Trouble shooting 9+ year old system...

Have you added an "new" loads to your DC bus?

In times past, we had one member that had "battery desulfator" on his battery bank. And the "electrical noise" from the desulfator was enough to cause one Outback charge controller to dramatically reduce its harvest.

Turned off the desulfator, and the Outback MPPT controller started harvesting correctly again (he had a second Outback, either on a second system, or the same system--Don't remember, but one controller was definitely impacted by the desulfator).

I always recommend a "Star" wiring connection for charge controllers (wire run from battery bus directly to charge controller). Daisy chaining (battery bus to controller A to controller B to controller C ) charge controllers can cause "cross talk" between controllers and confuse them (erratic battery bus voltage readings confusing the charge controller processor?).

Also, how is your solar array configured (A series panels by B parallel panels)? If you have parallel strings and you have per string circuit breakers, you can turn off one string at a time and see how well they are well they are sharing current.

Or you can get an AC-DC current clamp DMM and measure each solar panel string. DC capable current clamp meters are very easy, quck, and safe to use when debugging battery systems (also works for AC power too):

https://www.amazon.com/gp/product/B00O1Q2HOQ (inexpensive--Good enough for our needs)
https://www.amazon.com/gp/product/B019CY4FB4 (mid priced meter)

The above are just examples of DC Capable Current Clamp DMS... Check around and see what works best for you. There are AC only clamp meters--They are good units too... But AC only clamp meters do not work for DC power systems.

-Bill

My issue is trying to understand:

• Solar Panel / Array configuration (series/parallel/etc.) to see if one string is not carrying its share of current.
• Battery bus voltage (currently 25.5 volts)
• Charge controller "state" (yours says float)
• What is the system DC loads/current at this point (are DC loads greater than Solar Array output power?)
• What is the battery current (charging/discharging/etc.)...

Generally, I would expect "float" to be around around 27.2 Volts. And battery resting voltage (full charge, no loads, not charging) around 26.5 Volts.

Charging should be around 28.8 volts (in Absorb) and held for 2-6 hours (longer time for deeper discharge).

• Solar Array: 83 volts * 4.5 Amps = 374 Watts
• Controller output: 25.5 volts * 13.4 Amps = 342 Watts
• Controller eff: 342 W/ 374 Watts = 0.91 = 91% efficiency (makes sense for lower power levels)
• Mode: Float

It looks like the controller "thinks" your battery bank was charged to 100%... And In Float mode. Actual battery bus voltage (if float voltage was set correctly) suggest solar panel power in to charge controller is equal to power out to DC loads (and battery current is near zero Amps).

For off grid power systems--The total daily harvest (kWH) is based both on your daily loads and the amount of sun/solar available.

If you are using less power (and have "enough sun"), then it looks like you are using less power right now?

If the batteries are "under charging" when you have good sun--The possibly one solar array string is not supplying its share of current?

-Bill

The DC bus is you Battery Bank 24 VDC +/- Terminals (usually the central point where all DC loads connect if not the battery terminals themselves).

The DC Bus should be about the same voltage as the battery terminals (within a few 0.1 volts).

Each load (AC inverter), sources (solar charger) add and subtract their current(s) to the DC Bus. The battery bank itself is the "buffer" or giant capacitor) that supplies current when need (bus below ~25.6 volts) and bank discharging. Or absorbing current when over ~27.2 volts (float, bulk, or absorb charging).

What is the maximum battery bank voltage during the day (absorb setpoint of ~28.8 volts for AGM) and float around 27.2 Volts (aka solar array has more Watts available then the DC loads and battery bank charging are taking)?

How low is the battery bank voltage falling to in the morning (before sunrise)? What is the load current.

Do you know if the battery bank is not getting fully charged? How do you know?

I don't know your loads--kWH per day. If you are charging at 3.x kWH per day and discharging at 9.x kWH per day--That is going to quickly discharge your battery bank over a few days ("deficit charging")?

-Bill

Unfortunately, you cannot really measure per string "current" with just a volt meter (I have done it, but it is much easier with a DC current clamp meter.

If you have a combiner box with circuit breakers--You can turn off one breaker at a time and see how much the array current drops each time. Or you can even throw a dark tarp or cardboard over one or two panel in a string, and see how much the array current drops. Do these tests with lots of sun. (or you can turn on/expose one string at a time and check the current).

AC+DC Current Clamp DMMs:

https://www.amazon.com/gp/product/B00O1Q2HOQ (inexpensive--Good enough for most our needs)
https://www.amazon.com/gp/product/B019CY4FB4 (mid-priced current clamp DMM)

You could measure Voc with a meter and a good or bad string will read the same voltage. Volt meters draw almost no current and so if there is a poor connection/weak cell/etc.) somewhere, you need a lot of current to get a lot of voltage drop (Volts=Current*Resistance).

At the moment, I cannot tell if it is the Solar Array not outputting full/rated current (you should see Imp in the 50% to 100% range at noon on a clear/cool day). Or it could be the solar charge controller (terminating charge too soon, not reaching 28.8 volt absorb setpoint and holding for 2-6 hours). It could also be the battery bank having problems (high internal resistance, not fully charged, etc.).

When the inverter faults, what is the voltage reading (both on the "DC bus" and the DC input terminals) on the AC inverter (looking for poor electrical connection from battery bank to DC input terminals on inverter).

What is your array size (i.e., 9x 200 watt panels or what)?

Things I would do:

• Reboot the Charge controller. 1. turn off solar panel power (or do at night). 2. turn off DC bus power to the charge controller. 3. Wait 1 minute. 4. Connect DC bus and let boot. and 5. reconnect solar panels (if you connect solar panels first, it can confuse the charge controller or even damage it--DC bus needs to be powered before solar panel connection).
• Get a DC current clamp meter and check the array current (AM bright sun) and check the current for each array string. They should be very close to each other (10% or less good. 50% or greater difference, string wiring or panel problems). You have 3 "identical" strings--So doing A/B/C testing is really quick and accurate. It is unlikely that all panels have the "same fault").
• Review the settings for the MPPT charge controller that all voltage/timer/etc. settings are correct. You could factory reset the controller and reprogram too (possible corrupted database).
• Checking the bus voltage early evening--It is possible that the AC inverter is faulting by reading the "wrong" battery bank voltage--But having multiple problems (array+inverter, etc.) is unlikely with "new" problems.

I am not quite sure... Do you have the original FLA batteries in parallel with the new AGM batteries? Or did you replace the old batteries with AGM instead.

With the battery bank--Check and log each battery's voltage (resting, during "normal to heavy charging" and during "normal or heavy loads".

You have 4x identical batteries--And ideally the voltage across each battery should match the rest during operating conditions... If you see one battery with very high or very low voltage--You need to figure out why.

"Standby use only" batteries will "last OK" if shallow discharging (to 85% or so State of charge)--But they are designed for UPS installations (only discharged if there is an AC main power outage)... If cycled to 50% or less SoC daily, you can end up with very short cycle life (a handful of "months?).

Your batteries, if going down to (for example) 23.0 volts after a little evening use--They either severely discharged, or not long for this world... With your genset--Are they charging as one would expect?

-Bill

The DC Bus is where all the cables (charge controller, AC inverter, battery bank, backup battery charger, other DC loads all meet).

It may be real (large hunks of copper or brass with lots of wires coming to it. Or it may be simply all the wires bolted to the + and - terminals of your batteries.

It is where you will find your 24 VDC connection points. A random example:


This is an example of a physical bus bar. A chunk of metal with screws to hold various wires. 1-2 heavy power cables, and smaller wires going elsewhere.

They can also be Swiss cheesed with hold to take raw wire ends:

Or just wires stacked on battery teriminals:


Just slang for where all of your DC connections are made (to battery/charger/etc.).

Regarding your array. 9x 235 Watt panels (3s * 3p). The typical to maximum current I would expect to for your array (full sun/cool clear day):

• 9 * 235 Watts * 0.77 panel+controller derating =1,629 Watt "best case" a few times a year:
• 1,629 Watt best harvest / 29.0 volts charging = 56 Amps best case harvest to 24 volt battery bank
• 112 Amp best case * 1/2 = 28 Amps "best case" random middle of day to 24 volt battery bank

And each array string. Guessing Vmp~36 volts per panel:

• 235 Watt panel / 36 volts Vmp = 6.5 amps per string "best case" current
• 6.5 amps per string / 2 = 3.3 amps per series string "average case" current
• 3 * 6.5 amps Imp = 19.5 Amps "best case" current from array
• 3* 3.3 amps Imp "average worst case" = 9.9 Amps worst case "good" current from array
• And your photo is 4.5 amps from the array (may or may not be working correctly--too many variables for me to guess right now)

Depending on where you live and season, array tilt, etc... Your best case average harvest assuming at least 3 hours of sun per day (need your location):

• 9 * 235 Watt panels = 2,115 Watt array
• 2,115 Watt array * 0.52 off grid AC system eff * 3.0 hours of sun per day = 3,299 Watt*Hours per day early spring / late fall harvest estimate
• MPPT controller output * 2,115 Watt array * 0.77 panel+controller deratings = 4,886 WH per day controller harvest (best case ~ 3 hours of sun per day)

8.6 kWH per day output from your Outback with this array would be on the order of 5.2 hours of sun per day (pretty sunny weather/location).

-Bill

Regarding 24 volt panels... There are really two general types that are called 24 volt panels... One has Vmp~30 volts. The other has Vmp~36 volts.

The details do matter here... I am trying to guess at what you should be seeing/looking for. Voltage and current levels will be "wrong" by 20% if I guess wrong (my luck, my guesses are not always correct).

-Bill