My Van de Graaff Generator is not generating sparks, how can I fix it?
Humid conditions are detrimental to all electrostatic demonstrations. Static electricity experiments and demonstrations always work best on a dry day. Air-conditioned air, or heated winter air tends to be drier, and therefore more conducive to electrostatic demonstrations.
If the conditions are right and the Van de Graaff generator still isn't charging, check the upper and lower comb positions. The gap between the metal combs and the belt needs to be approximately 0.5-1 cm. Make sure the combs do not touch the belt and that the combs point directly at the belt.
The Van de Graaff generator still isn't charging? This typically means that the belt and lower pulley need to be "reconditioned." Over time the belt and lower pulley may absorb moisture. To drive off the moisture, remove the belt from the Van de Graaff generator. If the belt appears worn, frayed, stretched-out or discolored, replace it. To recondition the belt, use a hair drier to dry it out for about 10 to 15 minutes. Make sure the belt does not get too hot or it might melt or burn. After the belt has been dried with a hair drier, place it in a plastic zipper-lock bag with a small amount (half a tablespoon) of fresh talcum powder. Shake the bag up for a minute to completely coat the belt. Use the hair drier to heat the lower pulley of the Van de Graaff generator to drive off any moisture that may have accumulated. Again, do not get the pulley too hot. Then, shake off any excess talcum powder on the belt and place it back over the pulleys of the Van de Graaff generator. Reassemble the combs and dome as necessary. The Van de Graaff generator should function normally.