Hello all you electronic guru's. I'm an inventor and a mechanical engineer so electronics are mystery to me. Check out my web <snip> to see one of my designs

I need assistance to add an intermittent switch/trigger to an existing circuit board. And I'll donate a dollar or 2 for anyone that can help.

I'm using the guts from a 240V AC power drill/engraver with a 170w motor. It has an on/off switch plus a RPM pot. In addition to these I'd like to add a trigger that engages the motor for only 1/5th sec to 1/50 sec. So it will have one mode; When ON the motor is at rest, when a trigger is pressed the motor rotates for a fraction of a second only. Plus I'd like to be able to adjust the time engaged within the rough parameters as mentioned.

Anyone got any suggestions?

Cheers

Ben

 

You are expecting a 170W AC motor to start, come up to speed, and stop in 20mS to 200 mS? With or without a load?

Ken

 

Don't forget that the period of the 60 Hz ac sine wave is about 17 ms, so that may be an added factor.

 

I suppose you could pre-load a decade down-counter with the number of AC zero-crossing transitions to count and then turn on a TRIAC for that number of zero crossings.

With 60Hz in, you'd get 120 zero crossings per second, so 8.333...mS per half-cycle. A TRIAC turns off automatically when current flow through it drops below a threshold value.

 

Ben,
If you're a mechanical engineer...surely inertia is in your area of expertise. Think about starting the physical mass of the motor's rotor plus it's load, running it at speed, and stopping it in the time frame you stated.

Perhaps if you elaborated on what you're actually trying to do, it might be easier for us to help.

Often, it's easier for us to help solve your problem, than help solve your solution.

Ken

 

Thank you for your responses. I can't reveal the nature of the invention unfortunately. No patents lodged yet.

I am currently using this 170w motor in a prototype and it works well. I'm simply using the on/off switch rapidly to test the concept. I most likely don't need the response as fast as 1/50th but certainly 1/5th with an option to go faster.

The motor when is in use it does not do a full revolution. It is a 30,000 rpm motor with great torque. It's the sudden torque that I need.

So with my basic knowledge I'm thinking a one-shot circuit that controls a relay?

 

Relays, being electromechanical devices, are slow to respond to input. Response time can exceed 100mS, depending on the device. You also wind up with pitting of the contacts.

Don't know what kind of precision you need, but a relay and timer for such short periods your accuracy will be dicey at best.

OTOH, a triac with a counter would give you increments of 10mS on a 50Hz line.

 

You could also use a zero-crossing TRIAC optocoupler. The advantage of this is that the driver automatically triggers on the zero crossing. Also, it's isolated from the mains - this may or may not be an issue for you.

An example is MOC3163-M (http://www.fairchildsemi.com/pf/MO/MOC3163-M.html), you will also need a external triac (the internal one can't control a significant load) and a few other components.

 

Thank you for your responses. I can't reveal the nature of the invention unfortunately. No patents lodged yet.

I am currently using this 170w motor in a prototype and it works well. I'm simply using the on/off switch rapidly to test the concept. I most likely don't need the response as fast as 1/50th but certainly 1/5th with an option to go faster.

The motor when is in use it does not do a full revolution. It is a 30,000 rpm motor with great torque. It's the sudden torque that I need.

So with my basic knowledge I'm thinking a one-shot circuit that controls a relay?

Another inventor who who thinks like an inventor instead of like a businessman is a huge red flag. Don't get sucked in.

 

You only need to search my user name or check out my profile to see that i'm well versed in business and inventing.

It makes sense that a relay would fail after excessive use. I'll look into the TRIAC octocoupler. Thanks for the suggestion.

Ben

 

You could also use a zero-crossing TRIAC optocoupler. The advantage of this is that the driver automatically triggers on the zero crossing. Also, it's isolated from the mains - this may or may not be an issue for you.

An example is MOC3163-M (http://www.fairchildsemi.com/pf/MO/MOC3163-M.html), you will also need a external triac (the internal one can't control a significant load) and a few other components.

So how much would you charge to design this circuit?

Note: please have a look at my Brakeboard website to see what I do.

 

So how much would you charge to design this circuit?

Note: please have a look at my Brakeboard website to see what I do.

I don't do consulting. However, if you found someone who did, you'd be looking at the average engineers salary ($50,000 - $100,000) / 12 (for one month's work.) That's going to be in the thousands.

You can simply use the reference design on page 7 of the datasheet. (http://www.fairchildsemi.com/ds/MO/MOC3163-M.pdf) Fig 10. Hot line switching. With a few hours of work, you could design a PCB to fit it. I'm sure we'd be more than willing to give pointers.

 

Not in topic but I see the word "patent"
Does patent protect ur invention?

 

You only need to search my user name or check out my profile to see that i'm well versed in business and inventing.

It makes sense that a relay would fail after excessive use. I'll look into the TRIAC octocoupler. Thanks for the suggestion.

Ben

U can always use solid state relays.

 

Not in topic but I see the word "patent"
Does patent protect ur invention?

The short answer to this important question is no. What a patent confers on you is the obligation to defend the patent against people who will infringe the patent and DARE you to sue. They have deeper pockets and better lawyers than you could ever afford, and there is no practical penalty for this behavior.

A businessman will bring the product to market, make hay while the sun shines and exit the business and move on when the copycats show up. An inventor will simply miss the boat, because he has his eye on the patent and not on the business.

 

The short answer to this important question is no. What it confers on you is the obligation to defend the patent against people who will infringe the patent and DARE you to sue. They have deeper pockets and better lawyers than you could ever afford, and there is no practical penalty for this behavior.

A businessman will bring the product to market, make hay while the sun shines and exit the business and move on when the copycats show up. An inventor will simply miss the boat.

 

Read this article by the famous Don Lancaster

www.tinaja.com/glib/casagpat.pdf

for the more detailed explanation.

Here is the Jeopardy quiz

A:It is worth less than a dime a bale in 10 bale lots
Q:What is an idea?