Simple enough project.
I've a motor in a machine, I want to put time (say 3 mins) on a clock, hit a button, and the motor will run for 3 mins.
Does anyone know of a single timer switch unit that would fit the brief?
Ta.
Is the motor too powerful for a time delay light switch? If not, do you need high precision on the 3 minutes?
As a starting point look at . tlc-direct.co.uk/Main_Index/Timers_Index/Timers_Time_Delay/index.html
If the current rating is not high enough, use the timer to trigger a relay/contactor
Malcolm
Let me take a 'wild' guess at your answer should the OP's replies be in the negative...
Use a 555 timer chip (with transistor driven 12v coil relay and mains voltage 10A rated contacts) to build a timer module? :-)
One problem with a 555 for long times (above a few seconds) is that the first time they are switched on they take longer[1] to start up the first cycle while the capacitor charges this can be as much as a 30% error in the first cycle.
[1] can;t remmebr if it;s longer or shorter depending onn the o/p required
Maybe one of these will do what you want (assuming mains single phase) ?
There's lots of timer relays on the market. Look at Rapid, CPC, or RS. I always use the ones that mount on a valve base because they are very easy to test by substitution.
I usually use both poles of a double pole relay in parallel to double the current rating.
Bill
Bloody poles coming over here taking our switching jobs ;-)
Thanks for all the responses.
I've got some Crouzet 814 timers but getting a headache looking at them. Might just man up and get my head around how to wire those?
I was going to say "Google for one shot din rail timers":-)
As used in microwave ovens and similar
Owain
How accurate does it need to be? Brian
Yes I did this many years ago now. Also had one that varied the time according to light as well. There are loads of circuits of these sort of things. However i imagine there still have to be digital timer modules about in the hobbyist press in adverts as well which can operate a relay. Brian
Actually you can actually remove this problem by a high value resistor I seem to recall. I still think there are modules that enable you to do timer based stuff. I notice many clock radios have snooze buttons which can be made to do much the same thing if you take them apart. Get an old one. Brian
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