12S7P flexible battery pack

ESK8 Electronics
43

Thanks a lot for the info and the link mate, it is really helpful! :slight_smile:

44

This makes no sense,

First, if you use quality cells and build your pack accordingly there will be hardly any unbalance at all, I’m probably at 100 charge cycles and can’t measure any diference between cells with my 2 decimal digits multi meter, that’s without a BMS and never balance charging

Second, no cells will be exactly equal, this can cause they to go off balance, but, the higher the P you go the more you smooth out the diference between groups, so less capacity (and due to that voltage) diference you have between groups

What makes sense is, for the same BMS model, that has the same balancing current, connected to packs that have the same voltage diference but one has more P groups than other, the larger one will take longer to balance since is has to bleed more energy from the higher voltage groups

45

Do not worry about all the “non sense” about lithium batteries people talk about… You don’t even need to balance, only sometimes… If you use new cells and they are all the same… Good cells will not go out of balance and that little will be dealt with by a BMS.

46

A guy that builds batteries tells me some of his friends don’t even use a balancer and have been riding for more than a year, battery holding up nicely… I am not saying that is wise, just that all the stuff about not charging to 100 percent etc… all the way up to “do not use parallel connections, as that is very dangerous” It’s all bull… :slight_smile:

1 Like
47

I think the concern being expressed is, on most bms we talk about here, the balancing current is 50-100ma, which is really tiny relative to pack size. If there is an imbalance and you’re using a fast charger, it’s very likely the charge will be terminated before balance is achieved. If you keep going, it’ll fall further and further out of balance.

This all depends on the behavior of the charger and bms though.

1 Like
48

I wonder is the DieBie bms works that way also

49

Do you have pictures?

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50

In case you’re still curious 7 months later (I’m about to build a 8p pack w/DieBieMS so was curious too): it will stop charge current when needed during balancing:

  • when any p group exceeds a cutoff voltage a flag will be set to stop charging here
  • the next call of modPowerElectronicsUpdateSwitches will turn off charge current
  • next time the voltage monitor runs past here it’ll notice chargeAllowed has flipped will call modPowerElectronicsUpdateSwitches
  • the next state loop will here will switch into state BALANCING
  • there is no transition back into CHARGING, but once balance improves chargeAllowed will be set back to true, and the charge current will be restored
  • this can happen even after the transition to CHARGED, so your pack may still be balancing when “charged.” This is stealth balancing (no indication of it except over uart) which I’m not sure I like. Shouldn’t stay in this state for too long but I don’t think you’d notice if it did.

(Sorry for necro but with more and more big packs being built maybe that’ll be useful to someone.)

5 Likes
51

Hey guys,

Thank for your suggestions and sorry that I haven’t been very active lately! Since the long canadian winter has passed, I think it is time to try and finish my build.

I have made the parallel connection and now I am planning the make the series connections using Kaly’s PCBs. I am a bit worried about the parallel ones, cause my spot welder was acting a bit weird at the beggining. They seem fine, but again, I am no expert. Since I’ll be using the PCBs I assume there won’t be too much stress on them. What do you guys think?

For the BMS, I went with @bartroosen12 suggestion and bought 12S 60A smart BMS from aliexpress. I have noticed that the balancing cables aren’t long enough to reach the last two battery packs. Would it be ok if I solder some remaining cables from the first packs to extend those?

Cheers,

Vlad

20190511_005841 20190514_205459 received_2056012481194631

1 Like
52

I made my 12s8p a similar way. I didnt need my battery to be flexy but i wanted to connect the p groups in series with silicone wires because it will handle vibrarions better long term than a solid connection.

Good job

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53

Just checked your board man… 12S8P and 4wd, looks sweet man! Did you use and anti-spark loopkey or a fuse to protect your board? I am thinking to use both, though I am not sure if it’s recommended…

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54

Thanks man Ended up using a Unity and its built in antispark and only use a fuse on the negative charge wire.

55

That’s cool! So I guess I could skip the antispark loopkey as well… What fuse did you use? I am thinkin to go with a 60A since my BMS has 60A. I assume you must have a 100-150A, since you have a 4WD?!

1 Like
56

Nah i have a 10amp fuse my charger is only 8a but the fuse is there to protect the system from a bad or faulty charger. I dont use fuses between the battery and esc never have, i wouldnt want the fuse to pop while im riding cause thats dangerous.

57

ah, that makes sense! Thanks a lot for the info! I’ll be thinking if I will put a 10A fuse as well, though I’ll be using a Cycle Satiator charger, which I know is pretty reliable. Since I am a bit paranoid about the batteries catching fire, I am still planning to use a fuse on the discharge wire. Do you know if I should put an 80A or even 100A one, just to avoid more the situation you described?

58

Well my Raptor 2 has a 70a fuse and i beat the crap out of that board and never blew the fuse. Your battery is capable of 140a constant so id go with something a little bigger than 100a.

59

I already have a 100A fuse, so I guess I will go with that one! Cheers man!!!

1 Like
60

Hey guys,

I managed to finish the battery and I would need some help to set up the BMS. I have connected it to the PC, also to my phone and it connects smoothly. The default settings look pretty good to me, so I am not quite sure what I need to adjust or modify. Since it’s a new pack, it looks pretty balanced… do I need to do a manual calibration? @bartroosen12 Do you have some tips or some links where I can find more information about setting up this smart BMS?

Cheers! 20190525_120758 20190525_120838 20190525_191534 20190617_191420 received_634345917078981

6 Likes
61

That’s a sick pack man!

The default setting were pretty good already, I only changed the settings overvoltage settings a bit higher (4.3V) and the undervoltage to 3V per cell so the unity will do the voltage cut off and not the bms, bms should only cutoff in cases when there’s really something wrong.

Then I set the balancing mode only when I’m charging my pack when voltage reaches 3.8V but you can do this setting also on the app, I find it easier to change this on the app.

So balancing mode: turned on

Balance type: charge

62

Thank you mate! That sounds good, thanks! Is there any reason why I can’t leave the balancing mode on all the time as well as when it charges?

And what about the charge and discharge amperage, should I set those too?

Cheers!