Electronics Lab Philippines

Refrigerator Power-ON Delay; PIC timer

Offline Super zHero

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Re: Refrigerator Power-ON Delay; PIC timer
« Reply #260 on: October 23, 2020, 01:58:17 AM »
Trying out the line drop-out test.
Top, yellow line is the 5.6Vdc.  Bottom is the AC input at around 400Vpp, interrupted by depressing the pushbutton switch.



This is a simulation of a power drop-out of about 150mS.  It looks like the DC went down to 4V, still enough to support a PIC's operation.

Offline Super zHero

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Re: Refrigerator Power-ON Delay; PIC timer
« Reply #261 on: October 25, 2020, 11:13:24 PM »
Couldn't figure out why my isolation transformers were dropping almost half the AC voltage and getting warm.  Well, I figured out that it must be the low Power Factor of this capacitor dropper PS which gives it low efficiency.

So I changed them to some hardier transformers I have on hand.



I still get some voltage loss but my AC is now above 215Vac.

Offline Super zHero

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Re: Refrigerator Power-ON Delay; PIC timer
« Reply #262 on: October 26, 2020, 10:34:03 PM »
Working on a better "Capacitor Dropper" Power Supply.  This one has a full-wave bridge rectifier, and the dropping capacitor is half the size.  There is an additional circuit to detect the zero crossing of the AC.



If you cout the bridge rectifier as a single component, then this has the same component count as the old PS, plus the 3-resistors and 1-NPN that make the Zero crossing detector.

Offline Super zHero

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Re: Refrigerator Power-ON Delay; PIC timer
« Reply #263 on: October 31, 2020, 09:31:40 AM »
Waveforms generated by the new PS:



Top are the Zero Crossing pulses at the "Zero X'ng point (see schematics).  Bottom is the fullwave retified AC across the output of the bridge rectifier.  Not so pretty but shows 6.20Vrms.

The pulses occur at 8.30mS apart or at 120.4Hz.  Line freq at 60.2Hz.  The pulses are less than 100uS wide.

Offline Super zHero

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Re: Refrigerator Power-ON Delay; PIC timer
« Reply #264 on: November 02, 2020, 05:55:21 PM »
I might raise the 0.22uF capacitor back to 0.33 - 0.47uF to increase the current.  If I were to have an LED indicator in the circuit, that alone would need 10 - 20mA.

Offline Super zHero

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Re: Refrigerator Power-ON Delay; PIC timer
« Reply #265 on: November 11, 2020, 10:28:05 PM »
I had been mulling this over in the last few weeks- whether to change the firing angle of the Triac from Zero Crossing to 90.  This is due to the argument that the Triac is switching an Inductive load therefore the Inductive load current lags the voltage by 90.  If the Triac is switched at 90, the load's current will come at the Zero Crossing so the motor will see a "soft start".

In my design I used the opto-isolator MOC3063 which has a built-in Zero Crossing detect and firing circuit.  This takes care of driving the Triac, just about any Triac, effortlessly.  The PIC was just a timer and AC line voltage detector.  So everything is as simple as can be.  No transformer used, no relay, less parts compared to a 555-based circuit.

But the thing is- the refrigerator motor will turn ON and OFF at times controlled by the thermostat.  With or without the POD, it will do so regardless of where the AC waveform is at.  And it does this several times a day, without drastic consequence to the motor.  So why should I change the firing angle of the Triac?

Offline Super zHero

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Re: Refrigerator Power-ON Delay; PIC timer
« Reply #266 on: November 12, 2020, 02:17:56 PM »
If the concern is the start-up current of the refrigerator motor, which obviously the motor can handle, then the question is- can the Triac handle it?

After 6-years of continuous operation, this circuit has been without fail.  So I think that answers the question.  I guess the RC snubber across the Triac and the small heatsink helps.

The Triac I used was just a 600V, 8A, TO-220.

Offline insomartin

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Re: Refrigerator Power-ON Delay; PIC timer
« Reply #267 on: November 28, 2020, 01:46:59 AM »
madami nang bagong triac sa market. lahat halos snubberless na yung mga triacs. hindi na din kailangan nang optoisolated drivers.

Offline Super zHero

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Re: Refrigerator Power-ON Delay; PIC timer
« Reply #268 on: November 28, 2020, 08:17:02 AM »
Good info.  I will look into that.

Offline insomartin

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Re: Refrigerator Power-ON Delay; PIC timer
« Reply #269 on: Yesterday at 12:59:32 PM »
Good info.  I will look into that.

triacs din naman laman nang mga SSR..