Because the original design thought, relays and "Waterproof Cooling Fan" of the current will not be great, each has 100mA nearby, but also add up to 300mA, with conventional optocoupler output triode connected to (this circuit itself has 1V drop), because the transistor voltage drop, actually to relay and "Waterproof Cooling Fan" in the voltage of 11V. In practice, it is indeed possible, but in the production of a number of more than 100 found that individual machines, there is a relay does not pull phenomenon, some machines, and even reverse the display, there will not pull the relay, the final test found This relay turn-on voltage is too low, in the vicinity of the normal 9V, 10V and the individual to more, and because of this connection leads triode 1V drop, it will cause a certain probability of failure, so for safety reasons, "Waterproof Cooling Fan"production side of the output voltage from 12V to put increased to 18V, with full margins, would like to solve this problem.