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@danielmalkin wrote:

Cost basis was $38,975 and took max Section 179 of $11,560 in 2017 (so depreciable basis of $27,415). 

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Because you did not elect our of Bonus, you are wrong about your depreciable Basis (for optimal results, you should have elected out of Bonus).

First year is $11,560 of §179 plus $13,708 of Bonus depreciation (50%).  That leaves your depreciable Basis of $13,708.  That gives about $3,495 for the second year using 150%DB.

Between §179 and Bonus, the preliminary amount for the first year is $25,268.  The Luxury Limits reduce then that to $11,560.  But that 'extra' $13,708 does NOT get added to the depreciable Basis for the next 5 years.  It goes to the END of the Recovery Period, when it can then be used (up to the Limits).

For future reference:  If you had elected OUT of Bonus, it would have been better.  And also only claim $8,000 of Section 179 which would further increase the depreciable Basis.  In the first year, you would still 'max out' the Luxury Limits because you would have also used $3,560 of 'regular' first-year depreciation.