What would you do?

[native pepper]

Four equal capacity cells in series and 3 lines in parallel, or batteries as you call them. The .3 v is a combination of the variations in all the cells in the pack, which I worked out by judging where the cells should be at that charge point and where they were.

That's it from me, when people accuse me of lying, I walk away, those types are from the lowest pits of life and unworthy of associating with.

[T1 Terry]

Dang Terry that's some good info there for sure! Now lets assume the cells are in balance. do you use a voltage or perhaps a SOC to bring charging back on?

Thanks

That is the whole point behind the long post, you can't assume they will be in balance at the top end of charging, SOC or battery voltage are wide open to creating a cell voltage run away so neither are suitable but battery voltage is a good primary control method. The battery protection control system must be cell voltage controlled, any other method is simply asking for trouble.

T1 Terry

Ok I can see that I am not being very clear. I apologize for that. My mind races and I don't type so fast. Let's try this again. I will have cellogs. (both s and m) on latching relays for high and low cut out duties. This should take care of any senior moments well I hope. My plan is to start with a 100 AH battery pack. I will run my FLA alongside and dedicate the LFP to inverter duties. It is likely that at first I will not charge the LFP while camping until I sort out equipment for charging. Terry you have talked of a management system you build and I am interested in that but I don't know if it is appropriate to discuss that in this forum? Okay, so I will ask my question again. When do you decide to "start" charging again after you have discharged it? At a SOC? or perhaps a voltage? With the idea that you want it topped off. (ya never know what the next day will bring)

Thanks

Follow you now Grizzman. We only use a latching relay on low cell voltage, something went very wrong if the battery discharged that low. The high cell alarm trips a timer and the timer stops the whole charging regime for a timed period after the alarm signal has cleared. The whole protection system is only concerned with cell voltage, as long as they are within the same range the battery voltage will also be within the safe range.
Depending on the load as to how long the off cycle is, from 1 min to 1 hr, also depends if another system is to be activated while the charge is off, water heater or air con comes to mind, that would require longer than a min but as soon as the load pulls the battery voltage below 13.6v the cells will return to very close to balanced, so an hr would be excessive in that case.
Once the timed period has ended the system resets and charging resumes, the trick is to build the timer so it triggers every time it sees an alarm signal but for the off period to remain until after the alarm has cleared. Many systems fail because the timer is triggered but once the timed cycle has finished it would require the alarm signal to be off and then trigger another cycle, if the alarm signal remains on the timer does not see another change of state so another cycle is not commenced. Sounds confusing I know, but after reading through it a few times it should start to make sense.

T1 Terry

[T1 Terry]

Terry, henceforth you shall be known as Monica - the patron Saint of those seeking patience.

No kidding Monica a saint

Well she wasn't the saint of doing laundry eh Did get a good laugh from the Donald Trump goes to hell joke

[T1 Terry]

Four equal capacity cells in series and 3 lines in parallel, or batteries as you call them. The .3 v is a combination of the variations in all the cells in the pack, which I worked out by judging where the cells should be at that charge point and where they were.

You have me totally confused now, it sounds now like you are saying you have 3 x 12v batteries connected in parallel with all the negative ends and all the positive ends linked but none in between?

T1 Terry

Ok, so I was right about the 3 x 12v batteries in parallel. For the last 10ys or more I've been trying to convince the critics that this method will cause uneven charging and capacity levels if batteries are linked in parallel, lithium batteries are no different, the path of least resistance will always be the case so that battery suffers the lighter loads on its own and accepts the charging first resulting in the battery terminal voltage going high before the other batteries in parallel equal the same state of charge.
The difference between this happening at cell level and happening a battery terminal level is the combined internal resistance to either charging or discharging. LiFeP04 cells from a quality manufacturer have a 0.05v resistance in either direction, 3.4v is full but it requires more than 3.45v for current to start to flow into the battery, at the same time, 3.4v is full but the voltage will drop to 3.35v as soon as a load is applied. As there are 4 cells in series to make a 12v battery, the voltage adds together, 0.05v x 4 cells = 0.2v on the charging side and the same on the discharging side. 13.6v is fully charged but the voltage must be greater than 13.8v for current to start to flow into the battery, if the charger senses 13.8v from the circuit because one battery is full it will not allow any more current to flow as it assumes this would cause the voltage to climb higher than 13.8v, the switch point is generally 0.5v below max set voltage so the voltage floats between 13.75v and 13.8v, not enough to charge the batteries at a very fast rate if they have not reached fully charged. As an example, a battery with a rested voltage of 13.5v is not fully charged, the voltage will need to reach 13.7v before current will flow into that battery, if the switch point is 13.75v then a differential of only 0.05v will mean very little current will flow.
This is not a serious problem when it comes to Li batteries, they don't need to fully charge, the problem is the flat charging curve, 3.2v to 3.3v in each cell could mean anywhere from 20% SOC to 80% SOC, at battery terminal voltage level this represents 12.8v to 13.2v, now a 0.2v differential means the battery with the lowest resistance path will get nearly all the charge current as it can accept the high charge rate without the voltage rising, now the result can be one battery at close to 80% capacity while the other could be as low as 30% SOC and this is when the problems occur.

T1 Terry

[grizzzman]

That is the whole point behind the long post, you can't assume they will be in balance at the top end of charging, SOC or battery voltage are wide open to creating a cell voltage run away so neither are suitable but battery voltage is a good primary control method. The battery protection control system must be cell voltage controlled, any other method is simply asking for trouble.

T1 Terry

Ok I can see that I am not being very clear. I apologize for that. My mind races and I don't type so fast. Let's try this again. I will have cellogs. (both s and m) on latching relays for high and low cut out duties. This should take care of any senior moments well I hope. My plan is to start with a 100 AH battery pack. I will run my FLA alongside and dedicate the LFP to inverter duties. It is likely that at first I will not charge the LFP while camping until I sort out equipment for charging. Terry you have talked of a management system you build and I am interested in that but I don't know if it is appropriate to discuss that in this forum? Okay, so I will ask my question again. When do you decide to "start" charging again after you have discharged it? At a SOC? or perhaps a voltage? With the idea that you want it topped off. (ya never know what the next day will bring)

Thanks

Follow you now Grizzman. We only use a latching relay on low cell voltage, something went very wrong if the battery discharged that low. The high cell alarm trips a timer and the timer stops the whole charging regime for a timed period after the alarm signal has cleared. The whole protection system is only concerned with cell voltage, as long as they are within the same range the battery voltage will also be within the safe range.
Depending on the load as to how long the off cycle is, from 1 min to 1 hr, also depends if another system is to be activated while the charge is off, water heater or air con comes to mind, that would require longer than a min but as soon as the load pulls the battery voltage below 13.6v the cells will return to very close to balanced, so an hr would be excessive in that case.
Once the timed period has ended the system resets and charging resumes, the trick is to build the timer so it triggers every time it sees an alarm signal but for the off period to remain until after the alarm has cleared. Many systems fail because the timer is triggered but once the timed cycle has finished it would require the alarm signal to be off and then trigger another cycle, if the alarm signal remains on the timer does not see another change of state so another cycle is not commenced. Sounds confusing I know, but after reading through it a few times it should start to make sense.

T1 Terry

seems that a device like a arduino uno could be used for a timer that would watch for the alarm and when it drops off triggers a timer or even have it watch a shunt to trigger a AH charge signal. You could even watch battery temps , perhaps trigger a disconnect on high temp also hmmm guess I need to think this out.

Thanks Terry

[T1 Terry]

Sounds like a lot of fun, I've seen quite a few attempt to go down the Arduino route, watching a simple script blow out into a long version of Leo Tolstoy's War and Peace and then go crazy trying to find the typo that causes the glitch at just the wrong moment
After way too many yrs in the automotive game seeing complex computers crash and burn due to the hostile environment they operate in you are a braver man than I Gunga Din. I'll stick with fail to safe multiple level redundancy using time proven circuit boards modified to suit, much easier to direct the use of a multimeter to pin point a problem than trying to guide someone by email or phone through pages of script

T1 Terry

[bagmaker]

Four equal capacity cells in series and 3 lines in parallel, or batteries as you call them. The .3 v is a combination of the variations in all the cells in the pack, which I worked out by judging where the cells should be at that charge point and where they were.

That's it from me, when people accuse me of lying, I walk away, those types are from the lowest pits of life and unworthy of associating with.

EH??!
Did I miss something???

[T1 Terry]

I had a read back through and I'm not quite sure just what triggered that response, might have been a pre coffee thing, we all have them every so often

T1 Terry

[Lance]

Sounding a bit like anuva place.....

Now, where were you up to chaps....


Keep calm..............and maintain the momentum

[BernieQ2]

Your reading the posts from your view point.
Not from second person's view point.
Bit like the PC thread.
Just my thoughts.
Bernie.