Defective stack of coins

You have 10 stacks of coins; every coin in exactly one stack is 1 g too heavy. Genuine coins weigh 10 g each. Using a digital scale, what is the minimum number of weighings needed to identify the bad stack?

Show hints (2)+
  1. Take a different number of coins from each stack.
  2. The excess over the expected total points straight to the stack.

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