Ethernet Switch UPS

The objective of this project is to build a 12V dc to 7.5V dc regulated power supply to provide power for an 8-port Netgear switch. This switch is used to network the key security and automation elements of our Home Control System (HCS) such as Ethernet IO interfaces, Axis netcams, etc. We have deliberately limited this to an 8-port switch to keep the power consumption down.

There are other larger switches used in our home but, these are for non-essential and entertainment devices only and don't require a UPS.

Design

This simply project provides a 7.5V dc, 2A regulator which is takes its power from our 12V UPS, to ensure the Ethernet switch still operates when mains power fails.

The Netgear power supply provided with the switch is rated at 1.0A but, for this regulator circuit to work reliably and without getting too warm, it needs to easily handle a load drawing 2A or more. This means that the regulator requires a reasonably large heatsink.

This design uses an LM317 adjustable voltage regulator and the circuit design used is described here. In our design R1 is 270Ω because that was the closest value we had to hand. To get closest to a 7.5V dc output the value of R2 used was 2200Ω.

Progress

7.5V regulator
The circuit now sits on a shelf in out Home Control System (HCS) rack.

Conclusions

In a lot of homes, some critical elements of you IP network and Intenet connection are likely to fail when the power goes off. In our home part of our IP network is a critical element in our Home Control System (HCS) and keeping this part of the IP network up and running is essential. With the home connected by both ADSL and FTTP connections, we can also keep Internet connectivity going during mains power failure too. The FTTP NTE has its own UPS capability and the modem/router is also connected into our UPS.

More and more, IP-network connectivity in the home is going to be a key part of the the automation, security and entertainment systems. Deciding how much of this is essential is down to each home owner. It is good practice to separate the networks used for automataion and security from those used for entertainment because the latter uses much more bandwidth. Physical security of an IP network (cables, ports, switches, etc.) is also a key factor in its overall security.

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