Dear members,

I can finally say I have progressed past the teething stages on solar conversion with the help of this forum and I have navigated all the difficult huddles of not understanding what I was buying and using installers that did not know what they were doing. I am at the point where I am comfortable with my system overall and can start to broaden my understanding of foreign concepts without trepidation.

My current area of concern and inquiry is around the topic of Battery State of Charge.

System details: 5KW MKS II Axpert (80A, 4500MPPT), 12 X Canedian Panels (9x330 + 3x335), 8 X 12V@110A Lead Acid Batteries(Flooded), BMV 712 monitor, Raspi ICC

Settings: Back to Grid Voltage 48V, Solar charging 20A, AC charging 20A, Back to Discharge Voltage 54V, Bulk Charging 58.4, Float charging 54.4, Battery Cut-off Voltage 47.8

Battery Control settings: SOC control 90% to Grid and 95% to Solar    -   Time Control 07h00 to solar and 17h00 to Grid.

Questions: 

1) Even without load with SOC at 100% (after 17h00), by next morning (07h00) my batteries SOC is already 97% is this normal and can the connected BMV account for the 3% drain on Battery bank.

2) When looking at battery trends graph of ICC, SOC drain is gradual but charging is not, it can shoot up from 92% SOC straight to 100%, is this normal? (see pic below)

3) Is there anything that needs to be adjusted on my settings?

In my journey towards going solar, I have already made a R15 000 mistake and damaged by previous batteries and hence the paranoia the second time around.

Your guidance in this regard will be highly appreciated and possibly save my marriage (no need to explain why I need to spend more money on 3rd new set of batteries 🤣)

Regards

Lindani

 

 

 

 

1) The inverter draws some power even when it's doing nothing, around 30-50W depending on the type.

2) Is that SOC charge from the BMV? If so when the charging current drops below a specified level, the BMV assumes the battery is full and resets the SOC to 100%

3) I'm sure some axperts will arrive just now with some suggestions! 

 

15 hours ago, LMthethwa said:

5KW MKS II Axpert (80A, 4500MPPT)

I think you'll find that the 4500 W is the maximum allowed PV array size; the MPPT is rated at nominally 4000 W (80 A x 50 V).

15 hours ago, LMthethwa said:

Solar charging 20A

By this I assume you mean that the maximum total charge current (solar plus grid, if both are charging at once) is 20 A, i.e. setting 02 is set to 20 A.

15 hours ago, LMthethwa said:

shoot up from 92% SOC straight to 100%, is this normal?

I wanted a BMV expert to confirm that this is the SOC resetting. But for the SOC to be so inaccurate (i.e. the jumps to be so large), I'd say that you have not set the settings in the BMV properly: the battery capacity in Ah (yours is nominally 220 Ah), and/or the Peukert factor. See your BMV documentation for details.

15 hours ago, LMthethwa said:

anything that needs to be adjusted on my settings?

They look correct for a 220 Ah lead-acid battery [ edit: as long as you are using ICC, and you are. ]

Edited May 16, 20197 yr by Coulomb

Thank you DeepBass 9 and Coulomb for you replies,

 

Bellow is the spect for the MKS II

Below is the setting where my charging setting are both set to 20A

 

This is my BMV setting., I have not changed the  Peukert setting and still on default values.

I did change tail current from 4% to 2.3% which I picked up on some old thread in this forum.

  

 

@Coulomb, if I understand you correctly,  are you saying that the SOC changes that I am experiencing is not correct?

6 hours ago, LMthethwa said:

are you saying that the SOC changes that I am experiencing is not correct?

I'm saying that if you use better parameters, the step will get smaller. A larger step implies that the SOC estimate before the step was further from the correct SOC value. You'll never eliminate that step, but I think it can do a fair bit better than what it's doing now.

I think you'll do better with a higher Charged Voltage setting, say 58.2 V. You might also try dropping your Peukert exponent to say 1.2.

Hi Coulomb,

I will explore the impact of the recommended settings and do a bit more read up on Peukert value.

Thank you for your  advise.

 

Here is a nice video - for ALL BMV users actually - as it needs to be regularly synced.