Sander switching system
Purpose of this project was to increase safety by limiting the amount of sanders operating at the same time. The current limit is set to be one sander at the time to be active. The learning goals for this project where to learn to work with 230V AC, guided by an Instalation engineer, find out how to meassure the current with non invasive means, and controlling air flow from a centralized vacume system. Achieving this with a minimal of extra parts to be bought and using what is available in the Hague University workshop.
At the start of the project I decided to deviate from the normal AC electronical colour code from the european union. Since this system involves 230 V AC and 5 V DC, Black will not be used as switching wire for the 230 V line. Instead Grey and Purple are used.
The system switches both the Line and the Neutral of each attached sander. Purple is used to mark the Switching wire of the Neutral Phase. For safety an 40mA RCD is used. Overcurrent protection is profided by a 10 A fuse.
The ciruit is controlled by an arduino nano, while the arduino platform not ideal for these kinds of applications, the availability of other methodes and price decided the use of the platform. The microcontroller does not only switch the relays for the power but also provide a signal to the air valves that controll the airflow from the vacume system to each induvidual sander.
Two seperate power supplies are used for the controll side of the system, both supplies give a 5 V DC supply, but there is a speration between the driving of the relays and the controll cirquit itself. Opto-copplers give an extra galvanic seperation to insure safety.
For the connectors on the 230 V side, I have choisen to use C13 and C14 connectors, both for size and to avoid students to be able to easily bypass the system. The valves use XLR 3 pin connectors, they are robust, can handel dusty envoirements, and profide an shield for the signals.
The case is machined by laser cutter out of 12 mm plywood and 3 mm cast PMMA