I plugged the first one into my computer and opened bfgminer, it was running at about 2.5 gh/s, even when I raised it to 55 bits, with <1% error rate.
Then I put the second Nano Fury into my computer and the first NF2 dropped to below 1.5 gh/s with an error rate of 4% and the second NF2 stayed at .5 gh/s with an error rate of 75%. I then went and bought a powered usb 2.0 hub and 2 usb fans and installed everything and plugged it into my computer. When i opened bfgminer it was the same results.
on to the several issues that I suspect - one at a time:
- 2.5 vs 5GH - this indicates that only one chip is hashing or being recognized by the software. That's makes me think you're using an older version of bfgminer. Note that 3.10 does not include dual-chip support. As 3.11 is not yet out you need to download the latest development (non-tagged) version - it may report something like 3.99.
- plugging a second miner causes drop in hashes - most likely both miners are powered by the same power supply which hits its limitations and there is no enough juice to run two miners. A powered hub should take care of the issue. Note also that there are some powered hubs that have very very crappy power supplies and they kick in after your desktop power starts going way down (by which time it might be too late). There is a whole thread on which hub to use, with people sharing their experiences.
I personally have very good results with the 7-port Amazon Basics one:
Actually they were $12 at some point ... I should've ordered more of them at that time. I've been using them for testing various quantities of NanoFury boards and so far they've been performing pretty well.
- plugging NF2s directly into the PC - this is not a good idea. When hashing at full power the NF2 will use 1.2-1.3A (and if you overclock it - even more). The standard USB2 connector can supply only 0.5A. For that reason you need to use an external powered hub (and make sure you leave enough power for each miner - e.g. of the hub comes with a 4A brick that would be enough for 3 NF2s).
- If you absolutely must plug it into the PC (or just for testing) then do not run it at full power. Underclock it to 30-35 bits. It will hash at slower speed but it will also use much less power.
You can use this approach to check that you have the correct version and that it sees all chips.