I need info on what size of a step down transformer to use. I want to use 110 V AC to run a 24 VDC Lawnmower (no battery). The motor is Eco Star Lem 015EZZ

It isn't quite that easy. You can only transform AC so you would first need a 120 to 24 volt transformer. Then you need a converter to go to DC or a bridge rectifier circuit. That 24 volt DC motor draws a lot of amps so you will need a good sized transformer and converter /rectifier. I just bought a 120VAC lawnmower on Craigslist for $40. Consider doing the same and sell the Battery unit.

Thank you for your reply, yes the dc motor would draw 10-15 amps. Wall warts putt out dc, I thought maybe I could use one .