This repo contains a simple python3-based implementation of a wrapper for controlling Maynuo electronic loads. My load is an M9812. It is the only one I have tested.

maynuo.py is a simple library with few extra dependencies, except for serial which you can install via pip or your package manager, and crcmodbus, which you can install with pip.

Most of the Maynuo products have a DB-9 connector on the back that looks like it is for RS-232. Though it is for serial, the voltage levels it expects are TTL, not RS-232, which uses 12V signals. If you hook up a "real" serial port to this connector, you will be unhappy.

You can use any of the common FTDI or similar USB-to-serial adapters, and wire them into a DB-9 cable. Alternatively, you can purchase one of Maynuo's cables for the purpose, which also provide galvanic isolation.

Using the library is hopefully straightforward.

First, instantiate a library object:

import maynuo

port        = '/dev/ttyUSB0'
speed       = 9600
device_addr = 1

m = maynuo.MaynuoLoad(port, speed, device_addr)

Note that the speed and device_addr can be adjusted from the front panel of your load.

Once you have an object to work with, you can just issue it commands. For example, do run down a battery, you can do:

v_terminal = 3.000
i_run      = 1.000

m.setReg('BATT', 0)
m.battTest(i_run, v_terminal)
m.inputOn()
while True:
    op = m.getOperatingPoint()
    print(op)
    if op['v'] <= v_terminal or op['i'] <= 0:
        break

Note that in battery mode, you have to turn the input on, but the device itself will turn the input back off when the voltage drops below the terminal voltage you specified. The break in the snippet above is just so that the python exits; the unit will already have turned itself off when that clause is true.

In addition to battery discharge mode, you can easily set up any of the other simple modes with .setCC(current), .setCV(voltage), .setCR(resistance), and .setCP(power).

You can also access any named register on the device using .getReg(n) and .setReg(n,v)

There are many other modes and functions on these units that I have not explored, but it should be possible to access them all by the register interface provided.

This code was based in part on MaynuoPi