What is the maximum refund that you can get by adding a child as a dependent in 2017? My refund amount increased by $1,240. How does this compare to the maximum amount?

I was surprised to see that my refund increased by $1,240 (of which $1,134 was from my federal taxes). I thought the limit was less and that it would be reduced given my income. I'd like to know this to decide if it's better to let my ex-wife claim her as I have read that certain income thresholds reduce the refund.