I bought the online a sainsmart 8 channel dc 5v relay module for arduino. When i powered my system up, the module turn really hot. My connections are, Vcc to 24vdc, Gnd to ground, In1-8 to the digital outputs of my arduino. Everything seemed connected right.. Another thing, when I tried pulling out the jumper connected between Vcc to JD-VCC, then powered it up, the relays and other components didn't turn hot, but the problem is, it didn't respond to the digital inputs that I sent from the arduino..
