FAQ
TL;DR: For a 230 V indicator, use a 0.22 µF X2 (≥275 VAC) dropper with a bridge; “0.22uF … just right for a typical LED.” [Elektroda, jta, post #16713649]
Why it matters: This FAQ helps DIYers wire a safe, clear power‑on LED for mains or 12 V lamps without dimming bulbs or wasting heat.
Quick-Facts
- Use X2 safety capacitors rated ≥275 VAC for mains droppers. [Elektroda, jta, post #16713649]
- Bridge-rectified LED: approx. 0.22 µF dropper hits normal brightness. [Elektroda, jta, post #16713649]
- Single LED with antiparallel diode: approx. 0.47 µF for full brightness. [Elektroda, jta, post #16713649]
- Add a ≥1 MΩ bleed resistor across the dropper to discharge safely. [Elektroda, jta, post #16713649]
- Simple 230 V indicator: LED + rectifier diode + ~470 kΩ series resistor. [Elektroda, kortyleski, post #16714321]
Quick Facts
- Use X2 safety capacitors rated ≥275 VAC for mains droppers. [Elektroda, _jta_, post #16713649]
- Bridge-rectified LED: approx. 0.22 µF dropper hits normal brightness. [Elektroda, _jta_, post #16713649]
- Single LED with antiparallel diode: approx. 0.47 µF for full brightness. [Elektroda, _jta_, post #16713649]
- Add a ≥1 MΩ bleed resistor across the dropper to discharge safely. [Elektroda, _jta_, post #16713649]
- Simple 230 V indicator: LED + rectifier diode + ~470 kΩ series resistor. [Elektroda, kortyleski, post #16714321]
Does my original 230 V LED indicator scheme make sense?
No. Your drawing ties both LED leads to essentially the same point, so no voltage drop appears to drive it. A small shunt resistor in the lamp line could create a drop, but it wastes power and heats badly as lamp wattage rises. “That’s all theory” here; it’s not a good practical path. [Elektroda, wniedzie, post #16713599]
How do I wire an LED so it lights only when the 230 V bulb is on?
Place the indicator across the switched live and neutral, in parallel with the bulb. Note an edge case: the lamp terminals still carry mains potential even if the bulb is off or blown, so the LED can still see 230 V. This method indicates supply presence at the lamp, not filament health. [Elektroda, wniedzie, post #16713610]
What parts make a safe capacitor‑dropper LED on 230 V?
Use a bridge rectifier, a 0.22 µF X2 capacitor rated ≥275 VAC, a series resistor of sensible power, and a high‑value bleed resistor (≥1 MΩ) across the capacitor to discharge after unplugging. “Otherwise you have a chance to discharge it through your hand and it’s not pleasant.” [Elektroda, jta, post #16713649]
Can I run a single LED without a bridge and still get full brightness?
Yes, pair the LED with an antiparallel diode and increase the dropper to about 0.47 µF for similar brightness. Keep the X2 rating on the capacitor and include a bleed resistor for safety. Add a modest series resistor to tame inrush at switch‑on. [Elektroda, jta, post #16713649]
Is a series shunt resistor in the lamp line a good current sensor?
It works in theory, but it is poor practice. Even a 1 Ω shunt must dissipate significant power as bulb wattage rises, running hot and wasting energy. If chosen, the LED can sit across the shunt, but thermal sizing becomes the challenge. [Elektroda, wniedzie, post #16713599]
Can I drop voltage with series silicon diodes and power the LED?
Yes. Three or four rectifier diodes in series with the lamp create enough forward drop to feed an LED indicator. This approach avoids a large resistor but still needs proper mains insulation and wiring discipline. [Elektroda, jarek_lnx, post #16713773]
Do I need a capacitor if I already use a large series resistor?
No. With a high series resistance, the capacitor is unnecessary. If you deliberately choose a capacitive reactance dropper, reduce the series resistor to about 1 kΩ to limit surge and shape current. [Elektroda, jdubowski, post #16713615]
Will a 1 W, 12 V supply run a 3 W bulb plus an LED indicator?
No. A 1 W supply cannot deliver a 3 W lamp’s load. Use a 12 V bulb and a supply with power equal to or above lamp wattage; a 6 W unit suits a 3 W bulb plus overhead. [Elektroda, jta, post #16714462]
Should I add an LED in the wall switch to find it when lights are off?
Yes, a locator LED in the switch is useful. Wire it to the switch contacts using proper limiting components rather than directly across mains. It indicates the switch’s position when the room is dark. [Elektroda, Marian B, post #16714765]
What single-resistor value is typical for a simple 230 V LED indicator?
Approx. 470 kΩ in series with a rectifying diode and the LED works for a basic mains indicator. Connect as in the forum’s Diagram 2 guidance for 230 V setups, observing polarity and insulation distances. [Elektroda, kortyleski, post #16714321]
Why won’t the thread’s System #1 work at all?
Because it lacks a valid voltage drop across the LED; both sides sit at essentially the same potential. Without a drop or proper current limiting, the LED cannot conduct and light. [Elektroda, Freddy, post #16714366]
What capacitor rating is mandatory across mains?
Use X2‑class capacitors at ≥275 VAC for line‑to‑neutral droppers. These are designed for across‑the‑line duty and fail safely. Do not substitute general‑purpose film or electrolytic capacitors here. [Elektroda, jta, post #16713649]
Quick how‑to: build a safe 230 V LED lamp indicator
- Rectify LED current with a bridge and use a 0.22 µF X2 capacitor (≥275 VAC) as the dropper.
- Add a modest series resistor and a ≥1 MΩ bleed across the capacitor to discharge on power‑down.
- Enclose parts, maintain creepage/clearance, and test with the lamp on a fused lead. [Elektroda, jta, post #16713649]
Will the LED still see voltage if the bulb is blown or switched off?
Yes. The lamp holder remains at mains potential in that wiring, so the LED may still energize. This indicates supply presence at the fixture, not filament continuity. [Elektroda, wniedzie, post #16713610]
