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Balancing troubles...
#41
Jim you waste more energy transfering energy back and forth all Day Long than burning off some energy ever other week. Active balancing is not for saving energy its for having a longer dod available but only att lower currents. Since if you charge or discharge faster than it can balance it cant Keep Up.

The most economic is actually to monitor and swap cells between packs when needed....


And One more things... You save more energy getting a proper inverter or thicker Wire. Balance is One of the places where it is very easy and cheap to so it cheap in terms of just building it well balanced from start and maintain Wink
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#42
(05-27-2019, 06:19 PM)daromer Wrote: Jim you waste more energy transfering energy back and forth all Day Long than burning off some energy ever other week. Active balancing is not for saving energy its for having a longer dod available but only att lower currents. Since if you charge or discharge faster than it can balance it cant Keep Up.

The most economic is actually to monitor and swap cells between packs when needed....


And One more things... You save more energy getting a proper inverter or thicker Wire. Balance is One of the places where it is very easy and cheap to so it cheap in terms of just building it well balanced from start and maintain Wink

I didn't now this was going to be a contest on who's is bigger

1) I agree    "The most economic is actually to monitor and swap cells between packs when needed....

2) I agree    "You save more energy getting a proper inverter or thicker Wire. Balance is One of the places where it is very easy and cheap to so it cheap in terms of just building it well balanced from start and maintain"

3)"Since if you charge or discharge faster than it can balance it cant Keep Up". --- The BMS cannot either

4) "its for having a longer dod available but only att lower currents" ---- more usable watts

5) once ballanced ,it uses very little power , about the same as the BMS

6) I am happy on your setup , Most of us out here can only dream for such a setup , But most of us out here do not
have the proper equipment,the money, or the time to build perfect battery banks. We use what we can get our grubby
paws on. And hopefully live to tell about it and finish the wifes list.

7) I would like to have a battery bank ballanced as much as possible , other than once or twice a week. Out of ballance it is a
geometric problem. In my opinion is to combat it 24/7 is with active equalization with out active intervention from me.
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#43
This is no contest. Its pure fact and many people dont seem to understand what the actual advantage of having a active balancer is and think they save energy or money... Thats not the case for most people...
#3 No and you dont need to keep up? Note that a BMS is a synonym for battery management system. A BMS can have balancing but dont have to. It can have either Active or passive so im not sure where this point is leading to? When you reach the end of SOC you stop charging or stop discharging. You reached a cycle. There is no system where you wait for energy to transfer in real life except very very low current systems. 
4# Not really. higher DOD = less cycles. So in most cases you dont want to go further
#5 Same as BMS? Please read my answer above. You mix things together.
#6 You dont need to build perfect battery banks. An active balancer does not help you save any money long term for a DIY sollution.

A balancer is just a part of most BMS systems. Active or passive, both exist.  Active balancers are well used on systems where you have deviations of 10-20% or even more between packs and where you cannot exchange packs. On systems with very very low current going in and out. Where you physically cannot sort the issue.

With that said it can for sure be used on a diy powerbank but dont think you save money using it and in most cases not even energy. Active balancers cost a lot initially and for each cycle you loose 5-15% of all energy that was transferred in heat.  

When you get to the point that you need to balance 24/7 or need to balance so you can gain 0.5% extra total energy between fully charged and discharged you need to consider adding extra capacity instead.

Working with batteries, energy saving systems, BMS systems and among many other things for last 15 years I have learned a fair share and I was one of the guys that only saw active balancers as the go to... After extensive testing, reading and talking to battery manufactures and electronic people i had to change my mind in terms of that part. I have active balancers here to but frankly I saved 1000x energy by getting a proper inverter instead of fiddling to much with the balance part in my BMS systems Big Grin
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#44
(05-27-2019, 09:02 PM)daromer Wrote: Active balancers cost a lot initially and for each cycle you loose 5-15% of all energy that was transferred in heat.  

Perhaps something has been lost in translation ....

Are you saying that a system that uses active balancing is likely to loose 5-15% of the energy that has been transferred inter-cell, during a single cycle, due to thermal loss alone ?
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#45
On the cheap balancers yes. I have yet not seen any 100% efficient and the ones i tested have been warm.

Though should have Said 3-15.
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#46
Apparently active balancers are popular on the Chinese electric bus fleets & this must be for a reason.
I think there is a place for active balancers in addition to another good BMS with all the monitoring:
- in large packs where balancing currents with a passive BMS eg batrium, etc is not enough (see below point re cell size).
- in packs that see more DoD which pushes the balancing needs harder.
- where spending more on BMS systems is OK for the owner.
- where the packs are not 18650 cells but larger eg prismatic cells & swapping them doesn't help the balance issue just moves it (replacing cell might help more but $)
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#47
I am using QNBBM unit on a starting 6s1p LTO 30ah set of cells in a 8 liter diesel farm tractor ,
The set tested at 14.4v-900 CCA at -18C with 400 usable watts at 1.0C. It has been tested once a month for 14 months. All cells within .02v and still at 400 watts with over 1200 starts and 4 left the lights on to 10v or less and several start days of -20.C.
It still performs in day 1 condition.

These cells are the grade ""B"-bad" variety,4 were close to spec. and the other two have a 30% loss per month discharge .
Before installing tested a led volt meter wired on all the time ,No external load, the loss was .1v per day and at 13.8v reached (2.3/cell) , the drop was only .05v/day.  At the end of 30 days 12.6 v @40% capacity- 500CCA
Granted the 30 day losses are very large , the daily performance is excellent , even with poor cells

This is why I prefer a voltage equalizer. as long as the equalizer works the battery will be fine


With the voltage equalizer I do not control the upper or the lower system voltage , these cells can handle 0v for a year plus
 and recharge with no apparent damage and limited exposure to 3v, The alternator free voltage ( no regulator) is @18v,
At 18v the rest the vehicle will burn out the computer and stop with only minor cell damage.

Other lithium chemistries are not even close to LTO abuse tolerance ,
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#48
One advantage of packs with *many* 18650 cells in parallel is that you can adjust the packs so that balancing is not required 24/7. In my case I had 2 issues that were revealed by Batrium in my 14s120p packs.

- Wild voltage swing - 5 (of 42) packs had voltage swings higher than the rest - e.g. charge up to 4.1 while others were at 4.0 and discharged to 3.2 while others were at 3.4. Turns out these cells were very high IR (200-300 range) and different type (Green G5s) of cell than the rest. Replacing these packs with cells that were 'more similar' to the other 37 packs in IR and manufacturer took care of problem. Not sure if high IR or manufacturer or both - but the problem was solvable.
- Low packs / not strong enough - a few packs were running lower than the rest by 150mv - e.g. discharging to 3.2'ish while rest were are 3.4 and not charging as resiliently. This was solved (on the running system) by adding a few more cells to each pack via alligator clip hacks until they firmed up / got the right number cells. Then permanently added cells to pack.

It does take attention/work! and if you don't have $ for this kind of pack adjustment then perhaps go with smaller battery so you have extra cells to make adjustments. Bottom line is that you can get your 18650 packs into good enough balance that ongoing daily balance is not needed all the time. I would think this would be one the reasonable design goals - even with re purposed cells.

For the LifePO4 Prismatic where each 'pack' might be 1 big cell... maybe that's not such a good design as you loose flexibility to adjust 'the pack'. Perhaps design to use lower ah in parallel (say 16x50ah or 8x100ah) for a 800ah battery instead of 2 x 400ah would be a reasonable goal.
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#49
Hello from Finland.

I just bought an active balancer for my 105 40Ah B-grade LTOs.
It is a normal 2A Bluetooth Balancer Li-ion Lipo Lifepo4 LTO Battery Active Equalizer 2~24S, from eBay.

Interesting was that it DID NOT work with my LTOs.   The seller claimed that it works with LTOs!!

So it looked all dead, no power led or anything, not enough voltage in cell 1. 
Main reason was that it needs at least 2.4V first cell before it starts to work at all.

I was using a 48V external power supply to test it, I had 6pcs of 40Ah LTO-cells in series.  Did not work.
Then I tested again, but had 3x2S cells in series as if they were cell 1, 2 and 3.  Double voltage, and suddenly everything started to work.

But there is an easy fix to it so that it starts with much lower voltage, see the attached pictures I got from another seller.

After this fix everything started to work beautifully, works right now with all the six individual serial LTO-cells and surely works with all 24 later.
The equalizer works extremely well and the bluetooth app is nice.

Since I am using hybrid MPPT inverters, I do not need a BMS I think?



/Piglet
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#50
Yes you need a bms. The balancer does not contain any protection
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