I am setting up my first SP20 but it is unstable and stop working after several minutes .

Try lowering your miner PSU limits.
do this above:
right now my settings are:
copy them use them note make your fan 70 not 50 these settings are under clocked they give me 740 watts and 1313 gh hash. you should be stable with these numbers. if you are good then try to creep them up a bit. or just leave them as they are very power efficient settings. I can stay between .55 watts and .6 watt with under clocking

