New to DIY Lipo pack building - questions

I've been building DIY 18650 (12s & 18s) ebike battery packs for a couple years now with good success. (spot welding / shrink wrapping etc)

I'm now considering taking the plunge into building lipo battery packs but realize there are more concerns with pouch cell batteries. I've been searching the site, but not finding the answers.

I've been running my existing 18650 packs without a BMS and relying on my controller LVC to limit the discharge voltage. I'm also using a quality balance charger to bring the packs back to running voltage.

Would this still be a good strategy for DIY lipo builds? Or do I need to now run a BMS to closely monitor individual cell discharge voltage? Or could I use a low cost battery pack monitor/buzzer to beep when an individual cell gets too low while riding?

I know there are also more concerns with the physical build of lipo packs because they are more delicate than 18650s.

If you know what you are doing, and you do, you can run lipo naked. Additional precautions mostly apply to making sure the packs don't chafe, or get dinged.

And then as I always write, for the others reading usually, don't store or charge the lipos in a place you would not build a fire.

But as far as lvc goes, you can do about what you were doing before. The main thing with lipo is they go over the cliff at about 3.5v, and managing them (avoiding needing to balance them) is easier if you limit discharge to about 3.6-3.7v. I can go at least 3 months without needing to balance if I just stop before the pack goes over the cliff.

Tools for keeping track of cells individual voltage are always good, particularly when evaluating new packs. But personally, once I know I have no bad cells in a pack, I just mostly watch full pack voltage with a cycle analyst. If I must discharge 100%, then I put a buzzer on the pack that has the lowest capacity cell in it. If I know which cell always empties first, I really only need to monitor that one pack. The others will be fine.

I like my BMS protected RC Lipo cell packs because they’ve “caught” a few things that I might have missed on my own. But they're not without Warts either.

Here’s my frequently posted graph which clearly demonstrates how little energy remains below 3.65V/cell.

Obviously, it becomes a crapshoot about which cell is diving ahead of the rest? Pouch cells are simply not as consistent as can cells.

This is good BMS protection to have for number of reasons. Sometimes, these damn things (pouch cells) simply degrade suddenly and when they do it’s nice to know there’s a problem before it becomes a much larger and potentially dangerous situation.

The “ironic” problem I’ve experienced is with the cheesy balance circuits which don’t seem to do much (80mA) on large capacity cell groups. I’ve had bleed channel transistors occasionally fail as short circuit and bleed the cell group down to OD (over discharge) levels.

The irony is that the BMS tripped ODDV (over discharge detection voltage) and alerts me to the problem. Trouble is, there wouldn’t have been a problem if not for bleed balance transistor failures? Ugh…

So, there you have it from my perspective using this hobby crap for several years on a regular basis. Both BMS protected and naked. It can work well any number of ways but go easy, go slow and test your polarities often when assembling…

Thank you very much Dogman Dan and Ykick!

As always, your responses are extremely helpful and well written. This is exactly what I needed to know!

While running 'naked' I also find stopping on the high side of avg 3.5v/cell is pretty mandatory.
Imo how far above (like 3.6, 3.8v) is directly related to how heavy you're pushing c-rate on discharge, because (say half) c rating will move that cliff higher in dod for the group.

I'm running about 107a (ca) from 11.6ah 25/30c (so 30-40% c) right now, and all seems well down towards 3.7v with paralleled balance taps among the 2p 5.8ah sides. The controller limit kicks in and stops od pretty well.

Ykick mentioned before about being careful of non-monitored cells sagging way further then you realize, which likely will and has lead to accelerated weakest cell degradation for me I think. I currently still have 2x 4s packs in the 16s2p that have a p cell group needing watching, and if I continue with draws below ~3.7 on avg I might be sagging them too low.
That's a great idea to throw a cell alarm on that parallel group for easy tandem monitoring/control beyond the settable low cutoff on controller for entire pack and the manual medic monitoring (which do work nicely for non-bms)

I've been meaning to go over the limit setting on my controller. It seems to be working great when getting that low in dod, but that one weaker group should be checked closer for sag and the limit setting possibly raised.

Really good tips on bms and non.
Htfan, imo the bigger the pack, the more nice it is to have bms. On an enclosed frame I think I'd also consider one. Sure they are not without error/reliability factors, but it seems most of the potential problems caused by their error/failure are still 'caught' by them, keeping that safety factor.

Also, on the aspect of delicacy, alot of guys like hardcase I guess which helps. Or use enclosed frames. My packs are in a top tube pannier strapped to top tube, and fully secured with 1.5" and 4-5" wide strips of 'velcro'. quick removal in emergency, and super sturdy.
In event of a 'drop', I found some sturdy plastic utility storage boxes to cut up and retained 3 sides of each box trimmed to fit in each side of pannier. They easily protect front, outside, bottom (and respective corners) of the pack. I've dropped the bike alot, and kissed a telephone pole and a tree. The packs show evidence of imperfect compression/form from my rudimentary enclosure but no associated cell degradation is notable.

Htfan said:

I've been building DIY 18650 (12s & 18s) ebike battery packs for a couple years now with good success. (spot welding / shrink wrapping etc)

I'm now considering taking the plunge into building lipo battery packs but realize there are more concerns with pouch cell batteries. I've been searching the site, but not finding the answers.

I've been running my existing 18650 packs without a BMS and relying on my controller LVC to limit the discharge voltage. I'm also using a quality balance charger to bring the packs back to running voltage.

Would this still be a good strategy for DIY lipo builds? Or do I need to now run a BMS to closely monitor individual cell discharge voltage? Or could I use a low cost battery pack monitor/buzzer to beep when an individual cell gets too low while riding?

I know there are also more concerns with the physical build of lipo packs because they are more delicate than 18650s.

Click to expand...

There has never been a better time to convert to Lipo, as Hobbyking continiously has some seriously dis-counted bricks on sale. And they happen to be form factors we like to use. They seem to rotate brands and bricks of various specifications on sale.

There is really only one configuration that can be reasonably used without a BMS and that is 12S/2P. But the good news is there are new high capacity 6S bricks in 5.2Ah, 5.8Ah, 8.0Ah, 10Ah and 12Ah, resulting in 2P packs of 10.4Ah thru 24Ah.
Why 12S?
Most 48V controllers have a LVC of 42 Volts which with 12S(46V nom.)results in a cell LVC of 3.6 V., pretty much the exact the time to shut down Lipo. Do not rely on "alarms when using Lipo.
Why 2P?
To avoid "breaking" the pack means some sort of bulk charger(there has been 12S balance chargers, but at this time there are none available. There is a 14S charger, the Thunder TP 1430)and bulk charging requires a method of ck'ing and balancing the cells. For me, that means either 2 or 4 Battery Medics(more on those in a minute). At 3P, the cost(number) and complication of many BM's make a BMS a better option.

Charging;
The are many options for the bulk charger, most being power supplies. They range from a $25 Mean Well clone to Grin's $300 CYCLE SATIATOR;
http://www.ebikes.ca/shop/ebike-parts/chargers/cycle-satiator.html
I use a Mean Well LED power supply;
http://www.trcelectronics.com/Meanwell/power-supply-hlg-h.shtml
It's Fully Potted
weather resistant
silent, no fan
CC & CV
Fast, no cycling
Typical "off-bike" charging;

Typical "on-bike" charging;

Battery Medics available today tend to over-heat in dis-charge mode, so I add sm. 40 mm X 40 mm fans to them;
http://www.amazon.com/Andoer-Battery-Voltage-Balancer-Discharger/dp/B00LFJ5BMW/ref=sr_1_2?s=toys-and-games&ie=UTF8&qid=1460298199&sr=1-2&keywords=battery+medic

http://www.amazon.com/0-1A-40mm-Connector-Computer-Brushless/dp/B00E1JO8SG/ref=sr_1_6?ie=UTF8&qid=1460299592&sr=8-6&keywords=40x40mm+fan
What Lipo?
I have used Zippy 20C and 25C
Turnigy 20C and
Multistar 10C

The larger the brick, the harder it is to fit on the bike and often there must be a compromise between brick size and pack capacity.
The Multistar is good up to 25A controllers.
I general, I prefer Turnigy over Zippy because I think it lasts longer, but if the Zippy is dis-counted, it's worth using.
Right now on sale, I see;
http://www.hobbyking.com/hobbyking/store/__9935__ZIPPY_Flightmax_5800mAh_6S1P_30C.html
http://www.hobbyking.com/hobbyking/store/__16228__ZIPPY_Flightmax_8000mAh_6S1P_30C.html
Higher C rate than needed, but it can't hurt and the prices is great.
Being modular, I can swap, or add brick/packs of varying capacity from 5Ah to 30Ah, the most common I carry right now is 15Ah or 25Ah. With this kind of capacity, I can easily stay in the 80% DOD range that adds to the service cycles and still have more range than I ever use.
Big Lipo packs and good, hard LVC's means worry-free Lipo riding and no range anxiety

I use Dogman's method for long rides, but I use a cell log to look at the voltage, but I currently have a 12s 32ah pack that I rarely use more than 16 ah out of. I use 4s 16ah multistar lipos and bulk charge with 2 24v meanwell HLG in series and monitor charging with cell logs. Battery medics are definitely on my buy list as my Hyperion finally crapped out on me..

You got a lot more service out of your Hyperion than most of us did. Mine went up in smoke with less than a year on it.
The Thunder 1430 on Amazon is actually a pretty good price. But it needs a serious power supply/supplies, which I don't have.
http://www.amazon.com/gp/product/B00681QVOY/ref=nav_timeline_asin?ie=UTF8&psc=1
I'm pretty happy w/ my Mean Well HLG anyway.
You probably remember the debates over types of Battery Medics, red boards vs green boards, blue case vs black case.
Right now, just the black one is available and it overheats and turns the screen black, especially when discharging 6S.
I hot glue the little 24V mini-fan on the back and run them on the 6S brick's full 22.5 Voltage via the JST extensions I always use.
I had some 12V mini-fans I tried first by tapping off 3 cells, but they added to the bleed-off of those cells and they wouldn't balance with the other cells.

I've thoroughly exhausted most forms of balancing RC Lipo and I find no redeeming qualities about any method of "bleeding" off high cells. RC charger, battery medics, BMS etc., all suck IMO.

If your pack has one high cell there's most likely a capacity deficiency with that cell. You're better off qualifying WTF is going on and replace what needs to be replaced.

On some occasions when a cell is lower resting voltage than the others I will charge it 1S directly through the balance connector using any number of methods ranging from 1S setting on RC Charger to USB port 5V through a 1S BMS scavenged from old cellphone battery packs. You do not need to break down series connections in order to so.

My Hyperion 1430 lasted 14 months. My 1220's lasted one two months and the second one 12 months with using both at same time 24s spilt as 12s for charging then just one. Now charge with meanwell set 29v and a computer power supply 12.6v at 16 amps. A..lways monitor always before and after monitor. I also use Lifepo4 A123 830cycles. Just giving charger news. Never taken the step to the dark side.

All good cells on my last multistar purchase and I will just balance charge each individual pack occasionally, but they are all still very close. Agree with Ykick on the bad cell culling....

Every manufacturer of every pack, be it for your toothbrush or car, uses a bms. This is all that is available to buy if your stood in an EV store, Or looking for EV parts online. Of cource if you insist on doing it differently, there are things in the model world that can charge a battery. Buy enough of them and you could charge a pack. It's too many boxes though and the cost reflects this. You also don't get the protection you should have. It's not going to be as simple as charging your phone, and swapping wires leads about all the time leads to fires. We have lost a few houses here, never mind garages and sheds. For what gain?

Buy a bms and charger, It's industry standard. Use them to safely exercise every Ah you have, to get the rated cycle life from your pack before it dies of old age. There mass usage makes them the cheaper choice. They are simpler. They do a lot more. Don't cause a fraction of the number of bike losses we see. Weigh less. It goes on... And then look at the batteries. You need to buy and carry less. Maybe a third less.

It's a no brainer and I can't understand why anything else is on your mind. We have seen the procession from newbie questions, too balance charger recommendations, too burnt down houses. I think some people are simply sick in the head and want to ill advise you.

The only time to ignore the industrys only solution and go your own way, is when there is no industry solution of merit. Perhaps you want 120v just to get a feel for it before heavily investing. Then your basically modelling anyway. Chances are if your asking advice you shouldn't be doing it anyway though.

A charger costs about what a psu does and a bms from $20

We should listen to your pack needs and offer a bms solution here. Nothing else. If you have a fire, I'm one step closer to not getting my bike on the train. I'm way too selfish to have you killing yourself. Pack it up. Properly!

That's a worthy reply and opinion, tho:

The only time to ignore the industrys only solution and go your own way, is when there is no industry solution of merit. Perhaps you want 120v just to get a feel for it before heavily investing. Then your basically modelling anyway. Chances are if your asking advice you shouldn't be doing it anyway though.

Click to expand...

Isn't this a 'DIY" forum, and not a babe sucking the teet? The op and thus thread show significant enough knowledge to not specifically cater to newb/green norms. . . imo.

Also, all the stuff about stuff burning down/fires is a misnomer when it comes to bms vs non . . . .
To me It's the users being smarter than their 'tools'.

High quality cells are best. I wouldn't make a battery out of HK lipo. Maybe for a drag bike and stored in a barbeque. But that's me. Plus lifepo4 is stable 15c. Yes A123 835 cycles. 0.035 balance. My solution to lipo.

friendly1uk said:

Every manufacturer of every pack, be it for your toothbrush or car, uses a bms. This is all that is available to buy if your stood in an EV store, Or looking for EV parts online. Of cource if you insist on doing it differently, there are things in the model world that can charge a battery. Buy enough of them and you could charge a pack. It's too many boxes though and the cost reflects this. You also don't get the protection you should have. It's not going to be as simple as charging your phone, and swapping wires leads about all the time leads to fires. We have lost a few houses here, never mind garages and sheds. For what gain?

Buy a bms and charger, It's industry standard. Use them to safely exercise every Ah you have, to get the rated cycle life from your pack before it dies of old age. There mass usage makes them the cheaper choice. They are simpler. They do a lot more. Don't cause a fraction of the number of bike losses we see. Weigh less. It goes on... And then look at the batteries. You need to buy and carry less. Maybe a third less.

It's a no brainer and I can't understand why anything else is on your mind. We have seen the procession from newbie questions, too balance charger recommendations, too burnt down houses. I think some people are simply sick in the head and want to ill advise you.

The only time to ignore the industrys only solution and go your own way, is when there is no industry solution of merit. Perhaps you want 120v just to get a feel for it before heavily investing. Then your basically modelling anyway. Chances are if your asking advice you shouldn't be doing it anyway though.

A charger costs about what a psu does and a bms from $20

We should listen to your pack needs and offer a bms solution here. Nothing else. If you have a fire, I'm one step closer to not getting my bike on the train. I'm way too selfish to have you killing yourself. Pack it up. Properly!

Click to expand...

Is this great blob of nonsense addressed to me? Who is the "you" you keep addressing?
If it is, I guess I will take my time to respond, otherwise, perhaps(hopefuly), it will disappear into Cyberspace where it belongs.
And who is "we"?
You have a mouse in your pocket?

Looks like all this criticism is aimed at me, although no one seems willing to say as much.
Well, I'm getting a little tired of hearing that there is only one way to maintain Lipo and any thing else will surely result in burned down houses, garages, flaming bikes and loss of battery service life.
I have been using the "hands-on" approach because I have the time(I'm retired) and enjoy checking and monitoring and the whole process.
I know every cell, brick, connection and wire, probably far better than the rider w/ a pack buried in a shell w/ a BMS.
No, perhaps my approach is not for everybody and I don't push it on anyone.
But it works for me and has for years.

motomech said:

Looks like all this criticism is aimed at me, although no one seems willing to say as much.
Well, I'm getting a little tired of hearing that there is only one way to maintain Lipo and any thing else will surely result in burned down houses, garages, flaming bikes and loss of battery service life.
I have been using the "hands-on" approach because I have the time(I'm retired) and enjoy checking and monitoring and the whole process.
I know every cell, probably far better than the rider w/ a pack buried in a shell w/ a BMS.
No, perhaps my approach is not for everybody and I don't push it on anyone.
But it works for me and has for years.

Click to expand...

+1

metromech, I appreciate the information you have put in this thread. I found it as I too am a newbie wanting to learn how working with and maintaining a LiPo actually works, pros and cons of both persuasions.

Oddly enough, the BMS tangent provided some good information. I'm trying get a 48V build started while I was aware of the low-discharge concerns with LiPo, I did not know of the LVC that most controllers have. The "alarms" comment got me reading up on Cell-log LVC/BMC. It would be folly IMHO to run a single, unified pack without a BMS or similar, that makes sense. That's why the 18650 shark pack I want to get is so svelte, and pricey.

From what I've been reading it definitely takes more time and effort to balance and maintain 5S or 6S packs, manage a myriad of connectors, parallel balance boards, etc. It doesn't look as clean and pretty as a unified pack, but it gets the job done.

I'm using a hub motor kit to transform my regular bike into an electric bike cuz DIY is something I enjoy. I'm working with old SLA cells from UPSes that I can get for nearly free. It's alot of work with planning, managing a myriad of connectors, serial and parallel adapter harnesses for charging... sound familiar? LiPo is the next step in the process for me...

I'm trying get a 48V build started while I was aware of the low-discharge concerns with LiPo....

Click to expand...

Not sure what you mean here, actually, Lipo has high dis-charge rates. Now, I am switching to the new Multistar, which has a 1C discharge rate, the lowest of any Lipo. Still, icecube57 , a member here who does lots of testing, estimates a continuous discharge rate of 25 Amps. That's conservative I think, since there are a couple of guys over @ pedelecsuk running them at twice that.

I did not know of the LVC that most controllers have. The "alarms" comment got me reading up on Cell-log LVC/BMC. It would be folly IMHO to run a single, unified pack without a BMS or similar, that makes sense.

Click to expand...

To run Lipo without a BMS, it's imperative to keep things simple(no more than 2P) and to have a fool-proof LVC.

That's why the 18650 shark pack I want to get is so svelte, and pricey.

Click to expand...

Check out the Li-Ion batteries @ BMS Battery.

From what I've been reading it definitely takes more time and effort to balance and maintain 5S or 6S packs

Click to expand...

Well, for a 48V build, one would use 6S bricks, 6S + 6S = 46V (nom.). 6S is no more easy or difficult to build and balance than any other configuration of <6S. It's when one goes to 7S, 8S or larger bricks that things get more complicated. That's because most balancing techniques only go up to 6S.

...a myriad of connectors, parallel balance boards, etc. It doesn't look as clean and pretty as a unified pack, but it gets the job done.

Click to expand...

It's funny you should write this as I spent most of the day changing out my batteries and trying to clean things up a bit. Since everything is a bag, "cleaning up" is more like hiding things, but like "dirt under the carpet", I know what's in there and I keep trying. This is the 5th. major revision in 4 years, so I'm getting better at it every time;

12S/10Ah in the bag.
.

The other half of the battery and the frt. controller installed.



Rear controller in, done.

That's 2 medium sized 9-FET controllers and 20Ah of 12S in there, not bad :lol:
Used 9 pairs of 4 m/m bullet connector and a bag of 10 JST extension leads for this redo.
Made my own Y parallel adapter leads this time.

Every time I hold a brick of Lipo in my hands, I'm just amazed @ the amount of energy it contains for it's size.

To further summarise BMS vs. no BMS;
Is it easier to build a Lipo pack without a BMS? Yes.
Does not using a BMS save space? Yes.
Does it cost less to not use a BMS? No, I don't think so. I use Battery Medics, one for each brick, and a BM is around $15.
Is it safe to not use a BMS? Yes, if done correctly.
Will the batteries last as long without a BMS? Yes, if done correctly.
Does it take longer to charge without a BMS. Yes. At the beginning of the charge cycle, I clip on the BM's and read all the cell Voltages. At the end of the charge cycle, I again read the Voltages and if the cells are straying, I will bring them down in-line with the BM's. Usually they are ok, or just a little off and it doesn't take long to balance this way. But it is an extra step.
Bottom line;
Running Lipo like this is best viewed as a hobby, as it can be time consuming.
But if one likes maintaining one's batteries "hands-on", it can be a lot of fun.

Note on my new Multistar.
Right now, the cells are unruley and not wanting to play nice with their brethen. I have seen this before with new Lipo and expect as I add cycles(short ones for now), they will fall in lock-step.
My experience is such, that if the pack is left together, they "learn" to work together and there is less and less need to balance as the cycles go by.

motomech said:

There has never been a better time to convert to Lipo, as Hobbyking continiously has some seriously dis-counted bricks on sale. And they happen to be form factors we like to use. They seem to rotate brands and bricks of various specifications on sale.

Click to expand...

On the flip side, 18650s get more powerful and cheaper every year, and are radically more consistent than Hobby King (or most pouch type cells).

I stand by every word I said. I have the entire industry behind me too. Every industry that uses this chemistry in fact. This is why nobody can pick up on something I have said that is wrong, and can only have a hissy fit knowing they are here giving out bad advice, based on it's worked for them so far. Get your head out the sand motomech. Methods like yours cost people their homes. Don't they!!

I know you wish I would leave. You want to spread your ideas without being undermined. I'm sorry though, I can't sit back while another person gets poor advice that could lead too yet another house fire caused by listening to posts like yours. It's just not funny. By now you should know better. Stop giving out bad advice then trying to undermine the industries position because it has worked for you so far. My post was very valid.

I will close with a quote from yourself, just so we can see who you are

I don't even use Fuses, pre-charge resistors, Ebrake switchs or an on\off switch.
Every now and then, I'll lean against the thumb throttle with getting ready to ride. The bikes jumps a bit, but is easy to control.
The other day, I soldered on the wrong bullet connector and tried to plug two hot wires together, big flash, but it only melted one connector

friendly1uk said:

Every manufacturer of every pack, be it for your toothbrush or car, uses a bms. This is all that is available to buy if your stood in an EV store, Or looking for EV parts online. Of cource if you insist on doing it differently, there are things in the model world that can charge a battery. Buy enough of them and you could charge a pack. It's too many boxes though and the cost reflects this. You also don't get the protection you should have. It's not going to be as simple as charging your phone, and swapping wires leads about all the time leads to fires. We have lost a few houses here, never mind garages and sheds. For what gain?

Buy a bms and charger, It's industry standard. Use them to safely exercise every Ah you have, to get the rated cycle life from your pack before it dies of old age. There mass usage makes them the cheaper choice. They are simpler. They do a lot more. Don't cause a fraction of the number of bike losses we see. Weigh less. It goes on... And then look at the batteries. You need to buy and carry less. Maybe a third less.

It's a no brainer and I can't understand why anything else is on your mind. We have seen the procession from newbie questions, too balance charger recommendations, too burnt down houses. I think some people are simply sick in the head and want to ill advise you.

The only time to ignore the industrys only solution and go your own way, is when there is no industry solution of merit. Perhaps you want 120v just to get a feel for it before heavily investing. Then your basically modelling anyway. Chances are if your asking advice you shouldn't be doing it anyway though.

A charger costs about what a psu does and a bms from $20

We should listen to your pack needs and offer a bms solution here. Nothing else. If you have a fire, I'm one step closer to not getting my bike on the train. I'm way too selfish to have you killing yourself. Pack it up. Properly!

Click to expand...

I'm not going to discuss the facts of your original post since it's obvious that you are a zealot on a mission and facts have little meaning to you.
But by omitting the antecedent to your accusatory use of the pronoun "you", you come off as a preachy Elitist wagging your finger those who obviously have inferior powers of observation than yourself.
The readers here are intelligent enough that they don't need you hovering over every DIY Lipo thread and issuing your rules of engaging Lipo. Don't you have some other cause that desperately needs your expertise? Perhaps a social one that takes you outside away from a computer screen?
And referring to yourself as "we" is just creepy weird. One half expects you to start interjecting "My Precious" into your phraseology.
At least that would confirm you to be more of a Troll, and less an insufferable Do-Gooder.

HI!

I´d like to get an advice on assembling my HK multistar pack:

It consists of six 6S/10Ah packs that I want to combine in a 18s 2P (20AH) config.
I will charge each of the three "double bricks" 6S 20AH with a singular Accucel6 balance charger.

Questions:

- should I keep the balance plugs in parallel also while discharging the battery in the bike?
- As I balance charge a parallel group of 6S, I always have two cells that cant´t be measured individually. Would you still consider this safe enough for regular use?
- What would you recommend for a safe discharge BMS? I want to use 3C / ~60Amp of current with that pack. Should I buy 3 Battery Medics and put one on the paralleled balancer plug of each "double brick"? Or is there a nice one board solution for the six 6S packs indivually?
- Is there a real advantage of the BMedic´s ability to blance while discharging? But on the same this is what overheats them, right?

Thanks!

Darowi said:

HI!

I´d like to get an advice on assembling my HK multistar pack:

It consists of six 6S/10Ah packs that I want to combine in a 18s 2P (20AH) config.
I will charge each of the three "double bricks" 6S 20AH with a singular Accucel6 balance charger.

Questions:

- should I keep the balance plugs in parallel also while discharging the battery in the bike?
- As I balance charge a parallel group of 6S, I always have two cells that cant´t be measured individually. Would you still consider this safe enough for regular use?
- What would you recommend for a safe discharge BMS? I want to use 3C / ~60Amp of current with that pack. Should I buy 3 Battery Medics and put one on the paralleled balancer plug of each "double brick"? Or is there a nice one board solution for the six 6S packs indivually?
- Is there a real advantage of the BMedic´s ability to blance while discharging? But on the same this is what overheats them, right?

Thanks!

Click to expand...

You put your post in quotes.
That's too much battery to try and use and charge without a BMS, period.
If you try and parallel the balance leads of 3P, the charger will read an avg. of the three cells and you won't really know what's going on with the individual cells. Battery Medics would not be appropriate, way too slow, as would be the charger you mentioned.
That is a serious pack you are thinking about(actually all Lipo packs are serious)and you can't take the path of using chargers and methods that are for model toys.
As I stated very clearly above, 3P means a BMS and you should start researching your options for one that fits your proposed battery build.