Mains Adaptors and Their Replacement

What are mains adaptors?

Many homes nowadays have several mains adaptors in them; some have over fifty. They are used for charging mobile phones, and other equipment which has rechargeable batteries, powering electronic equipment, from laptops and cordless phones to games consoles and printers.

They are needed because most electronic equipment works off low voltage (up to 12V) d.c., but mains supplies are higher voltage (110V in USA and 220 to 250V in most other countries) a.c. The adaptor converts the mains supply to that required to power the device. It usually plugs into the mains supply and a lead connects it to the device.

They should be switched off, or unplugged, when not in use, to prolong their life and save electricity.

When replacing them the following things need to be taken into consideration:

1. The mains (input) supply must be correct An adaptor bought, for example, in the USA and used in Europe (or vice versa) will not only fail to work, but could cause expensive damage to the equipment it is designed to power.

2. The plug on the end must fit the device it powers Many general purpose adaptors come with a selection of several plugs, which fit many devices, but some manufacturers are continually changing their plugs, to force customers to buy their own adaptors, which are usually much more expensive.

3. The output voltage must be correct Many, but by no means all, adaptors deliver 12V. Many general purpose adaptors are switched, typically in steps of 1.5 or 3V up to 12V. Once the correct voltage has been set, it is a good idea to put some tape over the switch, so that it cannot be accidentally altered.

4. The adaptor must deliver at least the current required by the device The cheapest general purpose adaptors typically deliver 300mA at 12V. If the device requires say 500mA, the adaptor will soon fail. The old adaptor will have written on it what current (or wattage) it delivers, and the replacement must deliver this current or more. If the adaptor is labelled in watts (or VA, which for the purposes of this article, is the same thing) divide the wattage by the output voltage to get the current. E.g. an adaptor labelled 12V, 6W delivers a current of 6/12 = 0.5A or 500mA.

5. The polarity of the output must be correct The inside of the plug can be either + or -. This can be reversed on all general purpose adaptors. It must be the same as the original.

6. The d.c. supply provided by the adaptor can be either regulated or unregulated Unregulated supplies have d.c. outputs which fluctuate. This is usually fine for adaptors which are only designed to recharge batteries. However if the adaptor powers the device directly, it often needs to be regulated (i.e. the supply fluctuates very little). Regulated adaptors are more expensive. They can be used in all cases, but not vice versa.

7. A.c. adaptors These are only transformers, and are used if the device runs off a.c. This is almost exclusively used in low voltage lighting.

A final word about mains adaptors for digital cameras, as these run down normal alkaline batteries very quickly. If you are using your camera inside mainly, it would certainly pay to buy an adaptor for these. Most are 7V, 2500mA regulated. They cost about 20. If you are using the camera outside, it pays to use rechargeable batteries, which can be recharged at home.

Barrie Newton B.Sc.
Owner of Rhyl Lightworks Co
http://www.thelightworks.net
or for mains adaptors see
http://www.thelightworks.net/index.php?main_page=index&cPath=68_77
for digital camera adaptors see
http://www.thelightworks.net/index.php?main_page=product_info&cPath=68_77&products_id=796

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