As mentioned in an earlier post, I did a fair amount of research before settling on my preferred option for dust extraction (an Oneida Dust Deputy) and it seems that at some point a few years ago there was controversy around its use with Festool Vacuums.
As per the picture below, although the Dust Deputy will work with any vac, it was designed to fit on top of a Festool vacuum, thus:
I came across some reports from owners of the original model claiming it had caused a their festool vacs to break, apparently because the Dust Deputy was capable of building up large amounts of static electricity that could fry the motherboard. Oneida produced a new version of the Ultimate Dust Deputy hat resolved the issue, and provided replacement parts to owners of the original, but I was still intrigued about whether my set-up would be susceptible to the same type of failure.
To fully understand how the problems occurred and the fix provided by Oneida I had to first learn about static electricity.
As any fule noes all things are made of atoms and all atoms are made of particles (neutrons, protons and electrons) and also that protons and electrons have a charge (by convention, electrons are regarded as negative and protons as positive).
It may come as a surprise to those of you who were taught that electrons circled atoms in a fixed orbit that they are in fact more akin to loose clouds of particles that can move between atoms. The tendency of a material to allow electrons to move is called conductivity: conductors permit electrons to flow freely whereas insulators impede their flow.
Indeed it is the free movement of electrons in conductors like metals that is the explanation of electricity (electricity is just the name for the movement of electrons).
Since electrons all have the same charge, and particles with the same charge repel one another, when you cause one electron to move between atoms it will tend to push others away – if you push enough electrons through a narrow strip of material, like a wire, then the electrons flow continuously from one atom to the next and this is called current electricity.
In order to cause the electrons to move you need a source of potential energy. Potential energy means energy that is stored somehow for use in the future. For example a tank of water held at head height has potential energy, because it has the potential to flow down to the ground, for example when a drain in the tank is opened.
A battery is an example of a source of electrical potential energy – a chemical reaction in the battery causes a build up of electrons at the negative terminal and this results in electrical difference to the positive terminal. The electrons gathered at the negative terminal could potentially move to the other terminal to balance the charge but the battery is organized to stop this from happening and this is the source o the stored energy.
If the battery is placed in a torch, the device makes a connection between the oppositely charged terminals and electrons are able to pass from one to the other have to go via the filament in the bulb. The electrons can’t all flow through the filament at the same time and they lose energy when passing through it. The lost energy is turned to heat which causes the filament to glow. This continues until the charges at each terminal are equal (that is to say, until the battery goes flat).
So that is how current electricity works, what about static electricity?
The behavior of an object that has been charged is dependent upon whether the object is made of a conductive or a nonconductive material.
If charge is transferred to an object made from conductive material at a given location that charge is quickly distributed across the entire surface of the object. If a charge is transferred to an object made from an insulator (e.g rubber or plastic) it will build up in the place it is transferred to. This is static electricity.
How is static electricity created?
Where two materials are placed together an electrochemical bond can be formed between the two surfaces such that electrons move from one material to the other. The strength of the bond varies according to the materials involved (some materials hold onto their electrons tightly, whereas other materials can easily lose them).
When the materials are separated the atoms in the material that has a tendency to hold electrons will keep some of the other material’s electrons with the result that it builds up a negative charge.
This is known as the triboelectric effect .
The two materials only need to come into contact and then be separated for this effect to occur but rubbing materials together increases the amount the materials are next to each other and this increases the effect.
The tendency for materials to gain or lose electrons is measured on the triboelectric scale. Materials at opposite ends of the scale tend to exchange more electrons with each other.
Wool and rubber are far apart on the triboelectric scale, and when rubbed to together the rubber tends to gain a negative charge. This effect therefore occurs if you walk across a wool carpet in rubber soled shoes. What you may be surprised to know is that this type of activity can build up a potential energy tens of thousands of volts.
Because the surface of the materials are now electrically charged, either negatively or positively, any contact with an object having substantially different charge may cause a sudden electrical discharge.
In the rubber sole scenario the shoes collected a negative charge that can’t easily disperse. Although the person wearing them is a good conductor (skin and blood are both good conductors) the charge can’t move until they touch something conductive that has a path to earth or something that has gained an opposite charge. This can happen when your reach out to touch e.g a door knob at which point there will be an electrical discharge. Often the potential energy is so large it causes the molecules in the air – which are normally poor conductors – to break apart (ionize) into charged particles and the gas becomes conductive. At this point the charge can “arc” across gas – sometimes jumping a number of centimetres – the electric current heats the gas and causes it to expand rapidly and the result is noise and light (a spark).
You may notice that you get more static shocks when the air is relatively dry this is because when there is high humidity the air is more conductive and this helps static charges to dissipate gradually, reducing the chance of shocks.
Although these discharges are sometimes a bit painful they are generally harmless because although there is a lot of voltage (electrons) there is very little current (flow).
We now know enough about static electricity to understand the problems caused by the original dust deputy and what Oneida had to do to correct it. See the next post for the thrilling denouement.