For most cases, a voltage ranging from 70-95 volts should work, voltages greater than 100 V might heat your buffer and melt the gel or cause distortion in your DNA bands. You should adjust these values depending on your electrophoresis buffer, the thickness, and concentration of your agarose gel, dimensions of the system's cuvette. There's an empiric formula used to determine the optimum voltage: (length of the matrix)* 5 to 8 V, for example, 10 cm of the gel * 8 V = 80 V.
I suggest you try different values to determine which one gives you better results.