From:
http://elinux.org/R-Pi_Troubleshooting#Troubleshooting_power_problemsYou can use a multimeter to compare power usage before and after you plug in your USB miner:
Results of tests:
Before tests: 4.90v available, 4.91v before polyfuse, 4.69v after polyfuse
With Eruptor: 4.54v avail, 4.91v before PF, 4.58v after
With no external power HDD: 4.90v before polyfuse, 4.46v after
Immediately after tests: 4.71v avail, 4.92v before fuse, 4.72v after and noted increased after 1min to 4.74v but after 5mins did not recover further; did not test for longer.
The HDD was noted as not fully spinning up.
Conclusions:
- a HDD needs external power no matter what. I expect if I was to test a flash drive power use is lower
- a Block Eruptor is right on the limit of what my Pi can supply. What probably happened was that it worked at first but then an increase in CPU load pushed the Polyfuse into action. This was then increased by the HDD when I tried that to test it. Now the PolyFuse has a lower limit so neither will work - I have to wait for the USB PSU to arrive before I can the Eruptor back in like I did before
- the PSU isn't supplying 5v, probably due to poor cabling
- the PolyFuse doesn't recover fully when stressed but this is no big deal
Thanks folks and in particular jbeale :-)
This has also been very useful in giving a way to measure what voltages USB devices consume.
