Support FAQs

Looking for information on a specific term? Visit our Glossary page.

Answers to more detailed questions are available in our Q&A blogs. Visit our Q&A Blog.

I sometimes hear a buzzing noise during charging. Is something wrong?

No. The buzzing sound is mechanical resonance created by the switching of current through the circuit board and solid-state devices. This is normal and not indicative of a problem.

How are temperature compensated charging adjustments calculated?

Here’s a brief explanation on how to calculate the temperature compensated adjustments our controllers make to their charging voltages based on the ambient temperature changes.

The charging voltages listed in the controller operator’s manual are specified at a 25C standard test condition ambient temperature with a -.030V (@ 12V battery) adjustment per degree C change in temperature above or below the 25C reference. The (-) in front of the .030V indicates that voltage adjustment is inverse to the change in temperature. In other words, if the temperature increases above 25C, the controller decreases it’s charging voltage by -.030V per degree C rise above 25C and vice versa. An accurate measurement of the ambient temperature is required for calculating the the controller’s temperature compensated adjustment.


An ambient temperature of 35C = +10C increase above the 25C base temp = 10 x -.030V compensated adjustment = temperature compensated -.300V decrease in charging voltage.
Therefore, a 14.4V charging voltage specified in the manual @ 25C would be reduced to 14.1V @ 35C or increased to 14.7V @ 15C.

The compensation rate is doubled to .060V/C for 24Vnominal battery systems and quadrupled to .120V/C for 48V nominal battery systems.

Can I mount the controller horizontally?

Morningstar controllers have been designed to mount vertically. This is the orientation in which the heatsinks are most effective. Mounting the controller horizontally will reduce its passive cooling efficiency, but the risk of overheating will be determined by the ambient temperature and the power level at which the controller will be operating.  All efforts should be made to mount the controller vertically.

Can the TriStar regulate hydro/wind/gas generators?

Wind/gas/or hydro-generators, and other DC charging sources can be regulated using the TriStar in diversion mode. Refer to the TriStar Operation Manual for more details.  Other resources are also available at the links below


Diversion Calculator TS.APP .Diversion.01.EN

TS.APP .Diversion.01.EN





Changing Charge Settings with RM-1?

The Remote Meter (RM-1) cannot be used to change charging parameters. The RM-1 only displays data and provides basic user commands, such as resetting Amp-Hour counters.  For further information, please consult the RM-1 manual.

Changing Charging Settings with TriStar Meter?

The TriStar Meter family (TS-M, RS-RM, TS-M-2, TS-RM-2) cannot be used to change charging parameters. The TriStar Meters only display system data and provide basic user commands, such as resetting Amp-Hour counters and starting/stopping an Equalize charge.

For more information concerning the TriStar Meter family, please consult the respective TriStar Meter manual.

Can I charge two different battery banks with one solar array?

Yes, however this can only be done with PWM controllers and cannot be implemented with MPPT controllers. MPPT controllers require their own isolated solar array.  You would need two PWM charge controllers to do it.  The “Charging Isolated Battery Banks with One(1) PV Array” Tech Note includes a wire diagram illustrating battery, controller, and PV Array connections.

Why does my controller's Charging LED stay lit after solar input has been removed?

Most Morningstar controllers will take up to 5 minutes to realize that the solar input voltage is no longer present before transitioning into the ‘night’ state. The controller performs periodic day/nigh checks (about once every 5 minutes). Depending upon where the controller is in this cycle when the input is removed, it may take anywhere from 0-5min for the controller to turn off its Charging LED and go into the ‘night’ state.

What battery chemistries do Morningstar controllers support?

Morningstar controllers can regulate charging in lead acid, lithium ion, nickel-cadmium and many other battery types.  See Morningstar Best Practices By Battery Chemistry page and Energy Storage Partner program page  for more information.

Does the SunSaver Duo need to be connected to two battery banks?

No.  For systems with a SunSaver Duo (SSD) and only 1 battery bank, only 1 battery connection is required for proper charging. It is not necessary to wire both Battery 1 and Battery 2 connections to the sole battery bank. The SSD will detect that only 1 battery is connected and provide 100% of charging current to the connected battery.

If a second battery is connected in the future, the battery will automatically be detected and charging current will be split according to the specified charging priority.

What are the common causes of MOSFET or power transistor failure?

The internal switches of a controller, called MOSFETs or power transistors, switch current on and off to control solar current and load current. Because these components are in the power path, the controller will no longer be able to switch current if they fail.

Power transistors can fail for the following reasons:

  • Over-voltage: lightning or other high voltage transients on the PV power cables.
  • Over-current: too much PV for the controller or a short in the PV line pulls too much currentout of the battery through the controller.
  • Extreme temperatures during charging.
  • A premature failure of the component. The transistors are solid state devices that are manufactured in huge volumes with extremely low failure rates. However, no electrical components are 100% defect free and can pass test and then fail after a short period of time.
  • Old age

Can I use 60 cell modules with a PWM controller?

Morningstar does not recommend using 60 cell modules for charging a battery system with a PWM controller.

There are a couple of issues with attempting to use 60 Cell modules with a PWM Controller. First, a 60 Cell module will typically have a Voc of ~36 and a VMP of ~30 at STC of 25C. Many Morningstar PWM Controllers have a Maximum voltage input rating of 30V when used in a 12V battery configuration, and 60V when used with a 24V battery configuration. The input voltage from a 60 cell module will exceed the 30V rating for PWM controllers when used in a 12V config, and if 2 panels are put in series will exceed the 60V rating for a 24V system resulting in a damaged controller.

For charging a 12V battery with a PWM Controller, a 36 Cell Panel is recommended.  For charging a 24V battery, either a 72 Cell Panel or (2) 36cell panels in series is recommended

What causes the controller to display a DIP Switch Changed Fault?

If one or more DIP switches are changed while the controller/inverter is powered, the controller/inverter will display a DIP Switch Changed Fault (and the LEDs will begin to sequence). Changing DIP switches while the unit is operating will cause the unit to stop charging until the unit is reset. A reset can be performed by removing power from the device (so that all the LEDs go off) and then re-starting the unit. This procedure prevents the inadvertent changing of operational settings while the controller/inverter is active.

After the controller/inverter has been re-started, it will operate with the new DIP switch settings.

Do Morningstar controllers use SOC calculations?

No. Morningstar Controllers regulate according to battery voltage setpoints. Because battery health and other factors affect charging over time, using voltage setpoints is a way to naturally track these changes and affords the user a complete understanding of the controllers operation. SOC calculations and algorithms may not be precise under all conditions and may leave the user with a “fuzzy” understanding of the workings of the unit.

Does the TriStar have any internal fuses?

There are no internal fuses in the TriStar. Short-circuit and over-current protections are electronic.

Does the TriStar have communication capabilities?

Yes.  The TriStar provides one 9-pin RS-232 serial connection. Communication is possible using the MSView PC software (free from our website) Alternatively, application-specific software can be written that communicates with the TriStar using the MODBUS industry standard protocol.

Where can I find flat (ribbon) type DB9 serial cables for the TriStar RS-232 connection?

Below is a link to DigiKey, a retailer of flat (ribbon) type DB9 serial cables that can be used with the TriStar RS-232 connection in place of the standard type of serial cables.  The stand-off height of the connectors on standard serial cables obstructs the re-installation of the TriStar face plate while connected.  The low-profile type of DB9 connectors used on these flat serial cables allows the TriStar face plate to be reinstalled without being obstructed by the RS-232 connection.  This is useful in applications that require a continuous RS-232 connection to the TriStar for remote monitoring/communications purposes.

What does the controller's Green/Red LED light flashing sequence indicate?

This indicates a High Voltage Disconnect fault.

Possible causes:

  1. wired past controller switches (bypassed the controller, system wiring error)
  2. sense connection problem
  3. RTS connection problem
  4. DIP Switch system Voltage wrong
  5. custom settings: setpoints too low (in load control mode, HVD only enabled in custom)
  6. other charging sources in the system. Other charging sources in the system may be charging the battery above the controller’s regulation set-point, causing the high voltage indication. The indication will clear when battery voltage has returned to normal.

Use the troubleshooting flow diagram in your operation manual for system diagnosis

Why is there a green flashing LED with no solar input to controller?

If no input source (solar) is connected to the charge controller, but there are other charging sources connected to the batteries, charge controller may still show a Green Flashing LED (indicating that the controller is in the absorption charging stage). The Green Flashing LED may appear on the Morningstar controller if the battery voltage is at or above the controller’s Absorption charging voltage setting. Although the controller is not delivering power to the batteries (because there is no input source present), the indication still appears. This is not an indication of controller malfunction.

Where can I find help using MSView Software?

MSView contains a built-in Help File (accessible from the Help menu -> Help Topics) which provides detailed information about using the software to connect to Morningstar devices, program custom settings, view and/or log real-time data, and evaluate system performance.

Can I use a higher voltage array with a lower voltage battery?

A higher voltage solar array (e.g. 24V nominal) can be used with a lower voltage battery bank (e.g. 12V nominal) if the controller used is an MPPT controller.

PWM controllers CANNOT be used to charge a lower-voltage battery bank with a higher-voltage solar array. Please use an MPPT style controller if this is required.

How do I size the diversion load bank?

The TriStar Operation Manual (pp 37-42) provides guidelines for diversion load sizing and addresses installation issues as well.  We also provide a calculator available at the link below

Diversion Calculator

How long is the warranty on Morningstar products?

Professional Series controllers have a 5 year warranty.  Essential Series controllers such as the EcoBoost MPPT, EcoPulse, and SHS have a 2 year warranty. The SureSine inverter has a 2 year warranty.

How many meters can I connect to the TriStar?

We allow up to 2 digital meters to be connected to a single TriStar. Any combination of local and remote meters is acceptable.

Note: due to power limitations on the bus, only one meter can have an illuminated backlight at any given time. A meter will turn off the other meter’s backlight if necessary before turning on its own backlight.

How should I mount the TriStar?

The TriStar should be mounted on a vertical surface out of direct sun with the TriStar heatsink fins oriented vertically. Allow at least 3 inches above the heatsink for airflow.

Is datalogging available on my controller?

Some Morningstar controllers have datalogging capabilities.  Check the datasheet and operation manual for your model. The MSView PC software will provide logging capability through the serial or Ethernet port. Additionally, a number of commercial dataloggers and PLCs support the Modbus protocol.

Is the chassis ground the same as the DC negative?

No, the electrical negative is isolated from chassis ground on Morningstar Controllers.  The chassis ground is used to provide the “Equipment” or dead metal ground in the system

How come my meter display buttons are not working?

The note below assumes the meter is powered and displaying text on the screen.

If a button(s) for any one of the following display models appears to stop working:

– TS-M / TS-RM
– TS-M-2 / TS-RM-2 – RM-1

there may be several explanations:

  1. You have reached the end of a menu, and there are no more screens to display in that direction (e.g. if you go to the bottom of a menu and continue to push the DOWN arrow, nothing will happen)
  2. If the backlight is OFF, the first button press will turn the backlight ON, but will not change the meter screen. E.g. if the backlight is OFF and you would like to move LEFT in the display, you must press LEFT twice – the first to turn the backlight ON, the second to move LEFT in the display). In brightly lit rooms or sunny conditions, it may be difficult to detect whether the backlight is ON or OFF.
  3. The button contacts have become dirty. To clean the button contacts:
    • Disconnect the meter cable from the back of the meter
    • Remove the two screws on the back of the meter, holding the meter circuit board to the faceplate – Wet a Q-tip or small paper towel with a small amount of alcohol – Clean the 4 contact points on the circuit board and the contact point on each of the buttons

If the meter button(s) still do not function correctly after checking the points above, contact your Morningstar re-seller / dealer for warranty replacement.

Why am I getting no output voltage from the Morningstar Charge Controller?

When a solar panel is wired to the solar input, no voltage output is measured on the battery leads. The Charge Controller is not damaged!

There is no voltage output because the Charge Controller requires the battery connection to function properly. Without a battery attached, the Charge Controller’s internal circuits cannot power up and allow current to flow from the Solar input to the battery.  You must connect battery to the charge controller first to allow it to properly bootup, and then solar can be applied.

Why does the start-up LED sequence stop on yellow?

This indicates that firmware is not properly loaded into the controller. Download the MSLoad firmware utility and the latest firmware. Follow the instructions to load new firmware into the controller. The SOC LEDs should then  perform the full start-up G-Y-R sequence.

If unsuccessful, contact your authorized Morningstar dealer for service.

How can I reduce noise interference during PWM charging?

Pulse Width Modulation (PWM) charging may cause interference in sensitive loads in the system during charging. The SunSaver switches current at 300 Hz. PWM switching noise can sometimes be heard in the controller itself, the wiring or wiring connections, or the system loads. AM radios and CB radios are especially prone to PWM interference. Noise in the controller or wiring is caused by mechanical resonance when current is switched through the circuits. There is little that can be done to remedy this issue. However, noise/interference in the system loads can usually be reduced or eliminated by the following:

  1. Minimize cable runs between components
  2. Twist power pairs(+/-) to reduce radiated noise
  3. Good system grounding
  4. Add capacitance across load power(at load input, 22000uf or more)
  5. Add a line filter. some have had success with car audio filters that eliminate alternator whine. If these measures do not eliminate or reduce interference to acceptable levels, the controller can be modified to reduce the switching frequency. The 3rd generation SunSaver has a wire loop under the faceplate. If this loop is cut, the controller will reduce the switching frequency to ~1 Hz. Refer to the SunSaver Operator’s Manual for more information.
  6. Some Morningstar controllers allow for operation in a ‘low-noise’ state. Check your controller documentation for details.

Can I parallel my SureSine inverter AC outputs?

No. Two AC paralleled SureSines would not be able to phase align their AC output waveforms, resulting in a very messy AC signal damaging to AC equipment or the SureSine inverters.

What are the guidelines concerning DC loads wired to the load terminals of my charge controller?

  1. Do not wire inverters of any size to the Load Terminals
  2. The total load draw should not exceed the load current rating for the controller (Consult the controller manual for technical specifications)
  3. Inductive loads such as pumps, motors, fridge compressors – should be wired directly on the battery bank.  Another option is to retain the load control functions (LVD/HVD) by adding a relay on the load terminals to make/break the power connection form the battery to the load (See diagram below).
  4. Another option is to install a clamping diode*  to protect the Controllers load switching circuit. *The diode should be placed across the Load terminals on the Charge Controller with the cathode of the diode on Load +. The forward current rating of the diode should be equal to or greater than the peak load current draw.
  5. The load lines should be fused for best protection.

Relay Load Control

What is the max solar input voltage rating for my PWM controller?

The maximum solar input voltage rating for a 12V Battery System is 30V, which equates to using a 36 cell solar panel

The maximum solar input voltage rating for a 24V Battery System is 60V, which equates to using a 72 cell solar panel or (2) 36 cell solar panels in series.

Do not charge a 12 Volt battery with a 24 V (72 Cell) solar panel. The solar panel will operate too far off its power point (very inefficient) and voltage spikes during regulation will damage the charge controller.  Damage resulting from an array >30Voc in a 12V battery bank system will NOT be covered under warranty.

What is the purpose of the battery sense connection?

When large currents flow through the battery power cables, a voltage drop results due to resistance in the cables. Since the controller regulates the batteries according to battery voltage, it is important that the controller measure the voltage directly at the battery. The Battery Sense connection allows battery voltage measurement directly at the terminals because the sense lines carry very little current (hence, small-gauge wire) enabling accurate regulation.   Without the sense lines, the controller must use the battery power connections, which may be different than actual battery voltage. The Battery Sense connection is optional and is only needed when significant voltage drops exist on the battery power cables.

What does red & yellow - green & yellow sequencing LEDs indicate?

Red & Yellow – Green & Yellow sequencing LEDs indicate one of the following faults:

  • Remote Temp Sensor Fault
  • Battery Sense Fault

Can I change SureSine DIP switch settings during operation?

The SureSine inverter indicates a fault with RED LEDs when one or more DIP settings switches is changed during operation.

Solution: Adjust the switch(s) to the desired position and cycle power by removing and reconnecting the battery. The SureSine will restart using the new configuration.

When should the Remote temperature Sensor (RTS) accessory be used?

The RTS is recommended whenever the temperature at the battery will be more than 5°C (9°F) different than the temperature at the controller. If an RTS in not used, and the charge controller does not have an ambient temperature sensor (Tristar, TristarMPPT, Tristar MPPT 600V) then the controller will not compensate charging setpoints for temperature.  If your controller has an ambient temperature sensor, then the controller will compensate charging setpoints for temperature, although it is best to use the RTS and measure the temperature of the battery.

What is the Remote temperature Sensor max cable length?

The RTS cable can be extended to a maximum of 30 meters (98 ft).

Do Morningstar controllers have reverse discharge protection at night?

Yes. All Morningstar controllers will automatically prevent reverse discharge of the battery back through the solar array during the night. No external diodes on the input of the controller are required.

What does a green blinking LED on the Remote Meter indicate?

A green LED blinking on the Remote Meter indicates that the battery is in the absorption state. This may happen under normal operating conditions and is not indicative of a problem.

How do I resolve serial connection communication problem?

If you are having problems communicating with a Morningstar product using a serial connection, try the following:

  1. Make sure that the unit is powered with a battery or power supply. The unit cannot communicate without power.
  2. Verify that the serial cable is not a Null Modem or cross-over cable.
  3. Verify that no other programs or managers are using the same serial port.
  4. Check the serial cable for continuity using a multimeter. The cable should have continuity from Pin1<->Pin1, Pin2<->Pin2,… If possible, try another cable.
  5. Shut down and restart the PC. Reattempt connection.
  6. Try another PC

For products that require the PC MeterBus Serial Adapter (Model: MSC), check the RJ-11 telephone cable. If possible, try another cable. It has been reported that some USB to Serial cables will not work with the MSC because the RS-232 output signal voltages are below the RS-232 electrical specification.

Should I add fuses and/or disconnects to my system?

Fuses, circuit breakers and disconnects should be included in your system. Refer to your local/national codes concerning requirements. The controller’s Operation Manual outlines NEC requirements for installations in the United States.

Why does my SunLight controller delay charging?

The SunLight has delays before charging begins and at dusk when charging stops. The SunLight uses the solar panel voltage to determine when dusk and dawn occurs. For this reason, the SunLight must be certain that dusk or dawn is actually occurring. The solar input  voltage is sampled and averaged. This process may take up to 10 minutes.

If the panel is connected, it may take up to 10 minutes before charging begins. If the panel and battery has been connected for more than 10 minutes and the SunLight is still not charging, refer to the SunLight testing document in the Related Documents list.

Why does my SunLight load connection measure -2V?

The SunLight controller will have a -2V load voltage measurement when in the LVD state with no load physically connected to the controller.  This is only a residual voltage that will be pulled to 0V when a load is connected.  It is not an actual -2V supply to the load.

This also applies to the SunLight controller during its normal daytime charging state.

Why is my SunSaver Duo flashing red and not charging?

If the SunSaver Duo LED is flashing Red and has stopped charging, it may be due to an RTS (Remote Temperature Sensor) fault. The RTS terminals on the upper left front of the controller can be susceptible to accumulating dust/moisture/debris. If these terminals gather enough dust/moisture a resistive connection across the terminals can form. To the controller, this resistive connection may seem as though a damaged RTS is connected. If there is no RTS present, the issue can be fixed by:  – removing battery power from the controller  – using a small piece of wire to connect the two RTS terminals together – reapplying battery power with the small wire connected (keep the wire installed until if/when you decide to install an RTS probe into the system).

Newer SunSaver Duo controllers come with a metal jumper pre-installed to help prevent this issue.

How do I enable lighting control for the SunSaver MPPT?

In Sept 2012, Morningstar released version 09 of the SunSaver MPPT” firmware. It introduced a new programmable lighting control feature that can be configured using Morningstars MSView” Software. This firmware MUST be downloaded and installed in order to enable lighting control. (Note: the SunSaver MPPT Solar Charge Controller does not come from the factory with lighting control enabled.)  This Tech Tip explains the process of updating the SunSaver MPPT firmware and how to correctly configure the updated controller for the desired lighting functionality

How do I program lighting control on the SunSaver MPPT?

Below is the document detailing how to program the lighting control on the SunSaver MPPT to account for longer days in summer, and shorter days in winter:

How do I deploy a SunSaver in a pumping application?

This document is a wiring diagram that shows the correct wiring and installation of a blocking diode when using the SunSaver in pumping applications:

Why won't the SureSine will not enter Standby mode with loads off?

The loads may be parasitic, drawing more than 8W (anything with a transformer). The first DIP switch may also be set to the ‘down’ position, setting the inverter to the ‘always on’ mode (provides continuous AC output). Ensure there is no power going to the inverter, then move the first DIP switch to the ‘up’ position to put the inverter into ‘standby’ mode. If a DIP switch setting is changed during operation, the inverter will display a fault. Remove and reapply power to clear the DIP switch changed fault.

How do I test the SunGuard?

The SunGuard can be tested for correct operation as follows:

  1. Wire the SunGuard into your system with Solar and Battery attached to the appropriate leads
  2. Measure battery voltage
  3. Measure solar voltage

If the battery is charging up (has NOT reached regulation voltage) the solar voltage and battery voltage will be about the same. If the battery is fully charged, the battery voltage will be at 14.1V* and the solar voltage will be higher. If solar voltage is greater than battery voltage and the battery is not yet fully charged, there may be a problem with your SunGuard.

* The 14.1V regulation voltage setpoint is temperature compensated. If the ambient temperature is warmer than 25C (~78F) the regulation setpoint will be lower. The regulation setpoint will be higher in colder temperatures.

NOTE: Measuring the SunGuard battery voltage leads without the battery attached is not a valid test!

How do I calculate the heat dissipation for Morningstar's TriStar (PWM) and TriStar MPPT charge controllers?

Morningstar controllers and inverters are very often installed within an outdoor enclosure. Many of these installations are located in warm climates where overheating of equipment inside the enclosure can become a concern. Since power electronic components will produce heat that can accumulate inside the enclosure, it is important to determine the effect of this heating on the temperature inside that enclosure.

This tech tip discusses how to calculate the heat dissipation for Morningstars TriStar (PWM) and TriStar MPPT solar charge controllers and then determine how that heat dissipation will affect the temperature inside a sealed enclosure. Using this information, system designers can start to make better decisions regarding heat management inside the enclosure.

How do I use the TriStar with a 36V battery?

For 36V systems, you will need to use the custom settings. The TriStar assumes that 12V nominal values are programmed into custom memory. When the user changes the DIP switches for 24V or 48V operation, the TriStar automatically doubles(or quadruples) the programmed values. In the case of a 36V system:

  1. Divide your desired regulation setpoints by 4
  2. Program these values into the TriStar using the PC software
  3. Set the TriStar in 48V mode with the DIP switches (DIPS 2,3 = ON)
  4. Set the TriStar battery type to custom (DIPS 4,5,6 = ON)

In 48V mode, the TriStar will multiply your setpoints by 4, attaining the correct regulation voltages you require.  Use the 48V setting because the TriStar will more accurately measure 36V system voltages in the 48V setting.

How do I ground the TriStar controllers?

Electrical negative is isolated from chassis ground in the TriStar and TriStar MPPT family of controllers. Morningstar recommends earth grounding the chassis per NEC guidelines. See the installation section in the Owner’s Manual for more details.

How do I deploy the TriStar in wind/hydro systems?

Alternate chargingsources other than solar (i.e. wind, hydro, etc) should only be used in diversion control mode configuration with the TriStar controller. Do not wire wind or hydro generators to the solar input of the TriStar. The TriStar was designed and tested only for solar input. Wind and hydro generators have different output characteristics that could cause damage to the controller. Further, the controller is designed to record and analyze day/night length, history, and charging characteristics based on the day/night transitions. Since wind and hydro generators produce output regardless of time of day, theTriStar will not be capable of determining day and night transitions and lengths. This will affect the automatic equalization setting and the controllers transition to the float stage.


Why doesn't the TriStar Meter match multimeter measurements?

If voltage and/or current measurements do not match the values reported on the TriStar meter (or values reported to MSView)

  • Measure the voltages directly at the TriStar terminals. Voltage drops due to line resistances can be significant.
  • Be sure the Battery Sense wires are not wired to the RTS(remote temperature sensor) terminals. Both terminals look similar and are easy to mix up.
  • Check for correct polarity at the Battery Sense connection.
  • Confirm your measurements with another multimeter.

How do I reset my TriStar MPPT IP address reset?

A controller may become inaccessible over a network if a static IP address incompatible with the network has been programmed into the controller. The only way to reset an IP address of a controller, or to re-enable DHCP, is to directly connect it to a PC. Direct connections include Ethernet (direct wire, NO router, etc.) or Modbus (serial interface).

What is the TriStar R-Y-G sequencing LED indication?

The R-Y-G flashing sequence indicates one of the following faults(no alarms):

  • MOSFET shorted (“FET short”)
  • software bug (“software”)
  • Changed DIP switch while running (“DIP sw Changed”)
  • EEPROM changed (“Settings Edit”)
  • Interrupted fault due to reset – clears after 10 sec (“reset?”)
  • system miswiring detected [load mode only]

How accurate are TriStar state of charge LED's?

TriStar state of charge (SOC) LED transitions are based on battery voltage setpoints, and provide only an approximation of the true SOC of the battery. A true SOC calculation is not performed because the TriStar does not have load current information (current drawn out of the battery). A TriStar in charge control mode (or a TriStar MPPT) can only measure current into the battery from the solar panels.

The LEDs will however provide a relative indication of how your system is performing. e.g.:

“Each day I charge to Green. At dusk it settles to Grn-Yel, by morning I’m at Yel-Red”

which may help detect problems if the LED behavior changes drastically. (charge all day and it doesn’t get out of red).

What are the unidentified / numbered Alarms in SunSaver MPPT's and TriStar MPPT's?

The SunSaver MPPT and TriStar MPPT have several unidentified / numbered Alarm states. Numbered alarm information is as follows:

Alarm 19 = Power On Reset (the controller has recently been reset/rebooted)
Alarm 20 = LVD Condition (an LVD – Low Voltage Disconnect – event has occurred) Alarm 21 = Log Timeout Alarm (the controller’s internal logger has not been able to write a log entry for the past 24hrs)


Can I use a DC power supply as a PV panel substitute?

MPPT controllers can be used for this purpose without issue. In addition, AC powered battery chargers are often the best option for systems requiring AC battery charging.

We do not recommend using a DC power supply with any of our PWM controllers. While they appear to be similar to PV modules in function, DC power supplies have considerably more output capacitance. Connecting a DC power supply to our PWM controllers may cause excessive heating and premature failure.

Can I use multiple controllers with one PV array?

Yes. Refer to the document, “Charging Isolated Battery Banks”. This can ONLY be done with PWM controllers. MPPT controllers cannot be used in this configuration.

What are the TriStar's four control functions?

The TriStar can function as a solar charge controller, a load controller,  a diversion controller, OR as a lighting controller. It can be configured to perform ONLY ONE function at a time.

What caused my controller terminal to burn/melt?

When two conductors (a wire and screw terminal for instance) are mated, there is a resistance at that connection. Usually this contact resistance is very low and poses no threat. However, when connections become loose, oxidation builds on the surfaces, or corrosion accumulates, the resistance at the connection can increase to a dangerous level.

When current passes through resistance, power is dissipated in the form of heat. If the value of the resistance goes up, so does the power dissipated (for the same amount of current). When a connection has high resistance, the heat generated at the connection can melt surrounding material such as plastics and actually catch fire.

Resistive connections can occur on any electronic device that carries significant amounts of power. It is important to periodically check the tightness of the connections and inspect for corrosion as suggested in the Maintenance section of the Operator’s Manual. Along with periodically checking the connections, dielectric grease can be applied to the terminals to avoid corrosion build-up on the conductor surfaces. Mobile installations tend to be the most susceptible to developing resistive connections because motion works cables loose from their terminals, however, resistive connections can occur on stationary installations as well.

What if the TriStar current rating is exceeded?

The TriStar has over-current protections built in, and will set an alarm and/or fault if the condition persists. The controller will limit input/load current to prevent damage and in severe cases, will switch off the current. Never design a system where the current will exceed the controller’s rating under normal system conditions. Systems designed to NEC standards must follow the current de-rating guidelines (as outlined in the user manual).

What is PWM charging?

PWM is an acronym for Pulse Width Modulation. When the battery is recharged to regulation voltage, the controller will begin limiting the amount of current into the battery so that the regulation voltage is maintained but not surpassed. The method of regulating the current, referred to as PWM, pulses current into the battery with pulses of a varying width. Wider pulses allow a greater percentage of the input current to flow into the battery, narrower pulses restrict current to a lower percentage. Refer to:  “Why PWM?”, for more technical and detailed information concerning PWM charging.

What is the Modbus protocol?

MODBUS® Protocol is a messaging structure developed by Modicon in 1979, used to establish master-slave/client-server communication between intelligent devices. It is a de facto standard, truly open and the most widely used network protocol in the industrial manufacturing environment. It is literally implemented by hundreds of vendors on thousands of different devices in order to transfer discrete/analog I/O and register data between control devices. It’s really a lingua franca or common denominator between different manufacturers. One report called it the “de facto standard in multi-vendor integration”.

What is the purpose of the Load connection?

The Load connection allows the user to wire DC devices such as fans, bulbs, or communication equipment directly to the controller. This allows the controller to disconnect the loads if necessary for protection of the controller, battery, or the loads themselves. This connection is optional and, as an alternative, the system loads can be wired directly to the battery bank.

What is the PWM switching frequency?

All Morningstar PWM type controllers have a PWM switching frequency of ~300Hz.

Some Morningstar PWM controllers have a feature which will reduce the switching frequency to ~1Hz (called on/off charging). This on/off charging virtually eliminates switching noise (both radiated and conducted) and can be used when experiencing noise problems with 300Hz switching operation.

Current models with this on/off charging option are:

– SunSaver Generation 3

– SunSaver Duo

– ProStar PWM

– TriStar PWM

What is the TriStar self-consumption rating?

The TriStar will consume less than 20mA. The digital meter and other options may increase consumption.

What pins do I use for making my own serial cable?

The serial port on the TriStar is opto-isolated per UL requirements. For this reason, the TriStar serial port is “port powered”, which means it requires a small amount of power from the host (PC or other device). In addition to pins 2,3,& 5, pin 4 and/or 7 should be connected. For more information, refer to the document, “TriStar RS-232 Wiring”.

Tristar RS232 Wiring

Where can I find an RS-232 cable?

RS-232 serial cables can be found at just about any computer retail store. In most cases, such as mating the TriStar or SunSaver Duo to a PC, you will require a cable with one male and one female connection. Linking a PC with the controller will require a straight-through serial cable (NOT a NULL Modem cable).

Where can I find the MIB file for the TriStar MPPT?

A link to the agent Management Information Base file (*.MIB) is available for download directly from the controller. Access the TriStar MPPT Live View Network Settings page and use the MIB download link.

Where can I find Tristar alarm/fault information?

The TriStar an TriStar MPPT Operation Manuals provide detailed explanations concerning the flashing LED sequences that occur when a fault is present. The TriStar Digital Meter Installation and Operation Manual provides definitions for each of the faults and alarms displayed in the Diagnostics menu.

Where do I get software to program my controller?

We supply PC software free of charge (called MSView). It is available for download on our website. Sorry, Apple Mac is not supported.

Why is a 100Amp DC fuse recommended for the SureSine?

The recommended 100A DC fuse for the SureSine may seem excessive. However, because the inverter has a large amount of input capacitance, upon startup the unit can potentially draw much higher currents than in steady-state. In order to prevent inadvertent blowing of an undersized fuse, a 100A fuse is recommended. This size provides the necessary protection to the system wiring, while also allowing the inverter to draw its large startup surge without tripping. Using a fuse rated less than 100A will risk nuisance tripping when the inverter is powered up.

Will other charging sources backfeed into my controller?

Other charging sources can be used in parallel with the Morningstar charge controller; you do not need to isolate the controller from the battery. For best performance when using other charging sources, ensure the charging source and Morningstar controller are set to charge to the same (or close) voltage. If the supplemental charging source is set to a higher charging voltage than the Morningstar controller, the Morningstar controller may go into a fault state temporarily when the battery voltage rises higher than the controller’s setpoint. The controller will automatically recover from this state when the battery voltage drops to a lower level.

Will the TriStar perform lighting control?

Yes. While it is not documented in the user manual, the TriStar is capable of lighting control. Lighting control must be configured in the custom settings. For more information, download the TriStar Lighting Control document.

Can I wire an inverter to a charge controller load output?

We do not recommend wiring inverters to the load terminals of our products because of current in-rush on start up. Inverters typically have large amounts of input capacitance (for input filtering). When power is first applied, these capacitors can draw very large currents in the 100’s of amps, albeit for a short period of time. These current surges can stress our power transistors and will trip our short circuit protections. The inverter may start eventually after several attempts to reconnect from the short circuit condition, but this mode of operation is not normal. For this reason, we do not recommend wiring inverters directly. Many inverters have their own LVD circuitry and will not allow the battery to discharge too low. However, if the customer requires load control and LVD functionality, they can switch the inverter through a relay wired in series between the battery and inverter.

Can I wire multiple controllers to one battery bank?

Yes. There can be as many Morningstar controllers as required in parallel on the same battery bank. For best performance, set each controller to as close a charge setting as possible. Since the controllers will not have direct communication with each other, it is not unusual to see the controllers transition between charging stages at different times. This is generally not a concern.