---
title: "Utilising the SP PRO Battery Inverter with the CoolMax SRX Solar Charge Controller · Integration Guide · Technical Note"
revision: "2.0.1"
publisher: AERL (Australian Energy Research Laboratories)
url: https://www.aerl.com.au/docs/coolmax-srx-sp-pro-integration-guide
pdf: https://www.aerl.com.au/documents/misc/Utilizing_the_SP_Pro_Battery_Inverter_with_the_SRX_Solar_Charge_Controller_REV_201.pdf
description: "Guide for integrating SRX solar charge controllers with SP Pro battery inverters."
---

# Utilising the SP PRO Battery Inverter with the CoolMax SRX Solar Charge Controller · Integration Guide · Technical Note

*Rev 2.0.1. Markdown copy of the AERL document at https://www.aerl.com.au/docs/coolmax-srx-sp-pro-integration-guide; the PDF (https://www.aerl.com.au/documents/misc/Utilizing_the_SP_Pro_Battery_Inverter_with_the_SRX_Solar_Charge_Controller_REV_201.pdf) is the controlled version.*

Integration Guide · Technical Note

# Utilising the SP PRO Battery Inverter with the CoolMax SRX Solar Charge Controller

Solar Input Current Measurement with a Shunt, and a Voltage-Based SoC Reset

AERL CoolMax SRX · Selectronic SP PRO

This technical note shows how to use a current shunt to give the SP PRO the solar input current from CoolMax SRX solar charge controllers, so that its state of charge (SoC) stays accurate.

| | |
|---|---|
| Revision | 2.0.1 |
| Charge controller | AERL CoolMax SRX |
| Inverter | Selectronic SP PRO |
| Coupling | DC coupled (shunt) |

### Solar Input Current Measurement with a Shunt (100–200 A)

The SP PRO can only keep an accurate SoC if it measures the solar current that the CoolMax SRX delivers to the battery. Install a current shunt (typically 100–200 A) in line between the CoolMax SRX output and the battery.

The SP PRO has two shunt inputs. With more than two CoolMax SRX controllers, connect several controllers to each shunt. Rate each shunt for the combined maximum output of the controllers connected to it.

*For example, two CoolMax SRX 600/70-48 controllers (70 A each) can share one 200 A shunt and use one shunt input on the SP PRO.*

#### Implementation steps

1. Wire the shunt in line between the CoolMax SRX output and the battery.
2. Connect the shunt sense wires to the Shunt 1 or Shunt 2 input on the SP PRO.
3. In SP LINK, select that shunt (Shunt 1 or Shunt 2) in the SP PRO settings.
4. Set the shunt to Solar Input, and zero it in Service Settings before use.
5. Enter the rating of the shunt fitted in the SP PRO settings: **Max Voltage** is its millivolts and **Max Current** its amps. For a 100 A, 75 mV shunt, set Max Voltage = 75 and Max Current = 100.
6. With the CoolMax SRX controllers charging, confirm that SP LINK shows the solar input current on its dashboard.

### Voltage-Based SoC Reset

In a DC-coupled system, the SP PRO has traditionally used a float switch input to reset its SoC to 100% when the battery is full.

The CoolMax SRX communicates digitally (CAN and Modbus) and does not provide a float switch output. Instead, reset the SP PRO's SoC to 100% with a voltage offset, so that the SoC resets when the battery reaches float. This works as well as a float switch and keeps SoC drift small.

Where a system has both AC-coupled solar and a CoolMax SRX, decide which one has charging priority. The choice sets the charge voltages.

**DC coupling as primary:** if the system is mainly DC coupled, set the SP PRO's charge voltages (absorb, float, etc.) 0.2 V below the CoolMax SRX settings.

**AC coupling as primary:** if the system is mainly AC coupled, set the CoolMax SRX charge voltages (absorb, float, etc.) 0.2 V below the SP PRO's settings.

### Common Shunts

Most electrical wholesalers stock a suitable shunt. Common options:

#### Supply partners (SP PRO accessories)

- Part 004351: 100 A current shunt G3, 0.5% (100 A, 75 mV)
- Part 004352: 200 A current shunt G3, 0.5% (200 A, 75 mV)

> **Note**
>
> Supply Partners also stock 150 A shunts.