I'm completeing a project that I made involving an AC motor, but I need help designing a timer circuit for it, if some folks would be kind enough to help out.

Here's the motor's specs, from the manual itself:

120 V AC
60 Hz
3500 Rpm
108 Watts
(no listing for Amps, either in the manual or on the motor itself. Sorry)

It's currently switched on by a standard pushbutton switch. I plan to replace this with a rocker switch soon. Other than the switch, it's wired directly to main AC power - this is as it came from the factory.

What I'd like to do, is have a simple, but programmable timer installed in the base of the machine I built. Either with a dial-type selector or buttons inputting a time which is displayed onto an LED readout. The timer should have a range of 30 minutes to 4 hours. I want to be able to set the timer, then flick the switch, and it will run the specified time and then shut itself off after that amount of time. I also want to be able to turn it on and off via the rocker switch only, bypassing the timer if necessary.

I'll be putting this together probably via Radio Shack parts (in stock and special order). Cost is a factor, of course - cheaper s better. The timer does NOT have to be precise - a few minutes eiiher way is fine. I"m very handy and good building things, but I've not tried to build a circuit before - although I have modified and repaired some in the past, and my soldering skills are good.

Can anyone assist?

 

You should look at all electronics timer CAT# MCT-3. It's $5, originally made for a coffee brewer. All is local, too. You would have to reverse the switch since it's a delayed-on timer.

 

mneary,

Thanks for the tip. I don't know what you meant by "All is local", though. If you meant a local company to me, it's on the other side of the country, but a $5 timer might be worth the shipping.

I downloaded the spec sheet. It was just operating and install instructions. What did you mean by "reverse the switch"? Do I just reverse the leads on the auto on/off switch? How do I ID it?

Even if this isn't possible, this unit just might be the ticket. Specs say it's auto shut-off after two hours, which is right in my envelope. Less flexibility, but workable.

 

All is local to me, for you they are the other side of which country? In the US, their standard shipping is $7, so shop a little before you finalize your order.

If the auto-off is ideal for you, then you wouldn't have to 'reverse the switch'. But what I meant is that the output switch or relay probably has both NO and NC contacts.

 

Sorry about that - I meant the US. I'm in Florida. According to their website, All is in Cali.

Hmm... $5 for the unit, and $7 for shipping? That makes it a much different proposition. I could get a standard "plug in the wall" type of on/off timer at Ace Hardware for about that price. However, It might be worth it to hit a few thrift stores to look for a coffeemaker - that same unit or similar might be available cheap that way.

Still, though - might it not be possible to make my own timer? I do have quite a few parts already here (I have an LED readout, tons of diodes, resistors, capacitors, even a few breadboards, but no transformers or a timing chip yet - but they're not too expensive at RS). I'd try to design it myself, except for the 120 Volt problem and the fact that my electronics books aren't very detailed the way I'd need them to be for this. Most of what circuits that are in those books are DC circuits, as they're much easier to make & less risk involved.

I don't need this timer right away yet, but I'd like a couple of options.

 

When ordering surplus stuff, I frequently think about shipping but then I look at the total cost and if it's still reasonable I buy.

Last month I needed some 15 cent stereo jacks from them. I bought 20 just to make the total price an even $10. Still cheaper than driving 25 miles each way. So they were 50 cents each instead of 15.