Electrical timer that does this?

The 15A bit may be a problem. I'm sure one could be made quite easily. How accurate does it need to be? May I ask why you want one?

Yes I could make something with a 555 chip and a battery and a box and some R's and C a mains relay etc etc but I just wondered if there's some beefy timer-thing avaiable somewhere off the shelf I can just use. Accuracy is not an issue +/- 15 mins would be ok . It's just for some garage heaters I'm "experimenting" with.

ps Last week I finally scrapped a metal box and the circuit within that I made

Is this so you can turn them on remotely, by interrupting the supply? If so, why not use a remote controlled socket:

If not, you could use a PIR switch ("£4.99 from B&Q") plus a relay. Most PIRs do a self test when you first turn them on.

It's just the timer that's the "problem" - not where it is. Perhaps I didn't describe it very well in OP.

I wasn't sure if they were sure to startup on power up - although admittedly all the built-in ones on ext lighting I've tried have. Good idea - I'll check that out.

Many of them have a stay on feature if you have a small break in the supply. Probably not what you want.

However. They are very prone to failing shorted, not to mention that some will, if the power fails twice in quick succession, they may turn on permenantly.

I had a similar problem.

Yes one can knock up something with a 555 etc. and put it in a box. However, by the time power supplies are organised, it's not worth it.

Have a look at

In there you will find types such as staircase timers which will do what you want. Some are rated up to 16A as well....

Whats your budget?

For £100 you can get a siemens logo starter kit. Just have a search on siemens site.

I've been looking at various ones of these on the RS site for an application. They have Moeller, Telemechanique and Misubishi as well.

the ranges available are quite large, but it seems to me that the Moeller ones have more functions and options.

Any thoughts?

Bit OTT for this application. I found Entrelec MFE series of multi-function timers when looking for a non-retriggerable one shot for =

the "press for heat" function that the OP requires. Not quite sure what =

they do on power up. Try looking at RS 281-3915, oh begger discontinued =

but they where only =A330 + VAT. Not sure it would do 16A but a BFO contactor driven by it would...

I can vouch for the siemens logo, as I have used a on few projects at work. Maybe a little ott for this application, but a din rail mounted timer can set you back £30!. Download the software and have a play with it. You can design and simulate the software before even spending any money!

Yes, I did download the software and play with it a bit. The documentation is quite well written as well, with worked examples as explanation.

I was prompted to look at this for much the same reason. This was wanting to have something to control various lighting, heating, extraction, battery charginf,..... systems in my workshop, I realised that this was going to result in quite a lot of timers, relays, etc. to do it which seemed to be becoming quite expensive as well as inflexible.

All of the various logic controllers seem to have +/- quite similar functionality in terms of the logic blocks etc., and using a PC, it would appear that it's pretty quick to prototype and test befoe implementing.

A few questions though:

- What sort of projects did you do and were there any things that you wished had been present in the Logo! that weren't there?

- Did you find the amount of storage and the number of logic blocks (130) enough? Did you need to optimise and take stuff out to fit the programs in?

- Did you know if it's possible or did you use any of the external interfaces at run time? By this I mean use of the serial, EIB or AS buses to connect to another system. Here I'm thinking about if I wanted to connect to an external computer etc. for logging or other control... It seems that the PC serial interface is predominantly for downloading progrsms to the Logo! as opposed to run time use. I'm not that familiar with EIB and AS buses.

Not sure what your description is but try this :

EK320A 0-2 hour Electronic Timer Adjustable =A321.15 each

The lovely U6047B chip really designed for things like car rear window demisting was ideal for this. Could be toggled on and off or made to start at power up, etc. And could also drive the usual car 30 amp relay directly. Easily set from a few seconds to many hours via a couple of external components and very immune to PS problems. Its main virtue over a

I've used them for a pump over-run on my CH system and also for a Ni-Cad charging station to give the required 14 hour charge for cordless tools which I've modified to not cook the batteries.

permits.

At the moment I'm going full circle to the 555 idea. I think just a 555 monostable triggered and isolated from the mains by small relay (series HV cap to get it to pulse) - contacts to trigger the mono. They O/P to another relay (via a 1A power transistor) to close the 15A contacts. The user input button is then easy too (and safe as is on the relay isolated side of things). Clumsy. Yes probably, but safe, inexpensive - and I think it may even work!

sheet.

It's a 14 bit divider, and oscillator, in one chip. Add a capacitor from VCC to the MR pin, and a resistor to ground (say

You set the RC network so that it oscillates at about 0.5Hz, then 7200 seconds later bit 14 goes high, conducts through the diode to RS to short out the clock generator at high.

From bit 14, you run a resistor/NPN transistor to the base of a 5V relay. (with appropriate snubber to stop it frying)

Total parts cost - apart from the relay, maybe 1.50.

Dave, have you got a UK source for these? RS and Maplin's don't seem to list them and Farnell's website is down for the weekend.