Kilohashes versus power – safely mining Scrypt for profit

Everybody knows miners have one of the most dangerous jobs in the world. But what about cryptomining? How safe is it?  If you spend hours trying to boost your miner as fast as it can go from a remote shell, it’s easy to forget the electrical juice you’re pulling from that wall plug. But it is the difference between profit and a really big loss!

You should focus on getting the highest hashes/Watts possible while keeping your investment, and your home, safe.  Keep in mind that I am not an electrician, this advice is mostly common sense. Call your electrician before doing anything in here!

Tip #1: Get a Kill-A-Watt or other usage meter.

I got one for about 30$ off Amazon. This will help you find exactly how much power your miners are using at different speeds. Is it worth it running your cards at 1.250 volts for that extra 40 kH/s?  The only way to tell is by measuring how much electricity you’re using at the wall. You WILL be surprised. You might decide to tune down power a little and save on cooling too.

Tip #2: Do not use extension cords!

A quad card miner tuned for maximum output can easily chew through 10 Amps/1200 watts. It’s easy to just run your miner 24/7 without ever tripping the fuse. But that fuse is just there to prevent peaks, not for continual use at that power! The cables in the wall can easily overheat, melt and burn down your house on extended use at such high power. A miner causes “continual load” on the circuit; you should not continually load any home circuit at more than 80% its capacity!  For a 15 Amp circuit, this is a maximum of 12 Amps, but remember this is the MAXIMUM, it doesn’t mean it’s absolutely safe.

Your cheap extension cord is probably NOT rated for a 12 Amps continuous load. It is probably not even the proper gauge to run that kind of power for 15 minutes. It will heat up, melt, burn, cause an electric fire, kill you, kill your family, kill your dog, kill the neighbor’s dog, etc. Avoid them as much as possible, if you do end up using one make sure it is properly rated for it!  Not kidding here, they really can get hot enough to cause a fire very quickly, think of them as giant, cheap fuses.

If you’re running a miner 24/7 on a 15 Amp circuit, play it safe, use powertune or undervolting to go as far below 12 Amps as possible. Even at 10 Amps the wall sockets might get warm and eventually fail. A fire isn’t worth an extra 50 cents a day…

Tip #3: Use a higher rated circuit. 20 Amps, 250 Volts, lions & bears & electricians, oh my!

If your house has been properly wired for 20 and 30 Amps circuits, then you can exert a higher continuous load without getting in the danger zone.  80% of 20 Amps is 16, 80% of 30 Amps is 24.   You should even be able to run 2 low-power miners on a 20 Amp circuit and 2 high-power ones on the 30 Amps. If you don’t have any free circuits, an electrician can install them for you.

When he comes over, tell him that modern computer power supplies can automatically switch to use 220-250 voltage (there is a good variance here, usually that range of voltage is all the same to an electrician). Check your PSU’s manual; and ask your electrician what cords to use. Not only will it be safer to use lines designed for a higher load, power supplies are slightly more efficient at the higher voltages (1-3%).  At 1 kW/h and 8 cents a kW, that’s 21$ a year. And less heat/Amps on your circuits!

Tip #4: Get the best PSUs money can buy.

Another small % efficiency savings is in using the best PSUs you can get. There’s two ways you can use this efficiency to maximize your profits.

A 1000W PSU rated at 80% efficiency (Bronze) actually sucks up 1200 Watts at full load at the plug. First, get ‘Gold’ rated PSUs. As we’ve seen above, a 3% improvement in efficiency can mean 20$ saved a year, and you’re keepign this hardware for more than a year, right?  So a 40$ difference in price is easy to accept. (And in fact, Gold rating 87% efficiency).

The other factor is that 80% efficiency is at full load – PSUs are most efficient at 50% load. If you go for dual PSUs for your quad card miner, with a 600W load on each PSU, you could use two 1200W Gold rated PSUs and get 90% efficiency on each. That’s 120 watts saved, 84$ a year. Obviously this is more of a tip for bargain hunters, but on the other hand that’s 120 Watts you’re taking off your continuous load, and it basically makes your CPU mining ‘free’, if you’ve maxed out your cards. Your CPU should not get used otherwise.

Tip #5: Undervolt your cards/use a green OS

A proper undervolting should keep your cards at peak efficiency while using between 40-50Watts less than normal. On a quad miner that’s a pretty significant 200W total, 120$ a year or so!

Unfortunately the only OS that has the tools to undervolt/overclock all cards properly is Windows. It might also access other power settings (such as eco modes, hibernation, fan controls, CPU underclocks and so on) better than Linux can. The downsides are that it doesn’t seem to support more than 4 cards at a time (I’m not sure 6-card miners are worth the headache) and you need to buy the OS and a hard disk to install it on – a SDD will use little power, but it’s an extra expense nonetheless. But since you save 120$ every year, not such a big deal.

On Linux, there’s really no reliable way to undervolt every card out there reliably. Your best bet is to get a card that can be undervolted outside the OS. The best solution I’ve found is to get Gigabyte WF3s and flash them with the F43 bios. The cards run flawlessly and use 50Watts less at the wall.

It’s odd that card manufacturers would not include something as ‘safe’ as undervolting but I’m sure Gigabyte is glad someone found that loophole, I bet they’re  selling boatloads of WF3s!

That’s all the tips I have for now. Please share your own tips or point out flaws in mine. Once again, I’m not an electrician, but I hope I helped you mine safely and rake in the coins!