Triac for AC?

Hey Craig,

Won't you need a Triac for AC switching?

Regards,

Device Info Needed?

What are the characteristics of and or what is the device that is outputting the 1 VAC?

What device will the 12 VDC be driving, and or how much power (current at 12 VDC) will the output device have to drive?

Info

The 1 VAC device is a Walthers Traffic Light Controller.

When the red light illuminates, I want it to activate a relay that will send 12-16 VDC to an electromagnet.

Don't think so.

Don't think so.

Transistors

Been many years since I use discrete devices but all I do remember right now, you need DC to operate transistors.

Have to think about this for a while.

I have used a properly biased transistor to amplify AC but never tried to use AC to turn something on or off.

Rich

Question

Are you sure it is 1 vac? Have you measured the actual potential?

Rich

If rou run the

1.5vac thru a diode you will get about .5v DC half wave.  Add a electrolytic (polarized) capacitor between the output of the diode and ground (the other 1.5vac wire) and it will increase the voltage and eliminate most of the half wave function.  This small DC signal can now be applied to the base of a switching transistor to control your 12 volt circuit.  Google simple transistor switching circuits for some illustrations.  Finding the correct transistor is a process but not that difficult when using these low voltages.  Just about any will work.

Good News .Bad News

I found a circuit that uses an opto-isolator chip to drive the transistor which in turn runs the relay.  Bad news is I have no way to post this diagram.  I think I might even have all the pieces necessary for you build this.  Call me .  Michael in Oregon  541-946-8796

...

That's what I thought...

No offense, but it kind of spoils the discussion if you take the solution off forum.  I for one would be interested in the outcome.

Regards,

Circuit

I vaguely remember doing something like this back about 1970.

Had a low voltage AC signal and used a diode and 1000 ufd cap to get DC. I recall using three resistors to bias a transistor and used an open collector circuit to operate a 12 vdc relay. Junk box parts but it worked. Don't remember any other values.

Got the idea from a old train power pack that at the time that used a selenium rectifier to convert low voltage AC to DC. The capacitor gave ne a reasonable DC voltage. Might have added another filter cap. Time's fun when you are having flies.

Rich

Is this the device?

If this is the Traffic Light Controller you have the interface is actually very simple as the LED outputs are DC. You can use any of the outputs to drive a transistor, opto-isolator or solid state relay. In this case I would probably recommend a solid state relay similar to the one noted below.

Solid state relay example with LED input ( http://www.clare.com/home/pdfs.nsf/www/CPC1906.pdf/$file/CPC1906.pdf). You would need to add a protection diode across the output to shunt any inductive kickback from the electromagnetic.

That's it

Yes, Ken, that's it. Was pretty sure the sparse documentation said the output was AC but maybe I misread something. Was going to hook it up to the multimeter this weekend to confirm - but I may be able to achieve what I wanted with a light sensitive switch I found. Thanks for the scoop.

Ken K has the answer for

you Craig.  Much simpler than the opto-isolator that I have.  That was one of my questions, are you sure it's AC?

Working with DC is much easier.  I do not have a scanner to post my diagram.  Sorry

1VAC Relay driver

The 50Hz AC on the left is 1v, whereas that on the left is 9v and capable of lighting the lamp. The 6v DC drives the 6v relay when the transistor is on. The transistor is switched by the 6v via a 30k resistor provided that the AC sensor signal is zero. When the signal is 1v the negative part of the signal drains the 10muF capacitor via the two diodes - one diode would still drain the transistor at 0v.

If the light needs to light when the signal is 1v then other terminal of the relay could be used or a second transistor could be used to create an inverter.

The above is a working Yenka model.

The lower model uses 16vDC as the driver. DC doesn't need a relay.

Archie

@Archie

Is that your other left?

Electronics

Not contributing to the discussion here, but something I've noted to the magazine is the prevalence of electronics articles. Back in the day this used to be common in the legacy model press, but is almost nonexistent now. I'm happy to see that there's at least one model press publication with a healthy interest in electronics.