Prevent disconnects - turn off USB Selective Suspend

Discussion in 'Frequently Asked Questions (Public)' started by Colin Haig, Nov 9, 2020.

  1. Colin Haig

    Colin Haig Staff Member

    Oct 27, 2014
    Is your camera or other device disconnecting randomly ?
    Did it stop responding for no apparent reason?

    Windows Power Management may be contributing to the problem. It will shut down devices to save energy. Normally, saving energy is a good thing.
    However, if Windows powers off a device or hub, this can disrupt communications between software and observing equipment.

    There are a couple of things to check:

    Windows Power Management - USB Selective Suspend
    Go into the Windows Power and Sleep settings - Advanced.
    Find the USB Selective Suspend option by expanding the list until you find it.

    USB Selective Suspend should be turned OFF.
    Here's how to turn it off in Windows 10 version 1909:

    Windows Device Manager - Power Management
    Each device in your system may have some power-saving settings.
    For all devices in the hierarchy of USB hardware, you need to check that the power management settings are off.
    Start the Windows Device Manager.
    Look at the list of USB devices.
    Check their properties, and the Power Management tab.
    Disable (uncheck) the option [] Allow the computer to turn off the device to save power.
    You need to do this for all USB devices, USB hubs, USB root hubs, and PCIe devices.
    You can also View Devices by Connection, and expand it out, something like this:

    Typically you will see something like PCI Express - USB Host Controller - USB root hub - USB hub - Device.
    Turn power management off for each of them.

    USB to Serial Adapters and RS232 COM Ports
    Devices such as a focuser, telescope mount, weather sensor, dew controller or power switch may be set up with an RS232 serial communication port, and your PC may use a USB-to-Serial adapter to make the connection.

    Different vendors have different settings. Here's an example from an FTDIchip USB-to-serial adapter.
    Turn OFF (Uncheck) the USB Selective Suspend setting - this prevents unexpected powering off.

    Turn OFF (uncheck) the Serial Enumerator setting if this is an option - this prevents the computer from thinking a Microsoft Serial Mouse is on this port. This can give you an uncontrollable systems with random mouse clicks if it thinks your GPS or mount or some other device is a mouse.

    Windows Power Plan
    You may wish to save a new Windows Power Plan with these settings. It might make it easier to restore things in the future. The power plan may not save all of this, so if you suspect a problem, check the above tips again.

    Be Mindful of Updates and Upgrades
    Things that worked fine may suddenly seem broken after a Windows Update, Upgrade, or Feature pack etc.
    If you (or the automatic update) installs one, it is especially important to check these power management settings are still correct - sometimes they revert to the wrong settings.

    If you are running off a battery-operated system like a laptop, you may wish to experiment a bit to see the best reliability versus energy savings.
    Last edited: Nov 9, 2020
  2. Colin Haig

    Colin Haig Staff Member

    Oct 27, 2014
  3. Colin Haig

    Colin Haig Staff Member

    Oct 27, 2014
    A recent Windows update cycle installed an updated set of WHQL FTDIchip drivers. The new drivers are
    This may reset the settings of the drivers, and cause the Serial Mouse or Serial Ball Mouse problem again, which leads to erratic operation of the computer.
    Here's the stuff you need to check:
    and here is the correct settings:
    Check each port individually.
    After a reboot, if you see the Serial Mouse is back, you will need to Disable it by Right-Clicking, and Disable Device.

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