In this fifth and final installment of our litecoin mining rig guide, I’ll answer some common questions about building your own rig, profit expectations, and mining in general. If you’ve read the rest of the guide and still have some lingering questions, you might find the answers you’re looking for here.

Hit the “read more” button for the FAQ!

Build a Litecoin Mining Rig, part 5: Mining FAQ

 General Questions

• So how much money can I expect to make from mining, exactly?
• Why not just buy litecoins (or bitcoins) directly, and then sell them later at a profit?
• How noisy/hot are these rigs?
• How do I convince my significant other that building a rig is a good idea?

Technical Questions

• How do I turn my computer on without a case/power switch?!
• Why the Radeon 7950 GPU? Why not a 7970, or another video card entirely?
• Why stop at 3 GPUs? Can’t I pack 4-5 (or more) onto one motherboard?
• Can I get PCI-E risers anywhere locally? The ones that are linked in guide ship from Hong Kong.
• Don’t I need more than 4GB of RAM? I read other guides that say I need 1.5GB per GPU, minimum.
• My kill-a-watt shows power consumption spiking up to nearly 900 watts at times, on my 860 watt power supply. Isn’t that bad?
• Can I utilize my mining rig for anything else while it’s mining?
• How much of my internet bandwidth will my mining rig use?
• I’m getting “Error -5: Enqueueing kernel onto command queue.” when running cgminer. How do I fix this?
• I’m getting an error complaining about “libjansson.so.4” on linux. What do I do?
• Cgminer is complaining about a missing shared library file: libudev.so.1. What now?
• I have another brand of 7950 video card. Do you know what cgminer settings to use?

Other

• Can I buy you a beer? Your mining guide has been a huge help!

Answers

So how much money can I expect to make from mining, exactly?

This is the question that most people are interested in. The answer is fairly complicated, and changes daily.

Today, one litecoin is worth just over $4. A few weeks ago, that same litecoin peaked at a value of  just over $6. A month before that, litecoins were trading at 6 cents apiece. The volatility in digital currency value is extreme—the price today could be very different than the price tomorrow.

On top of that, the difficulty involved with mining a coin is also changing constantly. Today, the rig in our guide will produce about 5 litecoins a day. A month ago, it would have produced ~20/day. The more people mining, the more time/computing power it takes to produce a coin.

You can answer the question for right now by using a calculator such as this one. If you’re building the exact rig outlined in the guide, plug in 1900 in the box next to “scrypt”, make sure that “kH/sec” is selected, plug in 800 for “power” (or 700 if you plan to undervolt), and then plug in your electricity rate. Make sure that the time period you’re interested in is selected (day, week, month). The calculator takes into account the current mining difficulty.

At the time of this writing, assuming you pay $0.08 per kWh for electricity, the calculator would tell you that you should expect to make about $580 per month from your mining rig. Remember to subtract 1-2 percent for your mining pool’s fee. Taking off another couple percent for downtime and other unexpected issues is probably a good idea, too.

If the price of litecoins rises faster than the mining difficulty increases, then that profit figure will increase. If the mining difficulty outpaces the value growth of litecoin (and/or litecoin drops in value), then profit will decrease.

Since it is very difficult to predict the future, I’d strongly advise everyone reading this to treat mining as a hobby, and not a “get rich quick” scheme. Only invest what you’re comfortable losing, because losing is a very real possibility.

Why not just buy litecoins (or bitcoins) directly, and then sell them later at a profit?

If you believe that litecoins are about to shoot up in value, and you have a very high tolerance for risk, and you have some money that you won’t miss if it suddenly disappears, then this might be the best idea for you. Buying the digital currency directly enables you to get your hands on a bunch of it quickly, without having to wait for a mining rig to produce it for you. However, the “sell them later at a profit” part doesn’t always work out. =)

For most of us with a desire to jump into cryptocurrency, mining is probably the safer option. If you buy $1500 worth of litecoins today, and tomorrow they become worthless (and never recover), then you’ve lost $1500. If you purchase a $1500 mining rig today, and tomorrow litecoins are worthless, then you still have $1500 worth of hardware. You can sell it at a small loss, or re-purpose it (maybe try your luck at mining one of the other digital currencies, for example).

How noisy/hot are these rigs?

This is difficult to answer because it’s so subjective. I will say that an open-air mining rig with three AMD 7950 GPUs in it will certainly not be “quiet”. If you’re planning to occupy the same space as your rig, you may very well find the noise unpleasant. I’d suggest in that case that you purchase the Sapphire Vapor-X brand of 7950, as they are significantly less noisy than most brands.

The heat that a rig produces may be more of an issue, depending on where you live. I live in the northeast US, and in the winter, my rigs double as space heaters—I can easily heat a small room with one. In the summer, the extra heat is a nuisance.

Ideally, you have someplace that you can tuck your rig(s) where they’re out of earshot. Basements and garages are both good ideas if they’re relatively clean and temperatures don’t venture into extremes.

How do I convince my significant other that building a rig is a good idea?

You’re on your own with that one. Good luck! =)

How do I turn my computer on without a case/power switch?!

So you didn’t opt to purchase a power switch, and now you’re sitting there staring at a bunch of assembled hardware, and wondering how the heck to turn the thing on for the first time. Don’t worry, you have a couple options.

If you bought the motherboard from our guide, then there is a power button built right onto the motherboard. This is increasingly common these days, so even if you have another motherboard, check to see if there is a built-in switch.

If you don’t have a button on your motherboard, then grab a flathead screwdriver. Now use the head of your screwdriver to temporarily short the two pins on the motherboard that the power switch would be connected to (if you had a power switch). Just touch the head of the screwdriver so that it makes contact with both pins for a brief moment. Your system should immediately power on.

The first thing you should do at this point is enter the BIOS and change the power options to set your computer to automatically power on whenever power is restored. That way, you can use the switch on your power supply to turn it on and off going forward.

Why the Radeon 7950 GPU? Why not a 7970, or another video card entirely?

The AMD 7950 GPU is currently gives the best hashrate/watt ratio, and also has an excellent hashrate/purchase price ratio. It’s really the ideal GPU for mining, at least for now.

The 7970 does give (slightly) better overall hashrates, but it consumes more power, and costs significantly more. The 7850 is a nice budget option from a  purchase price standpoint, but it’s significantly less powerful than the 7950, and it’s hashrate/watt ratio is worse, too.

Nvidia GPUs are out entirely, as they’re just terrible for mining.

Why stop at 3 GPUs? Can’t I pack 4-5 (or more) onto one motherboard?

I like the way you think!

Yes, it is certainly possible to cram 4, 5, even 6 or more GPUs onto a single motherboard. You can actually make use of the 1x PCI-E slots on your motherboard to connect additional GPUs via 1x to 16x riser cables (you wouldn’t do this for gaming or other applications, but mining performance won’t be impacted at all by using a 1x PCI-E slot).

There are some things to be aware of, though.

First, if you plan to go beyond 3 GPUs, you’ll need to use powered PCE-E risers (something like this). Each 7950 GPU will draw 75 watts from the motherboard (and the remaining from the PCI-E power connectors to your power supply). Asking a motherboard to deliver 75 watts for more than 3 GPUs is very likely asking too much—you risk a fried motherboard if you use unpowered risers (like the ones in our guide) for more than 3 video cards. You can also use one of these to supply additional power to your motherboard for a 4th GPU, but you give up a PCI-E slot to do so.

Second, 4 GPUs is the limit in Windows. You’ll run into all sorts of strange issues if you try to add more than that. You’ll need to use Linux if you want to pack 5+ GPUs into a single system.

Finally, you’ll need a bigger power supply. For each additional GPU, add another ~200 watts onto the PSUs rating.

The rig in our guide can easily be expanded accommodate a 4th 7950 GPU by upgrading the PSU and either using one powered 1x to 16x riser or an unpowered riser and an EVGA Power Boost. You may also want to get a larger 6-gallon crate if you’re planning to run a 4+ GPU rig.

Can I get PCI-E risers anywhere locally? The ones that are linked in guide ship from Hong Kong.

Updated 5/8: The guide has been updated to link to fairly cheap risers available on Amazon. If you’re buying in bulk, eBay might still be slightly cheaper.

I haven’t been able to find any risers outside of Hong Kong or China for reasonable prices. I ordered a set from a Boston-based business, but they still shipped from Asia. Ebay is probably your best bet, here. The ones I ordered arrived in about 10 days, and they were decently high-quality (well made with locking clips on both ends). The eBay seller that I purchased from is linked to in the hardware guide.

You can run your GPUs directly off the motherboard while you’re waiting for your risers to arrive by setting up a box fan to blow air between them. They’ll still run pretty hot, though.

Don’t I need more than 4GB of RAM? I read other guides that say I need 1.5GB per GPU, minimum.

Cgminer uses the memory on your GPUs, so you don’t need much system memory at all. You can get by just fine with 1-2GB of RAM in Linux, and 4GB is plenty in Windows.

If you read other guides telling you that you need a ton of system RAM, the author was probably running Reaper as their mining software, which oddly uses system memory.

My kill-a-watt shows power consumption spiking up to nearly 900 watts at times, on my 860 watt power supply. Isn’t that bad?

If you’re not undervolting, but you are overclocking, then it’s possible that you’ll see power consumption numbers this high (or even higher), depending on how efficient your PSU is.

The number that your kill-a-watt shows you is the “at the wall” power consumption—basically, how much electricity you’re actually using.

The number that power supplies are rated for is how much they’re capable of delivering to your system components. This number is after accounting for efficiency loss. For example, the Seasonic PSU that I recommend delivers 860 watts and is 93% efficient (which is excellent). That means that when it is delivering 100% of it’s rated power, it will actually be pulling 925 watts at the wall (860w / .93). High-quality PSUs are typically capable of delivering more than their rated power without issues, as well.

This is why it’s so important to buy a high-quality power supply for a computer that is going to be running 24/7, especially if electricity is particularly expensive in your area. An 80% efficient PSU would pull 1075 watts at the wall when delivering 860 watts to a computer—a full 150 watts more than the 93% efficient Seasonic!

Can I utilize my mining rig for anything else while it’s mining?

It’ll make a great space heater in the winter. =) Oh, you mean application-wise.

The CPU, memory, and disk will mostly be unused while your rig is mining, but anything GUI-related will be pretty unresponsive. Applications that run in the background or over the network are good candidates, if you’re looking to get some extra use out of your rig. You should be able to run things like file servers and low-traffic web servers just fine without impacting mining performance.

How much of my internet bandwidth will my mining rig use?

Not much at all. Mine averages around 30 kb/sec when it’s mining at full speed, which is less than half of one percent of the average broadband speed in the US (~6.6 mb/sec). Bandwidth is basically a non-issue—you could run a mining rig off a dial-up connection.

I’m getting “Error -5: Enqueueing kernel onto command queue.” when running cgminer. How do I fix this?

You’re probably running a 32-bit OS (I highly recommend using a 64-bit OS for mining if it all possible). At least, that’s the only time I’ve seen this error pop up. Try changing your cgminer startup script to these parameters:

cgminer --scrypt -I 13 -g 2 -w 256 -v 1 --thread-concurrency 8192 -o [POOL] -u [USERNAME] -p [PASSWORD]

You may not hit quite the same performance level as you would using the settings I give in my optimization guide, but hopefully this will get you running. If it doesn’t, try also installing the latest Catalyst driver & SDK.

I’m getting an error complaining about “libjansson.so.4” on linux. What do I do?

If you’ve followed my guide exactly, you shouldn’t run into this issue. However, if you’re running a different distro, or another version of Xubuntu, it’s possible that you might encounter this.

To resolve, simply enter this on the command line:

ln -s /usr/local/lib/libjansson.so.4 /usr/lib/libjansson.so.4

Cgminer is complaining about a missing shared library file: libudev.so.1. What now?

If you downloaded a more recent version of cgminer than the one that I linked in my guide, this issue might affect you. The error message you’ll see looks something like “error while loading shared libraries: libudev.so.1: cannot open shared object file: No such file or directory.” To resolve this issue, you’ll need to run the following command:

sudo ln -s /lib/x86_64-linux-gnu/libudev.so.0 /lib/x86_64-linux-gnu/libudev.so.1

If that doesn’t work for you, try this:

sudo ln -s /lib/x86_64-linux-gnu/libudev.so.0.13.0 /lib/x86_64-linux-gnu/libudev.so.1

I have another brand of 7950 video card. Do you know what cgminer settings to use?

If you have a Gigabyte WF3 7950, make these substitutions in your cgminer startup script when following my optimization guide (leave everything else the same):

--thread-concurrency 25984 --gpu-engine 1065 --gpu-memclock 1500

If you have a Sapphire Vapor-X 7950, make these substitutions in your cgminer startup script when following my optimization guide (leave everything else the same):

--thread-concurrency 24000 --gpu-engine 1095 --gpu-memclock 1250

If you also follow my undervolting guide, you can use 1037 mV in place of the 1081 mV I recommend on the Sapphire card (and possibly go even lower, but 1037 has always been stable for me).

If you have another brand and are looking for settings, I recommend the bitcointalk forums or the litecoinmining subreddit.

Can I buy you a beer? Your mining guide has been a huge help!

Certainly! Well, virtually, anyway. I’d be happy to accept donations at the below wallet addresses:

Bitcoin: 1DpnANRtMDPe8jG3FXfkyczLFevM94Yjxv
Litecoin: LPuwBa3LbZZzcJaR3kEsGDBivAoc64fPUr

And thanks! =)