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Balancing troubles...
#31
The next firmware release for Victrons MPPT will feature tandem operation and tail current monitoring, which will make fully charging Li far simpler - ceasing charge based on hitting a bypass current level isn't really correct (which is what the WM4 does)
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#32
Active balancers work very in larger capacity banks and can handle as many cells in a series that you want.


There are two styles that I have seen on the market as of lately for larger banks

1) QNBBM  active balancer

https://www.aliexpress.com/item/32849144...autifyAB=0

2)5A - 8A Balance Current 6S 7S 8S Lithium Battery Active Balancer
https://www.aliexpress.com/item/33010871...st=ae803_4



The first one I have used and the second I have not , but have on order. The second one is capable of turning off with a switch. Both can be wired in a series to meet your needs.
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#33
I wouldn't trust either of those systems.
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#34
That's some great data, thanks... Interesting to see you run your float quite a bit higher than me. I run 53.68 float and 55.45 absorb. Those are voltages at the wm4. The fm60 is set a couple of .1's off that because their internal voltmeter is mucho rubbish.
Current system: 9.6kWh wet Nicad batteries, 16S1P Calb LiFePo4, 210aH, Batrium WM4, Outback vfx3048 inverter, mx60 mppt controller, flexware 500 mounting hardware, 2.4kW solar array, 6kW lister diesel genset.

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#35
(05-26-2019, 04:28 PM)Sean Wrote: I wouldn't trust either of those systems.

Why ?? The principle takes the total voltage and divides it among the number of cells equily , the cells above don't charge, and
 the lower do get a charge (multiple tap transformer effect )

Jim
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#36
You would still need a BMS like Batrium to track cell voltages.
I think Sean is wary of the active balancers hiding a problem, eg a self discharging cell or a weak cell.
In larger packs in the 100's of Ahrs it's true the Batrium cellmons can have trouble keeping cells in balance & take a while to restore balance.

Maybe some combined use might be needed? Eg sensing if balance is off significantly, enable the switch controlled active units & also alert the user to investigate?

(05-26-2019, 05:02 PM)HughF Wrote: That's some great data, thanks... Interesting to see you run your float quite a bit higher than me. I run 53.68 float and 55.45 absorb. Those are voltages at the wm4. The fm60 is set a couple of .1's off that because their internal voltmeter is mucho rubbish.

My thinking is that floating a bit higher is OK as long as I'm still on the voltage plateau & no cells are starting to rise up the J curve part when "full" 
At 53.68, that's approx 3.355V/cell & I feel for my cells there's some room to safely keep a few more % SoC there I think to 3.40 cell ish.
I found above about 3.45 a few cells would start rising too much so I backed off again.

Might not be only the fm60 with the accuracy issues, I have 3x Victron MPPT controllers, a Victrim BMV 712, the Batrium system's shunt & the inverter & there's a  range of readings!
One MPPT & the BMV & the Batrium shunt agree & my multimeters pretty much agree so I take that as the accepted voltage.  Two of the MPPTs are out, one by ~0.9V  ;-)

Only thing that really matters is cell balance & their behavior as a pack :-)

So when you're absorbing, how hard are the cellmons bypassing?
Running off solar, DIY & electronics fan :-)
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#37
You Need individual cell voltage monitoring and protection. Doesnt matter how advanced your balancer is.
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#38
(05-26-2019, 11:02 PM)Redpacket Wrote: You would still need a BMS like Batrium to track cell voltages.
I think Sean is wary of the active balancers hiding a problem, eg a self discharging cell or a weak cell.
In larger packs in the 100's of Ahrs it's true the Batrium cellmons can have trouble keeping cells in balance & take a while to restore balance.

Maybe some combined use might be needed? Eg sensing if balance is off significantly, enable the switch controlled active units & also alert the user to investigate?

(05-26-2019, 05:02 PM)HughF Wrote: That's some great data, thanks... Interesting to see you run your float quite a bit higher than me. I run 53.68 float and 55.45 absorb. Those are voltages at the wm4. The fm60 is set a couple of .1's off that because their internal voltmeter is mucho rubbish.

My thinking is that floating a bit higher is OK as long as I'm still on the voltage plateau & no cells are starting to rise up the J curve part when "full" 
At 53.68, that's approx 3.355V/cell & I feel for my cells there's some room to safely keep a few more % SoC there I think to 3.40 cell ish.
I found above about 3.45 a few cells would start rising too much so I backed off again.

Might not be only the fm60 with the accuracy issues, I have 3x Victron MPPT controllers, a Victrim BMV 712, the Batrium system's shunt & the inverter & there's a  range of readings!
One MPPT & the BMV & the Batrium shunt agree & my multimeters pretty much agree so I take that as the accepted voltage.  Two of the MPPTs are out, one by ~0.9V  ;-)

Only thing that really matters is cell balance & their behavior as a pack :-)

So when you're absorbing, how hard are the cellmons bypassing?

Because my pack stays well balanced without needing much bypassing, I set my bypass voltage above my absorbtion voltage. I bypass at 3.49/cell so it only clips off any cells that start to drift upwards. Most of the time they don't bypass much mA at all.

Current system: 9.6kWh wet Nicad batteries, 16S1P Calb LiFePo4, 210aH, Batrium WM4, Outback vfx3048 inverter, mx60 mppt controller, flexware 500 mounting hardware, 2.4kW solar array, 6kW lister diesel genset.

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#39
The sun is blazing down in the south of the UK at the moment and our loads are minimal. As a result we only dropped to 88% overnight and we have been in float for a good while now.

Pictures attached show how little balancing we had to do, and how balanced we are now we're in float. I'm quite happy with these voltage settings now:


Current system: 9.6kWh wet Nicad batteries, 16S1P Calb LiFePo4, 210aH, Batrium WM4, Outback vfx3048 inverter, mx60 mppt controller, flexware 500 mounting hardware, 2.4kW solar array, 6kW lister diesel genset.

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#40
I am not trying to step on any body's toes with active equalization .

 I am for getting the max life capacity, use full life out of a set of batteries safely.

I am for :

1) cell monitor BMS

2) limit the high and low volts( smaller range than factory specifications )

3) fusing each cell on lipo and lifepo4 and ltos in banks

A weak cell  or self discharge will occur and will show up as capacity loss or alarm if your BMS has the setting for it.

A shorted cell will either burn or blow the fuse or just go dead depending on chemistry.

These conditions eventually are going to happen whether your are there to monitor it or not.



Most BMS's limit highs and lows and some have cell "topping off each cell individually " but they do not control the voltage
 in each cell until at full voltage set.

The active equalization may "hide" a weak cell, but it will show up in overall capacity loss.
If you take out "50%" capacity and 1 cell or more is lower than the rest, the active equalization will attempt to make it equal to the others. Even being a weaker cell , you can get more capacity out of the bank.

You can occasionally disconnect it to see its condition if you want to check the actual condition of the cells if you want to

Active equalization just smooths out the volt differences, A dead or weak cell is still a dead or weak cell and will not bring from being dead .

While active equalization will not hide a shorted or dead cell , It will prolong a weaker one with more useful life.
I have a problem with with wasting power with passive  equalization ,unless your heating you shed from the cold.
Active equalization is a lot less work to achieve the end result. It's nice to know what's going on 24/7 , But my wife's "hunny do
 list" is long enough to choke a horse.
 
As long as you provide the safety measures for possible fire (fire,over-under volts,), Run them to end of useful life

Jim
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