Timer

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I've been bitten by the vinyl steam cleaning bug and have been toying with building a steam "station" to get all my stuff in on place. I'd like to design it so that I press a button and power is applied to the steamer, but which will automatcially turn off in 20-30 minutes if I forget to shut it off. I see a couple of schematics that seem to run off DC voltages, but nothing that would appear to work for this. Is there a way to build a timer for this, or is there a standalone product I could buy to insert in my cabinet that would achieve this?
 
Hi,
the 555 chip and similar do not work too well for long time intervals. The leakage current through the necessary electrolytic starts to approach the charge up current and causes big variations to the set time.

There are specialised long time interval chips that are much better at doing this job.

A relay on the output of this timer chip can control the mains power to your equipment.
 
You haven't really said if you are OK constructing something or are looking for a kit etc.
Steam cleaning ? so how much current are we talking of switching ?

Andrew is correct about the 555 but tbh I feel it would work OK at the delays you quote, although not with absolute precision of course. There is a CMOS 555 which would be more suitable. It's a very simple chip to use,

555 timer IC - Wikipedia, the free encyclopedia

Or you could "adapt" a kit such as,

ESR Electronic Components - Velleman Kits

by changing a couple of parts to get a longer delay and putting the triac on a heatsink for greater power control etc.
 
What's your budget, and skill level....?

You could just surf ebay for an industrial control timer, and wire it in to the system. These types of timers can be set up to start on power applied, and reset/shut down themselves. Having a switching rating of 10amps at 120v is common. Just use "timer" in your search with either "omron", or "allen bradley". I just did it quickly, and found a few things that may work for well under $20, some under <$10.

Not everything needs to be a board level electronics project.:2c:
 
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