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Hep please - what resistor size.

punkieys17

Feb 7, 2016
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Feb 7, 2016
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I am flummoxed. This is a commercial circuit from a pump. It incinerated the resistor and the thyrstor. The thyrsitor is correct but when i connect the pump and energise the reed switch it works once or twice then the thyristor burns out.
The only variable is the resistor size. Its on a 240V AC line. Yhe Igt is stated between 5 & 50MA and the Vgt at 1.2v. Please someone advise to the correct size...and show me the calculation. Any help greatly appreciated. The circuit diagram is complete as in thepump.jpg unit.
 

kellys_eye

Jun 25, 2010
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but when i connect the pump and energise the reed switch it works once or twice then the thyristor burns out.
Is the motor ok? Sounds like it's stalled, seized or otherwise knackered to me.....
 

bertus

Moderator
Nov 8, 2019
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Hello,

Have a look at the attached application note.

Bertus
 

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kellys_eye

Jun 25, 2010
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Might also be because you have the device connected wrongly - double check the pinout and your orientation.
 
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