My review and basic instructions on the Harbor Freight Thunderbolt Solar 68738 Solar charge controller. Although advertised and labeled as a 500 watt charge controller, documentation in the package indicates it is only rated for 18 amps, which is more like 300 watts of common panel power. Price ranges from $60-$90 depending on coupons and sale prices. It is the best charge controller available at Harbor Freight, but not quite a high grade unit. I suggest keeping a spare on hand if you use this on your power system since these lower grade charge controllers tend to be the “weak link” in power systems, although this one seems decently built and simple to use.