Saturday, March 17, 2018

Electrical wiring of the house

In last year we spend lot of time and effort to wire our new house by ourselves. To complete this job we took nearly 2 ½ months and it includes wiring, fixing electrical fittings, communication equipment, etc. In this post we describe how we archive this task with some technical details.

Due to large number of electrical points we decided to use use 3 phase electrical wiring in our house. To make it simpler we divide entire house wiring into 3 isolated circuits with 3 separate distribution boards. High level design of our AC wiring systems is illustrated in below diagram.

High level electrical wiring diagram up to distribution boards

In above circuit the 3 phase AC line is first fed into 4-pole 40A isolator. Then it connected to 4-pole RCCB with 3 separate indicator lights. We use indicator lights to see the status of the each phase, easily at any time. After RCCB we fed each phase into 3 separate distribution boards.

As seen in the diagram the first (phase) circuit is bit complex due to the change-over-switch. We use  change-over-switch to connect additional power source into AC line during the power failures. For the change-over-switch we use DIN-rail type, 2-way 2-pole 40A change over switch. In here also we use two indicator lights to show both mains and external (generator) line status.

4-pole isolator and RCCB mount

Sunday, March 11, 2018

Automatic fan controller for server racks

In this post we describe fan controller which we designed for our 9U wall mount server cabinet. This fan controller is designed to drive a 12V DC cooler fan with pre-configured intervals or by monitoring the temperature of the server cabinet.

Final version of fan controller with DC brushless fan and 12V - 60W PSU.

Core components of this fan controller is CD4060 binary counter, LM35 temperature sensor and LM358 operational amplifier. In this design CD4060 is used as long duration timer and it can configured to trigger cooler fan from 1-minute and up to 4-hour.

In this design LM35 temperature sensor is used to activate cooler fan in specified temperature. This sensor stage is useful to drive cooler fan when timer stage is in inactive state.

To control the cooler fan we use AP9971 dual N-channel power MOSFET transistor. We design this system to drive 12V cooler fans up to 2A of current. To test this controller we use commonly available 120mm × 120mm, 12V - 300mA brushless DC fan. In our server cabinet we mount this fan to push hot air out of the cabinet.

This fan controller is designed to work with 12V - 1A (or higher) power supply. For the testing and for the final installation, we use 12V - 60W power supply unit which is commonly used for LED lightning projects.

3D view of fan controller PCB.

Supplied PCB design of this controller is 64mm × 63.5mm and it based on standard through-hole type components. All the PCB designs and schematic of controller is available to download at google drive or from