You might want to have a look at cryptocurrencies like Verium or Magi. I for example have 4x Pi3 running in the basement on Verium and it works really well. No big profits but it is fun setting it up and it is running in the background 24/7 on a 5 port USB charger without any issues.
Odroid XU4 would be even more efficient with this but they are hard to get and expensive where I live so I went with the Pi3's.
Very interested on what you have to say here. Is verium a CPU locked coin? I assume? And what kind of hash are you getting with these Pi3's? Please elaborate on this.
Thanks
It is based on scrypt^2, so ASIC and GPU resistant. If you search the web you will find some tutorials on how to mine it with a raspberry pi3. Running the pi64 OS, CPU slightly overclocked to 1,3GHz I get about 195 H/m.
Enough about this here. This is the ROI forum