Wiring – How to use a 12VDC bilge pump with an Intermatic timer for pond circulation

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I have built a small rock water feature using a 12V bilge pump as the circulator. I purchased an Intermatic 12V light timer/transformer to power the pump.

There are two connection terminals on the timer which I assumed connected to the two wires on the pump.

When I connected the pump to the timer the pump ran rough and would not pump.

I checked the pump on my car battery and it ran great, fast and smoothly. I connected one wire to the + terminal, and the other to – terminal.

So my question is how should I correctly connect to the timer terminals?

Best Answer

A couple things could be going on, as @bib and @BMitch allude:

  • Your transformer could be putting out AC 12V instead of DC 12V. (Sometimes these are labeled VAC and VDC, respectively.)
  • Your transformer may not be able to supply enough current to power the pump. The pump and transformer should both have their current listed (in the case of the transformer it will be a max current). If the pump is trying to draw more than the transformer can supply, both will be unhappy.
  • Your pump could be sensitive to polarity and you've got the two wires crossed. I think most DC motors should work forwards and backwards, but of course the pump will only function properly one direction.
  • If the transformer is cheap it may be putting out "noisy" DC power which the pump isn't liking. A car battery puts out pure DC power but the transformer needs to rectify and filter your household AC power, and some transformers are better than others.
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