It that time of the year that outdoor dew points exceed 60^F in green grass climates. This data on the basement %RH verses the basements %RH. The finished basement has reached 69%RH. The house gets 80 cfm of fresh air ventilation to the mainfloor with the air handler "on" low. The lady that manages this home says this is enough of this "no dehumidifer" test.
The air in the basement is affected by the outdoor dew point and the moisture from the occupants providing moisture source. The material in the home along with slab under the carpet is absorbing the moisture. As the material moisture content rises, the indoor %RH rises. At +60%RH, the basements starts to smell like a basement.
Tomorrow the dehumidifier is maintaing <50%RH. The data is posted below via pdf.
May 2013 Wet basement data No dehumidifier.pdf