60
It seems that i will run for much longer with less number of devices.
I think this hub it is defective by design and cannot provide more power to each of the usb than
0.5Amp.
The power supply which is used is 12V DC, 5A. Shall i try it with a stronger power supply?
I may give it a try with dwc_otg.speed=1.
If it runs longer with fewer miners then it is almost certainly a hub power problem. 12V*5A = 60W = 3W/port = 600mA/port MAX (assuming 100% efficient power conversion). So it seems that the hub is designed to only deliver 500mA/port.
I doubt a bigger 12V power supply will work as the 12V - 5V conversion in the hub is going to be the limiting factor.