Who's using Lipo without a BMS?

[Sinewave]

anyone out there using Lipo without a BMS, just straight cells...and no BMS or Balancing circuit?

if so please let me know how long youve been doing this and if there has been any effects on their performance..oh and 'S' & 'P' specs would be helpful too.

i read by some users th Konion cells dont require a BMS or balance chargers?...lease please correct me if im wrong.

thanks

 

[Link]

LiPo's don't usually have BMSs. Typically it's their chargers that handle balancing functions. I think most are using Cycle Analysts for LVC functions.

As for not balancing LiPo, it's not really a good idea. You can get away with it for a while if you have a low voltage (like 12-24V) pack of matched cells, but they need balancing after every cycle once you start getting into higher voltages. Otherwise, they'll lose capacity pretty quickly.

Konions aren't LiPo. IIRC, they're lithium manganese.

 

[Ypedal]

Well... my take on this.

I have 3 year old Lithium Manganese 36v 20ah ( 10 cells.. 20ah prismatic cells )
(pictures and stuff )
http://www.ypedal.com/Chaos4.htm

When i received the packs, the green one had a dent on the bottom of cell no.9 , i pointed this out to the vendor when i got the packs, was brushed off as cosmetic and nothing he was willing to do about it ...

This cell, tested out at 17ah and holds voltage above 3.0v but will not stay fully charged at 4.20v.. no matter how much you try to ballance the pack or charge this cell by itself. it can be forced to go 4.2v but will drop to 4.14v the moment load is removed. From Day 1.

Now.. when i got the packs, they came with BMS, but the bms on this green pack had fried itself trying to ballance a 20ah pack to 4.14v and was no longer ballancing.. on top of that.. when used at 72v ( 2 packs in series ) the bms would trip on overcurrent with a 20amp controller (even tho the bms was rated at 30 amps ) ..

So out with the BMS.

I now have over 1000 kms on the pack this year alone, without bms..

What happens is that when i charge the 10 cells in series, at the end of the charge cycle, when the charger goes from Constant Current to Constant Voltage.. holding 42.0v .. 9 of the cells show 4.21v to 4.25v while cell no.9 ( have to run.. will finish story in a bit )

 

[Ypedal]

ok.. continuing..

So 9 of the 10 cells in this one pack get overcharged slightly because of the one low cell. I never use more than 10ah ( 50 % DOD) on these packs during my commute, ever.. i mean 72v 20ah is alot of battery so 10ah x 72v = 720wh / 20wh +- per km = 40 + kms per cycle and this is plenty for my needs..

I have taps on the cells and monitor them freqently during charge, and once every dozen cycles i hook up the TP210V ballancer for kicks but i find that it's really not requried.. the cells stay ballanced by themselves.

Moral of the story is: If your packs are getting all out of wack at every cycle. you have a pack made of horribly mismatched cells.. Healthy, matched Lithium cells stay ballanced under normal use without much intervention of the BMS....

The PSI cells, so far on cycle 10, no BMS yet, same thing , all within .010v of each other on 16 cells..

I do NOT advocate running lithium packs without BMS. but i can tell you that good cells stay ballanced under normal use.

 

[Sinewave]

thank you for your lengthy and detailed reply...i have had a suspicion regarding bms applications...

but those reading this post shouldnt throw away their bms units...ok...lol

anyone else?

 

[johnrobholmes]

I have been running 24 a123 cells in various fashion. 24s, 12s2p. I keep an eye on them and balance about every 10 charges. With exception to one runt cell, they are all within .02v of each other after non balancing charges. I never fully discharge them.

 

[Doctorbass]

I agree with Ypedal and johnrobholmes,

For any of these cells, A123, lipo, li-manganese, if you stay under the 80-20% DOD, they usually will never have any large unbalance. using a pack for 50% of its total capacity is the best solution for preserving it and avoiding it to become unbalanced.

BUT if you discharge it fasterwith high current or at 90-95% DOD it's another world.

Often people will calculate their ebike range and speed needed and will buy a battery pack thay can just satisfy this need and will often never pay for larger pack for this safety margin. Buying a 240Wh pack to comute 15-20km is a bit short and battery or their BMS have alot of chance to run out.

LVC and HVC are features of a BMS that are pratical for people that abuse their ebike and that have less knowledge in battery and electronic and that dont want the need of keeping an eyes on their battery charging.

The other side, people that like ingeneering and diy WANT to monitor and understand what happen and keep an eyes on their setup to know it work and what happen.. will often try to avoid using it cause they understand how to compensate or where to act to keep their battery top shape.

Also, there are 3 major factor that will make your cells becoming unbalanced:

-Using your pack too close to their low voltage safe limit.. that will amplify your cells capacity and internal resistor DIFFERENCES

-Having a battery pack with bad thermal management.. i mean.. some cells of the same pack to be more exposed to heat or cold than others.. that will make them to conduct more or less and will age them differently

-Generally unknown but still important! Having current leak thru the material of your pack that is exposed to moisture or material that are not good insulator.

Doc

 

[johnrobholmes]

I have avoided BMS systems to keep one less item off my bike, and reduce overall weight and possibility of bad components. Of course my commutes are also never longer than 6 to 8 miles, so I can get away with small packs with fewer cells.

 

[powermed]

No BMS on my old A123 dewalt packs, and no BMS on my current prius packs. No problems for the last 2 years. The key, as stated, is to know your ride, stop using battery power as soon as you notice any drop in performance, and not try to fully charge them - the mantra I go by is simply "don't drain them" and "don't stuff them"

I use a simple timed charge method - I've set up the (respective) pack chargers with enough amps so charges are no more than an hour in length. I don't mix old batteries with new ones - matched cells from the get go and the above methodology has worked fine.
z.