Forget the buttermilk powder. Go for the real thing! You won't regret it! The addition of baking soda and reduction of baking powder is due to the higher acidity of the real buttermilk.
 

My Super-Duper-Sized Pancake Recipe

Heat griddle to 350 degrees, if using one.

6 cups flour (I use ww soft pastry)
2 T baking powder
1 T baking soda
1&1/2 t salt
6 eggs
6 cups buttermilk
3/4 cup oil

In a large bowl, thoroughly whisk together (sift, if necessary) flour, baking powder, baking soda and salt. Set aside.

In another large bowl, whisk eggs; add buttermilk and oil and blend well together. Add to dry ingredients. Stir just until fully mixed.

Do not grease griddle. It's unnecessary. Pour about 1/4 to 1/3 cup of batter per pancake, depending on your preference. Bake until edges become a bit dry and middle is bubbly. Flip and bake until bottom is golden brown.

Remove to cooling racks. When fully cooled, store in Ziploc bags. Freezes well.