cyclo-vac: what to do about a defective on/off switch at the vacuum hose handle

I have cyclo-vac home vacuum cleaner system installed in the house. It's a vacuum cleaner installed in a fixed location in the basement and connected to pipes leading to various rooms in the house. The actual vacuum cleaner that you carry with you is then just a hose with a little on/off switch at the handle.

The big cyclo-vac vacuum unit in the basement.

The system is great because you don't have any noise or dust in the room where you vacuum. It's all in the basement. The unit that you carry with you is as well very light because it has no big motor inside. There is another advantage for North America which has power sockets limited to 120V/15A. 120V/15A (=max 1800W) is a bit too low for a powerful small portable vacuum cleaner. Thus the portable vacuum cleaners with motor which you can buy in North America are rather week. The fixed installation cyclo-vac home vacuum system are however more powerful because they are bigger and more efficient. Thus they can get a stronger vacuum out of those 1800W.

The cyclo-vac home vacuum system has "wall sockets" all over the house where you plug-in the hose. The hose has a built-in on/off switch at the handle which closes two 24V DC connection pins at the "wall socket". The actual vacuum unit has inside a 24V relay which gets then activated.

There is however a problem with those on/off switches at the handle. They burn after a few years. You would think that they last forever because the actual load of the motor in the vacuum unit is switched by the 24V relay. The switch at the handle just activates the relay. That should be no load at all on the switch.

The root case: cyclo-vac does not have a built-in fly-back diode

A high voltage gets induced when switching off the current through a big inductor such as a relay. This causes sparks at the switch and wears down the switch with every on/off cycle.

The simple and cheap solution that cyclo-vac should have chosen is to integrate a fly-back diode into their system but they did not do that. It's fortunately easy to add one.

Buy a 1N4001 diode (costs about 10 cent) and add it in parallel to the control wires for the vacuum unit with the cathode (marked with a white ring on the otherwise black diode) connected to plus and the anode (the side of the diode with no ring) connected to minus.

A fly-back diode prevent the wearing out of the switch

Have a look at the below Wikipedia article if you want to know more about the physics behind fly-back diodes.

How to fix the switch at the handle

You probably now wondering what to do about an already defective switch at the handle. I opened my handle and the switch had 2 contact pairs. Only one of them was used. Just disconnect the cables from the currently used one and solder them to the other contact pair. It will now "last forever" since the fly-back diode will prevent any contact fire and this will extend the life time of the contacts by a factor of 100 or more.

References, Wikipedia article explaining a flyback diode.

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