304Ah in parallel with 5Ah. Will it destroy the small battery? Battery Bank Parallel Extreme, Part1

[@dennis_m]

Andy, my answer to the question at the end: It's due to the internal resistance difference of the cells. The Palo cells must have having a fairly higher IR than the EVE cells, which is expected due to the huge capacity difference. Current always prefers to flow more over the least resistance path. However, this is only if we assume the batteries have the same SoC. One experiment suggestions is, let's assume that both the battery packs have a similar voltages but very different SoC, which is possible in LiFePO4 due to is flat voltage curve (3.2~V range). If the 5Ah cells have Lower SoC than the 304Ah cells, and the charging current is 20A. Then we have to see how the charging goes. If most of the charge current flows to the small battery and the JBD disconnects due to over current (>3A), then will the 5Ah cells never be charged up? Or it keeps on fluctuating after some seconds and charges the cells at >3A briefly and BMS shuts down, and the cycle continues. If this happens it will be bad for the small cells, right. Looking forward to part 2 and more experiments. Thanks for the video.

[@OffGridGarageAustralia]

Thanks Dennis, that's exactly the test I'm doing in part 2 of the series. Stay tuned...

[@Sasykes68]

Exactly what I was going to post here, not in so many words but, if the SOC in the Palo pack is extremely low there will be a large current flow so watch out! Looking forward to part 2.

[@davedave6404]

@@Sasykes68 In theory - but the BMS is set to 3A so there is a lesson on there. A decent BMS correctly set up covers all eventualities. The effect shown in this test is due, I believe, to the internal resistance differences.

[@Sasykes68]

@@davedave6404 Right, I was being dramatic.

[@SuperBrainAK]

dont forget the voltage rising quicker because the cells have less capacity.

[@solargarage]

Thanks for doing this Andy. I ran for several months a string of 180ah, 145ah and 100ah mixed and saw the same as you show here. In fact getting ready to add our Fortune 100ah banks into the back running the 280ah cells. Another item to look into that can affect things a bit would be the internal resistance of the banks and resistance of the wires, that may be different based on the length of the wires. I look forward to the upcoming parts.

[@OffGridGarageAustralia]

Thanks for your comment. I have actually measured the internal resistance of each string in part two, so stay tuned...

[@dreupen]

Andy, Voltage is electrical pressure. So charging the two battery banks is like filling two containers with a pressured water hose connected to the bottom of each container. As the water level rises, the water pressure at the bottom of a container increases (battery voltage) and the flow (current) decreases until the container pressure(battery voltage) equals the water supply pressure (charger voltage) at which point the flow (current) becomes zero. A large capacity container needs a lot more water (flow/current) to increase the water level (container pressure/voltage) compared to the smaller container, so as the smaller container increases its pressure (battery voltage) the in flow (current) will favor the container with the lower pressure (i.e. the larger one). This analogy also predicts the discharge behavior. Draining both in parallel will result in equalizing pressures (voltages) so that the relative capacities drain equally (i.e. both batteries track the same percentage in SOC). So the small battery will last just as long as the big battery, it will just supply its energy much much slower. It should also not matter if you configured 2P4S rather than 4S2P, but in the first case you only need 1 BMS. . In both cases, you need to be equally concerned with exceeding the cell C-ratings while charging.

[@frits183]

Is tis the same rule for AGM battery 🤔

[@dreupen]

@@frits183 It is the same Physics except that for lead-acid batteries (including AGMs) the battery's internal resistance is no longer negligible. In fact, this internal resistance is large and depends on the current (Peukert effect)! Then when the LiFePO4 battery reaches max terminal voltage (V_term) the AGM's internal voltage will be less due to the voltage drop of the internal resistance(V_agm = V_term - IªR, yes a power to "a" ). That is, the large internal resistance decreases or drops the electrical pressure. But this is the usual problem of charging lead acid batteries. If a constant voltage is supplied, the LiFePO4 battery voltage would reach the supplied voltage first with the current into the LiFePO4 battery decreasing to zero, but the AGM would continue to charge (absorbing) until the AGM internal voltage reaches the supply voltage which also loses energy as heat in the process. Now most LiFePO4 battery chargers don't keep a constant voltage. For example, my charger turns off the charging voltage when the terminal voltage reaches its set value. Then for a mixed LiFePO4 and AGM, the charger would shuts off, and the LiFePO4 battery will provide charging (absorbing) current to the AGM until the internal voltages equals, with the AGM being effectively in float at the whatever terminal voltage remains for the LiFePO4 battery. Note that this would waste total battery capacity as only some of the LiFePO4 capacity goes into the AGM capacity with the remaining being lost as heat due to the large internal resistance of the AGM. How much of a problem depends on the relative capacity sizes. Bottom line, it is not worth combining the chemistries.

[@velocitor3792]

Great explanation! Thanks!

[@sia3540]

I asked you this question after the vendor I purchased my batteries said it could not be done. My batteries in parallel are working great! I really appreciate your videos!

[@OffGridGarageAustralia]

Thank you, yeah, I had a few comments about that in the past so was really curious to test it and see what happens.

[@xNYCMarc]

For the last two years I've been running 5 year old Calb 180 cells (now 7 years old) with brand new Eve 280 cells (now two years old). But I don't run them as two separate banks. I put in parallel one of the 180's with one 280 to create a "super cell" of 450 ah (180's were degraded after 5 years of use). Then I put in series 16 of these "super cells" to create a single pack. It's still working fine after two years of daily cycling.

[@Tamilarivu782]

Andy ...You are the right man answering the questions of diy solar geeks like me ......

[@OffGridGarageAustralia]

Thank you Bruce. These are all the questions I had once myself and I could not find answers so started doing all these experiments and tests myself. I'm really glad I can share this all here on the channel with you.

[@sl0rion]

This is fantastic Andy, exactly what I was so interested in learning about! I appreciate how you investigate the 'why' as well as the observation of the 'what'. Prost!

[@OffGridGarageAustralia]

Thanks for your feedback Chris 😊

[@mashun-o4d]

You learn only by doing experiments like this. I learnt a lot this way by charging my lead acid with a dc charger. Great video

[@SuperBrainAK]

Yep that is an awesome experiment, most people would have guessed that it would behave like that, but seeing it actually happen and just how much current flows is really nice to see to fully understand it. To answer your question in the last minute of the video, the reason that the power is distributing itself is because of two things, ESR and Ah capacity acting to change the voltage it presents to the bussbar (hopefully that ambiguous term makes sense). For the Palo cells with only 5Ah of capacity 1A for 10 minutes will increase the voltage of the cells by a large amount compared to doing the same thing to the EVE cells, their voltage will not change hardly at all (this is where an accurate voltage measurement would be handy). So speculating the voltage difference between the bussbar and the cell voltage adding in the voltage drop from the resistance between the bussbar and cells and also the internal ESR of the cells themselves we can find that there will be a greater voltage difference for the EVE cells since their voltage will not increase as quickly, but the Palo cells will quickly increase to the voltage on the bussbar so the voltage from the bussbar to the Palo cells will be lower and we all know that a lower voltage across a resistance results in a lower current. Another way to think about it is two weights being dragged across the ground being pulled from one point with strechy ropes at the same time, the weight represents the capacity, the strechy ropes represents the ESR and the force acting on the rope represents the current. If the thing pulling the weights moves forward there will be much more force on a less strechy rope pulling a heavier object.

[@CitizenOfBabylon]

I have 100ah, 280ah and 2 200ah 48v banks paralleled for 2 years. I have 400ah, 50ah and 4 100ah 12v bank and batteries paralleled for 5 years. Same batteries no problems. They deviant while charging and discharging small amounts , but they settle quickly. The secret is having enough amp hours to run system near nominal voltages.

[@asderven]

No magic smoke please. Safety first, health and equipment should be treated with respect. I noticed that the small cells took 20%~25% of the charge at different Amp levels usually. Great video, very helpful. I hope to join in soon, just trying to figure out how to pay for the cells legally.

[@kevinroberts781]

Just want to say this before I finish watching. Most of us that understand batteries aren't to worried about paralleling batteries. With lithium it's a much easier deal than when we used LA. LA would burn up plates inside the cells if not matched correctly. With Lithium, it's much easier. Keep the cells the same.

[@thedavesofourlives1]

How would it burn up plates? My understanding is it would drawn down the better battery first, then after load removed, the lesser would be slowly recharged by the better one, increasing cycling, is that what you mean?

[@danielglang6312]

Th simplist answer to your question at the end is that the battery with the highest current outflow also has the highest current inflow.

[@OffGridGarageAustralia]

Don't spoil it 😁

[@danielglang6312]

@@OffGridGarageAustralia solly

[@adykapa6752]

I was watching you for few months... You are by far my FAVORITE

[@lukefarmer5391]

Love the initiative of taking the risk of destroying it all for the thirst of knowledge. Excellent video. Thank you!

[@meganote]

Interesting experiment Andy. It takes me back to the days of learning basic DC electronics of understanding current flow in parallel circuits. Very interesting to see the behavior of the two BMSs in parallel… but it makes sense.

[@OffGridGarageAustralia]

Yes, it was an expected outcome but still good to see it is actually working.

[@AndreaFurlan-ro8cw]

Thank you Andy to share all this with us!

[@edwinkania5286]

That is exactly how batteries and electricity works. I dont listen to those that say CANT BE DONE. Those words mean challenge to me, challenge accepted. Awesome video.

[@OffGridGarageAustralia]

Thanks Edwin!

[@mikemorin3131]

A BIG thanks for doing this experiment

[@w.schmidt323]

Saubere Arbeit Andy, hast dir ein Ötti verdient. Eine physikalische Überraschung sehe ich beim Experiment nicht, dennoch schön zu sehen, wie alles läuft. Ich habe ein ähnliches Szenario in meinem 2x12V parallel System verbaut. Dabei ergibt sich beim JBD BMS eine Besonderheit: Wenn 1 Batterie voll ist, da eine Zelle auf die 3.65V läuft, springt der OVP rein. Resultat ist, dass die andere Batterie welche parallel geschaltet ist, eine Spannungsspitze abbekommt, welche durch die Trägheit des Systems hervorgerufen wird. Du konntest ähnliches beobachten: Dein BMS der kleinen Zellen hatte über 2A Ladestrom, was das BMS eigtl. vermeiden sollte. Für kleine Ströme ist das kein Problem, stell dir aber vor, dass du ein System mit 40 A hast, und die hälfte der Ladezellen auf einmal aussteigt --> Spannung springt, da Chargecontroller zu träge sind --> OVP des Chargecontrollers oder der parallel geschalteten Zellen, die nicht voll sind. Was würde helfen? Ein Widerstand? Unschön, da er dauerhaft sinnlos Energie verballtert. Evtl. hast du einen Vorschlag.

[@rogga3]

Thanks for this video Andy. I’ve been watching all videos from you. This one were like a football game! Absolutely loved it. Can’t wait for the semi finals! About the inrush current, it wouldn’t get very high even with a big difference in the SOC. The voltage will stabilise quickly and all the mayhem will slow down pretty quick. Try when the Palo cells is at a low state of charge and the Eve in a high state of charge! I’m sure that it will only be a high current for a few minutes! During this few minutes you have the BMS in control. What could possibly go wrong?… I’ve seen tests like this before on Lead acid batteries.. Greetings from cold Sweden!

[@Shep5847]

Experiment suggestion: Take 2 of your large capacity cells and do a ‘current rush’ experiment between them by discharging one to 3.0v and having the other at 3.5v. I have done this in the lab for my own curiosity and the current rush is not as bad as people make it out to be when the difference is only a few tenths of a volt. However, when you put a full volt difference between them, then it gets fun. But not dangerously fun…. As long as you are not in both the upper or lower curves at the same time, the rush is not bad. However, then it can take a long time to balance the lower cell while holding the higher one in the upper curve. I had fun with it. 🤷🏻‍♂️😊

[@glencooke494]

Andy has already done this in a previous vid and was very interesting as to the results. Check it out Full and empty Jul 13, 2021

[@OffGridGarageAustralia]

I will do such a test again in part of the video. I now know that the Palo cells have a lower SOC than the EVE and once the voltage rises in the EVE... it will get interesting.

[@andrewradford3953]

I'm thinking of doing this from my 1p 48v Nissan Leaf gen 1 bank to a partially depleted 2p pack on my ride on. Fast charge then top up with 100a from the Victron smart solar. Mower battery temperature will be critical for this to work or not.

[@OffGridGarageAustralia]

@@andrewradford3953 Be careful with that as the mower battery can pull a lot of amps. It's easier with LiFePO4 due to the flat curve but with liion you need to match the voltages first.

[@Digimer]

Thanks for doing this, Andy. I plan to parallel equal batteries, so really interesting. Thank you also for coming out to the live! ^_^

[@OffGridGarageAustralia]

Thank you!

[@dirkityourself]

Hi Andy - you are braver than 'Crocodile Dundee'! Thanks for this video. This is what I call real edutainment according to the 'Sendung mit der Maus' style. Keep it up.

[@1981dasimpson]

from my tests over the years the lower capacity cells with run along side of higher ampage ones with no problem as they are tied in voltage commenting befor i have scene the video and results

[@steved2701]

I love your videos but rarely comment. I've been curious about this topic as well. Bravo for covering all the bases with this experiment, especially the safety goggles! "Eddy current" as I've been taught is the stray current inside a conductor induced by magnetic fields, perpendicular to the main current flow. This current performs no useful work, only producing heat. I would use "equalization current" to describe what you are seeing. I'd like to see how the unequal banks perform during a few charge and discharge cycles. My gut feeling is that nothing exciting would happen (hopefully). They would charge and discharge strictly according to the parallel voltage both banks see.

[@solventtrapdotcom6676]

You are correct. He probably knows, but English isn't his first language. He does this occasionally.

[@OffGridGarageAustralia]

Eddy current has come up in the Orion BMS PDF and was associated with the equalization currents in between battery banks. This has nothing to do with any language I speak or know, total rubbish. www.orionbms.com/manuals/pdf/parallel_strings.pdf

[@evil17]

@@OffGridGarageAustralia yes of course ur right Andy, I think this guy is referring to Eddy currents as found in ac equipment, transformers are laminated to help prevent these Eddy current build up & heat. In your dc case we are referring to the induced Eddy currents between 2 opposite conductors & electron flow, does this sound about right?

[@evil17]

@@OffGridGarageAustralia ok, I read ur Orion pdf, I get it, sort of, however, another but. I do keep annoying you with Capacitor stuff Andy, 1) I do like the idea of a large supercar at the inverter, possibly kept to a higher charge level with battery’s. Simple, and keeps a good dump area for ripple, burst and battery changeovers. 2) A big one at the Bus Bars would also be a great option or both for extra battery surge protection & filtering & charging 3) A big one at each battery bank isolator so switching between battery banks has good in/out current buffer, again caps could be kept at a higher SOC/voltage and let bms do the charging of battery cells, would allow extra burst currents to and from inverter & solar charging gear too with maybe a pre charge switch/button for each cap bank if you want to equalise them first. And again, another at inverter or busbar would have to further help. I’m not sure Andy if this type of capacitor technology/usage is as much of a thing nowadays with this new lipo4 chemistry and high C rates, which could bring up an idea of a smaller perhaps , LTO setup instead of caps to do a similar job, but caps would still be cheaper and quicker and better. If you are interested at all in any of these capacitor ideas I have, I would really love to see some real testing on these caps and ideas. I think a local Brisbane mob, FPV or FPV Power has some really cheap Maxwell Capacitors in 48v & 16v banks, (2nd hand ex train, bus, tested, supposedly) & seem ok so far. They are on YT too. I hope I haven’t bored you with all this, I would like to here ur idea’s about using capacitors in these ways. Thanks for all ur really great vids Andy, it must take you heaps to do all this work, study, edit, reply, testing,etc. Cheers

[@luc_libv_verhaegen]

Now this is indeed what I have been waiting for. Have at it Andy.

[@OffGridGarageAustralia]

Enjoy!

[@MarkusIngalsuo]

A bigger rock is harder to both push and pull than a smaller one 🙂 Andy, test a diode protected setup! Connecting the battery banks through individual diodes to the load and charging them separately would be much safer than letting current flow between banks.

[@OffGridGarageAustralia]

That would not work as you cannot discharge the banks any more ;)

[@MarkusIngalsuo]

@@OffGridGarageAustralia yes it does. If each bank has a diode in series before the main positive busbar, current will be allowed from the bank to the busbar but not in reverse. Each bank must then also be charged from inside the diode, individually. This is the main drawback. There are very good diodes today so losses are not that bad. Also, there are ideal diodes but those have to be hugely dimensioned and then also expensive.

[@resenmkd]

Very informative experiment, this should put few people in their place on the forums

[@OffGridGarageAustralia]

Yes, I was always interested in how this works and the forums didn't give me the answer. So I had to do this test myself in all details.

[@resenmkd]

@@OffGridGarageAustralia so today I installed 330ah and 370ah 12v based on your video with same results…..all I can say is keep this videos coming mate 🍺

[@dig1035]

Waiting for discharge test to see if different than lead acid?

[@OffGridGarageAustralia]

Coming very soon.

[@wideawaketotruth5301]

Wonderful demonstration Andy. You always come up with the most interesting tests.

[@OffGridGarageAustralia]

Thank you very much!

[@arj1978]

thank you for sharing this experiment. i learned a lot.

[@OffGridGarageAustralia]

Thank you! Yeah, me too. I was always curious what would happen...

[@GarethJones-dk9yp]

This is a great video. Your right not much on this topic. I am running different size battery banks in parallel. You do have to be carefull doing this. Each parallel string can still go out of balance. My advice is either have multiple BMSs for each string or tie the balance wires together for each bank and fuse them both ends. So C1 of B1 sting to C1 of B2. Looking forward to next video :-)

[@amudlifecrisis]

Awesome video Andy! I love this experiment! Looking forward to the next one.

[@OffGridGarageAustralia]

Coming soon!

[@HarmonyExpressSkoolie]

Quite fascinating experiments, Andy. This is completely applicable to my situation as I'm about to add a separate bank of Nissan Leaf cells to my system to increase storage capacity. This is fascinating. Cannot wait for the next one!!!

[@OffGridGarageAustralia]

Are you going to mix LiFePO4 and Li-ion?

[@HarmonyExpressSkoolie]

@@OffGridGarageAustralia absolutely not. Right now, I have nine leaf packs in series parallel in the Skoolie. I have 6 more packs and will arrange them in series parallel with their own BMS. Basically the same situation that you have with these two different groups of cells with the same chemistry, but different capacities.

[@OffGridGarageAustralia]

@@HarmonyExpressSkoolie Will your Skoolie be fully electric eventually?

[@HarmonyExpressSkoolie]

@@OffGridGarageAustralia right now, we have a propane water heater and propane stove. We’ve thought of going to an induction stove and electric oven, but this takes serious power to achieve. It will take a lot for us to convert our water heater to electric, but we’ll see how much storage we can amass. Space is limited for panels on the roof.

[@HarmonyExpressSkoolie]

@@OffGridGarageAustralia So... Now I'm wondering if I should completely reconfigure my entire battery. Currently, I have three packs in series to get to 24 volts and then three of the three packs in parallel to get the increased capacity. Using this method, I am not really balancing the individual cells since I have one BMS protecting the whole 24 volt big battery. I'm thinking that I should break up the three packs and have a separate BMS for each small 24V battery, then connect the smaller 24V batteries to a main buss bar. This would give maximum protection to the battery and would help with balancing. The bonus would be that each individual BMS could be a lower amperage. In your way of thinking, Andy, would there be a negative to this way of connecting other than having to purchase 5 separate smaller BMS systems?

[@easylooker]

This is what you want for parallel packs, to balance each other. If you introduce a new pack that is 50% to an 80% pack id say you need to get the packs closer than that. Current is going to flow in the path of least resistance, if those smaller cells have more resistance then current is mostly going to flow in the big ones with those nice big busbars. Id like you to do a test with the 280AH and the 304ah in the same manner to see if they charge the same. Or one side is taking all the current. If one side does simulating solar panels charging them and sun goes down does the lesser pack equalize with the most charged up one.

[@KoiAquaponics]

In a large bank with multiple packs, do we want them to flow current to equalize or is that not a good idea?

[@ranig2848]

Thank you! Can you also do a test with 2 BMS (eg 2x 100amp BMS with 180amp current) on a *single* 304AH battery pack (ie 4 eve batteries)

[@OffGridGarageAustralia]

Oh, that's not a good idea. I already replied to your other post about this. If one BMS turns off a bit earlier than the other all the current goes through just one BMS. Are two 100A BMS not more expensive than 1 200A BMS?

[@ranig2848]

@@OffGridGarageAustralia they might be a bit more expensive but assuming I can place them on two sides of battery so better thermal dissipation. Also, I don’t think Ciabatta/JBD makes 300amp BMS and their 150amp BMS appears to be a really nice BMS…

[@marcelolima-adv]

Congratulations for sharing your vídeos with us. This Marcelo typing from Brazil.

[@upnorthandpersonal]

You'll even see different current distribution (initially) with two packs of the same capacity when they're not at the same state of charge (but same voltage). The reason for this is that the internal resistance of the cells change with their state of charge.

[@OffGridGarageAustralia]

Yes, I'm expecting this as well. We will see this when we connect the two big banks together.

[@stefanknospe181]

Andy, thank you. It is the same experience that i have with my 2x16s (200Ah and 280 Ah). Now i am waiting for the next video :-).

[@JR.M.S]

Looking forward for your next videos!

[@OffGridGarageAustralia]

Coming soon!

[@bigbeef2654]

Eddy currents (also called Foucault's currents) are loops of electrical current induced within conductors by a changing magnetic field in the conductor

[@upnorthandpersonal]

Eddy current is such a badly chosen term for this. I know I've come across it in the battery literature, but there is a very specific definition of Eddy current in the electric world (the one you mention). Wish whoever did that hadn't done so...

[@andrewradford3953]

Sounds like it could do with a suppression ring..

[@newton833]

what about making 24v system from 2 12v systems with bms in series? what are the limitations?

[@homsolar1590]

This is our strength. We mainly do BMS and ESS.

[@wayne8113]

Thanks Andy

[@1over137]

100mV creating initially 1.5A suggests a total series resistance of 60mOhm. A thing to watch out for though. That number is not constant for a battery. Not for a single instance of a battery or for batteries generally. The total series resistance of the battery depends on everything from the size of the battery, it's SoC, it's temperature and how many amps are going in or out. In "layman" terms this often behaves and is described as "springy-ness" of the battery. During the "bulk" phase of charging the resultant voltage across the pack is "elastic" based on the current. It usually what is used to determine the maximum charge and discharge currents. That elasticity is in the series resistance and how many of the voltages you are pushing with are dropped across the battery. Think about this: A lead acid at 10V (flat). If you put 100A across it, the voltage will almost instantly rise to 14.40V and the current start to fall away. If you now immediately, stop that charge. The voltage will settle back down to 10V again, or 10.1V. The 'real' battery voltage is 10V the 14.40V the charge is seeing is the battery voltage + the voltage drop across it. 4.40V @100A = 440W which is NOT going into the battery, it's being wasted as heat or damaging the battery internals and that's why you don't do it. It is this elasticity that almost prevents current run away between two batteries. Different chemistries have different "elasticity". Playing with LiFePO4 at either ends of the their SoC is probably ill advised if you want to avoid high current, but with 100mV, not an issue. The elasticity, even of LiFePo4 is very likely to absorb that in portion to the battery size. Larger batteries will appear less elastic and require more current to force their voltage up over "actual", smaller batteries will appear more elastic and their voltage rise more rapidly with current.

[@flechner]

Hello Andy, this is Franz from Austria (not Australia 😏). We have her a discussion about paralleling LiFePo4 batteries (where each battery got its own BMS). Did you ever do a test if the capacities add up or if the total capacity is less than the sum of the individual capacities? Best regards from Austria, Franz

[@madcow3417]

I'm in the planning phase and I spotted a problem with my mismatched capacities. I wanted a 100A BMS for my 280Ah cells, in parallel with a 100A/100Ah battery that I already have. 74% of the capacity is in the new battery, so to match voltages 74% of the current will be drawn from that battery. (Battery resistances will throw these off, but close enough). This means that any current draw greater than 135A on my system will draw over 100A from the 280Ah battery. I'm purchasing a 300A BMS for the cells now.

[@OffGridGarageAustralia]

Yes, that should work. It basically balances the current between the two banks where the higher capacity bank gets a higher current (charge and discharge). Set the BMS for both banks correctly tot he specs of the cells so in case the balance shifts, it will turn off the smaller bank for safety.

[@honumoorea873]

I got a 280Ah 48v in parallel with a 80Ah for years with no problem. The only problem would be the impossibility of using all capacity if their soc/voltage curves (charging and discharging) are too different.

[@Sylvan_dB]

Same SoC you are mostly okay. The problem is when you are parallel a series sets instead of paralleling each cell. If you parallel each cell they are forced to be at the same state of charge except under very large currents. If you parallel series sets then the best case is similar to paralleling individual cells, but in the real world minor differences mean each set will vary and may need to individually charge each set to get back to same state of charge. And if they vary then current will flow between the sets, at potentially dangerous or harmful levels. General rule for reliable battery operation: Parallel at the most granular level possible, ideally each cell. But if you have appropriate automated safeguards and you monitor your battery closely then you can get away with a lot because current will flow between and somewhat equalize SoC between parallel sets. Paralleling cells means the equalizing is only between paralleled cells and the potential voltage difference is small. Paralleling the full "48v nominal" battery means the equalizing current has to flow from and to the entire battery - thru every cell in both batteries - and the potential difference is much larger meaning much higher current. And FWIW paralleling lead-acid battery banks works the same and has the same issues. If you have a 48v (24S) lead acid battery it is better to increase capacity by paralleling each cell. If you parallel in 3S sets (common 6v battery) it isn't as good as paralleling each cell, but it is better than paralleling 24S sets. Often with lead a compromise is made - parallel the 24S sets, but add a few smaller cables to subdivide (or parallel) smaller sets - e.g. a single cable in the middle means you are paralleling 12S, or with two added cables you reduce that to paralleling 8S. Key is to maintain same SoC as much as possible and reduce the path of equalizing current as much as possible.

[@OffGridGarageAustralia]

I don't like paralleling cells actually. You lose control over single cells as they all appear as one. This is much better and I can monitor all cells through the BMS.

[@Sylvan_dB]

@@OffGridGarageAustralia It really doesn't matter what you like, but yes if you want to control individual cells then you must accept the compromise.

[@lucasokomuniewski6525]

I have 3 banks set up in parrallel 2 x 280ah and 1 x 200ah, charging and discharging is great this way as the amps are split and lower for each bank. Only issue is I haven't found and bms that can be parralleled togeather.

[@resenmkd]

How’s this working for you as I also don’t have bms and scared to charge now?

[@lucasokomuniewski6525]

@@resenmkd I have an active balancer per bank and this is fine for now as I regually check the banks voltages.

[@resenmkd]

@@lucasokomuniewski6525 thank you

[@gregb1714]

There is no problem when you put battery banks of different current capacities in parallel. Charge and discharge currents will automatically balance out. The reason is simple - ohms law. Large batteries have a low internal resistance compared with small batteries that have a high internal resistance. So for example, if you have a constant charging voltage, more current will flow into the large battery bank because of their lower internal resistance.

[@OffGridGarageAustralia]

Yes, I show this in the next video. Very interesting stuff...

[@jeremygonzalez3042]

Would be interesting to see a similar experiment but with lead acid batteries!

[@feinedrachenrogerrumpel2126]

looking at the numbers: EVE has 13,6V at 2,9A; palo has 13,6V at 0,7 so total resistance of circuits is: eve: 46Ω and palo: 194Ω. 194Ω/46Ω = 4,2 and 2,9A/0,7A = ~ 4,2 perhaps you want to check this with an ohmmeter. your circuits will always share the current with the factor of ~ 4,2.

[@OffGridGarageAustralia]

I measure the internal resistance of both banks in the second part. The main problem here is the voltage drop from the power supply to the bus bars.

[@junkerzn7312]

Yah, it should work fine. But there is one provisio, and that is you must make sure that the maximum charge or discharge current does not exceed the capabilities of the lowest-capacity cell (see notes). So if you have a 300Ah and a 25Ah and the first can handle 150A and the second can only handle 12A, then you cannot charge or discharge at greater than a total of 12A for a parallel cell group. The reason being, of course, that if the big cell(s) fail, the last man standing has to take the whole load and you never want to put the battery bank in a situation where there is any chance of overheating. NOTES: If paralleling just two batteries, then do not exceed the current capabilities of the lowest-current-capable cell. When paralleling many batteries, the rules change (current can be scaled up as long as sufficient safety margins are maintained for reasonable failed-cell cases). Since, obviously, paralleling is often done not just to increase capacity but also to increase current capabilities. How much license you take really depends on the topology, safety margins you desire, and how easy or hard it is to disconnect parallel elements (you don't want to over-current by accident because you disconnected something and forgot). -Matt

[@immrnoidall]

The Breakers confuse me. i must have missed that part. I looked them up and they said nothing of "DC" , just AC. Also, 32 amps seems small for DC currents we are using. I want to sett up these kind but could use some explanations of their amp and volt ratings.

[@trevortrevortsr2]

Andy - in both BMS the charge passes through mosfets - if the R value of the mosfetts in both are not the same it would dissrupt the proportionate distrabution of charge - which it seems to have done - although your test clearly shows the larger cell taking more charge it should have been proportionate to capacity 302/5 (

[@OffGridGarageAustralia]

I don't think this has anything to do with the BMS. I could swap them around and we would see the same outcome. The current distribution is purely dependant on the internal resistant of the string. I'll show this in part 2.

[@trevortrevortsr2]

@@OffGridGarageAustralia I look forward to that Andy - Its likely to be a combination of "resistances" in the charging loop - we have built quite a few motor controllers and have raised a few eybrows the impact of the forward resistance of different mosfetts, the impact on efficiency and heat sinks - it would be interesting to see the refrences codes from the mosfetts used in both BMS's

[@jamessellick6721]

Hi Andy, really been enjoying your video's. Think you hit CV when testing so current slowed into the smaller cells. If you had some headroom with the voltage I'd imagine the current to stay high and damage your little cells. What do you think? From not so sunny, hot, UK. Cheers

[@OffGridGarageAustralia]

Could be the case, we will see in part 2 when we push 2A into the banks.

[@adrianschutte]

Andy, Again tx for an informative video. I stumbled across you channel and have been binge watching. If I can add to your "todo" list is to explore the canbus implementation of the JK BMS. This would be especially good in a marine application where the BMS can preemptively orderly stop charging sources such as Alternators coupled to an external regulator such as Wakespeed.

[@Mark-wv6sg]

I bet Will would like to get his hands on that battery cabinet

[@OffGridGarageAustralia]

He's building his own from what he said in his videos.

[@mprelectrical]

Hello, I am using 2 x 100Ah 12v Lithium batteries in series 24V, my question is can I add another string of 2 batteries but use 105Ah batteries for the second string.

[@OffGridGarageAustralia]

Yes, that works as well. As long as the batteries in series are the same capacity.

[@dig1035]

Interesting! Thumbs up and subscribed! No Arcs, sparks, or smoke, nice!

[@Bartbobo]

Thank you Andy I have two 12v lifepo4 one is 12.8v 200AH 200A BMS and the other is a 12.8v 190AH 150a BMS two different name brands a Powerqueeen and a Timeusb plus ... looks like I can parallel with these two I have and it will work for charge and discharging with no issues I just want to know if you can confirm by the info I stated ...but by your example here I should be ok to do so..let me know what you think if you would be so kind

[@TimHayward]

DC clamp meters are very inaccurate. I would recommend using leads when measuring low currents.

[@OffGridGarageAustralia]

That is correct but for this test the accuracy was not so relevant as showing how much power went into each battery bank. You can also wrap the cable several times through the clamp to increase accuracy and then divide the result by the amount of coils in the clamp.

[@jmaus2k]

Maybe adding a resistor between packs would be a good idea. Switch a 100ohm resistor to parallel, then flip circuit breaker. These bms mosfets are likely to fail with high currents, but you don't have a good idea of current before flipping breakers. Well, i guess you could figure it out voltage difference / battery resistance.

[@OffGridGarageAustralia]

Yeah, but if you only measure the resistance of one string (so include BMS, cables, connections, cells,...) and calculate the max current to be expected, in reality it is far less as there are other limiting factors as well (rising cell voltages in the receiving pack for example). At least this gives you a good estimate what you could expect.

[@ChamaraWeerasinghe]

What is the difference between top balancing active balance... My question is high capacity LFP first time need to top balance? Easy enough to use active balance without top balance....

[@thedavesofourlives1]

I was hoping this would be about adding a single smaller capacity cell to a weak cell in a pack to reduce the bad cell runner.

[@nerdrulesu]

just waiting for some gremlin to jump out of the shadows and yell bang.....another great video 👍

[@OffGridGarageAustralia]

Hahaha, that sometimes happens and it scares the 💩 out of me. It's enough if just a fan comes on exactly at the time when you connect a cable to something 😂

[@MarkO-ee1dz]

Greetings from Poland Thank you for everything, master I am your student

[@OffGridGarageAustralia]

My pleasure!

[@babaluto]

And here I thought you would never get political. So much for "internal resistance".

[@OffGridGarageAustralia]

Ah, you got me here 🤭

[@petertrebing6875]

I always ask myself: How dangerous are the balance cables? What will happen in case they create a short? Will they burn or does the bms switch off? And most important: is the balance circuit of the balancer secure? Can it create heat, fire and damage in case the circuit has a defect? Is there any kind of ‚passive‘ safety device inside the bms?

[@Josh-b3c]

I've been running six different batteries in parallel all 12 volt I have two x 280ah. Two x 100ah and two x 60ah sets

[@OffGridGarageAustralia]

All the same chemistry?

[@Josh-b3c]

Yes

[@peteradshead2383]

This comment was made before watching your video , it will be interesting to find your result , because I want to know if I can mix 2 x 50ah batteries with a 200ah battery . if I pull 100 amp from the batteries does the 200ah take the loins share or will it be equal 33amp ? , can't wait to find your result on can I mix different battery capacities .

[@kswis]

What about trying this with different chemistries? Say running lifepo4 parallel with lithion 18650-21700 ect? I have a 100s of ah's worth of lithion it'd be nice to add it to the bank. Never really put much though into it, a 3s pack might be better suited than a 4s @ 16.8 volts fully charged. In theory long as you have a bms on every pack. Idk could be interesting

[@BajanAlan]

Read REN comment above

[@todamnbad]

I have two 300AH cylindrical cell batteries, two 300AH prismatic cell batteries (150AH cells) and five 200AH prismatic cell batteties (100AH cells), none of my batteries are DIY and are from three different manufacturers so im not sure what the BMS is except they are all rated at 100 Amps, I have always been curious what would happen if I wired them all together, manufacturers all say not to mix brands of batteries or cells but im starting to wonder if its because they want you to buy more of their batteries

[@OffGridGarageAustralia]

That's actually a totally different situation. Each of the 12V (I assume?) batteries have their own BMS already and should take care of the internal cells, voltages and current. I think the warnings are overrated as I can not see a problem if you stay within one chemistry and the curves are much the same. Once you mix them, it will be different, I would expect. However some here have stated that the system still works fine with a mix of LFP, Liion and even acid batteries all connected in parallel. So much still to test.

[@kipdennis3796]

​@@OffGridGarageAustralia Hi Andy,I have 4pcs of 200ah lfp cells and 8pcs 100ah cells,can i connect 100ah cells in 2p configuration then in series with 200ah cells to form 8s 200ah battery?I have jk bms pls reply if possible

[@TimHayward]

I'm thinking at using 3.4v to the inverter so I don't have any need for balancing and the BMS only needs to do the simple stuff. That way I can mix and match cells, I can charge from lower voltage sources. Up conversion is so efficient I can't see a reason not to do this

[@OffGridGarageAustralia]

Yes, that is a possible solution but 3.4V is just at the rise of the curve but it is still a bit too low for having a consistent charge. I made a few videos and tested this in all details. From what I found you should charge at least to 3.45V and even then it is dependant of your charging current (the speed of charging) and the absorption time (kzbin.info/www/bejne/p4vKZX2um9mqY8U). I like to stay fairly low with the charge voltage as well and at 3.45V and 30min of absorption I'm getting over 99% of capacity out of the cells without stressing them.

[@TimHayward]

@@OffGridGarageAustralia thanks! I will check it out. I have a lot to learn before I get to experimenting.

[@agusmuharam6491]

Andy I am about to parallel PV instead, current parallel 2 X 5 ea (500 wp) I got nother 2 ea 500 wp. it become 1 array 5 of 500 wp, 1 array 5 of 500wp and 1 array 2 of 500 wp. they are connected to PV Combiner. For some reason re arrange pv (to 2 X 6 instead) is not possible at the moment. the question is if this option is possible safety wise?

[@merren06]

Hi Andy can you please recommend a good bench supply to charge a 48 volts system thanks

[@OffGridGarageAustralia]

I have two, the small one with 5A and the large one with 21A. Both go until 60V and are linked on my website: off-grid-garage.com/measurement-tools-and-analisers/ I made videos about each here on the channel as well...

[@merren06]

@@OffGridGarageAustralia thanks Andy

[@mitchrothermel8157]

The load will pull more from the higher residence battery first then stabilize as the voltage lowers all in all they will be the same voltage just opposite of charging

[@savydude1]

On Amy's website it shows that the 280ah battery is 6000cycles and the 304ah is 3500, is this accurate?

[@OffGridGarageAustralia]

Yes, the LF280K series can cycle 6000 times under compression and 25°. I have ordered these now and also the 304Ah cells with welded studs.

[@solaredd7805]

Have 2x14.4kwh eve batteries. It is paralleled and being charged by the Deye inverter. Can a separate charger be addded to the batteries while Deye inverter is charging or not charging? Will it damage either my inverter and/or LIFEPO4 portable charger? Thanks !!!

[@judgedredd8876]

I connected an engine starter SLA 12V 80Ah battery while at 12.2V (engine off) with a LiFePO4 206Ah at 13.14V and the current started at 5A and within 5 minutes it was 1A then it very gradually reduced as both batteries reached 13V. When I open the hood and connect a car charger to the 80Ah engine start battery I see output of 4-5A but the BMS on the house 206Ah battery only shows its getting charged at 2A so the other 3A are kept by the engine 80Ah battery.

[@NSWMods]

Thank u Andy Have a Great Week Mate Besafe

[@vonasi2]

Andy - some of your product links no longer work. I was looking at the 304aH cells but it just takes me to the Ali home page now. Maybe you need to update them?

[@vonasi2]

...it might just be that the 304aH cells are out of stock so the listing is down. I just messaged Amy and she told me that.

[@aatdekwaast3968]

To answer the last question...it's occuring because the small cells have a higher internal resistance, i think.

[@OffGridGarageAustralia]

Yes, that is correct.

[@smntsn]

I mixed my lifepo4 batteries with gel acid and liion(18650)s. These 3 work together without problem over 4 years. But gel batteries started to show some age... lithium ones has their own bms(s) but gel batteries have none. They charge over solar panels with 2 epever mppt contollers (11v min/14.20 max). lifepo4, liion, gel acid banks connected parallel.

[@OffGridGarageAustralia]

I heard this from people ... How do you manage the charging current for the Gel batteries as they should be charged with only 0.1C max. Is this also something it regulates itself due to the internal resistance?

[@smntsn]

@@OffGridGarageAustralia yes gel batteries regulates themselves but my gel banks have triple capacity than lifepo4s and liions. i think this helps too.

[@MR-ub6sq]

14:02 I don't think that 500mA went into the big battery and 310mA went into the small battery from the charger. Before, the bms device used it for its own life. For example, a 200A jk-bms shows 0.0A when the charging controller gives 24V to the battery and 15W. Only the charging power exceeding that reaches the battery. So I believe that with these currents you are only feeding the controller. And since you didn't have exactly the same controls for your batteries, one might be more energy efficient than the other... As long as the bms app shows 0.0A, the situation is that almost all the charging current is going to the bms - not the battery.

[@ronny7380]

Sehr interessant. Hätte ich nicht gedacht. Hätte gedacht das jeder die Hälfte zieht. An ladestrom.

[@richeagleton5285]

What breaker are you using 309 amp what manufacture

[@OffGridGarageAustralia]

I'm using the NOARK MCCB from this video here: kzbin.info/www/bejne/hWrSZKZ8o52rhK8

[@martink9785]

This is very cool. Thank you for doing this 👍

[@derina.maleek9408]

you have unique style

[@OffGridGarageAustralia]

Thank you!

[@DaleKlein]

Very good topic, thanks. I like paralleled smaller banks. If a given cell becomes an issue, only that bank is removed, not the whole system. BMSs can be smaller, although need one for each bank.

[@SemiDeSemi]

Amaizing work ! Thanks )

[@RayBuildsCoolStuff]

hi Andy Thanks for exploring this topic. I love your testing and your thought exercises about the issues we face in our projects. I built a solar generator with 302AH cells and used lesser quality 271AH cells to make a booster pack that connects in parallel. I found that when doing a full discharge or full charge cycle the better bigger cells would discharge at almost twice the power at first until the voltage of the higher resistance lower capacity cells became slightly higher than the better pack. Then they would drain more equally based on their relative capacities and in the end the lesser pack would start to pick up more of the load until they both cut off almost at the same time. On charging the same kind of dynamic happened. The bigger capacity lower resistance pack takes a charge much easier at first until it starts to have a higher voltage and that then regulates the balance of current into the two packs through the middle of the charging. I made a video about the booster pack and did a deep dive video later and I discussed this in both of them. In the big systems I'm making now, I am using the midnite solar battery combiner boxes which will have 8 of these big batteries feeing into each and will then feed three 8kw hybrid inverters. They will find their own balance based on resistance and voltage, never getting two far apart in voltage as that will be the primary regulator of the balance between the packs. I visualize it like 8 tanks of water being filled through different sized hoses. No tank will get much higher than the other but at high fill rates the small hose will create a different level in its tank than a tank with a larger hose due to resistance to flow but the difference will never be very great and at low fill rates will be very minuscule.

[@mannyfragoza9652]

I'm guessing Victron is a little surprised there is no need for a Batter Combiner to get the same results you did in this experiment. Isnt their Battery Combiner suppose to do the same thing you have done here ? I was always told you cant put different batteries in parallel unless they were very similar in amperage. Andy You def put that theory to rest.

[@OffGridGarageAustralia]

The voltage is critical here. They need to have the same when you connect them. In the second test we will find out more...

[@mannyfragoza9652]

@@OffGridGarageAustralia ok

[@navegnadezena]

I have my byd 12V10Ah batteries every day on charge in my 12 V net, in parallel with a 700Ah lifepo 4 batterie. The resistenze of the cables and brakers is ok as protection of my smal batteries are lo, The 4A brakers tripped only one time, with a bad small battery.

[@OffGridGarageAustralia]

You don't have anything limiting the current into your 10Ah battery?

[@excillisbank2611]

Oui effectivement je me suis toujours poser cette question pour les batteries lithium ! merci la réponse est donner... merci et à bientôt.

[@jnjentinc]

This is all amazing, HOWEVER can we please see sooome smoke at the end at least 🤣🤣 come on !, I can’t be the only one thinking about some magic smoke 😆😆

[@OffGridGarageAustralia]

OK

[@danielglang6312]

@@OffGridGarageAustralia Be careful, when you let out the magic smoke you also let out the angry pixies. And the bite.

[@danielglang6312]

correction, they bite

[@edwinrebece9832]

Nice informative video learned a lot!

[@AllAroundTube50]

Amazing!