Capacitive discharge battery tab spot welder

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Sully Kubillas

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Hi,

I am planning to build a capacitive discharge battery tab spot welder according to a schematic the image of which I am sending attached to this message. The question is: as the tyristor used in this project holds 50A, and I needed more than this, is it posible to wire two tyristors in paralell using the same control circuit? I should appreciate very much your help in this project.

Sully
 

Hi,

Sorry, I was inable to sen the circuit image. I am giving here its URL:

**broken link removed**

This circuit uses a IR50RIA20 tyristor and I would like to know wether I can wire two tyristor in paralell to get more current. I have found out that with more current I can have better welding mainly on Li-Ion battery tab.
Many thanks for your attention to this matter.

Sully
 

The continuous current rating isn't of much interest in this application, you'll rather look for I²t and dI/dt.
Paralleling multiple SCRs is possible, but the gate current must be high enough to achieve low trigger delay and delay skew. Gate series resistors for equal current sharing are suggested.
 

Q1 when on has Ib = 4.4mA, min Hfe = 80?, therefore Ic > 350 mA, but the continous Ic rating is 100 mA, and the pulsed is 350 mA. So I reckon holding the foot switch down is continous so I think the Q1 will cook, it needs an Ic limiting resistor somewhere.
Frank
 

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