Comfortable LFP State of Charge

[CaptainRivet]

Originally Posted by newhaul

I have to ask . as it seems all of your posts here are doom and gloom do you have a really bad install that is constantly being an issue? The other question is considering the above and my experience here in various battery threads .
Do you have actually have a LIFEPO4 bank on your boat and please for all describe your install in detail .

i am dealing with Lithium, Lifepo4 and LTo since 30years, 25years in car stereo and about 5 years in boats...work with this chemistries when there was no documentations or BMS avaliable...burned a car, melted cables and tortured several cells to death...so I know a bit how to work with this chemistries and what are typical issue.


attached my install diagramm, one mistake that in need to correct is the remote cutoff for the charger of the Multiplus needs to go on the charge cut off optocoper, not to the load optocopler. Correctly installed, wrongly documented...

running all fine, adding another 4 cells to go from 3P4S to 4P4S 1100AH.
pulling 550A for 20min the cat would already burn if the installation is not properly done try to find installation material that are rated for 600A....


will convert to 24V or dual voltage bank 12V and 24V as running 12V 550A is dangerous and gives me a lot of losses.

[sailorboy1]

I remember why I put polls on these things. So I can just stop reading it.

[fxykty]

Originally Posted by sailorboy1

I remember why I put polls on these things. So I can just stop reading it.

Polls aren’t visible in the phone app (or at least not in the iPhone app that I have) and I hardly ever access CF on a computer so sorry, not answering your poll.

[newhaul]

Originally Posted by fxykty

Polls aren’t visible in the phone app (or at least not in the iPhone app that I have) and I hardly ever access CF on a computer so sorry, not answering your poll.

Easy question he asked.
How low a state of charge are you comfortable getting down to regularly?

[donradcliffe]

Originally Posted by sailorboy1

Guess I will leave my alarm set at 30%. Should never get near that as I would perfer to manage the generator use to only have to listen to it for an hour each day instead of 3 hours every 3 days.

If you use SOC to manage your batteries instead of voltage, your experience will not end well. Batteries are not damaged by going out of SOC limits, they are damaged by going out of voltage limits. Besides, a voltmeter is a hell of a lot less money than a SOC meter.

If I go to bed with a voltage of 13.2, I sleep like a baby. If I go to bed with a voltage of 13.0, my pissed off wife will wake me when the inverter driving her CPAP cuts out.

[fxykty]

Originally Posted by newhaul

Easy question he asked.

How low a state of charge are you comfortable getting down to regularly?

Down to 20% is comfortable, 15% is ‘oh yeah, this is LFP so no problem’, 10% or lower is ‘time to charge’. If we had a grey day previously a morning SOC of 20-25% is normal. If decent solar the next day then no worries, if not so good then we wait until noon or so to decide whether to turn on an engine to charge. Generally we try not to be below 35% the night before.

We charge up to either 80% or 90% regularly with solar (we have a variety charge profiles that we select from based on what we’re doing and the expected weather, as solar is our primary charge method). At that point the stop charge signal is sent, except for every 30 days when the BMS goes to 100%, based on charge voltage 13.8V and tail current at 2.5% C for 30 seconds. Our BMS does this to resynchronise the SOC. Cell balancing doesn’t require a certain voltage.

Note that SOC is our first level battery management. Voltage based limits are the second level. Audible alarms and manual disconnect are the third and final level. In two years full time use haven’t seen 2nd or 3rd levels.

[Off Trail]

One critical factor I forgot to mention. If our bank is below 25% in the morning, the inverter will cut out due to voltage drop trying to make coffee! Definitely not "comfortable" [emoji3]

[Pete7]

Originally Posted by CaptainRivet

Every BMS (except TAO) i know start every morning a new first calibration cycle which means the BMS wants the bank full and ignores all other parameters in charging like recharge value till it hit the end of charge set voltage. so if eg during that cycle the charge is interrupted it will continue charging even you are above the recharge value, only HVC is taken into account. So bank is daily full, except you don't have enough recharge capacity. so you cannot avoid SOC 100% daily, only alternative set it to 3,4V but then you don't get any balancing at all...because this end of charge value is valid for all cycles.

How does the BMS know when its morning?

Secondly the BMS doesn't want the bank full, it doesn't care what the SOC is, you might but it doesn't, because its not important for LFP.

We could expand on what John_Trusty said, by saying:

It's a battery not a pension fund. Just use it and accept one day it will die, then you buy another.

For once, I actually see where Sailorboy1 is coming from.

Pete

[CatNewBee]

My battery usually cycles between 60 and 90%.
I prefer to have at least half of the capacity available in case something happens to my charge sources...

[CaptainRivet]

Originally Posted by fxykty

At that point the stop charge signal is sent, except for every 30 days when the BMS goes to 100%, based on charge voltage 13.8V and tail current at 2.5% C for 30 seconds. Our BMS does this to resynchronise the SOC. Cell balancing doesn’t require a certain voltage.
.

What BMS do you have that does this very 30days, is this adjustable?

[CaptainRivet]

Originally Posted by Pete7

How does the BMS know when its morning?

Secondly the BMS doesn't want the bank full, it doesn't care what the SOC is, you might but it doesn't, because its not important for LFP.

We could expand on what John_Trusty said, by saying:

It's a battery not a pension fund. Just use it and accept one day it will die, then you buy another.

For once, I actually see where Sailorboy1 is coming from.

Pete

Hi Pete,
For example all Victron charge sources do that, reinitiate a new calibration cycle every morning… ask Victron how they exactly do it, it stands eg in the manual of the MPPT. Or ask Darcian Todeo the creator of Electrodacus BMS or the guys from REC BMS.
The only BMS I know is TAO where you can adjust this, and Fxykxy seems to have a BMS that does this all 30days, adjustable?

[newhaul]

Originally Posted by CaptainRivet

Hi Pete,
For example all Victron charge sources do that, reinitiate a new calibration cycle every morning… ask Victron how they exactly do it, it stands eg in the manual of the MPPT. Or ask Darcian Todeo the creator of Electrodacus BMS or the guys from REC BMS.
The only BMS I know is TAO where you can adjust this, and Fxykxy seems to have a BMS that does this all 30days, adjustable?

The bms has no clue what time it is it just sees a charge source or doesn't see a charge source . Has nothing to do with when . You state MPPT however I have seen power coming from a solar controller at 1am when it suddenly got hit with the search lights from the dive boat next to me .

[fxykty]

Originally Posted by CaptainRivet

What BMS do you have that does this very 30days, is this adjustable?

TAO BMS. The 30 days is adjustable.

With the 30 days setting for full charge the SOC display on the TAO BMS monitor goes yellow after 25 days to show that it is aged, then orange for a day or two then red at 30 days.

The BMS sets 100% SOC when the battery holds a constant voltage for at least 30 seconds with not more than some trailing amps value. We set ours to 13.8V and 17.5A (2.5 C) respectively. That’s also the maximum charge voltage on all of our chargers.

[CaptainRivet]

Originally Posted by newhaul

The bms has no clue what time it is it just sees a charge source or doesn't see a charge source . Has nothing to do with when . You state MPPT however I have seen power coming from a solar controller at 1am when it suddenly got hit with the search lights from the dive boat next to me .

Well then Victron magically know the time, just look at your MPPT manual and do some tests during this first cycle, you will be surprised what you find…
And yes this has to do lot with BMS because eg all drop in BMS and all only BMS (no battery optimization) use the charge logic of the mppt to charge and if BMS reaches end of charge value = full cut charge. And the BMS initiate that same calibration cycle every start of the day (Victron formulation better definition depends when morning is at your location)

Tao, I knew it. Trying to covience Darcian Todeo since month to implement this feature into the Electrodacus BMS but he disagrees to do so and states that the Electrodacus does a daily first calibration cycle (which all the other BMS do to) and there for a daily top balancing doesn‘t harm the LifePo4. That full cycles is a laboratory measurement to determine lifespan but in reality the bank in offgrid (or boat) runs about 100 microcycles or more a day and under load is not staying in the upper knee long. His focus of BMS is offgrid so i understand that systems are different having massive solar arrays in Relation to the bank (means his small bank is cycled heavily till 2,8V), in boating it’s vice versa.

[newhaul]

Originally Posted by CaptainRivet

Well then Victron magically know the time, just look at your MPPT manual and do some tests during this first cycle, you will be surprised what you find…
And yes this has to do lot with BMS because eg all drop in BMS and all only BMS (no battery optimization) use the charge logic of the mppt to charge and if BMS reaches end of charge value = full cut charge. And the BMS initiate that same calibration cycle every start of the day (Victron formulation better definition depends when morning is at your location)

.

Sorry to break it to you but not everyone runs VICTRON . My MPPT controller is a Tracer3210AN. And show me a BMS that actually shows me the time of day .
I know mine doesn't care about anything but charging, discharging, cell voltages, And battery temperature. DALY 200 amp single in and out 1p4s.