Bar to discharge about 150 (7)
I believe the answer is:
exclude
'bar' is the definition.
('exclude' can be a synonym of 'bar')
'discharge about 150' is the wordplay.
'discharge' becomes 'exude' (I've seen this before).
'about' is an insertion indicator.
'150' becomes 'cl' (roman numerals).
'exude' going around 'cl' is 'EXCLUDE'.
'to' is the link.
(Other definitions for exclude that I've seen before include "Ostracise" , "Omit or shut out" , "Keep out" , "Leave out, omit" , "Debar" .)