Just a quick question to those who have a better understanding of battery electronics than I do....
I have just installed a LiFePO4 Battery System in my van and I am interested in knowing what the ideal resting voltage should be of a 'full' battery. Currently is seems to be settling at 13.3 - 13.5 volts. What is the ideal voltage?
Thanks Mattt. So, it looks like mine is about right. I am heading to Greens Lake at the end of this week to give the system a good test 'off grid' I will be very interesting to see how it all performs.
Ummmm....... no idea where this sort of info came from because there is no way of knowing if an LFP or LYP battery is fully charged without checking/monitoring the cell voltages, cause that tells the true story of 100% and completely discharged. Rested voltage of 3.45v in all cells means the battery is at 100% SOC, a rested voltage of 3.5v in all cells still means it is at 100% SOC, the extra 0.05v is just the head on the beer. Anything less than 3.45v rested is not representative of 100% SOC in any cell and it doesn't indicate anything else, not 95% or 99% or any useable figure to just the SOC, it just means it is not 100%.
The lower end is the same, 2.8v says there is no more to be had without risking serious damage, that is under load not rested, if you have a rested voltage of less than 2.8v you have absolutely drained that cell and there is a high probability you have damaged that cell. It does not represent 0% SOC, that can occur with a cell voltage still above 3v, only coulomb counting backwards from 100% SOC will tell you that and you need an accurate battery monitor to do that. One of the better units available is the Victron 700BMV, but it must be programmed correctly or the readings will be incorrect.
So, to accurately follow just how you lithium battery is fairing you need to monitor both cell voltages and SOC, all the other information is just a general figure and useless for determining the SOC of your battery.
T1 Terry
__________________
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The system I have has BMS built in and I can view the individual cell voltage via a switch and display on the unit. The unit is from Lithium Power (based in Sunshine, Victoria)
I just checked the voltage of individual cells after a day of solar from the panel on the roof of the van... 3.41 - 3.42 - 3.36 - 3.44
I also have installed the Victron BMV 712 (this was built in bluetooth). I have configured this based on figures from the distributor.
-- Edited by revemike on Monday 6th of November 2017 04:10:53 PM
Just a quick question to those who have a better understanding of battery electronics than I do....
I have just installed a LiFePO4 Battery System in my van and I am interested in knowing what the ideal resting voltage should be of a 'full' battery. Currently is seems to be settling at 13.3 - 13.5 volts. What is the ideal voltage?
Thanks,
Mike
Funny you ask this on here if it's a vic based system is there no manual for it . Just asking that's how lithium gets a bad name people not building a good system and then people not knowing its settings . If it's a store bought system get straight onto them . Especially if there's warranty involved .
Just a quick question to those who have a better understanding of battery electronics than I do....
I have just installed a LiFePO4 Battery System in my van and I am interested in knowing what the ideal resting voltage should be of a 'full' battery. Currently is seems to be settling at 13.3 - 13.5 volts. What is the ideal voltage?
Thanks,
Mike
Funny you ask this on here if it's a vic based system is there no manual for it . Just asking that's how lithium gets a bad name people not building a good system and then people not knowing its settings . If it's a store bought system get straight onto them . Especially if there's warranty involved .
dibs
I did not think it 'funny'. I thought this was techie's Corner'. The dealer has been VERY good in answering my many questions and I have had plenty. I was just wondering that the resting voltage should be and did not want to trouble Peter again with a basic question like that and though I would as my fellow travellers. Sorry for being so silly... consider me suitably chastised and will 'lurk around' remain silent from now on.
Hi Mike, I think you might have misunderstood Dibs, he would be one of the nicest blokes you'll ever meet and very down to earth. Best to ask the manufacturer why there is such an out of balance even though no cell is over 3.5v, that just doesn't happen in a balanced battery pack. The only time you might see an out of balance is when the cell voltages are over 3.5v and stay there for any length of time as this is around the run away cell voltage point. They can reach 3.5v and still behave themselves, this is when they are actually still absorbing current (charging) but as soon as they can't absorb any more current the voltage climbs rapidly.... it can reach over 4v within in 1 or 2 mins, that quick, so a BMS system that will stop the charging if a cell reaches 3.6v is a must have if you want to get the expected long life out of the battery.
T1 Terry
__________________
You can lead a head to knowledge but you can't make it think. One day I'll know it all, but till then, I'll keep learning.
Any links to any sites or products is not an endorsement by me or do I gain any financial reward for such links
Hi Mike, I think you might have misunderstood Dibs, he would be one of the nicest blokes you'll ever meet and very down to earth. Best to ask the manufacturer why there is such an out of balance even though no cell is over 3.5v, that just doesn't happen in a balanced battery pack. The only time you might see an out of balance is when the cell voltages are over 3.5v and stay there for any length of time as this is around the run away cell voltage point. They can reach 3.5v and still behave themselves, this is when they are actually still absorbing current (charging) but as soon as they can't absorb any more current the voltage climbs rapidly.... it can reach over 4v within in 1 or 2 mins, that quick, so a BMS system that will stop the charging if a cell reaches 3.6v is a must have if you want to get the expected long life out of the battery.
T1 Terry
Thanks for the input Terry.
I will be talking to Peter later today to ask a few questions...
As I said, my knowledge is very limited. I am trying to grasp it all but it is taking some to time to process the whole thing.
Since my last post I have turned on the van's charger (I had been relying on the solar to keep it up as the van is currently not is full use (it will be for the next few day as I head to Greens).
The battery charger (Voltech BC-1240P-1AP) stayed in the Absorption phase for a short time then shifted to Float.
The readings from the batter display are now:
Combined: 13.9 -
Cell One: 3.47
Cell Two: 3.40
Cell Three: 3.40
Cell Four 3.53
I will discuss this apparent balance issue (if that is what it is) with the dealer today.
Hi Mike, I think you might have misunderstood Dibs, he would be one of the nicest blokes you'll ever meet and very down to earth. Best to ask the manufacturer why there is such an out of balance even though no cell is over 3.5v, that just doesn't happen in a balanced battery pack. The only time you might see an out of balance is when the cell voltages are over 3.5v and stay there for any length of time as this is around the run away cell voltage point. They can reach 3.5v and still behave themselves, this is when they are actually still absorbing current (charging) but as soon as they can't absorb any more current the voltage climbs rapidly.... it can reach over 4v within in 1 or 2 mins, that quick, so a BMS system that will stop the charging if a cell reaches 3.6v is a must have if you want to get the expected long life out of the battery.
T1 Terry
Thanks for the input Terry.
I will be talking to Peter later today to ask a few questions...
As I said, my knowledge is very limited. I am trying to grasp it all but it is taking some to time to process the whole thing.
Since my last post I have turned on the van's charger (I had been relying on the solar to keep it up as the van is currently not is full use (it will be for the next few day as I head to Greens).
The battery charger (Voltech BC-1240P-1AP) stayed in the Absorption phase for a short time then shifted to Float.
The readings from the batter display are now:
Combined: 13.9 -
Cell One: 3.47
Cell Two: 3.40
Cell Three: 3.40
Cell Four 3.53
I will discuss this apparent balance issue (if that is what it is) with the dealer today.
Mike
The Voltech unit is a good charger, what battery type have you selected? The Gel 1 or Gel 2 setting seems to be ok for most lithium batteries but the ones with a built in cell balancer might need the cells to reach a higher voltage for the balancer to kick in, so best ask the manufacturer what end of bulk/boost voltage they need for the balancer to function as designed.
Not my way of building a BMS system but they are the ones offering the warranty so go by their advice.
as far as getting your head around a whole different battery chemistry, I've been doing this hands on for around 7 yrs now and there are still new things to learn when it comes to house battery use. No one has actually studied the requirements for long term use and written a paper on the subject, so I have had to do all the test stuff myself. Fortunately I have over 200 system out there at the moment with the oldest up around the 7 yr mark now so I have a huge data collection base to work with and that is how I've learnt, near impossible just reading the interweb because half of them are talking through their backsides
T1 Terry
__________________
You can lead a head to knowledge but you can't make it think. One day I'll know it all, but till then, I'll keep learning.
Any links to any sites or products is not an endorsement by me or do I gain any financial reward for such links
I will be talking to Peter later today to ask a few questions...
As I said, my knowledge is very limited. I am trying to grasp it all but it is taking some to time to process the whole thing.
Since my last post I have turned on the van's charger (I had been relying on the solar to keep it up as the van is currently not is full use (it will be for the next few day as I head to Greens).
The battery charger (Voltech BC-1240P-1AP) stayed in the Absorption phase for a short time then shifted to Float.
The readings from the batter display are now:
Combined: 13.9 -
Cell One: 3.47
Cell Two: 3.40
Cell Three: 3.40
Cell Four 3.53
I will discuss this apparent balance issue (if that is what it is) with the dealer today.
Mike
The Voltech unit is a good charger, what battery type have you selected? The Gel 1 or Gel 2 setting seems to be ok for most lithium batteries but the ones with a built in cell balancer might need the cells to reach a higher voltage for the balancer to kick in, so best ask the manufacturer what end of bulk/boost voltage they need for the balancer to function as designed.
Not my way of building a BMS system but they are the ones offering the warranty so go by their advice.
as far as getting your head around a whole different battery chemistry, I've been doing this hands on for around 7 yrs now and there are still new things to learn when it comes to house battery use. No one has actually studied the requirements for long term use and written a paper on the subject, so I have had to do all the test stuff myself. Fortunately I have over 200 system out there at the moment with the oldest up around the 7 yr mark now so I have a huge data collection base to work with and that is how I've learnt, near impossible just reading the interweb because half of them are talking through their backsides
T1 Terry
I have set the charger to the number 2 mark which says LiFePO4. Would I be better selecting the Gel profile?
I will ask the supplier what he thinks I should do to get the balance right. As you say, he is the one I need to be addressing for this.
I do thank you for your useful input. I will continue to learn what I can from people with the practice working knowledge like you. Thanks.
I also read somewhere that for longer life it is best to keep the battery charged less than 100%. Is this correct?
-- Edited by revemike on Wednesday 8th of November 2017 02:02:13 PM
I'm about to hit the road for Crystal Brook to do an off grid install so my internet viewing might be a bit hit and miss. If I haven't answered any where that I should have this is the reason and I'll try to get back onto the forum every so often
T1 Terry
__________________
You can lead a head to knowledge but you can't make it think. One day I'll know it all, but till then, I'll keep learning.
Any links to any sites or products is not an endorsement by me or do I gain any financial reward for such links
I'm about to hit the road for Crystal Brook to do an off grid install so my internet viewing might be a bit hit and miss. If I haven't answered any where that I should have this is the reason and I'll try to get back onto the forum every so often
By any means no expert here . My lawn mower charger goes through a battery test before charging, seems to measure charge etc as it does . Heat etc . All I know it works and can cut 3 lawns . Some times working this stuff out needs trigonometry theory ?? Lol then you find the more you find out ?? The less you know !! Lol
All lithium variants are charged "per cell" not "per battery" this is because the charge current stops flowing through a cell once it is full.
LiFePo4 electrolyte does not decompose at fast charge rates or until the cell voltage rises to approx. 4.2V.
The charger should be constant current (max 3C) per cell until it reaches 3.5 volts then switch to constant voltage until it reaches 3.65volts.
Without a proper LiFePo4 cell charger or a battery of 4 cells with its own inbuilt charging controller charging will be hit and miss at best.
If all cells are new and identical you can bottom balance each of the 4 cells to a discharged voltage of 2.7 volts over 3 cycles and they may then charge up as a battery with a regular lead-acid charger or 14.4V car alternator to approx. 90% but many chargers float back down to 13.8V too early.
