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Old 06-09-13, 10:54 AM   #1
Pirate
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Default Looking for water heater timer

Does anyone know of a elec. water heater timer, that can be programmed to turn on for periods less than 30 minutes? Like 15 or 20 minutes.
My current one has a min of 1 hour.

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Old 06-09-13, 11:01 AM   #2
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Harbor Freight sells a digital timer that is programmable down to 1 minute resolution. It can switch a 120V unit (up to 15A) directly or use a contactor for 240V.
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Old 06-09-13, 03:44 PM   #3
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Thanks, I didn't think of using a contactor, which I guess is a relay. Can you recommend a particular contactor and source?
I have a digital timer I use on my lanai metal roof wattering/cooling system that would work. It goes down to 10 sec. on or off.
Thanks again
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Old 06-10-13, 07:49 PM   #4
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I installed an Intermatic EH40 electronic timer several years ago on a hot water tank at my Parish hall. The timer wires inline to the heater, can be set for up to 7 starts/stops per day, has a manual "on" button, and a battery backup. The time can be set for as little as one minute. It has been in service for several years now, and has worked flawlessly. At the time it cost me about $135.00Cdn, and I'm sure you can find the same product in the U.S.

If you do a search on this site with the key word "hot water timer" you will find the thread. Never mind, found it:

http://ecorenovator.org/forum/conser...ank-timer.html

Last edited by Daox; 06-10-13 at 08:09 PM..
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Old 06-10-13, 09:22 PM   #5
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You can build a timer using a solid state relay like one of these:
Dayton 5Z972 Solid State Relay 5Z972 40 Amp | eBay

Some solid state relays need to have a DC trigger while others work off AC, they are NOT interchangeable.
Then get a cheap digital timer that has 1min resolution.
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Old 06-10-13, 10:45 PM   #6
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Beware that a SSR will need a heatsink if used anywhere near its ratings. (A PC CPU heatsink will work nicely.) A contactor will not and will be more efficient for this application. On the other hand, a SSR (or SCR/triac) can be used to throttle back the power with the proper control logic.
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Old 06-10-13, 11:39 PM   #7
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Small computer fans draw very little power, I have some on my desk that draw less then 2 watts and if you combine them with a heat sink everything should stay cool and happy, you can also get solid state relays that can switch 100 amps, so switching 30 amps is not an issue, but I agree that a heat sink is a good idea.
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Old 07-15-13, 12:19 PM   #8
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electric water heater timer - Google

God bless
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Old 07-16-13, 09:23 PM   #9
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What are the advantages of a water heater timer?

What's the thermal time constant of a water heater?

How does shorter time help?
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Old 07-16-13, 11:58 PM   #10
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Quote:
Originally Posted by ham789 View Post
What are the advantages of a water heater timer?

What's the thermal time constant of a water heater?

How does shorter time help?
For me, my WH is located inside my air conditioned space. Lost heat from my WH, means additional cooling $$$ and additional WH heating $$$. So, I have mine timed to run 30 minutes before dawn. I put a hi/low recording digital thermometer with remote sensor probe against the wall of my WH to track the temperatures, and adjusted the timing of the run cycles to fit accordingly. Mind you, my water comes out of the tap at 76F from the cold faucet, not that ice water you folks up north have to heat up and shower with.

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