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Yet Another Soft Start Circuit
Yet Another Soft Start Circuit
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Old 4th July 2020, 03:41 PM   #131
tauro0221 is offline tauro0221  United States
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Hi,
About the EMI do have any equipment to test it. Now remember the ramp it is for a short period of time and like a said before the triac it is bypass once it is bypass the transformer will run like in a normal operation and the triac have built in EMI suppression. Right now my LM3886 it is a toroidal transformer and the Dynaco it is an EI transformer. I think that the size of the transformer depend of the size of the triac. The one I am using can handle 20 amps 220 volts AC non zero crossing since I am controlling the zero crossing with the micro. Sorry, if am misleading since this project was done 6 years ago and at my today age just remember one week after one week it is gone.
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Old 4th July 2020, 04:04 PM   #132
tauro0221 is offline tauro0221  United States
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Hi,
I have a suggestion if you want to use a big transformer just built the controller and just use the transformer with the capacitors bank and do the test to see how it will handle the AC ramp. From the results them decide to see if you want to use it or not. Simple. I am not using a PIC micro it is a ATmega328P chip and programming it with the arduino IDE.
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Old 4th July 2020, 04:07 PM   #133
Mark Johnson is offline Mark Johnson  United States
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Yet Another Soft Start Circuit
I think you'll be just fine if your triac's "IT(RMS)" datasheet specification, which is the maximum rated continuous current, is significantly higher than your transformer's max continuous primary current. In practice, this makes us very confident that the triac's "Non repetitive peak on-state current" will be waaaaaay higher than the soft start protected inrush.
  • Max continuous primary current = (transformer VA rating) / (mains RMS voltage)
So, for example, if your transformer is rated at 1000 VA and if you live where the mains voltage is 115V RMS, then
  • Max continuous primary current = 1000 / 115 = 8.7 amperes
So if you choose the $0.87 BT139 triac (datasheet), whose "IT(RMS)" specification is 16 amperes, you'll be fine, since 16 amps is much greater than 8.7 amps. The BT139's Non repetitive peak on-state current is shown in datasheet Figure 4, reproduced below. It certainly has plenty of safety margin for a soft start protected inrush.

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File Type: png Figure_4.png (49.8 KB, 40 views)
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Old 4th July 2020, 05:11 PM   #134
tauro0221 is offline tauro0221  United States
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Hi,
I my first prototype used the BTA25600BW. Attached photo because it is isolate and can be easily mounting in a good heat sink. You need to use and opte couple MOC3020 and few extra components for noise suppression to fire the traic.

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