A few people on this site and elsewhere have asked me how I use DC power supplies for my projects and where I get them from. So this is a simple guide to what I use, how to find them and what to avoid.
This applies to USA wall socket supplies as well, the only difference is the plug from the UK ones I have!
First, a bit of background - I tend to make all of my electronics projects to run off 12v DC, as used by most transformers, or 5v DC, so it could be run from USB. 12v is a good voltage to use as loads of components are rated for it and it can provide plenty of power without being a high voltage risk. I'd rather use a wall socket power supply than batteries just so I don't have to a) keep buying batteries and b) don't have to replace/recharge batteries.
Head over to the next step for some of the types and classifications.
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Step 1: Types of PSU
There are 2 main types of DC PSU:
Transformer: -these are big, bulky and heavy but provide good power smoothing - better for things like audio systems and measurement equipment where the device is sensitive to tiny fluctuations in the supply.
Switch Mode: -the more common, more efficient, small, light supplies but they are not isolated from the mains supply like a transformer and don't generally provide as much current.
The ones I have all have the 2.1mm DC jack fitted as this is a really common connection and is very simple to wire up. You can buy the sockets for it really cheaply - take a look at the pictures for more info. The sockets also often have an automatic switch built into them so you can run the device off a battery when the power supply is not plugged in - I used this feature on my portable speaker.
Click on the pictures to see the notes describing the different types of transformers I use.
Step 2: Recycling! or How to Find Them...
The really great thing about these power supplies are that they are readily available for free! As long as you don't mind picking them up out of skips... Skips, office waste and electronics recycling centres are good places to find them but often the best are electronic retailers (throwing out supplies that came with broken gadgets) and company IT departments (throwing out PSUs left over when their systems were updated). Don't be afraid to ask!
Of the six power supplies shown in the last step, I only paid for two of them, and only then as I needed a variable one and a high current one. The rest come from all sorts of places, such as:
- WiFi routers
- Camera chargers
- Chargers in general
- External hard drives
- Speaker systems
- Musical instrument devices
- Or pretty much any small mains-powered electronics!
All power supplies have to have a label on them by law, stating the voltage and current they can produce but most are 12v and it is quite easy to check them with a multimeter if you're not sure. Also worth noting is that they come in 2 polarities, positive or negative tip - this should also be stated on the label with the symbol you can see in the picture. From my experience, positive tip is more common and it only takes two minutes with a soldering iron to swap the polarity over if necessary.
A Word of Warning!
This is Electricity! Do not mess with it if you are unsure of what you are doing! Some power supplies if they go wrong can connect you to the full 230v AC power (110v in USA) so make sure you check them thoroughly for defects, cracks, exposed wires etc. Although most people will throw away perfectly usable power supplies when their device fails, some supplies will genuinely be broken and dangerous. If You Are Not Sure, Don't Use It!
That's all for this quick guide, please comment and ask any questions or add your own tips! Hope you found it useful and I'm looking forward to hearing what you use them for!
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