How do I make sure that I am ordering the correct power supply adapter for my device? Quick instructions on selecting a power supply: The only information you need to have in order to find the correct power supply for your device is the Voltage / Volts (V) and Amperage / Amps (A). Voltage has to be an exact match. A 12V DC device needs a 12V DC adapter. Amperage is the amount of power your device uses. The adapter you order has to be able to supply AT LEAST the amount of Amps your device draws. If your device states it is 12V 3A, a 3A adapter can handle that load, but so can a 4A and 5A. The higher amperage (amp) power supply will not have to work as hard to handle a smaller load, and will run cooler and more stable. If the Amperage of your device is uneven, such as 3.13A or 4.16A, always round up. 3.13A rounds up to a 3.5A adapter, a 4.16A device will round up to a 4.5A or a 5A. If you match these two specification (V and A), the power supply will work for your device.

In order to find the correct power supply for your device, you will need two pieces of information.hvac unit outside fan not running These are Voltage (measured in Volts or V) and Amperage (measured in Amps or A). air conditioning unit with ice on itYou can find this information off the back of the old power supply,york water cooled ac units or off the back of the device itself. If you do not find it on the device, you can check the manufacturer's website, or in the device's manual under "specifications". All of the power supplies we sell are 12V DC. They take any input from 100V up to 220V AC, which is what comes out of your wall socket, and output 12V DC. This is what most digital devices such as LCD screens, DVD players, Hard Drives, Audio

Gear, and most other digital devices use. We only carry 12V DC power supplies, so if your unit is not 12 Volt, you will not find the correct adapter here. Once you have confirmed that you need a 12 Volt power supply, you will need to find out how much power your deviceThis is called amperage. Next to the 12V in the specifications there will be another number followed by a capital "A" for Amps. You will need a power supply that can supply enough power for your device. If your device says it draws 3 Amp (3A), you need to use a power supply that can put out at least that many Amps. If your device states it needs 3A, then you can use a 3A, or 4A, or 5A unit. All our power supplies have a connector that is standard for a 12V DC device. Most 12V DC devices use the standard tip. This tip is 5.5mm (outer barrel) by 2.5mm (inner barrel) and is center positive. It is a simple round barrel connector. To repeat, if you match the voltage and amperage, then you should not have to worry about the connector type accept in the

rare occasion when your device has an unusual connector such as a double barrel, or a 4-pin, but these are easy to spot as the jack where the adapter plugs in will not be a simple circular barrel with a pin inside.These guys are everywhere - all sorts of voltage and current ratings. They're available for sale at any store just about, but there are some big things to watch out for! One is that the output voltage is not going to be 9V (for example) out of the box, that voltage rating is just the minimum output for the current rating (200mA for example). And also, the output is going to have a lot of ripple on it! Before we talk precisely about these guys, lets go back in time to when engineers had to build their power supplies with their bare hands! The good old days! check out the wikipedia page. and the other half would output 12V AC (the 'secondary' 'low side'). The transformer functioned in two ways: one it took the dangerous high voltage and transformed it to a much safer low voltage, second itisolated the two sides.

That made it even safer because there was no way for the hot line to show up in your electronics and possibly electrocute you. We'll use a schematic symbol to indicate a transformer, its two coils inside which are drawn out, the schematic symbol will have the same number of coils on either side so use common sense and any schematic indicators to help you out in figuring which is primary and which is secondary! power diode such as a 1N4001 What we have now isnt really AC and isn't really DC, its this lumpy wave. The good news is that it's only positive voltage'd now, which means its safe to put a capacitor on it. This is a 2200 microFarad (0.0022 Farad) capacitor, one leg has (-) signs next to it, this is the negative side. The other side is positive, and there should never be a voltage across is so that the negative pin is 'higher' than the positive pin or it'll go POOF! Because the voltage is very uneven (big ripples), we need a really big electrolytic-type capacitor.

Well, there's a lot of math behind it which you can read about but the rough formula you'll want to keep in mind is: Ripple voltage = Current draw / ( (Ripple frequency) * (Capacitor size) )or written another way Capacitor size = Current draw / ( (Ripple frequency) * (Ripple Voltage) )For a half wave rectifier (single diode) the frequency is 60 Hz (or 50 Hz in europe). The current draw is how much current your project is going to need, maximum. The ripple voltage is how much rippling there will be in the output which you are willing to live with and the capacitor size is in Farads. So lets say we have a current draw of 50 mA and a maximum ripple voltage of 10mV we are willing to live with. For a half wave rectifier, the capacitor should be at least = 0.05 / (60 * 0.01) = 0.085 Farads = 85,000 uF! This is a massive and expensive capacitor. For that reason, its rare to see ripple voltages as low as 10mV. Its more common to see maybe 100mV of ripple and then some other technique to reduce the ripple, such as a linear regulator chip.

You don't have to memorize that formula, but you should keep the following in mind: When the current goes up and the capacitor stays the same, the ripple goes up. If the current goes up and you want the ripple the same, the capacitor must also increase. The transformer AC/DC in practice Wow so this looks really familiar, right? From let to right, you can see the wires that come into the transformer from the wall plug, the transformer output has two power diodes on it and a big capacitor (2,200uF). You might be a little puzzled at the two diodes - shouldn't there be four for a full-wave rectifier? It turns out that if you have a special transformer made with a 'center tap' (a wire that goes to the center) you can get away with using only two diodes . So it really is a full wave rectifier, just one with a center-tap transformer. These transformer-based plug-packs are really cheap to make - like on the order of under $1! Testing the 9V supply Let's look in detail

With 35 ohms (230 mA draw) the voltage plummets to 7.7V! As the resistance gets smaller and smaller, the current draw gets higher and higher and the voltage droops (that's the technical term for it!) You can also see the ripple increase as the current goes up. Now we can at least understand the thinking behind saying "9V 200mA" on the label. As long as we are drawing less than 200mA the voltage will be higher than 9V. What does this mean for you?OK so after all that work, you're wondering why does this even matter? The reason it matters is that everywhere you look are these wall warts that are 'unregulated' and thus extremely suspicious. You simply can't trust 'em to give you the voltage you want!For example, lets say you have a microcontroller project and it requires 5V power as many DIY projects do. You shouldn't go out and buy a 5V transformer supply like the one above and just stick the power output into your microcontroller - you'll destroy it! Instead, you will need to build a 5V regulator like the common LM7805 that will take the somewhere-around-9V from the transformer and convert it to a nice steady 5V with almost no ripple.

So here is what you should always do: Always check your power supply brick with a multimeter to see what the maximum voltage is Assume that the voltage can be twice as high as you expect Assume that the voltage will droop as you draw more and more current If you're using a brick for low-power usage, say your circuit draws 100mA max, find one that has a very similar current rating. You might be wondering well why on earth doesn't someone make a power plug that takes a transformer and some diodes and a LM7805 and that will give you a nice 5V output instead of having everyone build it into the project circuit? While its an interesting idea there are a few reasons they don't do that. One is that the enclosed wall adapter would overheat. Another is that some projects need more than one voltage, say 5V and 3.3V both. But in the end, its probably for manufacturing simplicity. The factory that makes the wall plugs makes 100's of thousands in predictable sizes and rates, each country has plenty of factories to make the right plug packs for the wall voltage and plug style.