Learnings from this project:
1) Electronic Load modules can be paralleled for additional amps and power capability.
2) Additional voltage capability needs higher rated MOSFETs.
Changes to Chinese load kits
1) The 5W SOURCE resistors reduced from 0.22R to 0.1R. Improves loss at high currents at the cost of reduced sensitivity at very low currents. The resistors were mounted off board to improve cooling.
2) Substituted output devices with IRFP260N MOSFETs. These are rated up to 200v working.
3) 7812 voltage regulator was used to stabilise the TL431 voltage standard.
4) 15v supply was used to drive 3). The fans power was came from before the regulator.
5) All the metal film resistors were discarded! They were the wrong size and rating to properly fit the PCB.
A note on MOSFETs
I ordered 8x IRFP260N devices. Two different types were supplied in the batch. Five weighed around 5.5g each and the rest around 4.5g each. Clearly they were not the same and this was confirmed when I compared the labels. The lighter devices also had a smaller label area. I purchased 3 more of the heavier devices for this project.
A better way would be to purchase 20x MOSFETs and 20x 0.1R 5W resistors and set about matching them in batches of 4. Matching MOSFETs was covered in Reply #33:
https://www.eevblog.com/forum/projects/upgraded-lm324-based-150w-72v-10a-electronic-load/25/