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Camera grounding precautions
2018 年 11 月 06 日
How to avoid the problem of unreliable USB connection or port damage caused by leakage of computer or 220V to 12V adapter
Some computers or 220V to 12V adapters have leakage currents. If they are not well grounded, a high voltage is formed between the ground (metal case) of the USB interface and the ground (metal case) of the power supply line. If the USB and power supply wires are in good contact with the camera, the device can operate normally due to the formation of a common ground at the camera.

However, the common ground formed at the camera is very dangerous. On the one hand, it is easy to cause the USB connection to be unreliable, and the USB connection is often lost during use, and on the other hand, there is a risk of potentially damaging the port. Therefore, make sure the computer and adapter are well grounded before putting the device into service.

You can use the multimeter's AC voltage file to detect if there is any leakage between the computer and the adapter. The method is not to connect the camera first, one meter is connected to the metal case of the USB plug, and the other meter is connected to the negative pole of the DC output plug of the power adapter (generally inside and outside negative). If the voltage between the two is small, there is no leakage or a good ground has been achieved through the ground of the power plug. If there is a voltage of several V to several tens of V, there is leakage and there is no good grounding. Need to check if the 220V power plug can provide a good ground.

Another way is to use a test pencil. Test the negative pole of each power adapter, the metal part of the computer, and the metal part of the equatorial mount for leakage.
If there is no way to avoid it, you need to use a separate wire to connect the ground of the computer (usually connected to the metal case) and the negative pole of the 220V to 12V adapter to achieve common ground.

Commonly because the computer or power adapter leaks to cause USB instability or port damage:
A camera with a 9-pin socket and a USB socket is common at the camera.
A camera with a USB socket and a metal case. After connecting the telescope to the equatorial mount, the ground of the equatorial mount and the ground of the computer are at the camera.
After the QHY9 is connected to the color wheel through the camera's color wheel interface, it is common at the color wheel interface.
The above may cause the USB connection to be unstable, the connection is often lost, the USB port is burned, the color wheel interface is burned, etc.

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