Repeat timer hacked for 35 minute hydroponic cycles

[GrowColt] shows you how to modify a lamp timer for use with hydroponics. You can pick up this type of mechanical timer at most local big box stores for around $5. The timer plugs into an outlet, and the device you want to operate plugs into it. [GrowColt's] end goal is to make the timer repeat every 35 minutes, routing power to the connected device for about 50 seconds each cycle. It will operate the pumps and misters in his hydroponic garden to keep the plants hydrated and keep the nutrients flowing.

We’ve embedded his detailed process after the break. It’s not all that difficult, requiring a few common hand tools, some glue, and rubber washer. There’s a gear box inside which controls the timer. Reorganizing that gearing makes it repeat more frequently.

Not into hydroponics, but looking for watering help with your greenhouse? Check out this system which monitors water sensors and dispenses H2O accordingly.


  1. adamziegler says:

    Seems like a simple hack for the specific mod. Nice.

    Not sure why 1/4 of the height of the gear shaft was removed (6:20) prior to covering it with another gear. Seems unnecessary.

    Another idea… PWM the motor?

    • GrowColt says:

      The reason we trim down the shaft is because of the new spacing with the neoprene washer will cause the top gear to contact the gearbox case and create unnecessary friction, eventually killing the small motor.

    • D says:

      I’d guess he shortened the shaft because the hole in the topmost gear doesn’t go all the way through, but is only just deep enough for the length of shaft it went over as manufactured. Assuming that’s the case, if he didn’t make the cut, he wouldn’t be able to put the composite gear all the way back down the shaft into the socket the lower gear came from.

  2. zrzzz says:

    I went into a hydroponics store once because I thought it might be cool to grow my own vegetables indoors. Now the state police fly over my house all the time. I liked it better before 9/11 when we still had some presumption of innocence. Now you can’t even buy cold medicine without someone somewhere running your name through a database. Yaay… freedom.

  3. N0LKK says:

    So is this now an open hardware project? I see another Ebay seller is offering essentially the same thing for 2 bucks less, competition can be a beotch. Not to take away from the hack, but plugin timers that can be set at 15 minute intervals are available. In the event timer has to be purchased, why not purchase one of those? Is there something magical about the 40 minute timing interval that 5 minutes would make a difference?

    • Nick says:

      It’s not the 40 minutes that’s magic, it’s the fact that on-off intervals can be set in multiples of 50 seconds. That’s much finer than a 15 minute resolution.

      • Nick says:

        But, to support N0LKK’s point about careful shopping, I recently bought an electronic version of a 24-hr lamp timer for $2 at a dollar store, and it can be programmed with 20 pairs of on-off settings, to the minute. That might suit hydroponics applications.

        It’s pretty much like the mechanical version, plugging into the wall, with one 2-prong outlet on the side. It has 7 buttons and an LCD for programming (like a VCR), and trickle-charges an internal battery to retain settings over power failures.

    • Simon says:

      You don’t want to have the water running for a minimum of 15 minutes. Increasing the speed of a full cycle to 30-40 minutes enables you to control the timing in increments of about 20-25 seconds.

      Nevertheless each enabled step amounts to 15 minutes of watering per day of course…

      • Dude says:

        I bought 2 timers last X mass for 12 bucks with a 12$ rebate, you can set them in a 15 min resolution, each one of those stops is 15 min.

        so if you need 30 min 3 times a day, just set 2 nubs where you want them, problem solved

        other timers are even better cause they are not on a fixed resolution, you can set them to 12.8 min if you really sit down and fiddle with it…

        now more on the point these things loose time like mad, you can sync them one night and they will be a handful of min apart 12 hours later. so its not like your getting something even remotely reliable int the first place

      • Jason says:

        Dude, what if you want one minute out of every seven or three minutes out of every fifteen? The only off-the-shelf solutions are cycle timers that run about $150 a piece. Hydro/aeroponics and mushroom cultivation are both applications that require this level of fine tuning.

  4. Liard Nelson says:

    protip: Digital Timers consume much less power themselfs, those analog beeetches are hungry.

  5. Devilbunny says:

    zrzzz, try looking for advice on what grow lamps you should get for any plant other than pot. It’s impossible; I gave up. I wanted to keep my tropicals from losing most of their leaves during the winter without having to drag them out every day and put them back in for the freezing nights (I live in the South, days below freezing are very rare). Still no idea what the best way to do it would be, other than to tear down the workshop I store them in and put a greenhouse in its place).

  6. bob says:

    I work with a company that manufactures this type of product.

    Unfortunately, it may not last that long the materials of the cogs are chosen for a 24 hour cycle the material may wear far too quickly and jam, not to mention the silicon based crease my not be upto the job of lubrication,

    But good luck on keeping it running.

    • RealProsTipBetter says:

      Dear Bob from the mail room,

      Thanks for your concern about the life expectancy of our ‘cogs’ (called gears since they are no longer made of wood). Had we known that you enjoyed giving off-the-cuff advice on the Internet in your spare time, we would have pointed out the following facts to you:

      All of the gears are made of the same tough self-lubricating plastic. Most of the gears – all the fastest ones – are traveling at exactly the same speed before and after the conversion*, and their lifespan is likely to be unchanged.

      In the future please check with management before discouraging potential customers from buying our low-cost, well-made products for any reason.

      *Unapproved tampering voids warrantee, but is otherwise none of our concern.

      CEO, Cheap and Reliable Timers Inc.

  7. deep says:


  8. Snoo says:

    I wonder what kind of plants all this trouble is going towards. :)

  9. Alex says:

    I used digital timers for mine, only a few dollars more and very easy to set up.

  10. silverpalm says:

    i use hyrdo for my vegatable wink wink lol
    and i also have the ruuning pumping its only the light i have on a cycle,i perfer old fashioned feeding so i can keep a eye on things but this would be good to have a setup so you just leave it and come back,however i have seen ways of doing this rather than modding the timer

  11. NATO says:

    A hack would be modifying this device to do something it was never meant to do, such as slapping rabbits. In this case, he simply made minor modifications to the internal mechanism and changed the period of the mechanism…. I’ll call this a “mod” at best…

    Damn stoners :P

  12. Jason says:

    I just did this mod. I didn’t feel like going to ebay to get that stupid triangular driver, so I made one out of a metal rod using a dremel. It worked well enough, but I replaced the screws with regular phillips ones when I reassembled.

  13. Brian Shiau says:

    Does this work with analog timers from other manufacturers such as Brinks or GE? I cannot find the Westek analog timer in any big box store in my area.

  14. bygph says:

    I made a video addon for the video in this hack, that shows how to do this with a Westek timer.

  15. robin says:

    anyone know where i can get the 5/32 washers from in the uk…?

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