Minimum battery charge current for voltage regulation

[karrak]

Can anyone tell me what the minimum battery charge current  to maintain voltage regulation with the Classics is.

Thanks
Simon

[Vic]

Hi karrak,  Welcome to the Forum,

The current required to maintain any voltage that is regulated,  depends entirely upon the battery  --  battery type, battery Capacity,  its temperature,  the electrolyte SG (if Lead Acid),  battery age ...
EDIT:  OH,  and forgot to mention that the Voltage being maintained is also a large factor  --  higher voltage requires more current to maintain it,   and so on ..<

FWIW,   Vic

[karrak]

Thanks for the rely, sorry I didn't word my question very well.

What I meant is will the Classics maintain output voltage regulation without any load, or if not what is the minimum current load that they will be able to maintain voltage regulation.

Thanks
Simon

[Westbranch]

Simon, are you asking: if the battery is fully charged will it continue to send voltage to the battery when there are no loads on the battery?
If you have a value set for Float that is what it will output until  you 'bleed' off enough voltage and /or amps that the CC sees things  as '' ah ha, the battery needs to be charged (again) " and it goes into one of the modes available...
was that what you are after?

[karrak]

Simon, are you asking: if the battery is fully charged will it continue to send voltage to the battery when there are no loads on the battery?

Not quite. If left on float the charge current when charging LFP(LiFePO4) batteries will drop to virtually zero due to the very low "leakage" of these batteries. What I want to know is can the Classics maintain the programmed float voltage with no load or will the output voltage from the Classics drift up towards the solar panel voltage.

Simon

[Vic]

Thanks for the rely, sorry I didn't word my question very well.

What I meant is will the Classics maintain output voltage regulation without any load, or if not what is the minimum current load that they will be able to maintain voltage regulation.
Thanks
Simon

Hi Simon,  sorry that I did not quite get what you were asking ...

The Classic and most other CCs will provide the current necessary to maintain a regulated voltage stage (Absorb,  Float,  and EQ),    but,  for example,  for the transition from Absorb,  or EQ to Float,  the CC will provide NO charge current,  until the Float voltage is reached,  so  the battery voltage will take some time to descend to the float voltage.   The larger the battery Capacity the slower is this transition,  and the larger the loads on the battery (from the inverter,  primarily),  the more rapid will be the descent.

Some very stiff batteries,  like Lithiums can require a considerable time to reach Vfloat,  and need the Charge Controller (CC) to provide some current to maintain Vfloat,  in this case.

If that was what your were asking ...  FWIW,   Vic

[karrak]

The Classic and most other CCs will provide the current necessary to maintain a regulated voltage stage (Absorb,  Float,  and EQ),    but,  for example,  for the transition from Absorb,  or EQ to Float,  the CC will provide NO charge current,  until the Float voltage is reached, ...

Thank you, that was just what I was after, someone who says they are an engineer and posts on another forum swears black and blue that all controllers need some sort of external load to maintain voltage regulation. I have designed and built my own MPPT controller which has been running for over five years now and it definitely does not need an external load to keep the voltage regulated. I thought I had better check if this is true with commercially built units.

IMO it is a design fault if they can't keep regulation with no load current. Any controllers that can't keep regulation should not be used with LiFePO4 batteries. They could easily damage an LiFePO4 battery and its BMS.

Simon

[Westbranch]

Simon I think I understand, but just to be clear can you describe, say for a 24 V bank, what V & A values you want to see at each charge phase, charge no loads and then with a load applied?

[karrak]

say for a 24 V bank, what V & A values you want to see at each charge phase, charge no loads and then with a load applied?

The charging parameters I now use for my 24 volt 4P8S LFP battery are:-
Terminate Bulk and start CV(Absorb) at 27.6 volts
Terminate CV(Absorb) at an end current of C/50
Float voltage set to 26.8 volts

This regime charges the battery to very close to 100% full and keeps my battery to within a few % of 100% until the sun goes down.
My maximum charge current is around 0.1C and maximum discharge current is around 0.6C
My charge controller will regulate its output from the maximum that the solar array will provide to 0mA (actually negative because of the current draw of the control electronics) to keep the voltage at or below the set voltage of the particular charge phase that it is in. I would expect a commercial charger to do the same.

Simon

[dgd]

....
I have designed and built my own MPPT controller which has been running for over five years now and it definitely does not need an external load to keep the voltage regulated.

Ooops almost missed this and sounds much more interesting
So would you like to share some info about this controller? like general specs, processor type and which mppt algorithem are you using?  Did you design and write the code?

I built the well published Arduino based 12-24volt 15Amp MPPT controller designed for use with a 28v to 38v PV panel to charge an 80ah Lifepo4 battery.
Then spent some time modifying code to improve the mppt scanning moving away from the originals hill climbing mppt algorithm
I see there are also some rPi based low spec controllers.
I am also talking with two other NZ developers and we are co-operating in designing a more featured MPPT controller that will be based on the BBB processor.

dgd

[karrak]

The Controller is a patchwork of different PCBs

The control PCB is a general purpose microcontroller board that I designed ages ago based on an Freescale 68HC12  microprocontroller

The power circuitry is on a single sided PCB that I made up specially. The power electronics is slightly unusual in that I have a separate MPPT circuit for each solar panel. Another probably unusual feature is a 4 pole relay that connects the solar panels to the FETs. This is there as a safety mechanism in case of a blown FET or other fault. It also provide some lightning protection as it is NO at night.

Using the Wikipedia entry for MPPT definitions, the algorithm i have used is perturb and observe. It works well.

I did design and write the code. The software is written in assembler and Forth and runs under a multitasking Forth kernel. One of the tasks is a Forth interpreter connected to a serial port.

Another project I have designed and made and runs on the BBB is a Battery Monitoring System for LFP batteries that is written in Python and PHP. It is an opensource project here. https://github.com/simat/BatteryMonitor

Simon

[ClassicCrazy]

The Controller is a patchwork of different PCBs

The control PCB is a general purpose microcontroller board that I designed ages ago based on an Freescale 68HC12  microprocontroller

The power circuitry is on a single sided PCB that I made up specially. The power electronics is slightly unusual in that I have a separate MPPT circuit for each solar panel. Another probably unusual feature is a 4 pole relay that connects the solar panels to the FETs. This is there as a safety mechanism in case of a blown FET or other fault. It also provide some lightning protection as it is NO at night.

Using the Wikipedia entry for MPPT definitions, the algorithm i have used is perturb and observe. It works well.

I did design and write the code. The software is written in assembler and Forth and runs under a multitasking Forth kernel. One of the tasks is a Forth interpreter connected to a serial port.

Another project I have designed and made and runs on the BBB is a Battery Monitoring System for LFP batteries that is written in Python and PHP. It is an opensource project here. https://github.com/simat/BatteryMonitor

Simon

Simon - I just shared your post in the Beaglebone Black section of this forum 
http://kb1uas.com/mnsforum/index.php?topic=3189.new#new

Larry