Seeing strange things on my off grid system

Started by Jimigunne, November 30, 2022, 02:20:24 PM

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Jimigunne

Its a 2S lifepo4 24v 300ah system (6 100 ah 12v batteries) The solar panels are 5S 12v with many more paralleled into the five in series. In full mid day sun, I only get about 400watts. I run only a big fridge and freezer off of the system 24/7.  So typically the batt ah might go down from 300 ah  fully charged to 60% in the morining when the panels start generating power.  In mid- morning on a sunny day, I check on it and its still about the same. But If I come back to it only an hour later, its showing 99% and its in float mode. And stranger still, its been in float mode over three hours and the bank charging rate is still at 15 amps.   This would be .5C, right? The inverter load as shown on Wizbang display is about 1.5 to 4.5 amps only.  I thought that once float mode started, the charging amps would drop down to a very low value.

boB


What stage is the charging when you see only 400 watts or less ?   In Absorb or Float, it would be expected to see a much lower power and current in anything but bulk MPPT charging.

Is your Absorb time set to a very short time ?  Sometimes lithium batteries have a longer Absorb time and sometimes they are very short times.

boB
K7IQ 🌛  He/She/Me

ClassicCrazy

#2
Quote from: Jimigunne on November 30, 2022, 02:20:24 PM
Its a 2S lifepo4 24v 300ah system (6 100 ah 12v batteries) The solar panels are 5S 12v with many more paralleled into the five in series. In full mid day sun, I only get about 400watts. I run only a big fridge and freezer off of the system 24/7.  So typically the batt ah might go down from 300 ah  fully charged to 60% in the morining when the panels start generating power.  In mid- morning on a sunny day, I check on it and its still about the same. But If I come back to it only an hour later, its showing 99% and its in float mode. And stranger still, its been in float mode over three hours and the bank charging rate is still at 15 amps.   This would be .5C, right? The inverter load as shown on Wizbang display is about 1.5 to 4.5 amps only.  I thought that once float mode started, the charging amps would drop down to a very low value.

Could you give some more info ?
What brand of batteries are they ? ( so I can look up the manufacturer specs)
What kind of panels do you have ?
What are the Absorb, Absorb time, Float setpoints you have programmed in to your controller ?  What kind of controller is it  - Classic or Kid ?
The correct terminology for your battery setup would be 2s 3p    ( 2 in series  and 3 parallel )
Have you put the panel specs into the Classic string calculator ( there is a different calculator for Kid)
https://www.midnitesolar.com/sizingTool/index.php

Some considerations - wiring is important to try and have all wiring resistances be the same . See this
http://www.smartgauge.co.uk/batt_con.html

In general lithium will charge at the same voltage for a long time, then quickly rise to absorb setpoint, and go to float  . You may not notice the transition from absorb to float depending on your setpoints.

The reason you may see it at 99% in Float is because depending on your settings and load  it will have to use a bit of the stored energy in battery before it drops to Float voltage .
You may see it charging in float depending on your settings.  And it could be your don't have the Absorb voltage high enough so the batteries continue to charge in Float - really depends on what you have set for them and how you have them wired.

Larry

system 1
Classic 150 , 5s3p  Kyocera 135watt , 12s Soneil 2v 540amp lead crystal for 24v pack , Outback 3524 inverter
system 2
 5s 135w Kyocero , 3s3p 270w Kyocera  to Classic 150 ,   8s Kyocera 225w to Hawkes Bay Jakiper 48v 15kwh LiFePO4 , Outback VFX 3648 inverter
system 3
KID / Brat portable

Wizbandit

Quote from: Jimigunne on November 30, 2022, 02:20:24 PM
The solar panels are 5S 12v with many more paralleled into the five in series. In full mid day sun, I only get about 400watts.

My guess is the issue is here.   Incompatible arrangement of PV modules.  Will need a one-line drawing to see how they are hooked up...