just charge it up with your lab powersupply until it is within a small voltage difference to your system and then parallel it

[@kuznetsovsu]

smart ideas bro. Thank you for the time which you spend teaching us how to get the best solar power in our own houses.

[@Glennhawser]

Hi AndyIn my opinion top and bottom balancing are for 2 different purposes If you are going to run your battery flat on a regular basis ie in a electric vehicle bottom balance is the go If you are running your battery to full capacity every day as in a home based power system top balancing is the way to go. If you are going to expand your battery by paralleling a extra bank top balance is the way to go I have my 27kw system top balanced and it is still in balance after 3 years maintained with a Australian made bus Keep up the good work

[@jonpercy2258]

Hi Andy, use your new bottom balanced 24 volt bank to power DC LED work lights for your garage. Then add a 24volt DC truck stereo. DC is really easy and great lighting leaveing your 48 volt bank for your inverter.

[@Aconda]

Yes!

[@pritambissonauth2181]

Hi Andy, bottom balance each new strings of batteries once only, then maintain each string with a separate BMS with Top Balancing from time to time. Connecting strings of batteries in parallel, is by bringing each string to the same voltage, that is the existing battery pack with the new string, this will allow you to scale up. Each string to have its own disconnect to the common bus bar.

[@Sylvan_dB]

You cannot mix like that. Either bottom balance or top balance.

[@pritambissonauth2181]

Andy, you don't believe me watch this video just released by Victron kzbin.info/www/bejne/gpuVfWuemKh-nNU @5:01, you will see 10 strings of LFP connected in parallel to a ginormous busbar with 10 fuses . . .

[@WilfriedGV]

Hi Andreas, hi all, for now 2 years I'm running a 25 V / 1600 Ah system. There are 8 blocks with 8 x 200 Ah. Every block has an actice balancer, I'm using no bms. The upper voltage is regulatet by the charge controllers (3), the lower voltage is regulatet by the grid tie inverters (3). The blocks are connected with plus and minus together to big copper plates. With this connection every 24 V block has exact the same voltage as the others and the 8 active balancers are conrolling and keeping the voltages for each block. System is running for now two years without any problem.... Best wishes, Wilfried from Neuss, Germany......

[@jasondevine6014]

As some others have said. Bottom balancing is for those that run down to 0% regularly. For those of us off grid we like to live near the top so top balancing is the way to go because yes you would need to regularly discharge whole pack down to near 0% which is a pain in order to run bottom balancing.

[@paulgrant9243]

Andy - Relax and enjoy the project! No stress! I seem to remember you getting a little fixated with battery balancing and BMUs once before... (34.4Ah, 86.0% SoH BTW) Nice 🧢

[@dffghuytfvb]

About the battery swapping, the advantage is that you regularly hit top charge, thus make it possible to perform top balancing on a regular basis and avoid the issue that you had. a single battery bank must be undersized compared to the solar supply to hit the top charge. There might be a power glitch when swapping the battery connected to the inverter; this can be compensated with a supercapacitor that would be permanently connected to he inverter. I however agree that this option is quite hard to implement because the necessary mechanics is not available as a standard, and switching might create a lot of stress on the batteries.

[@marcobrian1619]

Good afternoon Andy. I really think after all the info IV come across on lifepo4 cells is top balance, I'll be doing this to my 3p 4s 600ah cells "when" I get them.

[@williamhustonrn6160]

Ive been through a few different solar setups over the years between my RV setup, then my monohaul setup, and now the setup on my catamaran. I personally prefer the series setup. Just one giant battery bank with all in series, but charged and discharged from different points. What I mean is for example, my current setup is a 96v battery pack, granted i have a single 96v inverter, but if I couldn't get one, then i would have bought 2 x 48v inverters and hooked up 1 inverter to the first 48 volts, then the 2nd to the last 48 volts. Then regarding charging, I would have separate solar charge controllers for the first 48 volts vs the 2nd 48 volts. The reason I prefer this method is your not masking any of the batteries in your battery bank like you could do in a parallel setup. In the future, if i want to add more capacity to my setup, i wouldn't do it via parallel installing the batteries, i would extend the series configuration from 96v to either 144v or 192v, but i would still stick to adding equipment in chunks on the entire series battery bank. Big pro to this setup is down the road, you will learn which cells in your bank are the weakest and which are the stronger ones. If you choose, you could rearrange the pack based on closer matched configurations, also in series you can overlap BMS modules for better protection. So in my case, i have 8 x SOK 12v204ah modules, each 12v battery has a 1p4s BMS internally, so they are balanced internally. To balance my 12v packs together, i use the 2S 12v BMS Victron uses, and i have 7 of them connected overlapping each other. So 1-2, 2-3, 3-4, 4-5, 5-6, 6-7, 7-8 wired.

[@libertyauto]

Not for Andy's build at this point in its life, but I would think bottom balance your first build. If and when you expand, readjust for top balance and keep using top for any future expansion.

[@Sylvan_dB]

Why bottom balance? Top balance is easier...

[@tomleenheer235]

Hi Andy, you could connect batteries with different voltage levels using blocking diodes between rich battery set. You would have to connect the chargers behind the blocking diode though. I want to use this system on my boat parrellelling LiFePo with lead accid.

[@evil17]

All good theories, I think to bottom balance from new at least is a good idea, and Im sure there is a number of ways this could be done with varying degrees of success. 1. Drain the bank 1 to 2 in series to get them down to a lowish set threshold, 2. Either parallel them all to take down some more capacity evenly using boost converters to maybe help even up some other cells in workshop or bank 2. 3. Then do an individual drain to set parameters so each cell can only produce a preset/ declining current and stop discharge. Hopefully this will get the cell set within some area of a similar low charge status ready for a first full charge, you will also be aware of individual cell capacity status as delivered. 4. Charge up full at most any rate without being silly, lower C rates I believe are better overall, life/cycle wise, etc, and may help if/when observing how they come up into the top balancing area, it would be good to see this type of information in a reasonably controlled way, as you would do Andy, 6. even noting how much current each cell absorbs either via BMS or individual cell discharges to a preset point again, noting how much power each cell drains again, 7. Yes, take them back up again, noting absorbsion current totals of each cell, this should give you a fairly accurate idea of the power capacity of each cell. IR is always going to be a issue, but Im guessing if you can match a large bunch of cells into 2 or 3 closer matched resistance ratings for each pack, that would also benefit. I think this would give reasonable data about bottom balancing and how it effects battery performance overall, it would be good to know more about bottom balancing effects and how this process would give results. It would be a lengthy and arduous task. There are a lot more factors involved of course. Lifepo4 has great performance anyhow, if ur going from 10% - 95% daily it going to last a very long time. Lengthy subject but Good discussion material. 5.

[@jadu79]

My thinking is as you initially thought to take up all the cells to 3.6v and let them absorb until they receive 1A or less when all are in parallel and let them rest a bit and switch on a BMS and when your first battery is approaching fully so you connect them. It's been a long time since I calculated on electricity, but if I remember correctly, the internal resistance will determine the voltage drop across each cell so the fall across a cell with 10% higher resistance will be too high compared to the others? (think that you connect 4 x 12v car lamps in series, but two of them are 10W and two are 55W, so the 55W lamps will not shine very brightly while those that are 10w will burn out quite quickly) one idea is that you do not screw the BMS cables M6 but solder it if you can otherwise screw it in a separate hole / thread (remember not if you have spot welding and nickel strips so you could solder in nickel strips and then weld (do not know if it goes in aluminum) otherwise thread a hole as small as you can if it is M3 or if you do even smaller) should give the least error in reading and all connections should be most equal

[@hommerdalor6301]

If you bring a new string, it needs to be balanced as the thirst one. I suggest balancing at bottom in the winter, and top during the summer, as maybe in the winter it maybe difficult to fully charge. Hehehe so much complications ;-)

[@SpeakerKevin]

This is shocking. I ran a test on a 280Ah EVE cell to see what the resting voltages are at different States of charge so I could accurately charge to 80%. I started charging an empty cell at 15 Amps and putting 28Ah into it (10% SOC). I let it stand for several hours to stabilize, and recorded the voltage. I did this in 28Ah (10%) increments. Everything looked fine until I got to 70% SOC. the resting voltage was 3.341V. Now here is the crazy part, 80% had almost the exact same resting voltage of 3.343 and 90% was also at 3.343. 95%? You guessed it, also settled at 3.343V! If you're going strictly by voltage to estimate state of charge, You could be anywhere from 70-95% at roughly the same voltage. I believe the best way to solve this is to charge and balance to 100% so the Shunt can reset the SOC back to 100% and it will count down from there, giving you the most accurate SOC reading.

[@Muppet_Interfector]

Pretty sure the Victron shunt/system also coulomb counts so not totally dependent on voltage measurement

[@opless]

Another vote for top balancing with BMS and a shunt for each bank, and each bank in parallel.

[@OffGridGarageAustralia]

The BMS has a shunt...

[@opless]

@@OffGridGarageAustralia of course, but one that's readable by your system. 😊

[@jmaus2k]

As for connecting 2 sets of batteries. Just make sure the wires attach on opposite plus and negatives. The strongest battery will always take the most current, but that doesn't matter much. Eventually, they will both be the same strength. Bank 1+ to inverter and Bank 2 - to inverter with cables connection + and - from each pack.

[@AveRage_Joe]

Bottom balance is for EV's as you are more often in the lower SOC range. Solar systems should be top balanced as you charge daily(except you -3a weather😆) and are more on the top end or SOC. Id never recommend using your charge controller for your over voltage or inverter for low cutoff. Eventually they will become out of balance and a cell will most likely overcharge! Just my 🪙🪙

[@OffGridGarageAustralia]

Great point! Thanks Joe!

[@michaelbouckley4455]

8S 310Ah Lifepo4. am getting a 24v inverter with programmable LVD/LVR which I plan to set higher than the BMS LVD, set up for 2.5 cell voltage. Common Port BMS, with 50A charge and 200A discharge FETs. Max load is 100A 3Kw, through 125A dual breaker, 50mm2. Length = 1 & 0.5 Meter cables. BMS is ‘DYKB metered’ Smart ANT, 8S to 24S = high voltage FETs and my max discharge current is half its capacity. I might eventually parallel 2 BMS’es if I need more solar charging.

[@OffGridGarageAustralia]

@@michaelbouckley4455 wow, that's a nice system. That's for your house?

[@michaelbouckley4455]

@@OffGridGarageAustralia yes. But already have a smaller system. This is first inverter, to run a small aircon in daytime, and run fridge & tv in brown outs

[@jwcolby54]

The same process occurred on the discharge side. As each battery approaches its knee the internal resistance to providing electrons rises. The smallest capacity battery will simply not provide electron and the higher capacity battery will. When every battery in parallel is exhausted, in other words has provided all of the electrons it easily can provide, then each battery has reached its knee, and the voltage will start to drop rapidly. That is the discharge the of the entire battery and you will see the voltage of the entire battery start to drop rapidly at that point you need to turn off the battery to prevent higher resistance and heat and higher damage.

[@cheetahkid]

No need to go bottom balance just to get them connected, if the voltage is way off between old and new. You need the battery to run your house. I have to say put a resistor in between new and old battery, not sure the value but 1 or 5amp flow is enough to balance between both battery. if it less than 200mV (or 1V if it in series) between them, you can forget the resistor and directly connect them both.

[@willrobertson826]

Hi Andy you have internal resistance tester I would tend to match cells in pairs top. Test ir test and bottom test resistance and go 16s 2p I'm doing that times 2 on my build underway. I used to top charge and wait a week or longer and then match all batterys.they drift to comfort zone. Lot slower with out internal resistance meter but I learned a lot over 6 months of mix and matching.i prefer top balance to 3.6 and wait to settle. It will come out close testing with ir by the way I don't like more than 2 p on large cells unless you active balance .keep it simple and let the battery do the work .

[@JeremyAkersInAustin]

Whether you top or bottom balance makes no difference. When you have two packs in parallel you have 2 separate BMS units to control them. So if battery #1 needs 13.8v and battery #2 needs 14.0v then you set those separate limits on each packs BMS. When you hit 13.8v battery #1 disconnects and your charger just continues charging battery #2 until it hits 14.0v. The same happens with top balanced packs at the bottom of the discharge: Battery #1 might disconnect at 10.0v and battery #2 might disconnect at 10.8v. At 10.8v battery #2 disconnects and battery #1 keeps running your loads until it drops to 10.0v. Separate parallel packs = separate parallel BMS units and the batteries can be disconnected separately. I'm not arguing in favor of (or against) bottom balancing: I'm simply pointing out it doesn't matter. Two parallel batteries will always have either a different "max charge voltage" or a "min discharge voltage". No two packs will have both max and min voltages equal. Top balancing means charge voltage is the same, bottom balancing means discharge voltage is same. Either way one will be different. One pack will either disconnect first when charging, or one will disconnect first when discharging. Either way one pack may disconnect while the other pack remains connected. That's just the reality of having parallel packs.

[@pritambissonauth2181]

One other thing, I prefer watching your videos than nonsense from Hollywood and other countries studios. These studios with their soap operas are making people becoming stupid all over the world.

[@bwye]

I like the idea of the bottom balancing Andy.. nice and simple. On the subject of connecting the two large batteries in parallel, can you not use some form of 'blocking diode system' so you cannot get any back current from one battery to the other..?? Each battery bank will have its own charging system and BMS for safety. They can then be connected in parallel into the large battery bank that you require with no back feeding of current from one battery bank to the other..?? As the system expands with another battery, just have this 'diode' scenario added to each new battery that you parallel up..🤔

[@clarkguest613]

I don't favor bottom balancing, but if you do: With two 4s strings, you have to charge all 8 cells to the capacity of the weakest one.

[@jwcolby54]

I watched a very good whiteboard lecture about the chemical processes involved. There is a metal film with a layer of iron phosphate deposited on it. This layer accepts or provides lithium ions. As the lithium ions have to be pushed deeper into or extracted deeper from this layer the resistance goes up. And thus the voltage required to push or extract the lithium-ion goes up. At some point this layer runs out of easily available positions And the cell has reached its knee.

[@adon8672]

Can you please post the link to that video here?

[@edwardvanhazendonk]

A solution might be diodes for the discharging and charging when paralleled with different balance levels, but I think it will be a hassle and a waste of power. May the sun be with you in your quest to find a great working solution.

[@JimmyLLL]

If you bottom balance and want to add a new series pack why not bottom balance the new batteries and charge to the same voltage or charge the same amount of amp hours and then connect? Its never going to be perfect but remember youre not going to be using 0-100% of your battery. You're charging to 90% and most likely have a generator to kick in at low levels. No one running a modern house with a family wants to discharge a pack to 2.5v and have a BMS suddenly disconect power to their house.

[@bboyda4399]

It sounds very complicated, à simple solution might be to capacity test each battery and add them together, at say 80%, wherever you want to run them up to. And use the bms just to monitor cell voltages and if the deviation gets too high, send you an alert. You could then adjust your charging and discharging strategies to allow more consistent operation.

[@jwcolby54]

My answer to your question is once again to stay away from the Steep curve past the knee. You connect the strain and parallel allow them to equalize. Operate. battery between 3.10 and 3.4. This that you have control over the vms4 the low side and the charge controller for the high side

[@Sylvan_dB]

* To parallel safely the voltages much match close enough to prevent high current flowing. * To parallel effectively so the banks will not rapidly drift apart the state of charge must match - the same point on the charge and discharge curves. Even then parallelling is sketchy as the paralleled will not share current evenly and will drift further apart with each cycle. The worse the match on the charge/discharge curve the faster the drift. * It is easy to match at full charged and top balanced and it is easy to top balance with a set and forget "charge all the cells to 3.6v until current stops flowing." * It is hard to match at full discharged and bottom balanced and it is hard to bottom balance as there is no set and forget - you must define a voltage and a discharge current and as soon as you stop discharging the voltage will rise. That is, unless you ruined the cell(s). What do you think will happen if you discharge "until current stops flowing" ? Now try to do that with multiple different banks at different times so they will be at the same points on their charge/discharge curve. It's hard. * It is impossible to match points on the discharge curve anywhere in the middle between full and empty. If you match voltage you can safely parallel, but the banks will drift far apart with few cycles.

[@solarautark4144]

Why would I want to do complicated bottom balancing if I want to keep my battery pack full most of the time? For bottom balancing, parallel switching is, in my opinion, only possible from almost identical cells (not battery packs).

[@OffGridGarageAustralia]

Yep, I agree.

[@gg-gn3re]

These methods are the old school methods, with 12v only batteries we just did parallel on everything and then people did some 24v decades ago and manually checked the series voltage every few weeks... Then BMS came out. It's like many things in life, we get automated things to help do repetitive stuff and some people don't like it..

[@mihaitaiosub]

My opinion is that to solve the problem forever, all the batteries should be discharged up to 2.6 volts, then done top balancing, after should be used an active balancer permanently in the battery bank. The active balancer works permanently regardless of the voltage in the batteries. The only problem with this active balancer, a minor problem, is that the parameter that triggers the balancing (voltage difference between the batteries) should be set to 20-30 mv. If this parameter is smaller, the device will permanently trigger the balancing and will transfer energy from a cell to another cell permanently.

[@roaridse]

Considered batrium watchmon bms ? Looks nice, and even possible to integrate with victron venus.. One module per batterycell , and multiple banks..

[@John-gm8ty]

$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$

[@kevinmills5293]

@@John-gm8ty yes, but look at the battery investment.

[@John-gm8ty]

@@kevinmills5293 all depends on your start up capital I guess, many off griders or solar sheders start off small and build up over time, as a full install runs in at 20+K easily.

[@kevinmills5293]

@@John-gm8ty I was thinking about Andy’s situation but of course you are right.

[@jmaus2k]

Bottom balancing would help if you expect to have a very high charge current. If you have a high discharge current a top balance would be better. But like you are figuring out, it needs to be automatic and I don't see a way to bottom balance automatically. Maybe with a BMS that activated a balancer only when voltages are low. Still the better automated solution is a resistor based BMS with higher shunting capability than your solar charge current. Then you never have a shutdown unless your entire pack is fully charged. Batteries are not the same efficiency so you will have some needing 101% to charge and some 102% to charge.

[@jwcolby54]

It is this varying resistance which allows two batteries of different capacities to work together seamlessly. At any given voltage the lower capacity battery will have a higher resistance to electron flow. As a result the higher capacity battery will accept electrons which the lower capacity battery cannot accept at any given voltage. Likewise on the discharge cycle, the higher capacity battery will provide electrons which the lower capacity battery cannot provide at any given voltage.

[@magicmanspaz]

Top balance. On the forums and pages i am on the large majority say top balance so its odd hearing on here more people are for bottom balance. I would also think the fact most balancers are made to turn on at higher voltages shows that top balancing is the better option. And for all the reasons your gut is already telling you why top balance makes more sense.

[@OffGridGarageAustralia]

Great, thank you!

[@smde1]

The use cases for bottom balancing is more appropriate for an electric vehicle than for a solar powered home or garage where you are almost always topping off the system and almost never running the battery to a low state of charge where bottom balancing would be helpful. Instead, since you are almost always topping off the system and only drawing it down a bit - and topping it off again - top balancing is most appropriate .

[@SenatorPerry]

You can mix and match capacities and chemistries, but with each of a like chemistry or capacity you would need two MPPT controllers and a HV/LV relay (or a BMS). In your example you have a 48v battery at 200 amps. You also have a second 48v battery at 100 amps. You can use an MPPT controller to charge the 200 amp battery from the 100 amp battery as long as you have a low voltage shut off between the MPPT and the 100 amp battery. Then you would use the second MPPT to charge the 100 amp battery from solar or whatever. The price of the two MPPT controllers + a HV/LV shut off relay is less than many other options. If you have a boosting MPPT controller you can even use a 12v battery to charge the 200 amp 48v battery. You can also use this set up to leverage cheaper cells or even those AGM batteries you have. The key, though, is that you can isolate the children batteries from the parent battery to allow you to remove batteries or add more even if the voltage is odd. Like using 5 batteries instead of 4 or 3 batteries instead of 4. It doesn't matter as long as the MPPT's solar side can accommodate the voltages. This also opens up the usage of the odd voltage recycled vehicle batteries like the 20v batteries in BMWs and Fiat 500e.

[@HansKeesom]

12:45 You DO double your capacity, you only have half of it online. At the input side of things I suggest two solarchargers, for each battery one and a 1-2-both switch between the panels and the solarchargers. As you have 4 strings I believe, you might wanna place 4 1-2-both switches so you can redirect where the solar is going. This can be helpfull as absorption is needing less solarpower. Also, with the solarcharger in parallel, most amps will likely go to the solarcharger connected to the battery with the lowest voltage.......... If not you can also remotely reduce the max current charge of one solarcharger to steer more power into the other solarcharger.

[@OffGridGarageAustralia]

Thanks Hans. That sounds like an awful lot of cabling with such switches...

[@brian1395]

please talk about nmc bateries. here in thailand they sell a 28s1p pack. basiclly a 96+v. they are made of 24v 135a laser welded packs from cars.

[@hommerdalor6301]

Andy, stop looking at me like that while I think about a solution. :-D

[@Muppet_Interfector]

I think it makes no difference to the capacity if you bottom or top balance. In a Series String of cells you will always be limited by your lowest capacity cell. Either top of bottom balance, what you will observe is that the cells will either have similar SOC at the bottom of their range if bottom balanced or similar SOC at the top end if top balanced. With either balance approach the capacity limit of the string will be determined by the cell with the lowest capacity. The cell with the lowest capacity will get to the highest/cutoff voltage first if you have bottom balanced the string. If you have top balanced then the lowest capacity cell will get to the lowest/cutoff voltage first under discharge conditions. Now, when do you couple additional cells? The simple answer is you couple your strings when at the the top SOC for top balanced strings and at the lowest SOC for bottom balanced strings. From what you have said Andy, in order not to be caught with with two string of discharged batteries for the purpose of coupling the batteries you best join the strings when at the top SOC. Previously I said the simple answer was to join strings at top SOC for top balanced and at the bottom SOC for bottom balanced strings. However I think you can still couple two strings of cells that have been bottom balanced at the top SOC. The issue here is that the string voltage for the lowest capacity string will dictate the maximum string voltage for the higher capacity string. The question of to balance or not to balance needs more thought about the self discharge mechanism and capacity variation depending on the rate of charge and discharge.

[@dazrichie897]

What's so funny? Bahaha! 😂 and 'sunny hot 🔥 aus straya' .. best video. 😊

[@1981dasimpson]

so your just doing a cc.cv charge

[@randycook4364]

I like top balance with a BMS on each bank. If a bank mis-behaves it self I can shut it off and investigate.

[@jwcolby54]

At some point the lower capacity battery reaches its charge knee and its internal resistance begins to rise rapidly. In the meantime the higher capacity battery is still merely accepting electrons with a lower internal resistance. The electrons simply flow into the higher capacity battery with the lower internal resistance. At some point, the higher capacity battery also reaches its knee and its internal resistance begins to climb rapidly.

[@jwcolby54]

My understanding is that when a battery reaches its knee , it is unable to accept or provide more electrons. So if you have another battery of Greater capacity, that battery will still easily accept or provide electrons. The two batteries will just naturally share the load or the charge based on their individual ability to accept or provide electron at any given moment.

[@1over137]

4S 14.40V 105Ah. No balancer. Been running for 2 weeks and the cells have a 0.007V min/max. How? Use absorption to top balance. You need to look at the ESR in that range and self-discharge. You will find after holding the cells at say 3.65V for a few hours their self discharge characteristics will bleed off the high cell anyway. When it defaults back to float (effectively disconnecting the pack if it's not loaded), the MAX/MIn delta settles down to 0.007-0.009V within about an hour. They basically all self-discharge back down to the flat part of the curve where they are pretty much identical anyway. The people who install this stuff profressionally for industrial sites tell me the best maintenance free LiFEPO4 setup is one which counts the colombs in each cell, gets an accurate assessment of each cells capacity and then augmenting each cells capacity with 18650 or other cells in parallel with it such that all cells have identical capacity. They are top balanced and put into service with no balancer and just a yearly inspection.

[@jamiebrock7157]

If you have separate paralleled inverters like David poz, he has three 5,000 watt grow watt inverters could you have a separate battery Bank on each inverter and with that keep them separate and acting independent but still have the same overall system capacity?

[@John-gm8ty]

thats getting crazy expensive though.

[@michaelbouckley4455]

@@John-gm8ty David Poz using Growatt 5Kw inverter chargers. Growatt also do 3Kw parallel enabled. They are not as expensive as Victron SCC & Inverter! But do need a lot of Solar panels, at high voltage (up to 250v) Can run without battery.

[@John-gm8ty]

@@michaelbouckley4455 I have seen videos on them ;)

[@jwcolby54]

The link to the white board lecture on LiFePO4 chemistry - kzbin.info/www/bejne/h52nlWagoMirpbM

[@reubenj.cogburn8546]

"Welcome to Scotland" ha ha, nice.....but, you know what we've been waiting for, right? "Get in the Choppa!" But we'll settle for "Come with me if you want to live".

[@andrewradford3953]

That's Austria - aka "Put another prawn in the barbie"

[@googyzzzz]

in my opinion: bottom balance, use for example diyBMS from Stuart Pittaway for monitoring and protection. Configure diyBMS to warn you if some cells go out of balance/range. Do not float/absorb, do not use whole capacity to increase cycle life. Better get more batteries then BMSs. If you parallel cells to one bank, use BMS without balancing. If you use two banks use two BMSs.

[@villacarinaapartments]

Hello Andy can you not use a battery combiner diode blok from victron. And then have each battery it's own charger.

[@OffGridGarageAustralia]

But only up to 80A... seen them, but it's not what I would need, as I have power going in an out of the battery.

[@villacarinaapartments]

80a is about 4000 watt and if you connect the solar charge from the east direct to one battery and the solar charger from the west direct to the other your problem is solved. And I think there are higher amps battery combiner from other manufacturers.

[@OffGridGarageAustralia]

@@villacarinaapartments Ah, right, you split the chargers as well. Yeah, that could actually work then... letting current only flow out of the battery to the inverter.

[@hommerdalor6301]

For paralleling the strings, the voltages must match, so with a dc/dc converter, we can bring them equal. the capacity off the strings does not matter, we could parallel a string with 5 Ah with 280Ah, once the voltages are the same. The difference in voltages or Difference of potential makes the current flow, no difference is 0 Amp between the batteries. This needs to take place only once, after that, they can stay in parallel forever.

[@hommerdalor6301]

Once any cell of any string is too high derterminates the maximum voltage of the all pack. Once any cell of any string is too low determinates the minimum voltage of all the pack.

[@Mr.X3D]

I’m no fan of bottom balancing, and I don’t think below solution is a good ide, but I actually think it will “work” in parallell as long as you have separate bms’s for the packs. A common port bms won’t know where the charge is coming from, and will do its work accordingly, ie shut of charging when the weakest cell peaks. The charge voltage would then be determined by the pack that has the highest sum of cell voltages, and preferably you would use mosfet based bms’s. In this configuration there should be no problem for the controller/inverter as long as the strongest pack remain balanced (ie the charge is not shut off by the bms but the charge controller). In theory you should be able to mix top and bottom balanced packs as long as they have their own integrity secured (BMS). Reagarding your early comment on absorption and floating; you will have kind of floating for the weaker packs, but more like trickle charge since the bms will control the charge. A sunny day when the bank is “full” the bms will trigger on and off constantly. (Again, mosfet based bms is preferred)

[@fredio54]

About your bad results while raining - I recall you had strings of 3 panels on your roof, are they ~20v panels? If so, they'll ONLY produce ANY power into a 55V pack when OVER 55V (depending on the charge controller). How high a voltage can the victron take? The panel outside produces 45V in even gentle direct light with full cloud, and about 10A dead short (I didn't measure power). But in the shade where I am now, 455W panel did a best of about 45-50W :-D And, importantly, the 45V panel produced just 13V when even darker eg shade + cloud, and below the 12.8 in the shit lead acid battery I get no current at all. IE, perhaps that's what's going on for you. I would expect you should still get some power out of it even when rainy and crap, but not if they're only 60V in sunshine ;-) Let me know - I'm curious. As for me, I have devised a plan to get the panel up and into the direct sunlight for a limited period of hours per day when I'm here, and that will make a huge difference to how much car idling alternator charging I need to keep the laptops, phones, power tools charged each night :-D

[@kerryb2689]

Just some logical thoughts: When connecting 2 cells or batteries in parallel, the current flow from one battery to another would depend on the internal resistance of the highest resistance battery at the time plus the resistance of the bus bar, and the voltage difference between the 2 batteries. As long as you're not exceeding the charge or discharge rate of either cell, I'm not sure there's a problem connecting them as long as the voltage is reasonably close. If you are concerned anyway,, you could connect them with a low value resistor (1-10 ohm) of the proper power rating (or an incandescent light bub) until they reach equilibrium. I guess if you're paralleling 2 batteries it would be best to parallel each cell of the batteries. I sort of suspect you're over thinking this....just connect them, measure current and see what happens... worst case you'll melt a jumper wire and have a small fire. I never would have guessed this could be so complicated.

[@kerryb2689]

ok, I may not be thinking about this enough. After watching some more videos, 10mv/0.15mohm =66 amps oops. Get the voltage as close as possible before connecting together, or connect with an incandescent bulb until equalized.

[@douglasmarquis3446]

Andy, is that an active balancer in the box?

[@mihaitaiosub]

I think so, in the box is an active balancer.Finally Andy will find the perfect solution for balancing the batteries.

[@michaelbouckley4455]

Or is it the next bms?

[@kswis]

I top balance because I am after balanced and even voltage. I am extremely hard on my cells. They will likely rarely see half full much less almost empty. I top balance also because my system runs and charges too 14.2. It always depends on their purpose

[@OffGridGarageAustralia]

Thanks for sharing.

[@MarkusIngalsuo]

How about connecting loads over diodes and using separate chargers? Then you could disconnect one battery for service without disruption and bottom balance :)

[@MarkusIngalsuo]

As clarification, the batteries would be connected to the 48Vdc bus over diodes, one each, which prevent batteries from charging each others while still powering the loads.

[@MarkusIngalsuo]

The diodes would have to be quite huge and fused so that diode failure will not cause too much havoc, since a diode may burn and create a bidirectional bridge, which can be bad for the battery.

[@ebenwaterman5858]

Top balance for backup applications like maybe yours and bottom balance for electric vehicle applications as someone has also mentioned. Parallel up the batteries for crying out loud. It's been done before. What's the problem? :)

[@volodumurkalunyak4651]

Top balance for everything and BMS for everything. Neither one of: Tesla, Nissan (Leaf, env-200), Chevrolet (Volt, Bolt), Audi (e-tron), Porche (Taycan), Mercedec (EQV, EQC) do use bottom balancing. EUC, electric scooters, Ebikes, electric cars - BMS everywhere, with top balancing.

[@volodumurkalunyak4651]

@@ebenwaterman5858 I do not believe in going out of my way doing bottom balancing if BMS already does per cell overcharge/overdischarge protections. Protections works either way, no matter how many cells hit high/low voltage cutoff, so there will be no difference where to balance (top/middle/bottom). I like top balancing from convinionce point: fully charge all cell's, assembe the pack and now you have a ready to use pack.

[@ebenwaterman5858]

@@volodumurkalunyak4651Right you are. I just picked up a couple of 5 amp active balancers from Heltec. I want a system I don't have to babysit. That should do the trick. First off, if you start with cells that are matched like Andy's were, there won't be much balancing to do anyhow. I think he's chasing his tail a bit. :)

[@SpeakerKevin]

You can absorb as long as you stay under 54.4 volts.

[@monsieurd.6890]

I have a different question that would need a complete video : how to parallel 2 Lifepo4 batteries (not modules) ? In fact if each one has a BMS, the danger is, I think, one battery could flow into the other because of discharge level that are not the same. The current flow could destroy the BMS. Am I right ? So the question are : how big is the current flow when paralleling batteries that have different voltages ? I fear it could be very high. Is it dangerous for the BMS ? The advantages of paralleling batteries is that if one fail the system could continue to work with only 1 battery. And that each BMS delivers 50% of the current. The disadvantage is that we need to be sure one battery does not go into the other. If you can help me to know more about this...

[@OffGridGarageAustralia]

Are you talking about battery banks in parallel or cells in parallel? I'll do a test and video about this soon.

[@monsieurd.6890]

@@OffGridGarageAustralia I talk about batteries in parallel, not cells. 2 batteries of 16 cells in series +1 BMS for each battery. If 1 battery is 3 v x 16 after maintenance and the other 3.35 v x 16, plug in back the 3 v x16 battery in parallel with the second one could make a big current flowing from the second to the first. And I wonder if that big flow could not destroy the BMS before he cuts this current.

[@OffGridGarageAustralia]

@@monsieurd.6890 Yes, that is correct. before connecting battery banks in parallel, they should have a matching voltage at least to avoid such high currents.

[@monsieurd.6890]

@@OffGridGarageAustralia the answer of the BMS seller : ****** Dear customer, our protection board does not support parallel connection. If the protection board is used in parallel, once the voltages of the two battery packs are inconsistent, the current backflow will damage the board. ******* So it is quite a danger if one day we plug a battery without verifying all batteries have exactly the same voltage. It seems the BMS does not protect at all from too big current flows. Even if I do not think my problems is paralleling related because the BMS refuses to work even when I used only 1 battery and they do not smell burned. I think they are just shity engineered products.

[@andresgodinho]

For single battery systems, bottom balance . For Multiple battery systems like solar storage, just top balance the pack!

[@OffGridGarageAustralia]

That's what I think!

[@andresgodinho]

@@OffGridGarageAustralia i have a small side business building solar batteries and i always top balance them except when my clients tell me they want something different. This seams to work really well in solar aplications.

[@pmacgowan]

Like any problem ... see what others out there have done to solve your problem, the answer is out there :-)

[@solaredd7805]

can we parallel 2 sets daly bms 48v 16s

[@jwcolby54]

When every battery in parallel reaches its individual charge capacity and its internal resistance begins to rise rapidly then the voltage from the outside starts to rise rapidly. That is the knee of the entire battery.

[@stadsimkerijhengeloe.o.4300]

You don't need to balance new cells! You should charge all batteries with the same charger to the same CV-voltage, after that you can connect all. I suggest 3,50 volt per cell, because of the point of SOC in the discarge curves. 3,50 volt is a very small spot/target voltage where not much current can go up or down whem parallelling the battery-banks. But this works only if you use them economical/long cycle life style. (max. 3,40 volt per cell and min. 3,10 volt per cell) If you connect the batteries in cross-parallel you will always have the same distance for discharging. So Plus for battery One, and the Minus for the last P-Parallel to the inverter, will do this trick. And you can parallel as many as you like between the first battery PLUS and last battery MINUS. Simple ;)

[@OffGridGarageAustralia]

If you charge them all up to the same voltage, you automatically balance them.

[@stadsimkerijhengeloe.o.4300]

​@@OffGridGarageAustralia And there is the critical point! Pls why go there, if you like longlife? There is no gain above 3,4 volt. If your pack looks oke, than use it. It's the high voltages that are the stress BIG factor, as well below 3,10 volt. Yes, a BMS protects bla bla bla, so does a seatbeld, but you DON'T want to test it. Why go high voltage, where cells diviation is much easier to see... Look and see that not all cells have same balance. duh. on 3,40 volt they where..... at 3,10 volt the are.... I like to see 10.000 cycles or more. your cells are most healthy state halfway. At Nominal Voltage 3,20 volt. Stay around that and your pack will never die. And remember don't go High don't go low! 3,4 volt is very nice for full. Who cares about capacity, if to small... Buy a bigger battery. That doubles or triples lifetime. But check cell voltages often... or get a feeling for them. If your cells go out of line easy at medium voltages... Buy an active balancer. Buy a smartshunt for monitoring system.

[@OffGridGarageAustralia]

@@stadsimkerijhengeloe.o.4300 yeah, I agree with you.

[@bilalbhatti7549]

Temperature and charge with over heat underheated resistance would drift.

[@TheGalifrey]

Bottom balance is fine if you're not gonna charge to full. As soon as you charge to full they will be out of balance. Top balance and then only use between 20% and 90%

[@SpeakerKevin]

@Coach Life You can also say, Top balancing is fine if you're not gonna discharge to empty. As soon as you discharge to empty they will be out of balance.

[@TheGalifrey]

@@SpeakerKevin thanks it was almost as if I missed the upper and lower limits in my comment 🙄

[@tcloud24]

parallel battery1) float is not a form of absorbing. float comes into play once battery is charged, but a load & input (like solar or wind) are still present. float should allow the battery to maintain its charge level while still supplying power from solar/wind to the load's (as long as there is enough to cover demand). the idea is to cycle the battery as little as possible. there are only so many cycles in a battery. 2) BMS... your topic here is "parallel battery...." the bms addresses series more than parallel. so it is "off topic" here. 3) connecting 2 strings in parallel.... of course when you start, both strings will have a bms for watching each cell voltage closely. now simply connect the + of each string together and the neg of each string together. since neither of the strings were "overcharged" it will not be possible for one string to overcharge the other. 4)charging 2 strings together.... pick a voltage between the knees and charge/discharge to those values 5)mental masturbation.. it happens to us all. LOL!!. have a beer!!

[@deltoncbaker]

Not being able to do a deep absorption would nix the bottom balancing for me. I know batteries allowed to get full absorption don’t deliver as much current per charge.

[@OffGridGarageAustralia]

400kg per shelve and I doubled the metal supports underneath to 4 in the area where the battery sits.

[@keyem4504]

I guess it doesn't matter how the batteries have been balanced when you connect them in parallel. They will always stay at the same voltage. Even if one is in a higher state of charge. In that case its voltage would rise faster than the other's. Therefore, incoming current would go into the other battery preferably, because there is a higher potential.

[@keyem4504]

Before you connect the two batteries for the first time you have to bring them to the same voltage. That's not necessarily minimum voltage. Should just be something below the common maximum voltage.

[@nigelcharles511]

Why not just have changeover switch between banks. That way you can bottom balance and always have a bank on standby or for maintenance. The changeover could be manual or automatic. If automatic you can still use all the power by the changeover being dictated once the first pack is depleted to a nominated low voltage. All the power is still available you are just taking it from one bank at a time.

[@keyem4504]

The maximum voltage of the two combined batteries is the minimum maximum voltage of the two single batteries. Then you will never overcharge anything

[@trevilights]

I think that baby sitting the Batteries or Cells should not be done. It's exhausting. Just leave the work to the BMS and enjoy your solar power. Find your top and bottom voltage limits that works for you and let them be. I must confess that ever since I started watching your videos I find myself checking the voltage of every single cell three times a day just to see how are they doing. Why? In my Case All of my essential loads are power by solar, If the battery hits the bottom limit then the grid takes control and recharges the batteries in 3-4 hrs then the cycle starts again.

[@jwcolby54]

I am using Google Voice translate which has its limitations. I will need to edit my posts later.

[@teardowndan5364]

Batteries are never perfectly matched and their parameters will vary depending on a heap of parameters on top of that. Balance will never stay "perfect" for very long on its own. Also, the reason the balance current is only 200mA and can act on multiple cells at a time is because your BMS uses a simple resistive balancer, all it does is turn 3.4-4.2V/200mA into 700-850mW of heat. No taking energy from one bucket to put it in another here unless the "other bucket" is air.

[@jwcolby54]

You are trying to figure this out without thinking about chemistry. Any battery regardless of type is moving ions between two locations. The internal resistance to movement is determined by the number of ions in the battery. This resistance is a chemical resistant! How much energy is required to move an ion from point A to point B. If battery a has a million ions, and Battery B has a hundred thousand then battery A will move 10 ions every time battery B moves one ion. Automatically, you don't have to do anything. It goes without saying that the batteries have to be the same chemical composition. From our perspective, it requires electrons to do all of this! From the batteries perspective every ion requires a certain number of electrons to force it to move. Pretty simple concept!

[@SpeakerKevin]

When paralleling the 2 battery packs, they will be at the same voltage, but they each will have slightly different energy levels. Not a problem. The difference in voltage is so low, that the exchange of energy is quite slow. The current between the 2 batteries is so low that there will be nothing to worry about.

[@sjdtmv]

Never bottom balance, BMS is designed for top balance only and by design to shut the battery bank down if too high or too low voltage

[@TheGalifrey]

Parallel then series is the best way, it is the way Tesla do it.

[@tcloud24]

i don't think it is in his blood. if he can see and know each battery, i am sure he will!! HA! HA!

[@GNiessen]

After bottom balancing the new set, you would just need to charge them to the same voltage as the other sets and then connect them. No need to discharge the old ones. I think you are over thinking the problem.

[@OffGridGarageAustralia]

But the batteries won't have the same voltage when bottom balancing.

[@opless]

60th!

[@jwcolby54]

You can think of Equalization as Center balancing if it makes you feel better. However as long as every battery is operating in the center region that is not in either knee, then they will simply share current as required for their individual capacities and it is totally automatic. When the voltage starts to drop rapidly or rise rapidly, cut off the charge or discharge.

[@anthonyrstrawbridge]

🤔