Float of LFP

[rslifkin]

Originally Posted by Chotu

These threads make me nervous. Lol. It’s OK to go up and down right? Up to 98% around lunch? Float for a few hours in the afternoon, then down for the night 120AH? Then repeat daily?

My understanding is that doing that is pretty much ideal for running on solar only. It's holding the batteries near full (using float on the charger) for long periods of time that's not ideal. And using a float voltage at or above the 100% SoC resting voltage is bad.

[barcoMeCasa]

Originally Posted by Chotu

These threads make me nervous. Lol. It’s OK to go up and down right? Up to 98% around lunch? Float for a few hours in the afternoon, then down for the night 120AH? Then repeat daily?

I just look at voltage & pretty much ignore soc, solar charging up to about 13.8v (3.45v per cell) then dropping back to about 13.3v "float but not really float", this stops charging on the way up the "knee" which isn't far off full anyway then "float" just provides power for any loads so the batts just sit there & don't discharge any during the day after charging has finished. Don't really understand why so many are fixated by getting to within a hair of 100% soc every day, no need here, there's enough power to run for a few days without charging.

[Chotu]

Ahhh. Jedi told me this before. I think. But I think I need to dial it back a little bit.

Battery manufacturer recommends 14.4 as the finished charge voltage.

So I went to 14.2. I think that’s like a daily rebalancing.

Maybe I should back it down a bit

[sailorboy1]

He wants studies instead reading well made articles that made to understand how Lifepo4 chemistry works.
[/QUOTE]

That's called wanting proven facts instead of stories.

The same as wanting science instead of myths.

The myth may be right so find science to prove it. If you feel it is so established prove it!

If you can't or wouldn't just stop rewriting the same over and over and saying that makes it true.

[rslifkin]

Originally Posted by Chotu

Ahhh. Jedi told me this before. I think. But I think I need to dial it back a little bit.

Battery manufacturer recommends 14.4 as the finished charge voltage.

So I went to 14.2. I think that’s like a daily rebalancing.

Maybe I should back it down a bit

Charging to that is fine as long as you're not holding the voltage up there after the batteries are full.

[sailorboy1]

I am tired of this thread and am going to place on ignore because I am too weak to not read it. So now is every experts chance to prove themselves without push back.


If any has science to share and PMs me the link I will read it

[barcoMeCasa]

Originally Posted by Chotu

Ahhh. Jedi told me this before. I think. But I think I need to dial it back a little bit.

Battery manufacturer recommends 14.4 as the finished charge voltage.

So I went to 14.2. I think that’s like a daily rebalancing.

Maybe I should back it down a bit

Balancing could be part of it... Or throwback to lead acid where all you want in life is full batteries 🤣
I'm thinking keep the voltages away from the ends & cells should last forever. I don't have a balancing bms, cells still with couple mV in use since start of year.

[s/v Jedi]

Okay, let me, being the “Internet expert” who also happens to be an EE in real life, make this very easy for all:

Set your absorption voltage to 3.45V per cell. For a 12V bank this is 13.8V and for a 24V bank this is 27.6V.

Set your float voltage to 3.2875V per cell. For a 12V bank this is 13.15V and for a 24V bank this is 26.3V

These setting above are for daily cycling and solar charging. The float setting may not be used for a shore power charger, strictly for solar that stops charging at sundown.

For storage mode, program the relay inside the BMV to ON when SOC goes below 30% and to OFF when SOC goes above 40%. Connect the relay contacts (you have a NO as well as a NC contact available) to the MPPT “remote” contacts. If you have a small MPPT that doesn’t have those contacts, check the manual for how to use the VE-Direct interface to do this.

I have not tested being on shore power while in storage mode, but when using the BMV as described above to start/stop the shore power charger, this should work as well.

[s/v Jedi]

Originally Posted by Chotu

Ahhh. Jedi told me this before. I think. But I think I need to dial it back a little bit.

Battery manufacturer recommends 14.4 as the finished charge voltage.

So I went to 14.2. I think that’s like a daily rebalancing.

Maybe I should back it down a bit

See my comments above. 13.8 and even more important is the float voltage. But of course check the battery monitor for at which SOC% this sets you.

[CaptainRivet]

Originally Posted by Chotu

Ahhh. Jedi told me this before. I think. But I think I need to dial it back a little bit.

Battery manufacturer recommends 14.4 as the finished charge voltage.

So I went to 14.2. I think that’s like a daily rebalancing.

Maybe I should back it down a bit

Yes thats a good idea to go down to 14.2V.
Otherwise its absolutely not a problem how you do it.
I have my BMS connect the hot water boiler at 80%SOC as dump load, then comes the watermaker...icemaker, small AC so i burn off what i can during day and mostly end up with 90%SOC. Thats in summer but aside that i am on the edge of enough solar but have a massive oversized bank so i don't care if it runs down to 40% and then need 2 weeks to slowly climb up back to 100%, eveyday by 5-10%.
In summer its enough and then once a week or all two i purposly switch the dump loads off and let it charge to 3,55V and sit there for the rest of the day to get the top balance. My BMS let it discharge to 3,4V and then charge again to 3,55V while an active balancer does the top balance.

For your 1200AH (or my 1088AH) bank 100A charge is like floating it.

[CaptainRivet]

Originally Posted by s/v Jedi

Okay, let me, being the “Internet expert” who also happens to be an EE in real life, make this very easy for all:

Set your absorption voltage to 3.45V per cell. For a 12V bank this is 13.8V and for a 24V bank this is 27.6V.

Set your float voltage to 3.2875V per cell. For a 12V bank this is 13.15V and for a 24V bank this is 26.3V

These setting above are for daily cycling and solar charging. The float setting may not be used for a shore power charger, strictly for solar that stops charging at sundown.

For storage mode, program the relay inside the BMV to ON when SOC goes below 30% and to OFF when SOC goes above 40%. Connect the relay contacts (you have a NO as well as a NC contact available) to the MPPT “remote” contacts. If you have a small MPPT that doesn’t have those contacts, check the manual for how to use the VE-Direct interface to do this.

I have not tested being on shore power while in storage mode, but when using the BMV as described above to start/stop the shore power charger, this should work as well.

What parameters for end of charge and re-engage charge have you set your BMS then?
I have end of charge 3,53V and re-engage charge at 3,4V.

I agree with absorption at 13,8V (what time did you set?). but why float at 13,15V or 3.2875V and not at 13,4V or 3,35V?

I have it differently as i wanna have solar charge with max i have, so Absorption is set to 14,20V (and 15min time) and float at 13,4V. means solar kicks in all it has till 3,53V the BMS stops charging. It always overshoots a little so its effectively 3,55V. Then bank depletes till 3,4V and charging is re-engaged by BMS (for all charge sources)
Because the MPPTs are cut off all together on the output (see below) but are stilll on with no load they go into float so when BMS re-engage charge they are in float and stay in float because the voltage when engage is 13,6V but float is at 13,4V. There is always min a 8A load so bank further depletes so i end up in 90%SOC but if then a bigger load engages the MPPt goes back to bulk.

LFP needs no absorption and charging with 50 till 100A a 1088AH bank is basically absorption anyhow (yes not in technical term but the effect it has on the LFP yes)


If you wanna connect cerbo and BMV (or im my case electrodacus BMS) to the 100V MPPT range you need to use a battery protect thats steered by BMV or BMS to cut the output of the MPPT as the VE-direct is needed for the cerbo. I have 3x100/50.

[s/v Jedi]

Originally Posted by CaptainRivet

What parameters for end of charge and re-engage charge have you set your BMS then?
I have end of charge 3,53V and re-engage charge at 3,4V.

I agree with absorption at 13,8V (what time did you set?). but why float at 13,15V or 3.2875V and not at 13,4V or 3,35V?

I have it differently as i wanna have solar charge with max i have, so Absorption is set to 14,20V (and 15min time) and float at 13,4V. means solar kicks in all it has till 3,53V the BMS stops charging. It always overshoots a little so its effectively 3,55V. Then bank depletes till 3,4V and charging is re-engaged by BMS (for all charge sources)
Because the MPPTs are cut off all together on the output (see below) but are stilll on with no load they go into float so when BMS re-engage charge they are in float and stay in float because the voltage when engage is 13,6V but float is at 13,4V. There is always min a 8A load so bank further depletes so i end up in 90%SOC but if then a bigger load engages the MPPt goes back to bulk.

LFP needs no absorption and charging with 50 till 100A a 1088AH bank is basically absorption anyhow (yes not in technical term but the effect it has on the LFP yes)


If you wanna connect cerbo and BMV (or im my case electrodacus BMS) to the 100V MPPT range you need to use a battery protect thats steered by BMV or BMS to cut the output of the MPPT as the VE-direct is needed for the cerbo. I have 3x100/50.

The reason I set absorption at 13.8V (well, I don’t because I have a 24V system, but to keep it in your 12V system) is that the battery gets fully charged. The absorption time is tuned to get that full charge.

The reason for the float voltage at 13.15V is so that the battery discharges a couple percent before the MPPT take over. You want to see all current for loads come from the battery to bring it down a bit before letting the solar float take over.

What you write about not wanting to waste solar isn’t what happens with float at 13.15V and you will see that MPPT takes 100% of the load as soon as the battery has come down a couple percent.

This isn’t really a float stage, you hack the float stage to power loads from solar after the battery is already full but before the sun goes down. I find a float at 13.4V doesn’t take the pressure off the battery quickly enough.

To not waste solar energy after the battery is full, you need to consume more energy; keeping a high float on the battery doesn’t help at all because it’s already full. So start a water heater or watermaker, bake a bread etc.

I don’t have charge or re-engage charge parameters for my BMS. A BMS shouldn’t charge a battery imo.

[CaptainRivet]

Originally Posted by s/v Jedi

The reason I set absorption at 13.8V (well, I don’t because I have a 24V system, but to keep it in your 12V system) is that the battery gets fully charged. The absorption time is tuned to get that full charge.

The reason for the float voltage at 13.15V is so that the battery discharges a couple percent before the MPPT take over. You want to see all current for loads come from the battery to bring it down a bit before letting the solar float take over.

What you write about not wanting to waste solar isn’t what happens with float at 13.15V and you will see that MPPT takes 100% of the load as soon as the battery has come down a couple percent.

This isn’t really a float stage, you hack the float stage to power loads from solar after the battery is already full but before the sun goes down. I find a float at 13.4V doesn’t take the pressure off the battery quickly enough.

To not waste solar energy after the battery is full, you need to consume more energy; keeping a high float on the battery doesn’t help at all because it’s already full. So start a water heater or watermaker, bake a bread etc.

I don’t have charge or re-engage charge parameters for my BMS. A BMS shouldn’t charge a battery imo.

Thanks Nick, i will try the lower float and see what happens.
Regarding Absorption i tested both, in my system the way i do or lower Absorption result both in a full bank but with
A)13.8V Absorption it takes much longer. assume because mostly 30-80A charge into a 1088AH bank is absorption already anyhow indpendent from bulk or absorption setting. With a 0.2C charge that would look different for sure, need to add more solar.
B) during 13,8 V absorption with high loads kicking in like water boiler solar takes less over then in bulk mode means i waste solar and higher load on bank then in bulk mode and
C) because of the steering with BP mostly the MPPT stays in absorption because of the 3,4V re-engage charge voltage when it actually should be bulk or float.

[s/v Jedi]

Originally Posted by CaptainRivet

Thanks Nick, i will try the lower float and see what happens.
Regarding Absorption i tested both, in my system the way i do or lower Absorption result both in a full bank but with
A)13.8V Absorption it takes much longer. assume because mostly 30-80A charge into a 1088AH bank is absorption already anyhow indpendent from bulk or absorption setting. With a 0.2C charge that would look different for sure, need to add more solar.
B) during 13,8 V absorption with high loads kicking in like water boiler solar takes less over then in bulk mode means i waste solar and higher load on bank then in bulk mode and
C) because of the steering with BP mostly the MPPT stays in absorption because of the 3,4V re-engage charge voltage when it actually should be bulk or float.

The power output of the MPPT should be equal for different absorption voltages, because it depends on the solar generation, not the output. When you lower voltage it will output more current for the same power.

When your absorption charge takes less power than what solar delivers, you need to start consuming more power earlier. For example, I can start a 750W water heater from a programmed relay in my Cerbo GX based on SOC%.

I am fully recharged at noon and will start using a lot of power like for a watermaker or the galley where bread oven is used etc. Sometimes my MPPT’s manage this in float mode, sometimes they go back to bulk which is all okay with me.

[CaptainRivet]

Originally Posted by s/v Jedi

The power output of the MPPT should be equal for different absorption voltages, because it depends on the solar generation, not the output. When you lower voltage it will output more current for the same power.

When your absorption charge takes less power than what solar delivers, you need to start consuming more power earlier. For example, I can start a 750W water heater from a programmed relay in my Cerbo GX based on SOC%.

I am fully recharged at noon and will start using a lot of power like for a watermaker or the galley where bread oven is used etc. Sometimes my MPPT’s manage this in float mode, sometimes they go back to bulk which is all okay with me.

Well thats the theory, i tested mine and that was the result. so i adapted accordingly.
What time did you set in Absorption? the 30min per 100AH??
i need to get familiar with all i can do with the cerbo, just got my 3 MPPT and the 2nd shore charger (110V version) connected via VE-Direct. need to get the 4 Ve-Direct to one USB board from italy, couldn't fit 4 cables in the cable channel but one USB-C was possible. need to integrate the BMV712 but its not that easy to get that shunt inbetween the main negativ busbar and bank terminal. the Electrodacus has still no interface into cerbo.

my BMS is actually doing that:
at SOC 90% 230V dump load curcuit on, at 50% off: waterheater and icemachine, all thats on that curcuit plugged in
at SOC 25% switches off the inverter as the big load in the system

watermaker i do manually as its 12V one and only push one button.
I have a smalish waterheater (only 23l/700W) so it runs on max temp setting to get more mixed water out. but that means its not so efficent and need to partly reheat more often. was in the engine room but due to bigger engine now under bed in guest hull and only a smaller unit fitted.



on a good day (dumb load curcuit off) i am at 100% at early afternoon 3pm, normal 5pm...so i am mostly somewhere between 70 % till 90% during the day and 20% lower in the morning with dumb load curcuit on means the waterheater on 24/7, without it 5-10% lower.
if i stay longer on anchor i am between 60 and 90%, only when i go on passage or see a bad week coming or all 2 weeks i go to 100% to top balance and switch the dump load curcuit off.