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Oil Filled Dummy Load for DEC H777 power supply

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intabits:
This is a cheap and cheerful method to make a dummy load that will happily dissipate 150 Watts for 15 minutes, which is long enough for most types of testing.
It consists simply of PVC piping with end caps, immersed in mineral oil.




In this instance, it is used as a fixed load for the H777 power supply used in Digital Equipment Corporation PDP11/04 and PDP11/34 minicomputers.
It appears as a fixed load of about 95% of rated current for the four voltage supplies provided by the H777.






But the method could easily be adapted for higher power dissipation, or longer operation:-
- Thicker tubing, and/or higher volume of oil.
- The thing could be weighted down in a bucket of water.
- The containing tube could be made of aluminium, with heatsinking and/or fan cooling.
- Several standard fixed resistances could be built inside, with Wires be brought out to a switch panel,
  so that various switch combinations could select a range of different loads.
- Even an active electronic load could be immersed inside to extend its specifications.

Schematic used for this unit:-


Video:-

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