6S LiPo BMS for (2) 3S LiPo in Series?

[torqueboards]

I've read quite a few of the posts on here regarding BMS systems on 12S, 24S, etc systems for Ebikes and attaching BMS systems to LiPo batteries. I'd like to see if I could add a BMS system to my 6S 25V Lipo Batteries. Couldn't find exactly what I needed. Need a few pointers on where I can look to learn more about how to wire the BMS system.

Currently, my system is strictly LiPo's - (2) 3S 5000mah Zippy Flightmax 30C in series. I run (2) 6374 Sk3 RC Motors on 6S. After a run they do become unbalanced by 0.1 - 0.8v usually it's 1 cell on each 3S pack. I end up running both of the batteries on a battery medic from HobbyKing to get the cells equally balanced. Once balanced I pop it onto my charger and charge multiple packs on a parallel charging adapter board. This method has been working great and batteries have lasted a ton of charges. However, I'd definitely like to explore the option of a BMS system and be able to charge directly to my board.

(1) I would like the option to switch batteries as I currently have (3) sets of (2) 3S 5000mah 30C Zippy Flightmax in series for 6S 5000mah. Would I be able to with a BMS?
(2) I want the batteries to balance themselves while in use.
(3) I want to be able to plug a charger in and charge batteries without a regular LiPo charger. How does the charging work when plugged in? Is there a button to flip or does it automatically charge? Is there an LED that lights up when charging and/or when fully charged? Does it auto turn off when it's fully charged?
(4) Can I install these rocket switches as an on/off button for my board itself? eBay List of Switches - http://www.ebay.com/sch/i.html?_trksid=p2050601.m570.l1313.TR0.TRC0.Xrocker+switch&_nkw=rocker+switch&_sacat=0&_from=R40

I know people have been recommending http://www.bestechpower.com/ for PCB/BMS boards. Are there any other places that are good too for PCB/BMS Boards?

Any links to any setups that could provide helpful info would be great through. I don't mind reading through posts as well. I just couldn't find anything I was specifically looking for.

 

[friendly1uk]

Is balancing during discharge a good thing?
The best cell could spend a lot of time being drained down to the level of the worst cell. A balance circuit I have here(just a random like)can drain 0.1Ah per hour. I reckon you could see more than 0.1Ah capacity difference between cells. So if the pack lasted an hour, it would spend the entire time balancing the top cell down to the bottom one.

Now lets charge it. All cells are equal, so our best cell will be last to hit full charge. The worst cell will finish first and start being drained while the biggest catches up. The only reason the biggest cell is more heavily discharged though is because it was balanced that way during discharge. All the cells lost the same Ah during use, but the best cell was also balanced down. Now during charging your balancing it back up again. Another hour on the charger balancing because it spent an hour going out of balance during discharge.

It's 9am and I'm doing alcoholic hot chocolates. I hope that made sense

 

[torqueboards]

Agree with the first thing you said but once I balance them it goes back up to the top equally again. I'm not sure but it may seem like it's an issue with the ESC controller that I am using perhaps as it happens with any battery and/or new batteries which I plug into my current system. However, I've been doing it this way > balancing cells with a battery medic > charging to 4.2v for I would say over 40-50 charges and it seems to work perfectly fine. Is this not normal for a LiPo battery as far as becoming unbalanced after being in use? I remember someone said that it was normal but maybe I heard wrong. I had about (4) 5S LiPo sets that I used in series for 10S and I didn't balance the LiPo's with the battery medic and overtime it ended completely unbalanced and I was never able to get a full charge from them. I don't even bother using it as 1 cell was always at half charge so the range of the battery wasn't even really useful anymore. I can re-create the pack but haven't bothered with it yet as I downsized to 6S as well.

I get what you are saying but don't get what you are trying to tell me, sorry. If you don't mind re clarifying.

I also found this article which I've learned quite a bit - http://endless-sphere.com/forums/viewtopic.php?t=48961.

 

[dogman dan]

Uh, I'm a bit confused by what you want.

You balance at the end of the charge, at top of charge. Some do balance at the bottom, but I don't think it's an advantage. You cannot effectively balance if the pack is in the middle of the charge.

If you are using a bms, you will need a charger that is compatible with that bms. In other words, get a bulk charger that is adjustable, so you can set the voltage to what you want. Ideally it would be able to turn on again to charge the low cells after the bms has bled down the highest cells. The bulk chargers show a green light when current is not flowing, and a red light when it is flowing.

The bms won't care if the packs are 3s or 6s. It will only care that you have 6 cells in series. You will have to make adapters, or hard wire the correct balance wires to the correct place on the bms.

 

[torqueboards]

I simply want to keep the cells balanced and also be able to plug in with a charger.

 

[friendly1uk]

Got 4 hours in my chair. Woke up and carried on lol

If I set my bms to balance when idle, it will spend a lot of it's time draining off the best capacity cells, to ensure they stay as full as the smallest capacity cell. Then when I come to charge, It is the smallest capacity cell that will fill first, and then need draining while the other cells fill up. This cycle will continue, with the biggest cells being balanced down during use, and the smallest cells being balanced down during charging.

Now step back and look at the pack charging. It's bleeding off power from the small cells(painfully slowly)Waiting for the bigger cells to fill up. Now ask the question, why are the bigger cells more deeply discharged anyway? It is because they were drained by the bms trying to balance while in use.

If the pack took an hour to drain, then that could be an hour of balancing down the big one's. Needing an hour of balancing down the little one's on the charger to correct it.


I'm losing my way. It is all too complicated. Normal is best. Just balance at the top. It don't matter if all the cells are different sizes, they will all discharge the same capacity before one yells "no more" and it all stops working. Then all cells will want exactly the same time on the charger to hit 'full' at the same time. In a perfect world needing no balancing at all. Balancing is slow, you don't want an hour of it. You want so little to be needed that you can have it done before any cell actually reach's full. So there is no time spent watching the charger going red/green/red/green/.... As that should only really occur as a fault. Telling you of excessive balance times.

How about this, $20 http://www.bmsbattery.com/smart/330-lifepo4lithium-ion-smart-bms-for-513-cells-in-series.html
Does this answer your questions? http://endless-sphere.com/forums/viewtopic.php?f=14&t=56886
I did the above thread hoping it explained it. Either i did a great job or a rubbish one as nobody has responded lol
Crossbreak can configure them boards just about any way you like.

Supports 5-13 Series Li-ion and Li-polymer
Battery Cells or 20/30 Series NiMH battery
Cells
• Multi-channel ADC for current, voltage and
temperature measurement
ƒ 13 channels for cell voltage
measurement (signed 13 bits)
ƒ 2 channels for 20S NiMH cell voltage
measurement
ƒ 3 channels for 30S NiMH cell voltage
measurement
ƒ 1 channel for current measurement
(signed 16 bits, accuracy down to
2.1nVhr)
ƒ 1 channel for internal temperature
measurement (signed 13 bits)
ƒ 3 channels reserved for customer
specific applications (one
programmable 13-16bits; two 13bits)
• Built-in 2-level protections
ƒ First level protection
9 Over voltage (OV)
9Under voltage (UV)
9 Over current (OC)
9 Short circuit (SC)
9 Over temperature (OT)
9 Under temperature (UT)
ƒ Second level Permanent Failure (PF)
protection, each PF mode can be
enabled individually by properly setting
EEPROM
9 Extremely high voltage PF
(VHPF)
9 Extremely low voltage PF (VLPF)
9 Cell voltage Unbalance PF
(CUPF)
9 MOSFET Failure PF (MFPF)
9 Deadman PF (DMPF) (Software
Mode only)

Must dash. I'm eating in to my drinking time here

 

[dogman dan]

Well, if you need to balance every cycle you are doing something wrong. Get rid of a problem cell ASAP for starters.

10 months into using a 14s 10ah pack I got last spring, I have needed to balance it about 3-4 times. It's like a once in 3 months kind of thing, and always after I discharged deeper than 3.5v. 20c cells, typically discharged at 3c, or less if I make the pack bigger for a longer ride.

I gave up on slow RC balancing with my cheap chargers, and just discharge any high cells with a turn signal light bulb. About 5 min per cell or less. A high cell is 4.2v, I charge to 4.15.

I don't discharge deeply and unbalance the pack every ride, so I rarely see anything much more than .03v off. I carry plenty of range, so I never have to worry about overdischarge much.

Even though I seldom balance, I check often, but not every cycle. I often watch the cells as they finish a charge. The best solution might be chargers that charge each cell through the balance plug. Those will always balance the pack, without waiting so long for a discharging circuit in a bms or charger. I'm not anti balancing, just anti doing it so slow for minimal benefit.

Regular RC chargers do have a bulk charge setting. You don't have to wait for a balance every charge if you don't want to. Back when I charged with the RC chargers every cycle, I rarely selected the balance charge. Why balance if it's balanced enough already and stays that way?

99% of my charging is done on a bulk charger, no bms. I trust my pack, because I know I weeded the shitty cells out of it.