LiFePO4 - How are you controlling your SoC?

[Iron E]

From what I'm reading controlling charge/discharge voltage may be a better way to avoid LiFePO4 battery degradation than % of charge/discharge (ex: 80/20DoD 70/30DoD, etc).

So long as charging doesn't rise above 3.4v (per cell) or discharging doesn't fall below 3.1v the battery remains healthy and cycles aren't degraded.

If this is true and you are following this idea, how are you achieving this SoC?
For example, how do you keep batteries stored at 95-97% I can see that the Victron smart shunt can prevent batteries from falling below x%

I'm interested in hearing about the plan you're implementing... Smart Shunt? Advanced BMS? Coulomb Counting?

[CaptainRivet]

Originally Posted by Iron E

From what I'm reading controlling charge/discharge voltage may be a better way to avoid LiFePO4 battery degradation than % of charge/discharge (ex: 80/20DoD 70/30DoD, etc).

So long as charging doesn't rise above 3.4v (per cell) or discharging doesn't fall below 3.1v the battery remains healthy and cycles aren't degraded.

If this is true and you are following this idea, how are you achieving this SoC?
For example, how do you keep batteries stored at 95-97% I can see that the Victron smart shunt can prevent batteries from falling below x%

I'm interested in hearing about the plan you're implementing... Smart Shunt? Advanced BMS? Coulomb Counting?

Either a Victron BMV 712 or smart shunt or good BMS like ElectrodacusBMS measure SOC quite accurate.
You never store LFP at 95-97, you discharge to around 50% which is around 3,2V rest voltage and then you disconnect everything incl. Bms.
There is basically no self discharge.

Otherwise i have with my ElectrodacusBMS to start dump loads like water heater if SOC is above 85% and if SoC is below 25% then all inverters will be shut off. An 5A active balancer is switched on above 97%SOC during charge to support the passive balancer to balance cells. The passive balancer is a bit small to handle a 1100AH bank, works good till around 600A, from then on you need an active one especially if you rarely charge to full 100% SoC like i do.

On the other side you charge your LFP to 100% to recalibrate SoC and balance the cells but you don't keep it there for long. That happens with my bank normally all 2 weeks till monthly but its mostly anywhere between 60 and 90% as my solar with 1200W is on the low side for a 1100Ah bank. Will add more....
I have LVC cut off at 3.0V per cell but anchor windlass and starter is still connected as i use my LFP bank as hybrid starter and house. With a 1100AH cut off at 3.0V i have more capacity=more starts available to start the engine as a fully charged 120AH 30kg heavy lead junk.
My bank is never below 30% SOC except i do on purpose a full cycle discharge to 2.8V and charge to 3,6V to recalibrate everyrhing.
Normally it cycles between 60 and 90% SoC.

[Iron E]

Originally Posted by CaptainRivet

Either a Victron BMV 712 or smart shunt or good BMS like ElectrodacusBMS measure SOC quite accurate.
You never store LFP at 95-97, you discharge to around 50% which is around 3,2V rest voltage and then you disconnect everything incl. Bms.
There is basically no self discharge.

Otherwise i have with my ElectrodacusBMS to start dump loads like water heater if SOC is above 85% and if SoC is below 25% then all inverters will be shut off. An 5A active balancer is switched on above 97%SOC during charge to support the passive balancer to balance cells. The passive balancer is a bit small to handle a 1100AH bank, works good till around 600A, from then on you need an active one especially if you rarely charge to full 100% SoC like i do.

On the other side you charge your LFP to 100% to recalibrate SoC and balance the cells but you don't keep it there for long. That happens with my bank normally all 2 weeks till monthly but its mostly anywhere between 60 and 90% as my solar with 1200W is on the low side for a 1100Ah bank. Will add more....
I have LVC cut off at 3.0V per cell but anchor windlass and starter is still connected as i use my LFP bank as hybrid starter and house. With a 1100AH cut off at 3.0V i have more capacity=more starts available to start the engine as a fully charged 120AH 30kg heavy lead junk.
My bank is never below 30% SOC except i do on purpose a full cycle discharge to 2.8V and charge to 3,6V to recalibrate everyrhing.
Normally it cycles between 60 and 90% SoC.

Thanks for the detailed description CR.
Is your Smart BMS using Coulomb Counting functionality to calculate SoC?

[CaptainRivet]

Originally Posted by Iron E

Thanks for the detailed description CR.
Is your Smart BMS using Coulomb Counting functionality to calculate SoC?

Yes and it has two shunts on the positive side of the bank, one is measuring all that goes in/out and the 2nd is a charge shunt means it measures all the charge sources deliver. So i have a very accurate in and ouput calculation and value. That together with Colomb counting and 2 other methods garauntee a very precise SOC, even better then the victron one.
And the best is ElectrodacusBMS is 200Euro and not current carrying, means you can also use it for hybrid banks as the typical FET BMS type will be killed by reverse current and startup surge of a starter or a windlass motor.thats why you cannot use a dropin LFP as starter as they have FET-BMS.
ElectrodacusBMS is only limited by the size of the shunts you use to about 1000A continous and can run at 12V or 24V.

[Iron E]

Originally Posted by CaptainRivet

Yes and it has two shunts on the positive side, one is measuring all that goes in/out and the 2nd is a charge shunt means it measures all the charge sources deliver. So i have a very accurate in and ouput calculation and value. That together with Colomb counting and 2 other methods garauntee a very precise SOC, even better then the victron one.

Perfect, thanks. I wasn't aware of Electrodacus... looking into their products now.

[CaptainRivet]

Originally Posted by Iron E

Perfect, thanks. I wasn't aware of Electrodacus... looking into their products now.

Its an open source BMS from a canadian guy call Darius developed and manufactured in the canadian wilderness. He is very responsive and there is also a good forum.
He has a different philosophy then all other as it works like the spider in the web and also controlls all charge sources and switching them off/on and not eg the MPPT decides when bank is full.
Huge advantage it does that all on cell voltage level.
Only disadvantage its not so good for a multi battery bank consisting of multiple 1p4S or 1p8s battery
It must be then a 2P4S or 3p4S with one ElectrodacusBMS. Thats due to its philosophy as the spider in the web. You can do it but then each 1p4S/8S battery needs an ElectrodacusBMS, a shunt and a disconnect relay and one ElectrodacusBMS will be then the master who steers all the sources charge and load. Thats then too expensive and complex, makes sense to use a different BMS then like a seplos BMS

[Iron E]

Originally Posted by CaptainRivet

Its an open source BMS from a canadian guy call Darius developed and manufactured in the canadian wilderness. He is very responsive and there is also a good forum.
He has a different philosophy then all other as it works like the spider in the web and also controlls all charge sources and switching them off/on and not eg the MPPT decides when bank is full.
Huge advantage it does that all on cell voltage level.
Only disadvantage its not so good for a multi battery bank consisting of multiple 1p4S or 1p8s battery
It must be then a 2P4S or 3p4S with one ElectrodacusBMS. Thats due to its philosophy as the spider in the web. You can do it but then each 1p4S/8S battery needs an ElectrodacusBMS, a shunt and a disconnect relay and one ElectrodacusBMS will be then the master who steers all the sources charge and load. Thats then too expensive and complex, makes sense to use a different BMS then like a seplos BMS

I was considering a house build using one 460ah 12V battery instead of two 230ah.
I have a 6 series 100amp Balmar with an internal regulator, as well as the ARS 5 external regulator.

Wanting to keep it simple and have it last.

[CaptainRivet]

Originally Posted by Iron E

I was considering a house build using one 460ah 12V battery instead of two 230ah.
I have a 6 series 100amp Balmar with an internal regulator, as well as the ARS 5 external regulator.

Wanting to keep it simple and have it last.

For that its perfect. No solar?
Have a look at 304AH EVE Cells, they are around 180Euro per cell, 2P4S with 8 of them is 608AH and hard to beat from price. More capacity is good to have.
The 304AH cells are proven best cell for the buck and have a much better terminal which is basically impossible to strip compared to the old 280AH which are tricky.

[Iron E]

Originally Posted by CaptainRivet

For that its perfect. No solar?

Absolutely, Solar is on the list.

Have a look at 304AH EVE Cells, they are around 180Euro per cell, 2P4S with 8 of them is 608AH and hard to beat from price. More capacity is good to have.
The 304AH cells are proven best cell for the buck and have a much better terminal which is basically impossible to strip compared to the old 280AH which are tricky.

Will do, thanks for the tip.

[sailorboy1]

I'm not controlling my discharge at all. The combined rating of the batteries is 400 amp and the fuse on the main line is 300 amp. Just like it was for the acid batteries. The only thing the controls the charge is the source and what the batteries can accept. I could run my solar at max, my alternator at max, and my charger at max all at once and not exceed the allowed.

Why do people want to turn these things into science fair projects?

[fxykty]

Originally Posted by sailorboy1

I'm not controlling my discharge at all. The combined rating of the batteries is 400 amp and the fuse on the main line is 300 amp. Just like it was for the acid batteries. The only thing the controls the charge is the source and what the batteries can accept. I could run my solar at max, my alternator at max, and my charger at max all at once and not exceed the allowed.

Why do people want to turn these things into science fair projects?

Because not everyone has a system like yours. It works for you, so stick with it.

I have 8 charge sources and not all of them can be controlled precisely and not all those that can do I trust. Plus, I don’t believe that everyday charging to 100% SOC is suitable for best longevity. I thinks it’s also worthwhile to see what is happening and to control things like charging and discharging based on cell measurements.

[Iron E]

Originally Posted by fxykty

Because not everyone has a system like yours. It works for you, so stick with it.

I have 8 charge sources and not all of them can be controlled precisely and not all those that can do I trust. Plus, I don’t believe that everyday charging to 100% SOC is suitable for best longevity. I thinks it’s also worthwhile to see what is happening and to control things like charging and discharging based on cell measurements.

Absolutely agree

[Iron E]

Originally Posted by sailorboy1

Why do people want to turn these things into science fair projects?

Maybe wanting advanced monitoring/controlling doesn't apply to you... You do you

[sailorboy1]

Originally Posted by Iron E

Maybe wanting advanced monitoring/controlling doesn't apply to you... You do you

I will. I get all the useful info off my battery monitor.

[CaptainRivet]

Originally Posted by sailorboy1

I'm not controlling my discharge at all. The combined rating of the batteries is 400 amp and the fuse on the main line is 300 amp. Just like it was for the acid batteries. The only thing the controls the charge is the source and what the batteries can accept. I could run my solar at max, my alternator at max, and my charger at max all at once and not exceed the allowed.

Why do people want to turn these things into science fair projects?

Till your cells bloat because you floated them to death...if you would read Eric Bertschers article then you would know that...