Looking for a 250vAC Mains > OFF timer circuit

Den mandag den 21. oktober 2013 09.05.50 UTC+2 skrev Charlie+:

3kw that's a big coffee machine

when I was at universitty we had to have timers on coffee machines don't remember any names but it was just a plug in timer, so it could be set to only be on at certain times and it had a manual 1 hour override

-Lasse

Google stairway timers. There's probably one with a 30min delay that would do the job - you may have to use it to switch a relay capable of handling 3kW.

Timers are free add-on now with $1 embedded uC on Smart Coffee makers.

To add one to a not-so-smart coffee maker does not seem worth the trouble w ith the retrofit involved. The CMOS 4060 clock counter chip could be used with appropriate reset input and timer period output for interfacing to a 1

5A Triac or Relay with suitable DC power avail.

Doubt it would do 3kW, but it could switch a relay or contactor.

Cheers

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Syd

Are you sure all of the temperature limit switches are working? I wouldn't expect a normally operating machine to cook itself like that.

At a previous job, the safety people insisted that the soldering irons had to shut off after a while. For the older irons that didn't do this automatically, we got switches that consisted of spring-wound timers in an enclosure with a line cord and a socket. The soldering iron power supply plugged into the switch, and the switch plugged into the wall. These were designed to cope with US-standard 120 V, 15 A (1.8 kW) loads, but I am sure something similar is available for 240 V land.

It's also pretty easy (here) to get spring-wound timers that are designed to install in a standard wall switch box, for running vent fans, heat lamps, etc. These have maximum on-times of anywhere from

30 minutes to 12 hours. Put one in a box with an outlet, cord, and a plug to make your own.

might do what you want, if "countdown" means what you hope it does. You wouldn't use the "turn on at 7 AM every day" function; you'd just use the "run for 30 minutes and shut off" countdown function.

or will definitely do what you want, and have a simpler user interface too (one button).

Standard disclaimers apply: I don't get money or other consideration from any companies mentioned.

Matt Roberds

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Schematic?

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http://www.amazon.co.uk/Energenie-Minute-Down-Timer-Plug/dp/B003QPCH2A/ref=cm_cr_pr_sims_t#productDetails

Reminds me of the time my friend set up a coffee pot at work as he usually did the night before, which turned on and perked the next morning on a timer, but forgot it was the Friday before a three day holiday weekend. So on Saturday it perked and sat there hot for a few hours and turned itself off, then repeated it on Sunday and Monday and on Tuesday when the crew came in. There was one guy who really liked strong coffee, and when he got his big cuppa he remarked that "this is the best coffee you have ever made"!

I have a fairly simple little circuit that fits in an octal relay can, and is designed to operate as a voltage sensing relay for 80-250 VAC, but it

uses a PIC so it can do a lot of other things too, such as a delayed turn-off timer. It has a DPDT relay which can handle 250 VAC and 8 amps,

with breaking capacity of 2000 VA, and it's only about $3. You could power the relay and the coffee pot through both contacts for 16A capacity, and it could shut itself off after 30 minutes or whatever time you wish. By using a NO pushbutton across the contacts it will latch on but then need another

push to start up again. The parts for this are just $10-$20, and can be built on a perfboard. I enjoy programming PICs, but YMMV.

Video:

A really easy and cheap way to do this is a microwave oven timer (or kitchen timer). Older microwaves had a spring-loaded clockwork dial you could crank to 30 minutes or so and it can handle a 1000W microwave so maybe also a

3 kW coffee pot. And BTW that sounds like a really big pot!

Paul

I also have a toaster with broken timer; so, i am in the process of building an add-on timer. I would probably use a 5V AVR, since my 5V/20mA,220V/10A relay won't work with 3.3V. My PICs are 3.3V only.

It will have some buttons and LEDs (any combination can be on):

1. 1 hour delay
2. 2 hours delay
3. 10 hours delay
4. 1 minute cooking
5. 2 minute cooking
6. 5 minute cooking
7. 10 minute cooking

Still thinking if i need a GO button or not.

Yank the over-temperature cutout and replace it with one that has 10oC lower setpoint, this will double the life of the gaskets.

A bathroom timer plus large contactor should do the job. Bathroom timers are the ones that are customary so people can let the fan run for a limited time after a major stinky deposit or after a hot shower. Hardware stores and Internet places have those, even fancy digital push-button ones:

On many of them you can also press a button again for more time before it lapses.

You need to have 120VAC available (can be a small transformer as well) and a big enough contactor with 120VAC coil (can be bought at electrician places in town).

--
Regards, Joerg 

http://www.analogconsultants.com/

The LM8560 LED alarm clock chip (which is typical for that application) will turn the aux output on for 60 minutes if the alarm is not stopped. so probably three one hour runs, (less 3x warm-up time.)

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you could use a transistor to drive the relay.

does this toaster use a electromagnet to hold the bread rack down or does it use an expanding hot wire?

led illuminated buttons would look good :)

what needs 10 minutes toasting?

probably not, my microwave in simple mode has buttons for 1,2,3,4,5,6 and 1/2 minute

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Then i also need a LDO from 5V, and 3.3V for the PIC. AVR can run from 5V directly.

Sorry, it's a toaster oven, with a door.

Frozen breakfast, out of the freezer the night before.

On Mon, 21 Oct 2013 04:32:41 -0500, John Fields wrote as underneath :

Brilliant - Just perfectly hits my spec. and all for a few quid!! By the way the ~3Kw part was not for this particular coffee maker but in case of wanting to use it for other things eg, heaters... Thank you John, Matt and to all others for your sensible suggestions. C+

On Mon, 21 Oct 2013 05:51:01 -0400, "P E Schoen" wrote as underneath :

snip

I like this solution, and a visit to the local dump would probably do the trick for peanuts! C+