SRX

Australian Energy Research Laboratories (AERL) was founded in 1985 by Stuart Watkinson to commercialise the Power Optimizer, which he developed while studying at the University of Queensland. It became the AERL MAXIMIZER™, a universal maximum power point tracker (MPPT).

Today AERL designs, integrates and supports power conversion, lithium energy storage, monitoring and earth-fault detection products for commercial, industrial and off-grid energy systems, including oil and gas, mining and telecommunications sites.

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Trademark & Copyright

AERL and the AERL logo are trademarks owned by AERL Holdings Pty Ltd and used by AERL Pty Ltd under licence. These trademarks may be registered in Australia and other countries.

CoolMax SRX Charge Controller User Manual © 2026 AERL Pty Ltd. All rights reserved. Effective November 2026.

This installation manual contains important safety information and installation instructions for the AERL CoolMax SRX MPPT Solar Charge Controller. The following symbols indicate ideal installation methods, potentially dangerous conditions, and important operational information.

Important

Information that must be followed to ensure proper installation or operation of the CoolMax SRX.

Caution

Indicates a critical procedure for the safe installation or operation of the CoolMax SRX.

About This Manual

• This manual provides detailed installation and usage instructions; read all instructions and cautions before beginning installation.
• Only qualified electricians and technicians should install the CoolMax SRX. This manual is intended for installation technicians and the system owner.
• Do not disassemble or attempt to repair the CoolMax SRX unless you have written authority from AERL.
• AERL will not be held responsible for mishandling or installation that does not follow this manual or AERL technician guidance.

Warranty

The warranty starts 30 days after AERL dispatches the controller, whether to you, your installer or the business you bought it from. If the controller connects to AERL Cloud before then, the warranty starts on the day it first connects instead.

Our goods come with guarantees that cannot be excluded under the Australian Consumer Law.

Full terms: AERL warranty statement for CoolMax SRX, aerl.com.au.

Thank you for purchasing an Australian engineered CoolMax SRX Series Charge Controller.

CoolMax Charge Controllers deliver an efficient, reliable charging process that maintains battery life while maximising generation from your PV array.

Features

CoolMax Charge Controllers use advanced Maximum Power Point Tracking (MPPT) to extract the maximum power available from your PV array.

AERL’s MPPT algorithm does not lock onto local power peaks, and its tracking losses stay under 0.5% across the array’s full operating temperature range.

• High input voltage for easier installation
• On-board ground-fault detection
• PV array oversizing up to 200% at 48 V, 130% at 24 V
• Compatible with most battery systems
• Reverse polarity & current protection
• Built-in overload & thermal protection
• Designed for long-term reliability
• Australian engineered

Firmware

This user manual covers CoolMax SRX Control Firmware Revisions v2.17.9 and later.

Handling Precautions

• The CoolMax SRX weighs approximately 5.65 kg (12.5 lb). Use proper lifting techniques when handling the unit to avoid injury.
• Always handle the unit with care to prevent damage to the electronic components.
• Never touch electrical terminals when the unit is connected to a power source.
• Ensure all power sources are disconnected before performing any maintenance or installation work.

Transport Guidelines

• Transport the CoolMax SRX in its original packaging whenever possible to provide maximum protection.
• If original packaging is unavailable, use appropriate protective materials to prevent damage during transit.
• Secure the unit properly during transport to prevent shifting or falling which could cause damage.
• Protect the unit from extreme temperature variations, moisture, and direct sunlight during transport.

Storage Requirements

• Store the CoolMax SRX in a clean, dry environment within −30 to 70 °C (−22 to 158 °F).
• Relative humidity must remain between 4–95% non-condensing during storage.
• Keep the unit away from corrosive materials and environments.
• For extended storage periods, periodically check the unit for signs of moisture or damage.

Pre-installation Inspection

• Before installation, inspect the unit for any physical damage that may have occurred during transport.
• Check all connectors and terminals for signs of damage or corrosion.
• Verify that all components are present and in good condition.
• Do not install a damaged unit. Contact your distributor or AERL directly if any issues are found.

Standards & Requirements

All installations must comply with national and local electrical standards and codes; AERL recommends professional installation. No ongoing maintenance is required.

Local standards & certified installation

Installation must comply with the electrical standards, codes, and wiring rules at the site; only an installer accredited or licensed in your jurisdiction should perform the work. Install in a clean, dry location away from direct sunlight on a flame-retardant surface. Standards cited elsewhere reflect design intent at publication; refer to current local standards.

Hazard (solar isolator)

Ensure the SOLAR ISOLATOR / BREAKER is in the OFF position before connecting or disconnecting the controller. Do not connect CoolMax controllers in parallel with third-party charge controllers.

Grounding

CoolMax controllers are designed for floating systems but include provisions for positive functional earthing for telecom applications if required. The chassis ground (inside the enclosure) is marked with the standard earth symbol.

Do not functionally earth the array

If a negative earth is used for the batteries, load, or DC system, do not functionally earth the array. If damaged, the controller should only be repaired by a qualified service centre; incorrect reassembly risks electric shock or fire.

Mounting the Controller

Use the mounting plate included with the controller to mount the CoolMax SRX on a vertical surface. The clearance zone shown below must be observed for optimal cooling under full load.

Wire and Disconnect Sizing

Wiring requirements

Wire sizes must comply with local and national standards. Input conductors and circuit breakers must be rated at 1.56 × the short-circuit current of the PV array. Copper wiring must be rated at 75 °C or higher.

Use a minimum of #5 AWG (16 mm²) high strand-count double-insulated cable for the output between the CoolMax and the battery bus bar or termination. Use an appropriately sized insulated crimp ferrule when terminating both input and output connections. Torque all CoolMax wire and ground terminals to 1.7 Nm (15 in-lb).

CoolMax SRX 600/70-48: output protection

• The output current limit of the CoolMax SRX 600/70-48 is 70 A.
• Use an 80–125 A non-polarised DC circuit breaker between the controller output and load as short-circuit protection and a point of isolation.
  Recommended: Beny BDM-125 DC breaker
• Refer to your local PV / electrical code for PV array cable sizing, length, and ampacity recommendations.
• All devices connected to the controller must have suitable insulation in accordance with the relevant product standards.

Removing the Access Cover

To install cabling, remove the access cover: undo the two M4 countersunk Phillips screws on the bottom of the enclosure and the four M3 countersunk Phillips screws on the sides, two on each side (Figure 2).

Hazard (cable entry)

All CoolMax SRX wiring must enter the unit through the entry ports located in the base and rear of the enclosure. Under no circumstances should holes be drilled anywhere into the unit to make other cable entry points; metal swarf can enter the internal electronics and damage the unit once powered up.

Wiring Compartment Layout

Hazard (polarity)

Reversing the polarity of either the input or output may damage the CoolMax SRX and void product warranty. Confirm polarity with a multimeter prior to closing the input and output circuit breakers.

Start-Up & Shutdown Procedure

The CoolMax SRX starts up once the PV input is above 60 Vdc and at least 10 Vdc higher than the connected battery voltage; the device will not power up from the battery terminal. To start: connect the battery first, then turn the PV isolator / breaker on; the LED flashes blue for about 60 seconds, then begins to charge. To shut down: turn the PV isolator off, wait for the LED to turn off, and disconnect the battery breaker.

Equipment damage (shutdown order)

Do not disconnect the battery fuse / breaker under load. Turn off the PV isolator first per the procedure above.

Programming the Device

When the CoolMax SRX is first powered on, the device runs a self-test and the LED indication strip flashes orange to indicate that no charge profile has been configured.

The CoolMax SRX is programmed via the USB-B port located inside the access cover, as shown in Figure 4. The AERL Link software for Windows 10/11 can be downloaded from aerl.com.au/professionals. Instructions for setting the charge profile are in the next chapter.

Device Status Indicator

Figure 5 · LED indication states

The CoolMax SRX uses an advanced three-stage charging process with pre-set voltage profiles for each supported nominal battery voltage. The controller does not charge until a charge profile is configured for the connected battery.

Default profile

The CoolMax SRX default charge profile is intended for a generic LiFePO₄ battery solution. AERL supports most other chemistries that do not require external BMS communications; always refer to the battery manufacturer’s specifications.

The programmable profile exposes Battery Charge Rate, Tail Current (end-of-absorption threshold), and the Absorb, Float, Re-Bulk, and Equalisation voltage points. Refer to your battery manufacturer’s specifications for the optimal profile; configuration with AERL Link is covered on the next page.

Equalisation

Equalisation is only required for flooded lead-acid cells with sulfation. It is not recommended for LiFePO₄ or other lithium-based solutions and will likely cause damage unless advised by the battery manufacturer.

Live Status with AERL Link

Once the SRX is connected over USB, AERL Link opens to the device’s Status tab, the default view for any selected device, providing a live, read-only view of operating values:

• Power: live charging power into the battery (W).
• PV Voltage / Current: live values at the PV input terminals.
• Battery Voltage / Current: live values at the battery output terminals.
• Status: plain-text description of the current operating state, including any active warning or fault.
• Firmware Version: firmware revision currently running on the controller.

Setting the Profile with AERL Link

Once connected over USB, the controller registers in AERL Link’s LOCAL devices list. Figure 8 shows the device tile that appears. Click its tile to open the device page, then select the OUTPUT tab to adjust the charge profile (Figure 9).

Click the device tile to open its page. On the OUTPUT tab, change values with the +/− arrows or the keyboard, then Apply to commit them to the controller.

Battery Profile Presets & Saving

The Battery Preset dropdown on the OUTPUT tab lists pre-tuned profiles for common battery products. Selecting a preset populates the absorption, float, and re-bulk voltages, the absorption time, and the temperature-compensation factor with AERL’s recommended values; presets refresh from AERL HQ on each AERL Link launch with an internet connection. Export saves the current profile to a JSON file and Import applies a saved profile; AERL Link verifies the saved profile’s nominal voltage matches the connected device, and warns before applying a mismatch.

Presets are a starting point

Always cross-check the applied values against your battery manufacturer’s published charge specification before relying on them in a production system.

Blackstart Guard

The CoolMax SRX includes a configurable Blackstart Guard that lets the converter begin charging into a battery bank whose voltage is below the controller’s normal “no battery detected” safety threshold (for example, a deeply discharged lithium bank that has been left flat for an extended period and now reads well below its nominal range).

Blackstart Guard is disabled by default. With it disabled, the controller performs its standard start-up safety check: if the output voltage is implausibly low, it refuses to enable and reports a Low Output Voltage / No Battery fault. Enabling Blackstart Guard from the Settings panel in AERL Link bypasses that check, allowing the controller to start charging the depleted bank from a black state.

When to use it

• Recovering a known-good battery bank whose voltage has fallen below the controller’s normal detection threshold.
• Commissioning a system where the bank arrived on site significantly under-charged.

Disable Blackstart Guard once the bank has recovered

Leaving Blackstart Guard permanently enabled defeats a key safety check; the controller will no longer refuse to operate into a disconnected or faulty battery.

Battery Temperature Compensation

Temperature compensation measures the temperature of the batteries and adjusts the float and absorb voltage set points by a user-specified factor (mV/°C, per bank). The factory default is 50 mV/°C. Compensation needs a battery temperature reading (see below); without one, the controller charges to the uncompensated set points.

Temperature source (Battery Sense)

The SRX takes the battery temperature from an AERL Battery Sense Remote Temperature and Voltage Sensor, whatever the battery chemistry. Plug it into one of the CANBUS RJ45 ports between the power terminals (Figure 3) until it clicks into place; check the orientation and do not force it. Turn on the CANBUS 5 V power switch (Figure 3). Locate the sensor centrally near the top of the battery bank, away from water, moisture, direct sunlight, or chemicals.

Low-Temperature Charge Cutoff

Many lithium chemistries are damaged by charging below freezing. The SRX can be configured to inhibit charging when the remote battery temperature falls below a user-specified threshold. When the Low-Temperature Charge Cutoff is enabled in AERL Link, the controller suspends charging when battery temperature falls below the configured set point and resumes once it rises back above. Both the cutoff temperature and the enable toggle are configured from the Settings panel; the cutoff is disabled by default.

Requires a battery temperature reading

The cutoff only operates when a battery temperature reading is available from an AERL Battery Sense sensor. Without a temperature source, the controller cannot enforce the cutoff and charging will proceed regardless of battery temperature.

The CoolMax SRX supports field firmware updates over USB via AERL Link. Updates are signed and encrypted; the bootloader will reject a corrupted or unauthorised image.

Before you begin: install the latest AERL Link from aerl.com.au/professionals, ensure the unit is connected to a battery and powered up, and use a stable PC. Do not disconnect USB, kill power, or open the PV / battery isolators during the update.

1. Connect a USB cable from the PC to the USB-B port inside the access cover (Figure 4).
2. Launch AERL Link. The connected charger appears on the Devices page. Click it to open. AERL Link checks the controller’s hardware revision and serial against its repository; if a newer image is available, an Update prompt appears.
3. Click Update (standard updates) or wait (critical updates start automatically and cannot be deferred). If calibration is required as part of the update, AERL Link will warn you and recommend that a digital multimeter is on hand. A progress bar shows upload percentage; the transfer typically takes 1–2 minutes.
4. When upload finishes, the controller reboots. The LED briefly flashes blue, then returns to normal operation.

Note & recovery

AERL Link refreshes its firmware repository from AERL HQ each time it starts; allow the PC to reach the internet briefly before connecting if it has been offline for a while. If an update fails partway through (e.g. the cable was disconnected), retry. The bootloader retains the previous valid image and the controller will continue operating normally until a complete, signed update is received.

Each CoolMax SRX is factory calibrated, but field re-calibration can correct for sensor drift or be requested as part of a firmware update. AERL Link guides you through the procedure step by step.

Before you begin: have a multimeter that reads DC to ≥ 0.1 V resolution, a connected battery with output voltage in the normal operating range, and a stable DC bus (isolate other charge sources, inverters, and large loads on the same battery).

1. Connect the controller over USB and open the Device page in AERL Link.
2. Click Calibrate. AERL Link checks for a connected battery and a sensible output voltage; resolve any prompts first.
3. On the Start Calibration dialog, click Yes. The controller disables its output and prepares for calibration (a few seconds).
4. Measure output voltage at the battery terminals with your multimeter and enter the reading. AERL Link only accepts values within ±5% of the device-reported voltage.
5. Click OK. AERL Link writes the new calibration multiplier; the device resets, re-enables the output, and resumes charging using the corrected voltage scale.

Do not interrupt calibration

Do not disconnect USB or interrupt power during calibration. The output is automatically re-enabled at the end of the procedure; allow it to complete cleanly. AERL Link re-prompts for calibration on first connect after install, and after a calibration-required firmware update; you can also re-run it manually at any time.

The CoolMax SRX features onboard PV and battery system ground-fault detection. All connected poles are checked for insulation degradation during start-up. The device chassis must be connected to the same earth as the PV array for ground-fault detection to function; the chassis earth point is inside the access cover, marked with the standard earth symbol (Figure 12).

Ground Fault Mode

The system earth-type configuration (Ground Fault Mode) must be adjusted in AERL Link for use with functionally earthed systems; otherwise an earth fault will be detected on the earthed pole. The SRX supports four mode configurations:

Mis-configuring this setting will either mask a genuine earth fault or trigger a false fault on the intentionally-earthed pole.

Ground Fault Sensitivity

The SRX trips a ground fault when the insulation resistance of a monitored pole falls below a fixed 50 kΩ. Check that 50 kΩ meets your local standards. Firmware 2.0.1 (February 2024) and later trips at this fixed threshold. Earlier firmware offered a Low/Mid/High setting; update the firmware with AERL Link to get the fixed threshold. The Ground Fault Mode is set in AERL Link (Figure 13).

The CoolMax SRX supports CAN bus and Modbus RTU (RS485) for remote monitoring; device control (enable/disable, setpoints, firmware updates) is available via CAN only. RS485 and CAN use separate RJ45 sockets inside the access cover, two labelled MODBUS and two labelled CANBUS (Figure 3); their pin-outs are below (Figure 14). The register maps are in the CoolMax SRX Modbus RTU and CAN bus protocol documents, available from AERL.

Pin	MODBUS port (RS485)	CANBUS port
3	RS485-A (non-inv.)	+5 V
4	—	CAN High
5	—	CAN Low
6	RS485-B (inv.)	GND
8	GND	—

Modbus RS485 network topology

On a Modbus RS485 segment, the SRX is wired as a slave on a daisy-chained two-wire bus, with the master at one end. Terminate the bus at both ends with 120 Ω: at the master (many masters have a built-in or switchable terminator) and at the far end, by enabling the 120 Ω termination switch on the last SRX only.

Configuring CAN and Modbus

Bus ID and speed are configured via AERL Link: open the Device page, select the COMMS tab, set the fields below (Figure 16), and click Apply Settings. The controller resets briefly when settings are applied. A changed RS485 or CAN bus speed cuts the controller off from any master still using the old speed: update the master to match before you leave the site.

If the CoolMax SRX detects an issue, a warning or fault code is triggered; refer to the tables below.

Warning codes

Warning codes (continued)

Fault codes

Fault codes (continued)

If your situation is not covered here, contact AERL on 1800 950 865 or [email protected].