Quote from: x^2 on August 06, 2013, 02:33:23 AM

Quote from: c789 on August 05, 2013, 04:56:51 PM

--snip--

This is a bit off topic, but are erupters a good investment these days?

Well, that depends on what you pay for them, what the actual difficulty increase will be and how that affects mining income.
It's been said that difficulty goes up every two weeks and they speculate that it increases 10 to 20%.

Lets just assume mining income goes down as much as the difficulty goes up. +20% diff = -20% income.
Currently, a USB Eruptor will generate 0.004BTC per day.
When difficulty goes up 20% every two weeks, you need 2 whole years of 24/7 mining to make 0,279997442372135BTC. At the 58week mark, the two-weeks income will have dropped below 0.0001BTC (thats less than 1 cent USD if 1BTC = $100). By this time, you'd be at around 0.25BTC total. The total increases so little by this time, it's not worth it anymore.

However, if the difficulty only increases 10% per two weeks, you'd have 0,55766224756596BTC after two years. Two-weeks income will drop below 0.0001BTC after 72weeks (approx 1,25yr) and by that time, you would have made about 0.52BTC

So yes, it'll make you a little BTC, and depending on what you payed for them, it may slightly be profitable, purely on the hardware cost. I Haven't factored in electricity, but these things hardly use any so thats almost negligible. ($1 to 2$ per year per Erupter would be about right)

Edit: Ofcourse, this is purely in BTC.
If you buy Eruptors using regular cash (either exchanging it or buying them with cash), you're depending more on the exchangerate. If the exchangerate goes up by the time you discard the Eruptors, it'll have been profitable. If the exchangerate stays roughly the same it really depends on what the difficulty does to income.

Edit2:
Oh, yeah, I forgot to mention that you can use an Eruptor for other coins than Bitcoin. As long as it's an SHA256d coin you can mine it with an Eruptor.
This may extend the life and increase your returns.