LiPo batteries in parallel

[vax]

I'm going to use identical LiPo batteries in parallel to have more Ah. 5S packs connected parallel both by power leads and balance leads. Let's say 6 batteries in parallel.
Also I want to connect those 5S6P packs to series so I have 20S 6P pack overall and use Li-ion Daly BMS to manage it.

It should play out ok, but there's always some itch in the back of my neck that I have been missing something completely.

So, what do you think about it?

 

[motomech]

I'm going to use identical LiPo batteries in parallel to have more Ah. 5S packs connected parallel both by power leads and balance leads. Let's say 6 batteries in parallel.
Also I want to connect those 5S6P packs to series so I have 20S 6P pack overall and use Li-ion Daly BMS to manage it.

It should play out ok, but there's always some itch in the back of my neck that I have been missing something completely.

So, what do you think about it?

I think your idea is no bueno.
If by LiPo, you mean Lithum Polymer, a Li-ion BMS won't work.
Besides being different chemistries and hence different Voltage values (top, storage, ready to take a dive at too low a Voltage), parallel balancing Lithum Polymer cells doesn't work out. Think about it, what does the balance charger see w/ a paralleled pair, The avg. right? One cell could be at 3.5V and the other at 4.0V and the balance charger or BMS will "see" 3.75. With Lithum Polmer's proclivity to have cells get out of wack, unless you are lucky that day, the 2 cells are likely to not be the same, say within .03V. If the 2 cells aren't close at the start and stay close thru the charge/balance cycle, a balance charger or a BMS for that matter, can't do anything helpful.
To balance paralelled Lithum Polymer packs, you need to "break" the packs into 1P. That's why the "Toy" balance chagers have many models that will charge multible packs at one time.
I start with the largest bricks I can use, like 6S/10,000 mA bricks, so two of them configured at 2S/1P gives me 48V or so and a theorictical 10,000 mA potential. But what I really like is 7S, so two of those are 14S
If one is careful about Depth of Discharge (DOD), don't overchage and don'y connect balance leads in parallel, pretty soon the cells will stay pretty much the same value, then it becomes a matter of just ck'ing the Voltages and for that I use Battery Medics. I got a bunch of them. If the cells are within .05V max at top charge, you are good to go. I always put my Lithum Polymer at storage value. if they are not going to be used for a couple of days or more, so at that point, they are get balanced.
I never go below 3.5V (there are alarms for this if the controller doesn't have a Voltage Cut-off , but they are hard to use. I use a LCD display Voltmeter, but I've been doing this for so long, I just know about where my batt.s are at by how long/how far I've been riding. Actually, I don't go below 3.7V because, With Lithum Polymer's sm size, I can carry more battery than I will ever use on one ride (No range anxiety here)
Your reasoning behind this plan is a little faulty too. Adding parallel batteries doesn't give the Ebike "more Amps., that is a function of the motor/controller/load synergy. What it does do, it doubles the rated max discharge rating of the pack, but that is not really a big concern with normal ebikes, at least not for me. Upping the system Voltage not only increases the speed, but adds a little capacity as well. Big Amps really help climbing hills, if the controller, wires, and connectors don't fry. Easier to up the Volts than Amps and that's why like 7S Lithum Polymer so much, the caps in most controller's are 54V rated and 14S (52V)won't blow them. Can't really get big bricks in 7S, so I make my own. Can't use a balance charger with 7S as well, so I use a Meanwell bulk charger and charge at 14S and use Battery Medics to passively balance. Slow, but one can walk away (no need to watch BM's work ).

 

[amberwolf]

To balance a paralelled Lithum Polymer packs, you need to "break" the packs into 1P. That's why the "Toy" chagers have many models that will charge multible packs at one time.

Unless I completley misunderstand what you're trying to advise (which is possible; I'm exhausted from being sick and not always great at understanding even at my best), I don't see why that would be necessary any more than it is for an 18650 (or any other) pack; if they're already paralleled at the cell level, they are effectively a single larger capacity pack.

Since the OP is intending to parallel not just the main power leads of each pack in his parallel groups, but also the balance leads, it does the above.


If they're connected this way, then all of the cells in parallel with each other will remain at the same voltage both during charge and discharge.

(assuming that the wires paralleling them are not so super-thin that they have a high resistance that would cause a voltage drop even for tiny currents).

 

[motomech]

Unless I completley misunderstand what you're trying to advise (which is possible; I'm exhausted from being sick and not always great at understanding even at my best), I don't see why that would be necessary any more than it is for an 18650 (or any other) pack; if they're already paralleled at the cell level, they are effectively a single larger capacity pack.

Since the OP is intending to parallel not just the main power leads of each pack in his parallel groups, but also the balance leads, it does the above.


If they're connected this way, then all of the cells in parallel with each other will remain at the same voltage both during charge and discharge.

(assuming that the wires paralleling them are not so super-thin that they have a high resistance that would cause a voltage drop even for tiny currents).

Aw wrote;
<<<If they're connected this way, then all of the cells in parallel with each other will remain at the same voltage both during charge and discharge.>>>
Not w/ Lithum Polymer they won't.
I've tried many times to use those balance lead Y-spliters and every time I ck'ed the cells individually after a few cycles, they were off.
As far as using a BMS on paralleled Lithum Polymer packs, has anyone here ever had any success? Not that I have seen.

 

[neptronix]

I think packs would be fine if you parallelled the balance leads and matched the packs well, then hooked them into the BMS.
You just need to make sure the absolute high cutoff point is 4.2v, the low cutoff point is 3.0v, no exceptions.

You would also need to make sure every pack is balanced to the same exact voltage and there are no dud packs in the assembly before you wire up the power leads and the balance leads.

You will need lots of harnesses, but hobby companies sell those. You also want to test those for faults, because no RC parts are particularly high quality.

 

[DogDipstick]

Aw wrote;
<<<If they're connected this way, then all of the cells in parallel with each other will remain at the same voltage both during charge and discharge.>>>
Not w/ Lithum Polymer they won't.
I've tried many times to use those balance lead Y-spliters and every time I ck'ed the cells individually after a few cycles, they were off.
As far as using a BMS on paralleled Lithum Polymer packs, has anyone here ever had any success? Not that I have seen.

I have done it an quite a few packs with zero problems.

 

[motomech]

My mistake, I still think people are talking about Lithum Polymer when they use the term Li-po and I should know better by now. The term Li-Po is really a misnomer IMO and used too casually.
I would stand by what I said in reference to Lithum Polymer (w/ pouchs), but I suspect he really meant Li-ion (round cells) and the advice here, of course, applies.

 

[eMark]

I'm going to use identical LiPo batteries in parallel to have more Ah. 5S packs connected parallel both by power leads and balance leads. Let's say 6 batteries in parallel.

The only thing "identical" is the label, exception being quality LiPos, and even then there is no guarantee they are identical unless the cells (20S6P = 120 individual cells) are all from the same manufacturing run.
RC Lipos whether 1S or 5S are all 1P. So to make up a 5S5P (4000mAhx5=20Ah would cost at least $260 using AliExpress HRB 4000mAh packs or $300 if purchased from Amazon. Then 4 times more expensive when making a 20S5P battery pack ...

https://www.aliexpress.us/item/2255801134515984.html?src=google&src=google&albch=shopping&acnt=708-803-3821&slnk=&plac=&mtctp=&albbt=Google_7_shopping&albagn=888888&isSmbAutoCall=false&needSmbHouyi=false&albcp=19108282527&albag=&trgt=&crea=en2255801134515984&netw=x&device=c&albpg=&albpd=en2255801134515984&gad_source=1&gclid=EAIaIQobChMI04mm1ajggwMVORatBh1M7A3IEAQYByABEgJAHvD_BwE&gclsrc=aw.ds&aff_fcid=c52b5e68fb4f4230a50c46489b82c0a1-1705353476954-07805-UneMJZVf&aff_fsk=UneMJZVf&aff_platform=aaf&sk=UneMJZVf&aff_trace_key=c52b5e68fb4f4230a50c46489b82c0a1-1705353476954-07805-UneMJZVf&terminal_id=18e3c9b51be94615819616c18c611cb1&afSmartRedirect=y&gatewayAdapt=glo2usa

https://www.amazon.com/HRB-4000mAh-Battery-Airplane-Helicopter/dp/B079ZT1SMN/ref=asc_df_B079ZT1SMN/?tag=hyprod-20&linkCode=df0&hvadid=309830051937&hvpos=&hvnetw=g&hvrand=15157183940122532400&hvpone=&hvptwo=&hvqmt=&hvdev=c&hvdvcmdl=&hvlocint=&hvlocphy=9019693&hvtargid=pla-585518621465&psc=1&mcid=49e3af5aaadb3bee948d0f9a243fa774&tag=&ref=&adgrpid=59137078302&hvpone=&hvptwo=&hvadid=309830051937&hvpos=&hvnetw=g&hvrand=15157183940122532400&hvqmt=&hvdev=c&hvdvcmdl=&hvlocint=&hvlocphy=9019693&hvtargid=pla-585518621465&gclid=EAIaIQobChMIrOPlpqrggwMVdKBaBR0KZwZdEAQYASABEgKEBvD_BwE

Also I want to connect those 5S6P packs to series so I have 20S 6P pack overall ...

So the least a 20S5P battery pack would cost for those HRB 4000mAH cell (4x4Ah=16Ah) is between $1040 to $1200 ... plus all the labor intensive effort and additional fabrication expense.

To use even cheaper LiPos than HRB 5S1P LiPo cells is (IMO) a crap shoot (risky). If you were to use top quality brand LiPo cells (i.e. Gens Ace a 20S5P) a battery pack could cost nearly twice as much as a 20S5P HRB battery pack.

 

[E-HP]

I'm going to use identical LiPo batteries in parallel to have more Ah. 5S packs connected parallel both by power leads and balance leads. Let's say 6 batteries in parallel.
Also I want to connect those 5S6P packs to series so I have 20S 6P pack overall and use Li-ion Daly BMS to manage it.

It should play out ok, but there's always some itch in the back of my neck that I have been missing something completely.

So, what do you think about it?

If you get decent quality LiPo's and all cells are matched, you probably won't need to balance them. I've been using three 6S Turnigy Graphine LiPos in parallel for a little over a year, charged maybe 500 light cycles, and I've checked the balance 3 times in that period and all cells were within 0.02V of each other, so I never balance them. I also have two 7S Turnigy Heavy Duty lipos in series for about a year and same thing, never need balancing. The key is to make sure they stay balanced in the first couple of charge cycles when they are new, and send them back if they don't. I bulk charge everything with a 20S charger.

 

[circuitsmith]

As far as using a BMS on paralleled Lithum Polymer packs, has anyone here ever had any success?

Yes, for 9 years:

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[calab]

Lipo fire- no one hurt- my fault

posting a pic of my 6s battery that went bad last week. Turnigy, 6s 5000mAh. 290 cycles. it now sits in a bucket of sand surrounded by nothing flammable for 10 feet. No fire yet.

endless-sphere.com

Endless Sphere Podcast

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endless-sphere.com

 

[eMark]

I have done it an quite a few packs with zero problems.

Aren't some of your salvaged EV pouch cells from a Chevy VOLT - not RC LiPo cells ? Yes they are both pouch cells and lithium ion, but the similarity in the quality (professional vs hobby/sport) and reliable specs (RC LiPo) is questionable.

You will need lots of harnesses, but hobby companies sell those. You also want to test those for faults, because no RC parts are particularly high quality.

VAX is wondering if it makes good sense to buy "identical" ( as close as possible) six 5S1P RC LiPos for a DIY 5S6P pack (6P x 4000mAh = 24Ah capacity).. Altogether build four 5S6P packs so as to connect them in series for a 20S6P DIY battery pack fabrication.

Whenever, i read such a post (RC LiPo 20S6P DIY build) my first reaction is: "Does he really know what he's getting himself into, not to mention the expense"; even more so when the OP never responds to the subsequent replies. Possibly he even plans to buy the less expensive ("identical") AliExpess Lipos.

A DIY 20S6P RC LiPo battery fabrication is almost toooo large; especially if the intended use is to locate a secure space on an ebike. He may think a 20S6P RC Lipo battery build is less risky (chance of fire, injury) than is a 20S6P 18650 or 20S4P 21700 build because the DIYer doesn't need to buy sensing leads, bus bars, soldering and spot welder equipment besides becoming proficient in use.

 

[neptronix]

I'd much rather build a battery with a N.E.S.E module today. Safer cells, no intense soldering, maybe even close in price.

Build 2 packs of 10S strings so that you can balance each pack with an iCharger 1010b+ when needed and forget the BMS.

 

[DogDipstick]

Aren't some of your salvaged EV pouch cells from a Chevy VOLT - not RC LiPo cells ? Yes they are both pouch cells and lithium ion, but the similarity in the quality (professional vs hobby/sport) and reliable specs (RC LiPo) is questionable.

Yes All I use are from different generations of Chevrolet Volt. The LG documentation refers to it as a " Lithium-ION Polymer Cell"... whatever that means...

. Yes, i use one, cell, with big tabs 5cm x 2 cm...... where another might use 5x hobby grade HK lipos all with the 1cm x 1cm tabs.

The first cell is ( of the four revisions in the car over ten years) th LGX-P1. then the number changes alittle ( LGXP1.5, P1.7... so on... ) .

It is much different I suppose but I have had no problems running them in parallel with no BMS for a few years. I built a 30Ah of the LGX p1.5 cell. It is a 15aH cell and i built a 20s2p. the car originally has the configuration of 96s3p...

It is nothing like this "modern mess" that i see friends of mine doing.

Pic one: cell I use. Pic 2, LG MSDS. Pic 3, what my friends are doing .. Lol.

I mean I dont think its the cell paralleling the problem is,......... its the whole mess of trying to string along 20x hobbyking lipo packs form china and thinking they will give reliability... all those connections... and noone makes for betttr, molex waterproof,, or cannon gold pins..., Anything good like that... or simplifying the balance harness to a reliable assy...

My pack has exactly 21 balance lines ...( so 21 contacts making conductivity not like 80+ with cheap Hobbyking silicone wire...) ) and the two main discharge.

Now figure how many this guys Lipo retail pack has. 10g wire is the biggest of any of them... 24g silicone for the balance... Connector failure. China lipos use the bottom of the barrel plastic contacts. My friend ( owner of that hobby grade lipo stack, pic 3....) paid 4000$ for 4kWh of China lipos... tested them, vetted them, and sent half them back for refund, only choosing the best of the best of his purchase...and got the whole pack down to a 20mOh measurement. 20s, 30aH....

Meeanwhile I threw a pack together in quarter of the time and mine is 22mOh measured @ 25aH ( including the 4awg..) . Mine cost 318$..... he spend 4000$ to get 2000$ back and have a 2000$ lipo battery of brand new cells. I keep on telling him there are other ways .

I have RC hobby grade lipos here, i have run bikes with them. gave up. No fun. Looked for a bettter way and found it IMO.

I am running on three ( third) years on the current Volt cell pack on my bike. I have balanced it exactly three times. Every time it starts at 0.0005v +/-... and ends at 0.0005v+/- on my 16 bit datalogger that measures up to four decimal under a volt. Its crazy they just stay balanced.... No where for current to go ( be lost, get a cell out of balance... or something like that... yes serial number order cells... out the junkyard modules...) .

 

[DogDipstick]

The only thing "identical" is the label, exception being quality LiPos, and even then there is no guarantee they are identical unless the cells (20S6P = 120 individual cells) are all from the same manufacturing run.

RC Lipos whether 1S or 5S are all 1P.

To use even cheaper LiPos than HRB 5S1P LiPo cells is (IMO) a crap shoot (risky). If you were to use top quality brand LiPo cells (i.e. Gens Ace a 20S5P) a battery pack could cost nearly twice as much as a 20S5P HRB battery pack.

I agree. In serial order. at lest then you got a bettr chance.

However, point two... No. Hobby grade lipos certainly come in 2p. They are not limited to 5s, nor limited to 1p.

Those in the pic I show you above are 4s 2p... Each of those black blocks is a 4s string holding 8 cells.

They come in 6s7s8s, and even 10s. many drone lipos are smaller cells in parralel.. ( LIke Tatu 20ah drone lipo packs, they are 2x 10aH cells in p and strung along... each )... and yes Hobbyking just parallels the balance leads cell to cell... so one balance wire serves two cells soldered into one tab and strung along..

 

[DogDipstick]

and I've checked the balance 3 times in that period and all cells were within 0.02V of each other, so I

That is great. Yup. Me too. Me too. I bulk charge. 83.95v on the dot. Third year. Any weather. Now dont get me wrong.. I do check check check. Got a port for reading the voltages at will.. My multimetr doesnt even have the resolution to do more than two decimals on the DCV setting.. Under 1v it autoranges... and it if auto ranges to DCmV... I get four decimals... but a cell is over 1v... so it wants to go to DCV instead... range... But my datalogger can do four decimals, it shows in the spreadsheets.