Max length of the cat 5e cable ?

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1

Hi,

I would like to know what is the maximum length allowable for the cat 5e cable between the weather module PCB in the FK case and the sensor board?

Thanks!
Shashi

2

Shashi,
Good question. We use a PCA9615 Differential I2C transceiver on both our weather and distance sensor boards. We’ve tested it at up to 30 m in ideal conditions on CAT5, but your results may vary at that kind of cable length depending on the quality of cable and the battery voltage that you’re operating at. The actual data sheet of the chip we use only recommends it for distances of up to 3 m at full speed, but we’re using it at low speed, so you can use longer cables.
TL;DR: Don’t use more than a 30 m cable on your unit in the best of circumstances.

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3

Shashi,
The Cat5 cable carries both signal and power to the remote instrumentation, and power will typically become a problem before signal does due to voltage drop. In ideal conditions we’ve tested 30 meters without apparent problems, but if you’re going to use longer cables than the one provided, be sure to test before deployment. We’re happy to try to help, but the system wasn’t really designed for the station and sensors to be separated by great distances, so performance at long distances is unpredictable. Cable selection will play a huge role, using 22AWG PoE style Cat5 cable will help.

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4

Thanks @petmar and @Bradley for your detailed replies. I tried with a long cable which I had lying around and figured out that it would support the length that I need - much less than the 30m you mention but longer than what came with my unit.

The only reason for increasing the cable length was that I wanted to keep the station indoors to avoid running a power cable to it.

Thanks again,
Shashi

5

Shashi,

Nice! Plugged in is ideal for long cable throws because you’ll be starting with a higher system voltage than you do with a battery, so that helps as well. Obviously long cables outdoors at high elevations are also magnets for lightning, and even when not directly struck can suffer pretty badly by induced voltages from strikes nearby. Not a huge amount you can do to offset that risk, but make sure your installation won’t support a fire indoors at the station if it gets hit, mount on non-flammable surfaces etc.

Cheers!
Bradley

6

Good point! This is indeed a point of concern. I plan to remove the installation during the monsoon period, however, we do get several western disturbances and associated storms occasionally.

We will try and minimise the length too.

Thanks!
Shashi