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LAN_403

Arcstarter

Tue Dec 02 2008, 08:15PM

Registered Member #1225 Joined: Sat Jan 12 2008, 01:24AM
Location: Beaumont, Texas, USA
Posts: 2253

I just recently got some pretty nice scr's for my 800volt 1950uf 600-something joule dual cap bank. I still need a reverse polarity protection diode, but for now i will use it with as little inductance as possible with wire exploding. They are part number sk065k(kinda small, hoping they are any good).

The first thing i want to know is, will these SCR's be any good? They are 950amps and 1kv each, if i put them in parallel, would that cause current sharing issues with 5 in parallel? If not will they withstand a short circuit with no inductance(some resistance in wires and the wire will explode, hopefully limiting the time the scr's have to stay on and prevent reverse charging)? With 0 resistance and and 50uh current is 4.996ka. That is just above the rating of all the 5 scr's together, and since there will be some resistance, it will probably be a little bit under their rating.

Also, the last(and 2nd stupidest,next to the current sharing) question, is how should i trigger them? I will use momentary push button, and a 9v battery or just aaa or aa. What resistor should i use?

Datasheet:

As you can see, i have never used an scr, and i pretty much know nothing about them..If it is not too much to ask, can someone tell me which pins go where? Well, i just need to know which is cathode and which anode, i know the rest.

Thanks ahead of time.

Berni

Tue Dec 02 2008, 08:30PM

Registered Member #1132 Joined: Mon Nov 19 2007, 06:15PM
Location: Slovenia
Posts: 84

Its pretty easy.Wire it the same as a diode in the conducting direction.Also don't go near the max rating, you want some head room so you don't fry something, especially if paralleled since they wont share exactly the same current. As for triggering you need to apply a certain amount of current in to the gate to turn it on.Typically around 20-100mA works fine (Depends on the SCR and its size somewhat) You should use a separate resistor on every gate and then connect a 9V battery or something to all of them

Arcstarter

Tue Dec 02 2008, 10:54PM

Registered Member #1225 Joined: Sat Jan 12 2008, 01:24AM
Location: Beaumont, Texas, USA
Posts: 2253

Well, what i meant was which lead is which for this particular SCR. Also, i know how to trigger but i don't know what the gate resistor should be.

teslacoolguy

Tue Dec 02 2008, 11:06PM

Registered Member #1107 Joined: Thu Nov 08 2007, 10:09PM
Location:
Posts: 792

If you are triggering it from a 9v battery 10ohms is usually good inough.

Arcstarter

Wed Dec 03 2008, 12:13AM

Registered Member #1225 Joined: Sat Jan 12 2008, 01:24AM
Location: Beaumont, Texas, USA
Posts: 2253

teslacoolguy wrote ...

If you are triggering it from a 9v battery 10ohms is usually good inough.

Standard phase control SCRs are triggered with few milliamperes of current at less than 1.5V potential.
;)

big5824

Wed Dec 03 2008, 04:53PM

Registered Member #1687 Joined: Tue Sept 09 2008, 08:47PM
Location: UK, Darlington
Posts: 240

i use 6v and 48 ohms for mine

Finn Hammer

Wed Dec 03 2008, 05:42PM

Registered Member #205 Joined: Sat Feb 18 2006, 11:59AM
Location: SkÃ¸rping, Denmark
Posts: 741

Arcstarter,

If you intend to pass any significant amount of current trough your scr, in a short pulse, being less than 10mS, i strongly suggest you build a proper gate drive circuit.

I stopped destroying scr`s when _I_ did.
Most important thing to avoid is contact bounce.
Nothing kills SCR`s as when they are turned on insufficiently.
A comparator with hysteresis and pull down resistor across a cap is good.
go from there with a device (smaller scr) that can pass enough gate drive current.

I would build something like this, shown on Sam Barros page, drawn by steve rodney, but add the debouncher.

Cheers, Finn Hammer

Arcstarter

Wed Dec 03 2008, 09:26PM

Registered Member #1225 Joined: Sat Jan 12 2008, 01:24AM
Location: Beaumont, Texas, USA
Posts: 2253

Finn Hammer wrote ...

Arcstarter,

If you intend to pass any significant amount of current trough your scr, in a short pulse, being less than 10mS, i strongly suggest you build a proper gate drive circuit.

I stopped destroying scr`s when _I_ did.
Most important thing to avoid is contact bounce.
Nothing kills SCR`s as when they are turned on insufficiently.
A comparator with hysteresis and pull down resistor across a cap is good.
go from there with a device (smaller scr) that can pass enough gate drive current.

I would build something like this, shown on Sam Barros page, drawn by steve rodney, but add the debouncher.

Cheers, Finn Hammer

That you for the website. I believe i will start getting some stuff together and build that, but i am first going to get a new scr. I have been thinking about it and there is no way these little scr's are going to withstand 950 amps, even for a short pulse, the leads would blow up it seems.

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