150V 20A 300W CC/CV Electronic Load

I recently bought this Sousim LG300WA electronic load from sincerepartner on eBay. They also have a 150W model, and higher current versions (30A/40A) of the 300W model . They probably also have higher current 150W models. The listings seem to come in and out of stock. Search their store for "electronic load" and if you don't find it I would suggest messaging them if you want to buy one.

Manufacturer's Taobao page: https://sousim.taobao.com/

The model in the picture is actually slightly different than what you get. I think it's either their older or newer model. They are developing a new model which can accept an external display and change voltage and current via a communication port.

I was impressed with the product quality and their support. They make this themselves and answered all the technical questions I asked. For the price it's very good value for money.

This is the model I received:


This picture shows the connections on the older/newer 150W model:


I have attached a PDF with the connections on my model. I'm guessing the CON3 port just outputs the voltage across the shunt. The C pin on the CON4 port outputs the load voltage. I'm not sure yet what the VCC pin is - I think it is the 12-15V input voltage.

The REF1 and REF2 ports are for adjusting the current (and voltage?) via an external DAC instead of using the potentiometers.

The left button switches the load on and off and the right button switches it between CC and CV modes. It has two potentiometers on leads for coarse and fine adjustment.

There is an RS485 port which can turn the load on/off, switch between CC/CV modes, control the fans and query the status of the module. They have offered to translate the Chinese protocol documentation for me.

By default at least, the fans run based on the heatsink temperature so they don't run at first or for small loads.

The microcontroller is an STM8S003 and I think it has the programming pins broken out.

I've confirmed it works as it should but haven't done too much testing yet. I will receive a 60V 17A PSU in a couple days so I'll play with it a bit more then.

Mods: feel free to move this to another category if you think it fits better.

Modbus ASCII Protocol

Serial port configuration
Baud rate: 9600
Data Bits: 8
Parity/check bit: none
Stop bit: 1

Command format
AddressCommand [AddressCommand]...
E.g. ALL-FS-ON 000CC 000ON ALL-CX
Write the address then the command with no spaces in between. Make sure you include the dash after the ALL address but not after individual addresses. You can include multiple address-command combos on a single line.

Return data format
Address Volts Amps Watts Temperature ℃ Mode Status
E.g. 000 0.00V 0.00A 0.0W 29C CC OFF

Commands
Address: ALL- Sends command to all modules (note the dash at the end) or 000-999 (default 000)
Query: CX Queries the data from one module or all modules
Mode Setting: CC CV Selects constant current or constant voltage mode
Status: ON OFF Enables or disables the load
Fan mode: FS-ON FS-OFF FS-AUTO (default: FS-AUTO) Selects the fan mode
Change address: Old addressDZNew address E.g. 000DZ001

Setting Constant-Voltage/Constant-Current/Constant-Resistance/Constant-Wattage
Not supported via RS485 with DG150WA or LG300WA models.

I've attached a bash script I've used with the load for battery discharge tests.

I've killed the mosfets a couple of times with incorrect limits set. They are IXTK62N25 which you can find on AliExpress.