Measuring Power

Introduction

This post is all about making sure your folding rigs are as perfect as possible. The key measure of perfection is of course the points that it produces, storming your way up the charts is important! However, one must also consider the cost of achieving those points. For those us that are at university, or live with family and friends where electricity is free or included in rent, then you don’t need to think twice about it. But for the vast majority of the population, we need to factor in how much power a rig consumes to achieve the points.

So the new measure is now Points-Per-Watt (of electricity). However, we don’t usually care about points, we care about our Points Per Day (PPD), so the measure is PPD/W.

What’s a Watt?

A Watt (W) is one Joule of electrical energy per second. You will notice that power supplies having a power rating, so a 400W PSU can supply 400 Joules of energy every second. Now one joule/watt is actually a really small amount of energy, so small we don’t care. Or rather, utility companies don’t care. Utility companies measure/bill you in units of KwH. I.e Kilo-Watt Hours. Bear with me, I know this sounds a bit odd, but it will make sense eventually. One KwH is the power consumed by a 1 kilowatt device in one hour. There are 1000 Watt’s in a kilo-watt. So a device that uses 2000 Watts in an hour consumes 2KwH. Also, a device pulling just 500W for only 30 minutes consumes 0.25KwH.
So if we have a PC that is consuming 400W (we will talk about how we measure that later), that means it is consuming 400 Watts per hour, or in Utility terms, 0.4 KwH. So if we left that PC running for one hour, we would end up with a bill that equates to 0.4KwH worth of electricity.

Measuring the Watts

In my previous paragraph, I spoke about how much power the PC consumes (or “pulls” from the wall). We can measure this by using a device called a power meter. Here is an example of one:

Power meter

It behaves a bit like those extension block cubes that you can get, you plug the meter into the wall and then you plug your device into it. There is nothing stopping you plugging an extension bank into it (which is likely, your PC will have a monitor, the tower, maybe speakers and a printer). So the power meter will tell you the total power consumption of whatever you plug into it. So knowing how much it pulls, and knowing the performance (point production) you can work out the simple ratio, points per day, divided by the power consumption is your PPD/W.

For these calculations, I strongly recommend that you only have the tower plugged into this device, have everything else plugged into a different socket. Why? The power draw of a PC does vary quite a bit so you want to know how much ONLY the tower is consuming since if you have a dedicated folding machine, you won’t have the monitor on, so why bother measuring it! If you are interesting you can watch the power consumption vary when you turn on the FAH client, after about 15 minutes of 100% components will be running hot, so fans spin up (increasing your power consumption)

Why are we working this out? Well take a few examples, one person is using their top-notch NVidia graphics card to fold on, and it is giving them 25,000 PPD, but, graphics cards are power hungry and it consumes 450 Watts. Another person has an average PC with an average graphics card and between the two devices it produces 12,000 PPD but pulls 300W. Another person has bought a very expensive workstation PC, it comes with two Xeon processors and a bit of RAM only and pulls 350W but produces 120,000 PPD. Which PC is best? Well its quite obvious that the last one (the workstation) is clearly a beast. But between the first two, which is it? The graphics card produces more, but consumes much more power (which will cost more to run, more about that in a minute). So what we do is work out the PPD/W ratio for each of them.

	PC 1	PC 2	PC 3
Points Per Day	25,000	12,000	120,000
Power Consumption (W)	450	250	350
PPD/W	55.6	48	342.9

So what can we see? So the first two PC’s are actually very similar in terms of the points per Watt, PC 1 is marginally better so you would choose to run that. However, if you had a very limited budget but still wanted to contribute then PC 2 is still pretty good and its low power consumption means it won’t cost that much to run. PC 3 is obviously a beast, it is doing a daft amount of PPD and is pulling a modest amount of power. For the record, PC 3 is typical of those who have 2P Xeon workstations or 4P AMD workstations.

How much is it going to cost me?

So we’ve worked out how much power a PC pulls, and we can compare various PC’s as well, but ultimately, how much will it cost me to run. Well there is a very simple formula:
Cost (£) = power consumption * time * cost per unit

Just to run through that, the power consumption we know from our meter. Time, how long will the PC be running? Ideally 24x7! Cost per unit, now this is where you need to look at your energy tariff. It varies alot across the country (UK) and even around the world. But it can even vary by time of day – if you have an economy 7 tariff, you get a discount for energy use at night (based on the fact that you can’t shut down a power station!) in the later case, it can be a bit tricky. For me personally, its about 12.1p/KwH. But lets work through some simpler examples.

Example 1

I have a PC that I want to run FAH on, but I will only be running it for on average 2-3 hours a day (it’s my gaming PC, so the folding software runs when I go to play games and generally use the PC), how much will it cost me over a month? I’ve used a power meter, and my PC pulls an average of 275W when under full load.
OK, there are three things we need to know to work out cost:

1. Power Consumption = 275W
2. Time = 3 hrs. (per day) * 31 days (per month)
3. Cost Per Unit = 12.1p

So, we substitute in our known values:
Cost = 0.275 * 3 * 31 * 0.121
Cost = £3.09
So the PC on its own will cost just over £3 per month to run

Example 2

I have a dedicated folding PC, it will run 24 hours a day, 7 days a week, 365 days per year. It pulls 350W, how much will it cost over the course of the year?
OK, same technique:

1. Power Consumption = 350W
2. Time = 24 hrs. (per day) * 365 days (per year)
3. Cost Per Unit = 12.1p

Cost = 0.35 * 24 * 365 * 0.121
Cost = £370.99

So the PC will cost me nearly £371 a year to run, that's about £35 a month to your bill. Now you can see why you want to use the hardware that gives the highest points, but for the least power consumption. Even though this second PC only consumes a bit more power (per hour), the fact its on 24 hours a day means that the cost rack up quickly which if you are not prepared for it, can be quite a shock, especially if you pay by the quarter as opposed to monthly like I do.
I hope that has been useful for you!
Ciao for now!