erratic charging (no Victron MPPT STATE change) when battery gets to be used, to then recharge

Cosmini

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Oct 30, 2021
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hello folks,

I have setup a fairly new, small system:

a 300A CHINS 12.8V 300AH battery LiFePO4
a Victron SmartSolar CC MPPT 100/30
a Renogy 500A Battery Monitor,
a Renogy 200 Watt 12 Volt Monocrystalline Foldable Solar Suitcase (with the PWM CC that I am not using, using the Victron one)
a Novopal 2000 Watt Pure Sine Wave Power Inverter 12V DC to 110V/120 AC Converter

On the Victron CC, I have set up the battery type to LiFePO4 (setting 7)
I have a small load, a freezer, using some 75W, on and off, for testing.

The system works beautifully, charging and discharging, but I have noticed that the Victron CC has a hard time changing STATE, from Float to Bulk, or Float to Absorbtion (as consumption increases and the battery percentage is 80-85%, during cloudy periods), UNLESS I disconnect the Solar suitcase from the Charge controller and manually reconnect the MC4 connectors)-- this does not seem normal, to me. I have the Victron firmware(s) updated to latest.

So, when it's saying it is in Float mode (even though battery capacity is 80-85% and very sunny) -- then I disconnect the Solar Panel from Victron CC, then reconnect, and then the STATE goes back to BULK -- this is a pain, to do manually though.

Am I doing anything wrong? Do I need to manually set parameters for this LiFEPO4 battery type, in the Victron CC? (I've left them to automatic, whatever the specs are)

The battery owner's manual states the following, as MPPT settings:
Charge:
Charging limit voltage: 14.6V
Overvoltage disconnect voltage: 15V
Overvoltage reconnection voltage: 14.2V

Discharge:
Low Voltage disconnection Voltage: 10.8V
Low Voltage reconnection voltage: 11.6V
Undervoltage warning voltage: 12.4V

Not sure how this matches the Float, Absorption and Bulk STATES/settings.
Do I need to make any changes to the default LiFePO4 Victron settings?

many thanks, helping out a newbie :)
 
Last edited:

sunshine_eggo

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300Ah LFP is typically fully charged at 0.05C @ 3.55-3.65V/cell. 0.05C for your battery is 15A

A 75W load is tiny.

In perfect solar, you can provide: 200W/14.2V = 14A

You're putting too much faith in the Renogy battery monitor. It's 100% criteria are different from the Victron charge termination. You can't make judgements based on it until it's properly programmed to indicate full charge at 14.2V and 14A or less.

On your system, if your battery is at 14.2V and getting solar charging with your low power input (14A or less), it is at 100% regardless of what the battery monitor says.

With the settings below, the battery will charge to 14.2V and hold for 2 hours. Once it's complete, it will drop to 13.5V and float. It will only re-bulk if the loads exceed the solar and pull the battery down to 13.4V.

You will not see a transition from float to absorption. It always follows the bulk, absorption (for 2 hours) and float order, but bulk could be very short depending on circumstances.

VC in demo mode for SS 100/30 MPPT:


1636500640869.png

Given your very low charge current, you should probably change the absorption time to 5 minutes and enable tail current to 15A.
 

Cosmini

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Oct 30, 2021
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thanks bunches, @sunshine_eggo --
I have calibrated the Renogy BM to 100%, after I have initially charged the battery, fully, manually, with a Victron charger (took about 15 hours, then went into float State).
Yes, indeed, the solar input, is very small, 2-10Amps at best, depending on clouds, but sometimes close to tops (12-13A)
Yes, need to increase the load consumption, but the BM seems to be fairly accurate, as far as charge/discharge (shows the correct increasing/decreasing Ah).

I believe it is just the Victron CC that needs to have the Expert params tweaked, as you've mentioned, and would like to read up more on it as well, but it looks like your points/advice seem(s) to be on the right track, although I'd love to be more sure that my changing of the Expert params is the way I should go ;-) -- I'm always leery of doing that for documented/undocumented (software) database parameters and the victron params, I believe, are no exception. Is there any documentation available anywhere on these params for LiFePO4 batteries -- for my own edification? :)

thanks kindly,
Cosmin
 

sunshine_eggo

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thanks bunches, @sunshine_eggo --
I have calibrated the Renogy BM to 100%, after I have initially charged the battery, fully, manually, with a Victron charger (took about 15 hours, then went into float State).
Yes, indeed, the solar input, is very small, 2-10Amps at best, depending on clouds, but sometimes close to tops (12-13A)
Yes, need to increase the load consumption, but the BM seems to be fairly accurate, as far as charge/discharge (shows the correct increasing/decreasing Ah).

Current counting battery monitors drift if the 100% criteria isn't met.

Essentially, if you ever see your battery at 14.2V flowing any current at all, and the Renogy doesn't say 100%, the Renogy is wrong, and it should be synched to 100%.

I believe it is just the Victron CC that needs to have the Expert params tweaked, as you've mentioned, and would like to read up more on it as well, but it looks like your points/advice seem(s) to be on the right track, although I'd love to be more sure that my changing of the Expert params is the way I should go ;-) -- I'm always leery of doing that for documented/undocumented (software) database parameters and the victron params, I believe, are no exception. Is there any documentation available anywhere on these params for LiFePO4 batteries -- for my own edification? :)

thanks kindly,
Cosmin

When you read cell data sheets, they are all pretty much the same. Full charge to 3.55-3.65V/cell, and they are fully charged once the current drops to 0.05C at that voltage. There are several cell datasheets in the resources section.

Are the above 100% accurate all the time? No, but probably within 1-2% for all LFP cells of any suitable variety.
 

Cosmini

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Current counting battery monitors drift if the 100% criteria isn't met.

Essentially, if you ever see your battery at 14.2V flowing any current at all, and the Renogy doesn't say 100%, the Renogy is wrong, and it should be synched to 100%.
understood and completely expected -- thank you, kindly.

When you read cell data sheets, they are all pretty much the same. Full charge to 3.55-3.65V/cell, and they are fully charged once the current drops to 0.05C at that voltage. There are several cell datasheets in the resources section.

Are the above 100% accurate all the time? No, but probably within 1-2% for all LFP cells of any suitable variety.
I'm most concerned about how to "assist" the Victon CC understand when the LiFePO4 battery needs to be entered into Absorption/Bulk states, depending on the current state of charge/voltage, irrespective of the Renogy BM. ;-)

thanks kindly, once again,
Cosmin
 

sunshine_eggo

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understood and completely expected -- thank you, kindly.


I'm most concerned about how to "assist" the Victon CC understand when the LiFePO4 battery needs to be entered into Absorption/Bulk states, depending on the current state of charge/voltage, irrespective of the Renogy BM. ;-)

It's all based on the voltages. While this is for lead-acid, the concept is the same:

1636508207264.png

Bulk is the stage of charging that is typically at maximum possible current while still under the absorption voltage.
Absorption is the stage where the voltage is held constant (solid line) and current tapers (dashed line).

The transition to float is determined by the charge termination criteria. For lead-acid, it's typically 0.01-0.03C and LFP is 0.05C.

Float is intended to provide a floor below which the battery voltage won't drop provided loads don't exceed available solar. If available solar is too low or loads are too high, the battery starts powering the loads. If this is enough to pull the voltage down 0.1V below the float voltage to trigger the re-bulk process to take the battery to full again.

This is more preference/situational than science. If on good sun days, if you see the charger re-bulking several times a day, you should probably raise it from 0.1V and allow the battery to provide a small % of the loads without needing to charge. It's probably not important that you start your overnight consumption at 98% vs. 100%.

Here's an example of re-bulk in action. It was cloudy for me today:

1636508571129.png

As my loads exceeded my solar, the battery voltage dropped and triggered re-bulk. This is what a more typical day looks like:

1636509201005.png
 
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