Working with Power Supplies
This is a guide on working with power supplies.
Input 115V vs 220V
In this presentation, we'll talk about some key power system terms beginning with the ampere, which is more commonly known as just an amp. And this is a base unit of electric current that measures the rate of flow per second. Now perhaps in simpler terms, you can think of this as just how much power. But you also have to consider voltage which is more commonly abbreviated as just volts. And this is the measure of work required to push an electric charge between two points.
Now you'll often hear it referred to as pressure as well. But a common analogy for both of these is water through a hose. So if, for example, you compare a garden hose to a fire hose, you can move a lot more water through the fire hose simply because it's larger. So a larger hose, more water, that equates to your amps. But you also have to consider the pressure. So if we just look at the garden hose, for example, you typically have a faucet. And the faucet is not usually just completely on or off, you can dial it to a certain amount. So if you just barely open it, a little bit of water will trickle out the end of the hose. If you open it a bit more, a little more water will come out with more pressure. And if you open it all the way, then you'll get full pressure and much more water coming out because you're pushing harder.
So you do need to consider both in terms of overall power consumption, and in fact, that's watts. So watts is simply calculated as amps times volts. So if your device only runs at half an amp, and you are receiving a 120 volts, which by the way is the standard amount of power delivered to your home through your wall plugs, then that device uses 60 watts.
[Video description begins] Two line graphs display, representing Direct Current (DC) and Alternating Current (AC). The Y axis indicates Voltage and the X axis indicates Time for both graphs. The DC graph shows a straight line parallel to the X axis. The AC graph is a curving line which moves from zero voltage to positive voltage. Then zero voltage to negative voltage and back to zero voltage. [Video description ends]
Now, with respect to the types of current, there are two, direct current or DC, and alternating current or AC. Now, I'll actually begin with AC because this is the type of power that you actually receive to your home from the power station. So again, all of your wall plugs are receiving AC. And the reason for this is because it travels better. If you had to deliver all the power that your home needs over DC, you would either have to be very close to the power station, or the wires would have to be enormous. So DC just doesn't travel well, but alternating current, quite literally, can alternate the voltage and even the direction of current. And this simply results in it traveling much better.
You can see that voltage is measured in a cyclical value when it comes to AC. We have the zero line that indicates ground, if you will, and that peaks up and it goes down to its trough and it comes back up again. And then that indicates one alternating cycle, or one hertz. But DC doesn't do that, it's just a consistent voltage all the time. But the electronic devices that we use typically tend to use direct current, but at a much lower voltage than what is delivered by AC. So we can get the AC to our homes, then we can use something to convert that AC into DC, because again, it's usually a much lower value.
So when it comes to our computers, this is performed by the power supply unit, or the PSU. It handles that conversion of AC to a lower voltage DC. [Video description begins] A Power Supply Unit displays. [Video description ends] And again, the components of the computer itself generally run at far lower voltages than what we get through the wall plugs.
Now you'd also have to pay attention to whether or not there is a voltage switch on the back of the PSU. And this is because there is a variance in what is delivered depending on where you live. In Canada and the United States, we typically receive between 110 and 120 volts at 60 hertz. In Europe, it's very different, 220 to 230 volts at 50 hertz, and these two are not compatible. So the voltage switch at the back, which by the way is the red switch in this graphic, allows you to set it for either one.
Now it depends on the make and model. Some of them won't have a switch, in which case, it either is specifically set for one or the other and can only be used in those specific locations, or it's able to adjust dynamically. And you'll notice on the labeling of the power supply itself as to whether or not it can accept that range. So if for example, you see that it can take in 110 all the way up to 230, then it's able to dynamically switch. But if you see that it can only take in 110 to 120 and there is no switch, then it can only be used in Canada or the United States, or anywhere else that delivers 110 to 120.
So you do need to be mindful of that, because again, you cannot just plug in a device that expects a 110 through 120, and then receives 220 to 230. You would almost certainly burn out that device, and you'd see smoke and possibly even flames. So you definitely want to be careful when it comes to knowing what voltage your device will accept.
Output 5.5V vs 12V
In this presentation, we'll take a look at the two more common output voltages in systems these days,12 volts and 5. [Video description begins] A 4-pin connector displays. Two of the pins have one rounded edge. [Video description ends]
Now beginning with 12, these tend to power the more demanding components of your system. Modern CPUs, disk drives, graphics cards, and cooling fans, all tend to draw more power these days, so they operate on 12 volts. But within your power supply, you may find what's known as multiple rails.
Now you can think of a rail as really just a separate independent power generator within the overall unit. And most power supplies these days will have at least one, possibly multiple positive 12 volt rails, and you might also see a negative 12 volt rail.
Now positive voltage versus negative voltage really is just a matter of perspective with respect to the electrical ground. And as an analogy here, just think about measuring your own height. You can measure from the floor up to the top of your head and get a certain value, or you could measure from the top of your head down and you'd get the same value. So it's really just how the power is being delivered with respect to the ground. And most modern systems probably won't have very much, if anything, running at negative 12 volts. But depending on its age, there may still be components that do require negative voltage, and in that case, you'll usually see one for backward compatibility.
Now there also will likely be an ATX12V standard connector, which is what you're seeing in the graphic here. This is a four pin, or what's known as a P4 connector, that typically connects to a specific place on the motherboard to directly power something like the CPU and maybe a graphics card. And it's just an independent dedicated connection for just those devices, so that it's guaranteed to get that voltage all the time and not have to share that with anything else.
Now you can't get this connector in the wrong place, because it's specifically configured so that it will only fit in that place. So you just need to make sure that if you have that connection on your motherboard, that it is receiving a connection from the power supply.
[Video description begins] A 24-pin connector displays. 12 of the pins have rounded edges. [Video description ends]
Now the other common output is 5 volts, and this uses a much larger connector, physically. And that might seem a little bit counterintuitive, because the 12 volt connector is only four pins. This connector is 24. But the 12 volt connector is usually dedicated to something like the CPU, whereas this connection is for multiple integrated circuits, older CPUs, and logic devices.
Now an example of a logic device was a chip that used to be known as the ALU, or the arithmetic logic unit, also sometimes referred to as simply the math co-processor. And it was literally just an additional chip to support arithmetic calculations. So again, this connector supplies power to multiple components, but again, at a much lower voltage.
But you may still see on your power supply that there are again, multiple rails, maybe a positive 5 volt rail and a negative 5 volt rail. And then you may also see an additional 5 volt rail labeled as SB for standby. And that's for any kind of component in the system that does have standby power, whereby the unit is officially off, but it maintains a minimal amount of power so that it can be turned on very quickly or by some sort of software trigger.
Now you may also find 12 volt-only power supplies, but typically with those models, they are able to convert to 5 volt on the motherboard itself. So in that kind of configuration, it would be compatible, but it is something that you would want to take note of with respect to whether or not your system is able to convert from 12 down to 5, because you cannot drive 12 volts down a connection that only expects 5. It will burn it out.
24-Pin Motherboard Adapter
In this presentation, we'll take a closer look at the 24-pin motherboard adapter. And this is often referred to as the ATX 24-pin. [Video description begins] A 24-pin connector displays. 12 of the pins have one rounded edge. [Video description ends] And recall that ATX refers to the form factor. And in terms of day-to-day conversation, most people would just refer to this as the standard motherboard power connector, as that's exactly what it was. It supplied power to all of the components of your motherboard.
Now it had uniquely shaped pins that would only fit on the plug in one direction. So in other words, you could not get it in upside down, it just wouldn't fit. And it provides more power than the older 20-pin connector that was its predecessor. And perhaps more specifically stated, it just provides more power to more components than did its predecessor. And in many cases, you might find a detachable 4-pin connector on some models over on the end of one side. And this essentially was just for backward compatibility because you might have had a situation where your power supply was a little bit newer, but your motherboard was a little bit older.
So the power supply had the 24-pin connector, but the motherboard only had 20. So in that event, you could quite literally slide the last four pins off and just plug in the original 20. Or it might actually still fit with those extra 4 pins in place, but they would just hang over the connector and not connect to anything. And in some cases, you might have actually seen where the motherboard had 20, but then there was the dedicated 4-pin connector for the CPU. But they were physically separate from each other. So again, you had to slide those four pins off and move them over to the CPU power. But in either case, it was really just for backward compatibility.
Now in terms of the wiring configuration, you would find eight ground pins, or eight wires, that were black. Four positive 3.3 volts of DC, which were orange. Five positive 5 volts of DC, which were red. One positive 5 volts of DC for the standby, which was purple. One negative 5 volts of DC, which was white. Two positive 12 volts of DC, which were yellow. And one negative 12 volts of DC, which was blue. One to simply indicate the power supply was on and this was green, and one to indicate that the power was good, that everything was receiving the correct voltages, and this one was grey.
Now there's nothing that you had to do in terms of connecting or configuring these wires. They were all hardwired into the single connector, but it could be useful for troubleshooting. If you weren't certain if the power supply was delivering the correct voltage or just maybe it got damaged, you could get your voltage meter and test each of those wires to make sure you are getting the correct output.
Wattage Rating
In this presentation, we'll take a look at some of the considerations for a power supply when it comes to deciding on what kind of values you need for components such as the overall wattage rating and the volts that are being supplied. [Video description begins] A Power Supply Unit displays. [Video description ends]
So recall that wattage is calculated by multiplying the volts times the amps, but you can find different values for each of those. So what you really need to know is the peak output rating so that you don't exceed either value. And this essentially will ensure that you supply power stable to all of your components. So every power supply is going to tell you that it has a maximum wattage output, but as mentioned earlier, there are also multiple rails. And those can be thought of as just separate little power supplies within the unit that deliver those specific voltages, +3.3 volts, +5 volts, and +12 volts. So you need to be mindful of the voltage along with the amps that are being delivered to ensure that you do not exceed the maximum wattage output.
Now in our next presentation, we'll actually see a table, and I'll show you how to calculate all of that. But with respect to the 12 volt rails these really are the crucial voltage rails because the component such as your CPU, your video card, your fans, they all draw 12 volts. So this is really what we need to ensure is being delivered correctly. So we need sufficient power to the 12 volt rails. And in most cases there are multiple 12 volt rails and you need to ensure that the total amps from all rails does not exceed the total output of the power supply. So again, what you also need to consider is the maximum combined amperage with respect to each rail. Now since watts is volts times amps, then the maximum amperage is watts divided by volts, okay?
So now, any power supply that you purchase will have a label on it indicating how this is all set up. So as mentioned, we'll see that in the next presentation. And it's usually not an issue with respect to buying a power supply that maybe delivers more power than you need because it just doesn't have to be used. You don't have to supply power on every connection. In almost every computer, you will find connections that just aren't made. They're just there for extra components. So it's never a problem to have an overall maximum output that is more than what you need. But you need to ensure that any individual combination of watts times volts does not exceed the capability of the power supply.
Number of Devices to be Powered
Now, in this presentation, we'll try to put everything together with respect to understanding your power supply in amps, and volts, and watts, and AC versus DC. [Video description begins] A Power Supply Unit displays. [Video description ends] But before we get to that, we'll talk about some general guidelines for power sizing. And you may not always need a power supply that is more robust than what the computer actually requires.
So, too large, in this case, refers to its capacity, not the physical size. And this is not a problem, but you might end up spending more money than you need for no additional benefit. In other words, a power supply that, let's say, delivers four times the power you need, does not help your performance in any way. It just makes the system more expandable. You can add a lot to it. But if you don't anticipate adding anything, then you could be spending money for nothing, but it's not a problem, okay? The system is not going to be damaged by any means just because the power supply is capable of supporting more than what you have.
Now you do need to consider the physical size. Now if it's a standard ATX power supply, that will fit in any standard ATX case. But a lot of proprietary systems have their own specialized power supplies. So certainly be mindful of the physical size that you currently have, if you feel like you need to replace it with a unit that is standardized. So everything really depends on size of the case and its physical configuration. And if you are building a new system or just replacing the power supply, you do want to try to calculate the total wattage required.
Now this involves looking at some of the specs of the hard drives, the optical drives, the fans, the processor, the video card, and you basically just have to add it all up. And in general, you do want the power supply to be able to deliver more than what is required. Again, you don't have to go crazy but you certainly don't want it to be underpowered. And special attention these days must be given to video adapters, particularly for something like a gaming system. They are very demanding in terms of power consumption. Most notably because they have, in many cases, multiple fans keeping them cool. So you just need to make sure that your video adapter is adequately supplied with power.
[Video description begins] A table displays. It provides details related to the AC Input, DC Output, Max Output Current, Max Output Power, and Total Power. The AC Input has an Input Voltage of 100V - 240V, its Input Current is 5A - 10A, and its Frequency is 50Hz - 60Hz. [Video description ends]
So when it does come to sizing overall and determining what your power supply can do, this is where we see this table. Now before we get to that, again, you generally want to try to prevent any kind of overload. Now again, that does not mean that the power supply itself can deliver more power than what the system needs. It's trying to draw more power from the power supply than it can deliver. So you want to analyze the worst case scenario. And that's where you interpret this table. And the rule of thumb is that 50% excess capacity is certainly fine.
Now, that comes back to what I just mentioned, whereby you don't want to spend money for nothing. But in general, a power supply should be able to deliver approximately twice as much power as what you actually need. This gives you room to grow and ensures that you really shouldn't be taxing the power supply too much.
So then looking at this table, this is something that you'll find literally right on the power supply itself. There should be some kind of label that indicates these values. Now for starters, look at the input versus the output. The input is AC, alternating current. That's what's coming from your wall plug. DC is what's coming out of it for the components inside the computer. And note that the voltage on the AC input is much higher than the DC output. That's where that conversion comes into play.
Now in this case, the input voltage, or AC, is 100 volts to 240 volts. That indicates that this power supply is capable of working in both US and Canada and Europe. That covers the whole range of voltages that are delivered in those locations, so this one is adaptable to both. The input current are the amps, and that's 5 amps to 10 amps. And note, this is actually a lot lower than the DC output. But because the DC voltage is so low, again you can always adjust volts times amps to get overall watts. So even though the input is low on the amps, the voltage is so much lower on the output side that we can deliver more amps on the output side by simply lowering the voltage.
[Video description begins] A DC Output of +3.3V and a Max Output Current of 25A must produce less than 140W. A DC Output of +5V and a Max Output Current of 25A must produce less than 140W. A DC Output of +12V and a Max Output Current of 50A must produce less than 600W. A DC Output of -12V and a Max Output Current of 0.8A must produce less than 9.6W. A DC Output of +5VSBV and a Max Output Current of 3A must produce less than 15W. The Total Power is 600W. [Video description ends]
So then in terms of the table, you can see the DC Output, the Max Output Current, which is amps. And then the Max Output Power, which is watts. So the way that you read this is kind of top down, so the very first column, for DC Output says, positive 3.3 Volts. That's an individual rail in the power supply. And the Maximum Output Current is 25 amps. As long as those two together, volts times amps, do not exceed the maximum output power, in this case of 140 watts, then you are fine. So 3.3 times 25 is only a little more than 80. So we are fine in this case. Now, the next rail is still at 25 amps, but it's 5 volts. Well, 5 times 25 is 125, so we're still below 140. That's that whole block there for those two rails.
Then we see a positive 12 volt rail. And again, you read this top down. So for that 12 volt rail, its maximum output is 50 amps. Now that's pretty high. You wouldn't have any single device drawing 50 amps in your computer. But again it's the combination of the two of them, 12 volts times 50 amps is exactly 600 watts, so you're still fine, okay? Then the negative 12 volt, in this case is very low. It's only 0.8 amps or a maximum of 9.6 watts on that rail. Then we see the 5 volt with the SB, that's the standby. And this is only drawing 3 amps for a maximum of 15, and that's exactly what we see for the maximum wattage there as well. So each of those rails is not exceeding the capability of the maximum output terms of the wattage or the overall power. But then the total power of any one rail is 600 watts, so we are still fine in that regard.
That's probably a little bit old. However, I will tell you that most power supplies these days would go quite a bit beyond 600 watts. I would say it would be more likely that you'd see something like 1200, maybe even 1500 on most power supplies these days. But that's how you interpret those values with respect to each individual rail. And again, the input values are AC and the output values are DC. So that's that conversion.
I suppose I should also mention that frequency range: 60 hertz is what you get in the US and Canada, 50 is what they deliver in Europe. So again, it's capable of operating in both locations, so that's something that you would also want to take note of. But in this case, no individual rail is exceeding the power capabilities of the power supply in total. So you would just want to ensure that the power supply has enough physical connections for the devices in your computer and that you aren't driving it on any rail beyond those values.