So you've done your homework, bashed everything into whattomine.com and determined the best type of cards for your vision. You've even got time to read some stuff online again - since you're here. However, what that website and auto-profit mining pools / miners all do not factor in how income, hashrates, power consumption and depreciation work together to actually determining what's most profitable.
What I have done here is worked through it for one card, as an example, to illustrate this and I'll show you how I got there, so you can apply this from time to time for your own mining. Better efficiency (as in profit, not hash/watt) will always help you through.
Choosing the card
In this instance, I've picked the card that given all factors (cost, resell value, hashrate, power consumption) performs best on the currently most profitable to mine coin, Monacoin. It's the 1080Ti. The lessons are for any card - just in case the 'Ti' makes for a frightening example. The 1080Ti is just absolute best in mining coins that use the Lyra2REv2 algorithm.
The assumptions
- Cost: $745 USD
- Resale value after 15 months of mining: $375
- Electricity: $0.12 / kWh
These assumption are important as changing any of these will have an influence. Taking the above, the total depreciation of the card is 745-375 = $370. But what about the PC itself? I assume you can run 8 cards in a rig, so for this one card I'm going to add the depreciation for the rest of the components at $35 for the same 15 month period (aka 8 card = 8x35 = $280 depreciation for the whole PC).
Looking at the hashrate vs power consumption
As you know we can tweak power consumption. In fact, a 1080Ti has a curve where voltage is set vs frequency. Algorithms like Lyra2REv2 heavily depend on the core frequency. As you can see there's a diminishing rate on return by increasing the voltage. Not only that, power consumption increases not by voltage but by voltage square. So what we can expect from the below graph is that we will have rapidly declining results for increased power consumption.
Actual results from the 1080Ti
Below are my results. The first one is a simple 105% power draw +38 Core and +504 Mem setting that would be a good gaming setup. The other 3 settings are where I flattened the power curve on a fixed voltage & frequency, so we get stable results in power & hashrate.
From this table we can determine that the efficiency - as predicted- is best at the lowest setting. A lot more power is need to increase the hashrate each time. This is why those who tweak their mining rigs, often choose low power settings. But as you will see in the next sections, this is not what determines profitability.
Tweaking for profit instead
What I've done below is enter my hashrate & power consumption + electricity cost into whattomine.com - but you can do you own calcs equally. I've then added in the depreciation I spoke about earlier and put that in as a daily depreciation cost. Here's what that looks like:
As you can see from that, profitability peaks at around 0.85V. This is because coming from 0.8V, if we add 7 cents in electricity costs a day, we gain 14 cents in clean profit / 21 cents total. Looking at the 0.9V data, it looks like we may find that that the optimal value is actually 0.875V.
At 0.9V we still get more profit, but the return on our investment as a percentage (the efficiency of capital put it in) is starting to decline.
In Conclusion
The profits calculated through various website calculators, mining pools with auto-coin selectors.. all of them never take depreciation and the tweaking levels of a card into account and are likely to not give you the optimal results. As shown, the best results are dependent on your card, it's purchase price, it's resell value, the period over which you'll be mining, the electricity costs all considered - and may change over time as a result. It's also not that hard to figure out: once you can establish the daily depreciation, and measured the hash-rate for a couple of power levels, you can add in the other factors from other calculators.
In the end, being aware of this and checking the profitability calculations this from time to time can help you get the best returns. You will even see that some cards have negative returns for certain algorithms - but that's something for a next article. In the mean time..
Happy Mining!
Ed.
Disclaimer: not affiliated with any website or vendor - these are just things I've personally chosen