FAQ
TL;DR: To ramp 230 V AC without relays, use a phase‑control triac dimmer driven by a 0–5 V or 0–10 V ramp; “the terminal marked ‘control voltage input’ takes the control voltage.” Add an instant‑off path. [Elektroda, Rohit Dubla, post #21668061]
Why it matters: This FAQ shows how to get a compact, repeatable 0–230 V ramp with a start/stop signal, safely and predictably. It’s for makers and engineers exploring non‑relay AC soft‑start/power‑ramp control.
Quick Facts
- Target spec from the thread: 230 V AC input, up to 20 A; ramp 0–230 V over 0–5 s. [Elektroda, Andrew Betts, post #21668050]
- For pure sine output, prefer a variac; triac dimmers distort the waveform. [Elektroda, Rohit Dubla, post #21668059]
- Add a solid‑state relay path for instant OFF while the ramp decays. [Elektroda, Rohit Dubla, post #21668051]
- Control ramp can be 0–5 V or 0–10 V DC into the dimmer’s control input. [Elektroda, Rohit Dubla, post #21668061]
- Design to repeat start/stop thousands of times; cycle window ≈ 0–3 s per the use case. [Elektroda, Andrew Betts, post #21668060]
What’s the simplest small-footprint way to ramp 0–230 V AC without relays?
Use a phase‑angle triac dimmer with a low‑voltage ramp generator (0–5 V or 0–10 V) driving the control input. This keeps size down versus motorized variacs. Add a solid‑state path to force immediate OFF on stop. “The terminal marked ‘control voltage input’ takes the control voltage.” [Elektroda, Rohit Dubla, post #21668061]
When should I choose a variac instead of a triac dimmer?
Choose a variac when you need a pure sine output, such as for sensitive transformers or induction motors. A triac dimmer chops the sine wave to control power, which changes the waveform. “If it’s a pure sine wave you need then I don’t see anything better than a variac.” [Elektroda, Rohit Dubla, post #21668059]
How do I get instant OFF while still using a gradual ramp?
Use a solid‑state relay (SSR) or equivalent solid‑state cutoff in series with the load. Drive it OFF immediately on stop, while the ramp generator resets to zero for the next cycle. This provides repeatable immediate shutdown. [Elektroda, Rohit Dubla, post #21668051]
Can this be done with a microcontroller instead of analog ramps?
Yes. A microcontroller can generate the ramp profile and timing, then command a power stage. “It can be accomplished by both analog and digital means.” Start simple and prototype at low voltage first. [Elektroda, Frank Bushnell, post #21668057]
What control‑voltage range should I design for?
Design the ramp source for 0–5 V DC or 0–10 V DC, matching the dimmer’s control input. Keep the ramp linear over 0–3 s if that’s your window. This supports clean 0–230 V transitions. [Elektroda, Rohit Dubla, post #21668061]
Does a triac dimmer keep the AC waveform pure?
No. Phase‑angle control slices each half‑cycle, so the output is not a pure sine. That can cause hum or EMI on some loads. Use a variac when sine integrity matters. [Elektroda, Rohit Dubla, post #21668059]
I need thousands of repeated start/stop cycles; is that feasible?
Yes. The thread’s use case calls for repeats every 0–3 seconds, thousands of times. Ensure your control ramp resets to zero on stop, and your power stage is rated for the duty. [Elektroda, Andrew Betts, post #21668060]
What are the baseline electrical targets from the thread?
Input is 230 V AC, up to 20 A. Output ramps 0–230 V AC over 0–5 seconds. These drive component sizing for dimmers, SSRs, heat sinking, and wiring gauge. [Elektroda, Andrew Betts, post #21668050]
Is there a ready reference circuit for the dimmer approach?
Yes. The suggested path is a voltage‑controlled AC light dimmer. Feed it with a DC ramp and gate the sequence with your start/stop. Ensure your chosen design matches your current rating. [Elektroda, Rohit Dubla, post #21668061]
What’s a variac?
A variac is a variable autotransformer. A motorized variac can move its wiper slowly with a control signal, producing a clean sine at adjustable voltage. Size and VA rating set maximum current. [Elektroda, Rohit Dubla, post #21668051]
What’s a triac dimmer, in simple terms?
It is a phase‑control circuit using a triac to delay conduction each half‑cycle, adjusting delivered power. Some versions accept a DC control voltage, enabling smooth ramps from an external generator. [Elektroda, Rohit Dubla, post #21668061]
How do I keep the solution compact?
Avoid motorized variacs because they’re bulky. Use a solid‑state dimmer plus a small ramp generator or microcontroller board. This meets the small‑as‑possible goal stated in the thread. [Elektroda, Andrew Betts, post #21668052]
Any safety advice before building?
Work at extra‑low voltage first, then move to mains with proper isolation and enclosures. “It is also wise to begin with low voltages.” Size parts for 230 V and 20 A, with margin. [Elektroda, Frank Bushnell, post #21668062]
What edge cases should I expect?
Some loads dislike chopped waveforms. Inductive loads may buzz, overheat, or misbehave with phase control. Use a variac when waveform quality matters, or validate on your exact load first. [Elektroda, Rohit Dubla, post #21668059]
Can you outline a quick 3‑step build plan?
- Choose your path: triac dimmer with 0–5/10 V input, or motorized variac for pure sine.
- Generate a linear DC ramp over 0–3 s and gate it with start/stop.
- Add an SSR for instant OFF; test at low voltage, then scale up. [Elektroda, Rohit Dubla, post #21668061]
What if I need guidance before I have a firm application?
Clarify function, power, and load type first. Share a simple block diagram. That enables targeted, safe circuit advice tailored to your goal. [Elektroda, Frank Bushnell, post #21668053]
