Building 420 watt Dump Load (UP DATE)

[snowcrow]

  I thought I'd share a few pictures of my small temporary setup for a dump load.  I decided to leave the Air-X on it's own built-in regulator because of the dump load's small size.

  Here is the dump load before I added the heat sink and fan.  The orange snap disc at one end was moved to the heat sink so I could add one more 5 Ohm 30 Watt resistor, making 15 parallel resistors in all.

  Here is the dump load mounted and ready to be wired in.  The dump load is mounted on 2" standoffs, although it doesn't so in the photos!?

  Just temporary, I'll just cannibalize the thing for parts when I finish building my 10' 12 volt Mill and LARGE dump load later this summer.

Snow Crow

[Drives]

Looks good, those "Dale" style resistors can handle high heat when properly mounted to a heatsink.

Couple of observations

If the heatsink has a flat surface on one side, and the Aluminum plate that the resistors are mounted to is flat on the opposite side of the plate, I would mount the heatsink on back side.  Flat surface to flat surface, very thin layer of heatsink compound.

If the heatsink, as currently mounted, is making solid connection to the top of the resistors, then the way you have it will probably work fine as well.

Second, you should always mount a heatsink with the fins running vertical.  The "Chimney Action" helps to naturally move air across the fins.  Horizontal positioning, even with a cooling fan, typically does not move as much air across the fins.

The snap action disc is a very good feature, does it control the fan?

Are those circuit breakers/overloads in series with the main leads running to the resistors, or just terminal blocks?

I notice many people mounting heatsinks hoizontally, especially inverters.  Heat (in my opinion) is the #1 killer of power electronics.

[snowcrow]

  Thanks Driver for the good advice!!  The resistors are making good contact with both the plate and heat sink.  I did use the compound on both sides of the resistors as well.

  As for the way it is mounted, I wasn't sure that vertical would be best in this case?  As it's mounted now, I thought the air could chimney up between the resistors and the fan cooling the heat sink would be enough, but maybe I was wrong?!

  Yes, those are 50 amp short stop breakers (auto-reset), but NO, they are not in series with the dump load.  I just used them as terminal blocks, for lack of something else to use at the time.

Blessings, Snow Crow

A.K.A. (Chief Run'a'muck)