halogen dimmer

Homer J Simpson schrieb:

Hmm. As to my experience the triacs's gate normally is sensitive enough to get the triac triggered by two zeners. BTDT: 24 V halogen lamp controlled by a triac triggered by a "two-5.6-V-zener-diac".

CU

Reinhard

Breadboard it up and find out, a light dimmer circuit only has a few components.

But how does the zener help?

Sammy ha escrito:

Please notice that a BTB04-600 *IS NOT A DIAC*. It is really a 4AMP

600V TRIAC. Check for yourself here:

Before replacing it, you should find why the original exploded. Probably you have a shortcircuit somewhere in the bulb wiring.

I had a bad feeling that he didn't mean a diac!

Maybe, but IME they can and do burst like that with halogen loads because the bulbs present a very low resistance when they fail. Almost every time my

500 watt uplighter bulb used to fail it would take out the mains fuse, the triac or both.

Morse

Homer J Simpson schrieb:

If we talk about two back-to-back zeners: to provide a defined, constant threshold at which the triac becomes triggered.

On the other hand: for me it's just a quick and dirty solution for replacing a faulty diac if there's no original replacement at hand.

Bye

Reinhard

James Sweet schrieb:

...

As I wrote yesterday: BTDT ...

Bye

Reinhard

Correction to my last message. . . I should have said that the faulty component (diac) is marked Z2 07D431K. It is blue, with 2 leads. It measures low resistance in both directions. An exactly similar component on the board measures high resistance both directions. The component BTB04 600SAP (a triac, on a heatsink) is in the 300w lamp circuit which is working ok. In the 12v circuit, which has a transformer, are two transistors? Q1 and Q2, which are marked U07772. I don't have a schematic, but should manage a repair without it. == Sammy ==

You have to connect Zener diodes in series, not parallel, if you want it to clip at the same level in both directions. Connect the two cathodes or anodes together, and use the other set of leads to connect it into the circuit.

--
Service to my country? Been there, Done that, and I've got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida

On Mon, 13 Nov 2006 20:21:32 -0000, "Sammy" put finger to keyboard and composed:

The 07D431K sounds like a 430V, 7mm diameter MOV. The fact that there are two of them rather than just the one seems to confirm that it cannot be a diac.

In fact go here:

DS=3DContains

- Franc Zabkar

--=20 Please remove one 'i' from my address when replying by email.

"Michael A. Terrell" schrieb:

Hi Michael

That's exactly what I tried to describe with "two back-to-back zeners", but, obviously, this description has led to a misunderstanding - sorry!

Thanks for clarification

Reinhard

And they frequently fail shorted . . . and blow fuses

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Or shoot flames out the top!

Place I worked had some Reliance DC drives 5-100 HP range. The MOVs would be give an audible indication that the fuses were blown - not even the leads remained.

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So it's a MOV, not a diac, as Franc pointed out. It serves a passive role until there's voltage spikes etc and then presents a very low impedance across the mains and blows the fuse and usually itself.

You can leave it out really, there's no user safety issues I can think of, though a bad mains spike could take out the triac without one fitted, then you'd get an 'always on' lamp. It's not like it's a box of sensitive, expensive electronics though so I wouldn't worry about it too much.

At the very least, leave it out, replace the fuse and test the light, it may well work. Replace the MOV once you've cleared the fault, if indeed there is one other than the MOV itself, if you really feel happier with one back in circuit.

You're lucky you didn't put two back to back diodes or whatever in its place, they would have exploded and possibly embedded their casing in your flesh or eyes! What made you think it was a diac? Did you give the circuit layout a look over before you came to that conclusion? Diacs are always in line with the triac gate, never across the supply!

A friendly tip: Always be sure about components before naming them, misunderstandings can be very dangerous when dealing with mains operated equipment.

Morse

Another, more urgent repair has cropped up, so the faulty halogen is put aside for the moment. Thanks again for your informative and useful replies.

I thought overvolted triacs just turned on harmlessly, hence no need for a MOV.

NT