BruceS wrote: ↑Tue Sep 05, 2017 6:53 pm
Enjoy your trip Chris!!
Do you have CELL top limit alarm? (just in case a couple drop down and one of the others bolts.......)
Sorry Bruce. A bit slow to reply. I have no individual cell monitoring or alarms. The main charge source is from my 1200w solar bank through a Fangpusan "knock off" Flexmax Outback 80 controller set to 13.8 volts bulk and absorption and 13.3 volts float. Float mode rarely operates as 13.3 volts is the static lightly loaded voltage of the bank even as low as 70% SOC.
The new budget auto cell balancer is brilliant with the cells keeping accurate perfect balance to two decimal places at any state of charge experienced so far - Have not gone below 70% SOC.
Cheers
Chris
You won't see an out of balance at those charging voltages until the out of balance is quite large. Then the cell balancer will not be able to cope. The out of balance will start to show up at 3.45v in any cell, the first one to reach there will be most likely be the one that runs away and if you don't stop it by the time it reaches 3.6v the horse has bolted and damage is mins away. 13.8v with 3 cells at 3.35 means the remaining cell is at 3.75v, you would need to be monitoring each cell group to see that out of balance and cell voltage occurring because 13.3v float would be 3.25v per cell and even if the capacity difference is 5 Ah (huge out of balance) all the cells will be within 0.03v of each other. An out of balance pack to the point of cell damage when the end of boost charge is reached only require 0.01% difference between the cell groups, in a 400Ah pack that represents 4Ah and there is no hope of any balancer on the market to being able to shift 4Ah in the few mins between everything being ok and cell damage occurring. To shift 4Ah in one min would require a transfer rate of 240 amps, even if those balancers could really shift 10 amps it would take 25 mins. For those balancers to shift 10 amps the voltage difference needs to be measured in volts, not 10ths of a voltage that 0.1v differential represents or four 10ths of a voltage in the example I mentioned earlier with the 3 cells @ 3.35v and the last cell at 3.75v.
On the drop in 12v batteries I recently worked on, the balance charge rate was 0.5 amps, it took 12hrs with the terminal voltage at 14.4v for the cells to get within a level of balance that allowed a terminal voltage of 13v to be maintained under load, as there was no way of monitoring cell voltages or charging individual cells, that was about the best I could achieve. Previously the 2 x 120Ah advertised capacity batteries could not power the fridge over night, that was how much each of the batteries was out of balance. The cell with the least capacity at the end of boost charge (lowest voltage) determines the actual battery capacity, not the battery terminal voltage.
T1 Terry
A person may fail many times, they only become a failure when they blame someone else John Burrows
Those who struggle to become a leader, rarely know a clear direction forward for anyone but themselves
I am going out to the van and will set my mains charger to 14.8v and turn it on. Will then monitor the cell balance until the pack reaches 14.8v to see how the new magic black balancing box can cope
Chris why are you going to 3.7 per cell, when 3.5 to me is the maximum voltage for lifepo4. Any higher and you may reduce the life of your cells and using a float setting is a killer for lifepo4, they absolutely hate small input charging when over 3.3v.
Those cells balancers, do a great job of keeping cells balanced but they will fail if you over stress them and running over 3.5v, is asking for a cell to runaway if there are any weaknesses in it. By keeping them under 3.4v when settled and 3.5 when charging, in my experience, allows the cells and balancers to function effortlessly.
The claim of memory charging in cells, even though it is minimal compared to lead acid, tend to operate when cells are constantly used and never go over 3.3v or constantly charged over 3.5v. These are delicate but very rugged storage systems, they will take a beating as long as you treat their charge discharge parameters with respect.
Have witnessed tests of fast charging and rapid discharging, over a period of 5 days, the cells that were kept between 3v and 3.4v settled were fine, but those that underwent the same regime, but were reduced to 2.5v and 4.7v charge, starting failing after 5 days of constant charge discharge.
Have no idea why this is, but have stuck with the 3v-3.5v charging and 3.4v settled since and after 11 years using my portable pack and 10 years on the house, couldn't be happier.
nut17 wrote: ↑Sun Sep 24, 2017 1:31 pm
I am going out to the van and will set my mains charger to 14.8v and turn it on. Will then monitor the cell balance until the pack reaches 14.8v to see how the new magic black balancing box can cope
Cheers
Chris
I'd start with 14.4v Chris, but you need a cell monitor connected so you can see the cell voltages simultaneously, some form of alarm would be an advantage to warn you a cell has gone over 3.6v, the climb is almost vertical and as can be seen by the graph below occurs without warning. That charging part is at a peak of 10 amps
Discharge and recharge graph for Sinopoly 400Ah battery.jpg
T1 Terry
You do not have the required permissions to view the files attached to this post.
A person may fail many times, they only become a failure when they blame someone else John Burrows
Those who struggle to become a leader, rarely know a clear direction forward for anyone but themselves
native pepper wrote: ↑Sun Sep 24, 2017 2:16 pm
Chris why are you going to 3.7 per cell, when 3.5 to me is the maximum voltage for lifepo4. Any higher and you may reduce the life of your cells and using a float setting is a killer for lifepo4, they absolutely hate small input charging when over 3.3v.
Those cells balancers, do a great job of keeping cells balanced but they will fail if you over stress them and running over 3.5v, is asking for a cell to runaway if there are any weaknesses in it. By keeping them under 3.4v when settled and 3.5 when charging, in my experience, allows the cells and balancers to function effortlessly.
The claim of memory charging in cells, even though it is minimal compared to lead acid, tend to operate when cells are constantly used and never go over 3.3v or constantly charged over 3.5v. These are delicate but very rugged storage systems, they will take a beating as long as you treat their charge discharge parameters with respect.
Have witnessed tests of fast charging and rapid discharging, over a period of 5 days, the cells that were kept between 3v and 3.4v settled were fine, but those that underwent the same regime, but were reduced to 2.5v and 4.7v charge, starting failing after 5 days of constant charge discharge.
Have no idea why this is, but have stuck with the 3v-3.5v charging and 3.4v settled since and after 11 years using my portable pack and 10 years on the house, couldn't be happier.
Are you sure it was 4.7v? An LiFeP04 cell will turn into a vapour spewing pregnant looking door stop at 4.5v, anything over 4v for more than a few seconds creates so much heat the cell starts to separate the volatile elements from the electrolyte and coats the negative plate in a high resistance coating that rapidly effects the plates ability to accept and release lithium ions. This is the cause of that apparent loss of capacity and excessive voltage difference between charging and discharging.
T1 Terry
A person may fail many times, they only become a failure when they blame someone else John Burrows
Those who struggle to become a leader, rarely know a clear direction forward for anyone but themselves
Oops, 3.7v Terry, didn't read the notes, just plucked 4.7v from my memory and being a technical dunce didn't think about it until you pointed it out. Now have to try to find 4.7v I've read in the notes and what it related to, probably some failure after a ridiculous experiment to test limits. If I find it, will post about it, but it could be my aging failing mind.
I have been a bit tardy responding on here, but after six weeks on the road, the magic black box cell balancer appears to be coping absolutely fine. We have had the battery discharged to 53% and about a week later to 61% due to a couple of 3 - 4 day stints of overcast weather. Because the cell balancer is working continuously it seems to have no trouble keeping on top of things. At $NZ65 it is certainly a cost effective peace of mind solution.
