Thyristor as switch off device . 1

[AliBaba100]

Hi ,
What code no. of thyristor can be used to protect 220 volt ac 3 amp power source from over current by using thyristor with gate voltage which makes it off not more (5-9)ac volt

note : I want to build this circuit

patrin

 

[ScottyUK]

Use a recognised circuit protection device, e.g. a fuse, a miniature circuit breaker, etc. Why would you want to use a thyristor?


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Sometimes I only open my mouth to swap feet...

 

[jraef]

A standard thyristor does not switch off by command, it is "self commutating". This means that it stops conducting when the current passing through it crosses the zero point in the sine wave (and the gate is no longer energized of course).

There are special versions called GTO thyristors (GTO stands for Gate Turn Off) which have 2 gate signals,; one to turn the thyristor on, another to force it off. These have fallen out of popularity lately because there is a significant ringing effect on the line when they are gated off, which becomes severe electrical line noise that must be dealt with or it will damage other sensitive equipment.

But maybe we are missing your real point because of some translation problems. Are you really asking if you can turn power completely off with a thyristor, or are you wanting to LIMIT the output voltage by phase-angle firing of the thyristor? If you want to do limitation, it is not the thyristor that is different, it is the gating scheme.

 

[Skogsgurra]

I try to rephrase Ali's question:

"How can I build a thyristor controller that has 220 V AC as an input and outputs between 5 and 9 V AC?"

If that is the meaning of the question, there are two answers:

1 It is simple, use a standard dimmer or one of hundreds of application notes found on internet.

2 Do not do it. Transients are likely to turn on your thyristor and then you will fry your low voltage load. Use a transformer instead.

Gunnar Englund

http://www.gke.org

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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

 

[AliBaba100]

Hi,

I want very fast switch off device please.

AliBaba

 

[jraef]

Again, you fail to provide adequate details for eliciting a meaningful response. Do you have an aversion for typing?

"Very fast", as compared to what? Compared to a glacier moving down a mountain, the flow of lava is "very fast". Compared to an electro-mechanical contactor opening, allowing an SCR to self commutate on the next zero cross is "very fast". Compared to that, a Darlington transistor is "very fast".

How much power are you looking to switch as well? If it is .00000001A, then there are a completely different set of tools available to you compared to trying to interrupt 100,000A!

 

[Mike2468]

If you are switching a AC power line, the fastest turn OFF will be at the next zero crossing mark. This could be as much as 8.3 msec (60hz, 10msec at 50hz).

If you want to avoid the zero cross limitation, then you may be able to achieve this with an IGBT.

 

[AliBaba100]

Thank so much about your response.

I want to switch off 220 volt ac for over current of 3 amp,the time of this switch off device should be less than of miniature C.B or fuse time .

 

[Skogsgurra]

You still haven't explained very well what you need.

There are extremely fast fuses. Fuses that act in a few milliseconds. Do you need faster than that?

If that is so, a thyristor is not an ideal component. You may use an auxiliary thyristor and a capacitor to switch off the main thyristor. Or you may use a GTO (Gate Turn Off) thyristor. But both lead to complex circuitry. An IGBT would be a lot better.

Gunnar Englund

http://www.gke.org

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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

 

[AliBaba100]

Hi Skogsqurra I appreciate you respone . It seems to me you did n't get the point,due to shortage of power in IRAQ my home feeded from private power provider 220 volt ac max. 3 amp. and they limit the power by using miniature c.b and fuse , if we consume more than 3 amp. c.b or or fuse will act and the power provider will keep the power off for somtime and plenty us a cetain amount so to get rid of this case I to build a switch off device and this device should be faster than mcb and fuses .

hope this very clear

 

[Skogsgurra]

Hello Ali,

If you need faster than a fuse or a CB and the current isn't the result of a short circuit, but beacause you draw slightly more current than your utility allows you to. Then we are talking minutes - not seconds or milliseconds. Your best choice would be a contactor and a circuit that senses current, plus a comparator with a slight delay - let's say a second or two. Make the output from this circuit keep the contactor pulled in as long as there is no more current than 3 A. And drop the contactor if current rises above 3 A for more than a few seconds.

There are some other issues. Like RMS. Inrush curents and such. But you do absolutely not need a very fast switch for this. A contactor is fast enough.

Gunnar Englund

http://www.gke.org

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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

 

[AliBaba100]

Hi Skogsqurra ,

thanks so much about your nice idea,Iwould know more about comparator property and is it possible to build it my self cause I can not find such component here due to our hard situation .

 

[jraef]

It would be difficult for you to build one on your own. What you need is called a "current sensing" or "Current Monitoring" relay. They are available from a lot of manufacturers, but unfortunately for you, most of them are going to be difficult for you to get service from. If you can give an idea of what resources you have available to you, as in product brand names etc., we may be able to help a little.

Here is an example, Siemens relays are available worldwide, but maybe scarce in Iraq at the moment:
Siemens Function Relays The one you could use is shown on pages 8 and 9; the 3UG4622-1AW30. For only a 3A load you could switch your load directly with the contacts of this relay, but I would recommend using this relay to switch another cheaper one that actually switches your power. That way if there is a problem with your power or the suppliers power, it damages only the cheaper relay. There are a lot of other similar products on the market, your challenge will be to find one that you can get your hands on.

Good luck, I feel for you.

 

[rootsxrocks]

This Is My first post, and I believe I am looking to do something similar.

I would like to build or buy 6 SSR that are normally closed and trigger on with a 120v input 120 v 2amp out.

Basically I am looking for a NOT circuit for a 120v plug.

I will be using these as a part of a Christmas light show doubling my 6 channels by inverting the output of the prebuilt GE lights and sounds of Christmas. 2 amps should be more than enough for the LED lighting I am using.
any pointers to cheap and easily accessible parts?

 

[rootsxrocks]

After reading that I see I didn't word it corectly,
I should have typed " SSR that are normally closed and trigger off with a 120v input for 120v 2amp out.

 

[itsmoked]

You should've started a new thread, not responded to a 5 month old one....

I do not know of any SSRs that are AC input DC output.

I think you need to come up with an alternative solution.

Can you not use mechanical relays for this short lived application? Most have normally open AND normally closed contacts so you get your inversion automatically.

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[rootsxrocks]

Thank you Keith,
I have concidered mechanical relays. but what I am really doing is expermenting with this circuit to determine the number of channels and ratings I will need for the one I wish to build next year.

I'm not sure were you got the Idea of Dc out,perhaps the LED load. but the load is a 120v 60hz A/C load. well technicly The LED's will only draw in one direction I don't want to create a latched circuit.

Thank you for taking your time,

 

[itsmoked]

Hi rootsxrocks.

Yeah, I was thinking LEDs => DC.

You can get SSRs that are AC(control) AC(output) but they still aren't negative logic.

None of this is a problem if you were building from scratch your own product but, off-the-shelf...

Okay what you need is two SSRs, one to shunt the control signal of the second. Something like:

http://www.crydom.com/userResources/productFamilies/24/crydom_S1.pdf

You set up the control inputs of the the second SSR to be in series with a light bulb. So as hooked up the supply Hot runs thru the lamp to the the second SSR's control input and from the second control input to the neutral. Now just sitting there with the power applied the second SSR is ON its controlled output closed and running whatever.

Now you send your controlling signal to the control input of the first SSR. Whenever your control signal is ON the output of the first SSR is ON (more correctly, closed).

Hook the output of the the first SSR across the input terminals of the second SSR.

The idea here is that when the first is ON the input to the second is shunted or shorted. This would rob the second SSR of its control signal. The lamp is needed because if you shorted the full AC power running the second SSR it would blow something up. (A fuse hopefully)

The lamp will be dim when the first SSR is non-activated and the only current is the 2 or 4mA needed to activate the second SSR. Once the first SSR is activated, shorting the second's control inputs, the lamp will go to full brightness and the second SSR will shut OFF.

Pitfalls. The first SSR will likely need to be a snubberless output type or the current that normally leaks thru the snubber circuitry may be enough to turn OFF the second SSR's control input regardless of the control signals sent into the first SSR.

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[JayCarp]

I am a Mechanical Engineer and from my limited background it looks as if what he is looking for is a " crowbar " circuit ?

Is this the case ?

 

[itsmoked]

The thread that would not die....

Beats me JayCarp. By now he has probably grown old and died.

Mayhaps you were confused by his initial nonsensical "ON triggered ON" that he ultimately corrected to a true normally ON/OFF situation.

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com