Wiki

Il n'y a aucune raison d'avoir peur en ouvrant votre objet. Voici quelques conseils pour vous encourager à vous lancer.

Guide de sécurité pour débutant à la réparation d'objets électriques et électroniques.

Vous êtes donc fébrile, ou presque, à l'idée de réparer un appareil électrique...

Voyons ensemble quelques vérités de base.

Oui, l'électricité peut tuer, mais seulement dans certaines circonstances bien spécifiques.

Bien sûr, vous ne devez pas prendre de risques : si vous n'êtes pas sûr à 100 % de ce que vous faites, trouvez quelqu'un de compétent pour vous aider, mais il n'y a aucune raison d'avoir peur. L'électricité n'est pas une force magique, c'est un phénomène scientifique bien connu qui obéit à des règles très simples.

Tension et courant

La première règle est :

• La tension provoque des chocs électriques et le courant tue.

Si on fait une analogie entre électricité et eau :

• Voltage is the pressure, formally known as "potential difference" measured in volts, symbol "V"
• Current is the flow rate, measured in amps, symbol "A".

It's the flow of electricity (amps) that will kill you, but it's the pressure (volts) that will push the flow through you, so you need enough of both to kill you.

Some examples

• A very high voltage with a tiny current may hurt you but it won't kill you. This is what static electricity is: when you get a shock from, say, walking across a nylon carpet, it may be several thousand volts but it's only millionths of an amp, so it may hurt, but it won't kill.

• On the other hand, touching a car battery which is capable of supplying a huge amount of current (say 50 amps), but only a little bit (12V) of "pressure") will give you at most a slight tingle: there's not enough "pressure" to push all that current (flow) through you.

• Mains electricity is 230V in Europe, usually 110V or 220V in the USA: that is enough "pressure" to push the current through you and, if it goes through your heart or brain, it can kill you even if there's only a tiny bit of current. The amount of current it takes to kill someone is not much: about 0.2A (200 milliamps), which is about enough to light a 40Watt lightbulb.

What is safe for beginners

OK, enough talk: how much is safe? Simple answer: Anything below 20 volts won't kill you. Anything above, say 40 volts can give you a nasty shock or kill you.

In practice what this means is that these things are safe

• low-voltage lights
• most battery operated devices, especially mobile phones, tablets, torches and most other battery operated devices (**except digital cameras with flashes**)
• most car electrics except the spark-plugs and the circuits which supply them
• laptops but not the mains-operated power supply.

Unless you know what the voltage is, DON'T TOUCH IT!

When you look at a piece of electrical equipment, it will usually show the voltage, so check all labels and markings first. Let's look at some real examples...

Some concrete examples

• Work out the voltage of a torch by adding up the voltages of all its batteries: if it has 4 batteries each of which is 1.5V, the total voltage is at 6V, which is not enough to do any harm.
• A laptop power supply (picture) is connected to the mains (240V), so that part is dangerous, but the part that supplies the laptop is only 18V, so that's safe to do repairs on: you'll get at most a bit of a tingle if you touch it.
• A mobile phone charger is connected to the mains, so that part (240V) is dangerous, but the part that plugs into the phone is probably 5V (check the label on the part that plugs into the mains), so very safe.
• USB sockets provide a maximum of 5V, so they're very safe.

Now, be aware that by "safe" I mean that you can't hurt yourself by touching any of the wires, but you can damage the equipment by, for instance, accidentally joining 2 wires together and causing a "short". In other words, causing 2 wires which want to be at different voltages to try to get to the same voltage...

So, the next thing to think about is

How not to damage the equipment.

First of all, always go carefully and don't rush it. Spend a little while trying to see how it's put together and which screws might be the key ones to allow it to come apart.

For delicate electronic equipment, earth yourself before you start and during the process by touching a radiator, a water pipe or an earthed electrical appliance. Avoid such tasks if the air is very dry such as in very frosty or hot and dry weather and if you seem to be picking up static from the carpet or nylon clothing.

If there aren't any screws visible, look for a label that might be covering them, or maybe the plastic case is in two parts held together with hidden clips that can be separated with a small screwdriver, a guitar plectrum, or (with great care!) a small knife.

Once it comes apart, there may still be delicate wires connecting the two halves. Separate them carefully.

Mechanical parts often contain springs. These can fly across the room when you release whatever is holding them in place. Screws and other small parts sometimes fall out unexpectedly. If any such parts head for the floor, lock your eyes onto them or they may be lost for ever.

An egg box is good for keeping screws and small parts in, or a set of pill boxes for smaller screws. You might think you'll remember where they all came from, but if there are more than a very few and if they're different sizes, you'll forget like the rest of us. Keep careful notes or take lots of photos as you proceed.

The best time to practice reassembly is just after you've disassembled something. If it's anything less than completely straightforward, follow that principle at every stage.

If you get stuck, don't despair - it happens to the best of us. Put it aside, sleep on it, maybe dream about it, and come back to it a day or two later - or discuss it with another Restarter.

If you don't succeed in mending it, you will still have learned something, but make sure you dispose of it responsibly. Here is our guide to what to do with unwanted, unrepaired devices.