Battery levels are different on 2 Charge Controllers HELP

gnoeld

I have a Renogy 100/40 and a 150/60. Each has it's own panel array but connected to the same battery bank via buss bar.
Challenge is that the 40 amp shows 77% battery level and the 60 shows 92% and etc. What can I do to get them to match and which one is correct?

BB.

Hi Gnoeld,

Can you tell us a bit more about your battery bank? Flooded cell lead acid, AGM, Lithium LiFePO4 or what?

Also the size of the solar arrays, the size and length of cable from the two charge controllers to the battery bank, etc.

As far as I know, the Renogy controllers do not have the ability to "sync"--So they will never be in-sync with each other.

How are the controllers behaving? Do they stop charging because the sun goes down, or do they stop charging (enter float charge) in the middle of the day?

-Bill

gnoeld

Not avoiding your questions about specs however all the wiring is the same to and from each CC. Why would the 40 say 77% of battery left and the 60 say 92% and how can I tell which one is correct? Lead Acid batteries 1200AH (12x 100AH each)

gnoeld

Cable battery connections are 2AWG @ 3 feet

gnoeld

Inverters to batteries 2/0 gauge 3 feet

littleharbor2

12 batteries you said 100 ah.. 
12 100 ah. batteries in what configuration? I am assuming 12 volt batteries from the ah. number. Even if you are running a 48 volt system I see opportunity for bad current paths.
 I guess my question is how many battery strings are you running?

gnoeld

Parallel

Photowhit

It may reflect one charge controller 'seeing' the higher voltage of the other controllers charging. 

Neither is likely correct! A single controller may sense lower amps passing into the battery and 'feel' it's closer to full. In general they are looking at the voltage and time in a state of charge. At 90% that charge controller has moved to the absorb stage of charging and holding voltage at a set level.

At 70% that charge controller may have the absorb voltage higher than the one at 90% and since the other one is holding the voltage there The 70% one will allow current to pass until it reaches about 80%.

Either way voltage is a poor way to establish the State of Charge (SOC). If they are flooded batteries, you could check their Specific Gravity (SG), but with so many in parallel, it is unlikely they are sharing the charging or loads equally. Some might show fully charged and others undercharged.

Basics of Charging;

The voltage you are seeing is the system voltage and not the battery voltage. If you are connected to charging or a load it will effect the system voltage.

During charging, there are basically 3 stages of charging, Bulk, Absorb, and Float.

BULK;

First thing when charging starts you will be in bulk, the voltage rises from what ever the system voltage was to a set point, around 14.5 volts. At that point the Charge controller stops the voltage from rising. Higher voltage can damage sealed batteries.

ABSORB;

Once the battery hits the preset point the charge controller keeps it at that point. Your batteries are roughly 80% full. Flooded batteries will start accepting less current at 80-85% full AGM/Sealed may go a little longer before accepting less current.

On many controllers you can set this point, Some will have different presets for Flooded, and sealed batteries, or flooded, AGM, and sealed batteries. 

The charge controller has a couple ways to know when to switch to float, Most inexpensive Charge controller are just timed for 1.5-2 hours. Some will also see less current flowing through the charge controller and shut it down when minimal current is flowing through the controller. On more expensive charge controller. You can set battery capacity to give the Controller a better idea of when to stop. you can also set a longer Absorb time. Or set 'end amps' a amount of amps flowing through the charge controller to stop Absorb and switch to the final stage.

FLOAT;

Once the Controller has determined the battery is fully charged it reduces the voltage to a point where very little current is flowing to the battery. This will prevent the battery from over charging and heating up.

While in 'Float' the charge controller watch for voltage drop, which would indicate a load. If the voltage begins to drop the charge controller will allow as much current to flow from the panels/array to compensate and maintain the voltage. If the voltage can be maintained, the load will in essence be running directly off the array/solar. If the voltage drops below the preset float voltage, the controller may start a whole new cycle if it stays there for a period of time.

The system voltage drop you see at night when the sun goes down is the charge controller moving into a resting mode with no energy to contribute to the system.

The morning voltage may reflect a load present that is effecting the voltage level. With sealed batteries, you would want to disconnect the battery from the system and allow it to 'rest' for a while to get an accurate idea of it's SOC (State Of Charge) from the voltage

littleharbor2

gnoeld said:

Parallel

You're not real forthcoming with details. It's really difficult to troubleshoot with so few details. 
 Anyway, you answered "parallel". I'm going with worst case scenario. 12 strings @ 12 volts. You have so many opportunities for uneven charging it's no wonder your controllers are confused.

BB.

There is an "optimum" method to connect lots of 12 volt batteries in parallel (using larger AH Batteries or cells is usually better than a bunch of smaller batteries in parallel for many reasons):

http://www.smartgauge.co.uk/batt_con.html

Most solar charge controllers just "estimate" battery state of charge... There are different Battery Monitors that do a much more accurate job of measuring/estimating state of charge... If you are interested:

Nice standalone unit that measures current into/out of battery bank:

https://www.solar-electric.com/victron-energy-bmv-712-smart-battery-monitor.html

Estimates battery state of charge based on voltage / time profiles:

https://www.solar-electric.com/mnbcm.html
http://www.smartgauge.co.uk/index.html

Some low cost options from Amazon and such:

https://www.amazon.com/s?k=dc+battery+monitor&sprefix=dc+battery+m,aps,610&ref=nb_sb_ss_ts-doa-p_1_12

-Bill