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Wire Wound resistor failure?

I've got an aquarium air pump on the pond to keep a hole open in the ice. This prevents the potential build up of toxic gasses that might kill the fish. However, aquarium pumps don't like the cold, it stiffens the diaphragm. If it gets cold enough (likely), the diaphragm will crack.

So I was looking for a simple solution (cheap) to heat my pump. I read over in the astronomy group, that they sometimes use wire wound resistors to build dew boxes for their scopes/cameras. Fortunately I had a supply of 1.2K ohm WR resistors that I scrounged many years ago. I think they're 5W (KKA5), but I'm not sure. I wired four of them up to give me 1.25K,which should only draw 12W. But they still generate significant heat. I'm getting about 30° C over ambient after an hour in my test container.

Will this lead to an early demise of the resistors?

Reply to
Bill Stock
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From your description you have a series/parallel setup of four resistors. If the resistors are reasonably close in value, the power dissapated should distribute evenly between the four. Just make sure you have a gap between the resistors so you don't create any hotspots. This should work out just fine for you.

If you're still worried about it, immerse the resistors in a glass jar filled with motor oil. The oil will transfer the heat to the glass jar and keep the resistors happy. Of course you'll need a cap and a means to feed the resistors inside of the closed jar.

Al

Reply to
Al

ice.

over

1.2K

(KKA5),

only

30° C

Thanks Al, yes a 2x2 setup. They're all spaced nicely. There's a slight smell, but not too bad.

Neat idea, but fish and oil don't mix.

I think once my air pump starts sucking cold air into the container, my 12W will be overwhelmed. Perhaps a heated sock would be better.

Reply to
Bill Stock

Uhhh, put the resistor assembly and the oil in a sealed glass jar and immerse it in the pond next to your pump. If you are afraid the glass will break, use a metal can, space the resistors away from the sides so they don't short, and immerse the contraption.

If you really want to try something a little more complicated, heat the pump's intake air. Attach your hose from the pump's air input to a cannister which holds the resistors. The heated air impinges on your pump diaphram and keeps it warm. The heated bubbles of air might be useful in breaking up the ice. And make sure the heated air is not so hot it damages your pump innards.

Al

Reply to
Al

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