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Power On Delay Circuit for 180V Cutoff, 191V Activation, 5-Minute Delay

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  • #1 21672685
    DJS Lambs Marketing
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  • #2 21672686
    Neil Mula
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  • #3 21672687
    DJS Lambs Marketing
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  • #4 21672688
    Rohit Dubla
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  • #5 21672689
    DJS Lambs Marketing
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  • #6 21672690
    Peter White
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    DJS Lambs Marketing
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    DJS Lambs Marketing
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  • #9 21672693
    Peter White
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  • #10 21672694
    DJS Lambs Marketing
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  • #11 21672695
    Richard Gabric
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    Peter White
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    DJS Lambs Marketing
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Topic summary

✨ The discussion focuses on designing a power-on delay (POD) circuit that cuts off power below 180 V and activates above 191 V with a 5-minute delay, intended for air conditioning and refrigeration applications. A recommended approach involves using a comparator with hysteresis to create voltage thresholds with a 180 V cutoff and 191 V activation, achieved by scaling the input voltage to within op-amp specifications. One solution suggests employing a 555 timer IC combined with additional components: zener diodes to establish the 180 V reference, a voltage divider to scale the voltage difference (11 V between 180 V and 191 V) down to a suitable level, and configuring the 555 timer pins 2 and 6 to detect threshold voltage changes. The 555 timer output acts as a switch, and a separate 555 timer circuit implements the 5-minute delay. Challenges include precise activation at 191 V, with attempts to adjust zener diodes not yielding exact results. Safety concerns are raised due to working with high AC voltages, recommending professional oversight. The discussion highlights the need for a schematic diagram for clarity and practical implementation.

FAQ

TL;DR: Build a mains undervoltage/restore controller with a 5‑minute delay and an 11 V hysteresis window; “The difference between 180 and 191 is 11v.” Use a 555 timer, a zener string, and a divider to hit your thresholds. [Elektroda, Peter White, post #21672693]

Why it matters: It prevents short-cycling and nuisance starts in HVAC/refrigeration when line voltage sags or after blackouts.

Quick Facts

What problem does this circuit actually solve?

It guards equipment from low mains and rapid restarts. It cuts power when voltage drops under 180 V and only restores above 191 V, then adds a 5‑minute delay. That protects compressor-based loads like air conditioners and refrigerators from short-cycling and brownout stress. [Elektroda, DJS Lambs Marketing, post #21672685]

How does a hysteresis comparator help here?

A hysteresis comparator changes state at two different thresholds. In this case, it turns OFF below 180 V and turns ON only after the line rises above 191 V. Scaling the mains down lets common op-amps handle sensing safely. “You need an hysteresis based comparator.” [Elektroda, Rohit Dubla, post #21672688]

Can I do this with a 555 timer, or do I need an op‑amp?

You can use a 555. Add front-end thresholding so pins 2 and 6 see a scaled, hysteretic signal, then use the 555 for switching and a separate 5‑minute delay network. “It is very easy to do. Just a few more parts.” [Elektroda, Peter White, post #21672690]

What’s the hysteresis window I should target?

Use an 11 V window: 180 V cut-off and 191 V cut-in. This gap avoids relay chatter and premature reconnects during marginal line conditions. Quote: “The difference between 180 and 191 is 11v.” [Elektroda, Peter White, post #21672693]

Why scale the mains by about 100× before the comparator?

Scaling keeps the sense voltage inside op-amp or 555 input limits. For example, 180 V becomes 1.8 V and 191 V becomes 1.91 V, which suits low-voltage circuitry and simplifies resistor and reference choices. This improves accuracy and safety. [Elektroda, Rohit Dubla, post #21672688]

How do I wire the 555’s trigger and threshold for voltage sensing?

Feed the scaled sense voltage to the junction of pins 2 and 6. With proper hysteresis and division, the 555 changes state as the mains crosses your engineered thresholds. The 555’s output then drives your relay or logic stage. [Elektroda, Peter White, post #21672693]

How do I add the 5‑minute power‑on delay?

Use a 555 delay stage configured for ~300 s. After the line recovers to 191 V, the delay times out before re-energizing the load. This reduces compressor short-cycling after sags or outages. A second 555 or RC timing around the first can implement it. [Elektroda, Peter White, post #21672693]

Is this suitable for air conditioners and refrigeration loads?

Yes. The stated use case is protecting air conditioning and refrigeration. The undervoltage cut-out, restore threshold, and 5‑minute delay align with common compressor protection practices to avoid rapid restarts. [Elektroda, DJS Lambs Marketing, post #21672687]

What if my build turns ON at 185 V instead of 191 V?

That indicates threshold-setting error or tolerance drift. In the thread, the builder saw 185 V activation while targeting 191 V. Adjust the divider ratios or reference elements, not only the zener, to shift the ON threshold accurately. [Elektroda, DJS Lambs Marketing, post #21672697]

Is swapping zener diodes enough to hit 191 V exactly?

Not always. The report showed zener swaps alone failed to reach 191 V activation. That suggests the divider and hysteresis network also need tuning. Component tolerances and temperature can move the threshold. This is a common failure mode. [Elektroda, DJS Lambs Marketing, post #21672697]

Is this safe for a novice to build?

Caution. You’ll work near lethal voltages. The forum advised direct help from someone experienced and a safety review before commissioning. Add isolation, fusing, and proper creepage to reduce risk. “Enlist direct help… ensure it is safe.” [Elektroda, Richard Gabric, post #21672695]

Can I rely on a bare 555 without a proper front end?

A bare 555 approach struggled to meet the 191 V turn‑on precisely. The poster using only a 555 couldn’t get it right. Add a proper hysteresis/front‑end to set clean thresholds, then let the 555 handle timing and switching. [Elektroda, DJS Lambs Marketing, post #21672689]

Three-step: how do I build the 180 V/191 V, 5‑minute controller?

  1. Create a zener string/reference so mains between 180–191 V maps to a 0–11 V window, then divide to a safe level.
  2. Feed the reduced signal to 555 pins 2 and 6; set hysteresis so OFF<180 V and ON>191 V.
  3. Add a 5‑minute delay stage on the 555 output before driving a relay. [Elektroda, Peter White, post #21672693]

What’s an example of a practical statistic from this design?

Scaling by ~100× turns 230 V-class mains into a ~2.3 V sense level. In this project, 180 V → 1.8 V and 191 V → 1.91 V, enabling low‑voltage comparators and timers to work accurately. [Elektroda, Rohit Dubla, post #21672688]

Can I tune it later for a different restore voltage?

Yes. Recalculate the divider/hysteresis so the scaled ON threshold equals your new target (for example, 200 V → 2.00 V). Keep the 11 V window concept if you want similar noise immunity, then re-time the delay if needed. [Elektroda, Peter White, post #21672693]
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