This liquid cooled heatsink can be used to greatly extend the performance of the 4QD-300. The green line on this graph shows how the internal temperature barely increased after 14 minutes running at a constant 100A [the water flow rate was 3l/mi]
The pipe end fittings are suitable for 10mm i/d pipe.
It is quite easy to retro-fit this heatsink to the 4QD-300. The control board needs to be removed and then 8 x 3mm screws undone to remove the existing baseplate.