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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?

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Are you sure the timer/transformer is outputting DC? – bib Aug 5 '13 at 17:21
What about amps? – BMitch Aug 5 '13 at 17:25

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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the transformer is intermatic ml121rt. in: 120v - 60hz out: 12v, 121 w max. the pumps are johnson pump 750gph 12vdc 3 amp. i want to run 2 pumps from the same transformer. – user14370 Aug 7 '13 at 15:20
the transformer is intermatic ml121rt. in: 120v - 60hz out: 12v, 121 w max. used for low voltage outdoor lighting. the pumps are johnson pump 750gph 12vdc 3 amp. i want to run 2 pumps from the same transformer. – user14370 Aug 7 '13 at 16:07
OK, looking up the specs, that transformer puts out 12 volts AC current so this isn't going to work. (I just looked up the specs on the Intermatic website and it says: "120 VAC input, 12 VAC output".) You should not hook up the pumps to it again or you risk damaging them (if they're not already). – Henry Jackson Aug 7 '13 at 18:50
thanks for the help....i would like your opinion on this setup as a replacement. timer; amazon.com/Amico-Digital-Power-Programmable-Switch/dp/… transformer; amazon.com/Schumacher-PC-6-120AC-Power-Converter/dp/B0012BL8LG/… – user14370 Aug 9 '13 at 20:57

I struggled with this same issue. Finally converted an old computer server power cord to run my bilge pump. It works great. You can get plans to convert this on the internet. Only took two solders.

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Some of the information contained in this post requires additional references. Please edit to add citations to reliable sources that support the assertions made here. Unsourced material may be disputed or deleted.

Instead of merely saying that the plans are available on the Internet, how about providing some links, or better yet, including them in your answer (if allowed by the owners' copyright). – Niall C. Jun 10 '15 at 5:26

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