The Outback FM80 / FM60 series charge controllers keep a 128 day running log of many different voltages, wattages and times. This information can be useful in troubleshooting problems, monitoring the status of solar electric systems, and determining system battery status. Data Logging can be thought of like a 128 day history of the charge controller and the solar electric system’s performance. This history will show how much power the PV panels produced each day, if a complete charge cycle was completed, and how well the batteries performed.
*The older MX60 charge controller also has a data logging function, however as it is slightly different then FM series charge controller, it will not be discussed in this Tech Update. Please refer to the MX60 owner’s manual for more information.
Accessing the Logging Menu: The Logging menu can be viewed on the FM series charge controller by:
- From the main menu, press the soft keys “->” to move the arrow next to Logging.
- Press “GO” to advance to the Logging menu.
The screen will display various voltage, wattage and time information.
- Pressing Soft Key 1 (leftmost) will return to the main menu.
- Pressing Soft Key 2 (one key to the right of the leftmost) will allow you to “Clear” or erase the logging history, this is not recommended.
- Pressing Soft Key 3 (two keys to the right of the leftmost) will go backwards in time and show the previous days logging data.
- Pressing Soft Key 4 (rightmost) will go forward in time and show the next days’ logging data.
Figure 1, from Outback’s manual (page 18), explains what each of these data points are.
Example 1: Figure 2 is displaying logging data at 9:00 AM on an overcast day.
- Today – This is today’s logging data.
- 014Ah – 14 Amp-hours have come from the PV panels to the batteries, or loads.
- 00.1kWH – 100 watt-hours have come from the PV panels to the batteries or loads.
- 059Vp – This is the peak voltage the PV panels have reached today.
- 36.3Ap – This is the peak amperage provided to the batteries today.
- 0.48kWp – 480 watts is the peak wattage generated by the PV panels today.
- MAX 13.3 V – This is the highest battery voltage reached today.
- ABS 00:00 – The charge controller has not started Absorbing today.
- MIN 12.5 V – This is the lowest battery voltage reached today.
- FLT 00:00 – The charge controller has not started Floating today.
Conclusions: It is too early in the day to make very many conclusions, however the lowest battery voltage recorded was 12.5 volts. As these are AGM SunExtender batteries, the approximate depth of discharge (DOD) was 25%, this shallow depth of discharge will help to ensure a long battery cycle life. A rough rule of thumb to have a long cycle life; batteries should not drop below 70% DOD, or about 12.5 – 12.3 volts.
* See Buying Batteries In-Country for more information on battery cycle life.
Example 2: Figure 3 is displaying logging data from the previous day (yesterday).
- Today – -1day, this is one day past, or yesterday’s data logging.
- 0638Ah – 638 Amp-hours have come from the PV panels to the batteries or loads.
- 0.85kWH – 8,500 watt-hours have come from the PV panels to the batteries or loads.
- 066Vp – This is the peak voltage the PV panels reached yesterday.
- 81.8Ap – This is the peak amperage provided to the batteries yesterday.
- 1.09kWp – 1,090 watts is the peak wattage generated by the PV panels yesterday.
- MAX 13.4 V – This is the highest battery voltage reached yesterday.
- ABS 00:00 – The charge controller did not start Absorbing yesterday.
- MIN 12.1 V – This is the lowest battery voltage reached yesterday.
- FLT 00:00 – The charge controller did not start Floating yesterday.
The PV panels produced a total of 8.5kWH on this day, this is a respectable amount of power from a FM80 on a 12 volt battery bank, this day must have had good sun and a clear sky.
The peak amperage was 81.8 amps, as the FM80 is designed to only produce 80 amps maximum, so the FM80 is maxed out, this is ok.
From the highest battery voltage of 13.4, the 0 hours of Absorbing time, and 0 hours of Floating time, the batteries did not receive a complete charge cycle. It is recommended that batteries receive a complete charge cycle a minimum of 4 out of 7 days. A charge cycle is considered compete when the charge controller has completed the Absorb cycle (usually 4 hours long) and started the Floating cycle. If a battery bank is consistently not receiving a complete charge cycle, there are a few possible problems; the loads need to be reduced, additional PV solar panels are needed; loose connections; or damaged batteries. Please consult with the NTM Tech Center.
The lowest battery voltage of 12.1 indicates that the DOD was lower than 50%. However, this can be misleading, if the lowest battery voltage was recorded when the batteries were under heavy usage. For example if the refrigerator, freezer, laptops, fans, lights, and table saw were all running at the same time, first thing in the morning before the sun was up. This would cause the battery voltage to drop, however when the loads were removed, the battery voltage would return to its actual “no load voltage”. If a low “lowest battery voltage” is observed, the battery voltage should be monitored several times a day for a week to determine if there is a problem. If this battery bank is consistently discharged to a low DOD the battery bank will have a low cycle life and will need to be replaced prematurely.
Example 3: Figure 4 is displaying logging data from 12 days previously.
- Today – -12day, this is data logged from 12 days ago.
- 0289Ah – 289 Amp-hours have come from the PV panels to the batteries or loads.
- 03.8kWH – 3,800 watt-hours have come from the PV panels to the batteries or loads.
- 064Vp – This is the peak voltage the PV panels have reached this day.
- 83.9Ap – This the peak amperage provided to the batteries this day.
- 14kWp – 1,140 watts is the peak wattage generated by the PV panels this day.
- MAX 14.6 V – This is the highest battery voltage reached this day.
- ABS 04:00 – The charge controller Absorbed 4 hours this day.
- MIN 12.5 V – This is the lowest battery voltage reached this day.
- FLT 02:34 – The charge controller Floated 2 hours and 34 minutes this day.
The PV panels produced a total of 3.8kWH on this day, this is a respectable amount of power from a FM80 on a 12 volt battery bank. Although, on Example 2 there was 8.5kWH produced, and as on this day the batteries were able to complete their charge cycle. There was likely extra unused power available on the PV panels which could have been utilized while Absorbing or Floating, if there is a good use for the extra power.
The highest battery voltage of 14.6 may be of concern. SunExtender AGM batteries should have an Absorb voltage of around 14.4 volts at 77 deg F. However, this should be a temperature compensated voltage. The Outback FM series charge controllers will reduce the charging voltage in proportion to higher temperatures. When used in a warm environment the Absorb charge voltage should be below the Absorb set voltage. The high battery voltage of 14.6 volts could be a transient, or very short over voltage. This is nothing to be concerned about, as a quick small overvoltage will not damage anything. However, if this overvoltage is found in several days’ data logs, then the battery voltage should be monitored several times a day for a week to determine if there is a problem.
As the Absorb time was 4 hours and the Float cycle began, the batteries completed a charge cycle.
This was a good day for the solar electric system, everything seems to be working correctly.
When considering adding additional loads or additional PV panels to a solar electric system, the data logging information is invaluable in determining the status of a solar electric system. When contacting the NTM Tech Center with problems, it may be helpful to include the past weeks data logging information to assist with troubleshooting.