Wallwasher Power Supply Unit



Specifications

Input: 100-240v AC 50/60Hz

Output:  18v DC at 3.0A

Centre pin - positive

Outer sleeve (barrel) - negative



Current readings

Measured output voltage = 18.5v


240v current used:

when the PSU is disconnected from the wallwasher = 0.035A / 8.4W

when the wallwasher is in standby = 0.05A / 12W

when wallwasher sidelights and sidelights are on max white = 0.1A / 24W

when all lights and fans and wrist rumbler are on = 0.15A / 36W


See the Wallwasher general page for details of the 18v current used by individual accessories and lights.


The current readings are approximate and can vary. It can be seen from the readings that if you leave the unit on standby, you would use about 2kW a week. This is a little more than having an energy-saving light bulb permanently switched on. These figures might not seem much, but at around 15p/kW, it adds up to nearly £16 a year per unit!

Personally, I always prefer to turn my computer equipment off at the mains switch (when you shut a computer down, its PSU goes into standby, so the PC is still drawing current). Not because I’m a miser, but it avoids any risk of potential damage caused by spikes in the mains supply during thunderstorms etc. I do have surge protection, but I’m not sure if I trust it that much!



The plug

The Power Supply Unit (PSU) is unusual in that it has a plug at the end of the cable, rather than a socket as usually found with PSUs. This is different from the common 2.1 or 2.5mm connectors that are readily available. The plug has an internal pin. The connector used is the EIAJ-05 type. EIAJ RC5320A type 5 is another type.  see http://en.wikipedia.org/wiki/EIAJ_connector

The plug is used on some Sony laptops, such as the Vaio that has a 19.5v PSU.

See the Components / Where to buy page for details of where to buy the plug

You are unlikely to find an in-line socket, but a PCB mounting socket is available

Note - Maplin sell a  power tip connector (AR28F) that looks similar, but at 7mm it is too big and won’t fit.



Extending the cable

I haven’t taken a PSU apart but, because the cable is round, then I suspect that it uses single core shielded cable, with the  shield being connected to the negative terminal at each end. Or it might just be two ordinary wires in the cable. Either way, it probably doesn’t really matter as it is only voltage and not signals that are being carried by the cable.

Use good quality cable and the largest you can get that will fit into the connectors. This will help to prevent voltage drop, although this may not be a problem unless the cable is very long. If you can’t get an in-line socket and use a PCB socket, the easiest way is just to solder the wire onto the PCB tabs. The socket will normally have three tabs - one for the ground one for the positive input and one for the positive output. The input is connected to the output via a switch which is opened when the plug is inserted into the socket. The switch is not needed here, so make sure you connect the positive to the socket output. An easy way to test is with a continuity tester or meter. Put the bare plug into the socket and test for continuity between the plug pin and the socket output.


If all this sounds like a lot of hard work, it is!

The simplest (and possibly the cheapest) way to extend the overall length of the power connection is to extend the mains cable. This can be done in two ways:

If you only need a short extension, it may be possible to get a longer mains cable with the figure 8 socket on it that fits into the PSU.

The second option is to buy or make up an extension mains cable for the PSU to plug into. In the UK, this would have a 13A plug at one end and a 13A socket (or multiple sockets) at the other.