57 lines
3.0 KiB
Markdown
57 lines
3.0 KiB
Markdown
 
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# Safety
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About 175 V sits between the +65 V and −112 V rails. Treat every HV node as live until you have
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measured it.
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## Design measures
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1. **Only certified mains equipment.** The 12 V brick is the only mains-connected part. Buy a
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certified brand (e.g. Mean Well GST36A12) from a normal retailer, not AliExpress.
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2. **Hardware HV watchdog.** The relay on the HV modules' 12 V feed is driven through a charge pump:
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```
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GPIO21 ──┤├──── A ──►|── B ───┬───────┬──── 2N7000 gate 2N7000 drain ─► relay IN (active-low)
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100nF │ 1N4148 │ │ 2N7000 source ─► GND
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┴ 1N4148 ═ 10µF ▯ 100k
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▲ (anode GND) │ │
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GND GND GND
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```
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Node A gets a diode to GND (cathode at A), and a diode from A to B (anode at A). This rectifies
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the toggling signal into a DC voltage on B. A constant high or low level gives no charge.
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The firmware toggles GPIO21 once per scanned row (about 2 kHz). If it crashes, or the pin sticks high or low, or
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the ESP32 resets, the cap discharges and the relay drops within about 1 s. A stuck row can't burn the panel.
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(Check the polarity of your relay module's input. Some are active-low.)
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3. **Fail-safe defaults.** The relay is normally open. Put a 10 kΩ pull-down on the watchdog
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path. Pull the panel ENABLE line to its *off* state at the 74HCT245 input, so a booting ESP32
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can't light anything.
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4. **Sequencing.** 5 V comes up, then the ESP32 boots and starts scanning, and only then does the watchdog close the relay.
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5. **Fusing.**
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| Where | Fuse |
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|---|---|
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| 12 V input | 3 A |
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| Each HV module input | 1 A slow-blow |
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| Each raw HV rail | 100 mA fast |
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6. **Discharge.** 330 kΩ bleeders on raw and regulated rails. HV-present LEDs are a hint only;
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always measure before you touch anything.
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7. **Layout.**
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- Put all HV parts on one side, with ≥ 3 mm clearance between HV tracks.
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- Use wire and caps rated for ≥ 300 V/500 V.
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- Use a keyed connector to the panel.
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- Close it in a plastic enclosure with no exposed HV.
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- Tie all grounds at one point.
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8. **Semiconductors from real distributors** (Mouser, Farnell, Reichelt). Fake HV transistors are
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common on AliExpress.
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## Bring-up procedure
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1. Build the 5 V and 12 V side only. Check the voltages.
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2. Connect one HV module at a time, with **no load**. Set NCH6100HV #1 to 90 V and #2 to 130 V. Lock the pots with nail varnish.
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3. Connect the regulator section, still without the panel. Check for about +65 V, −112 V and −100 V and that the bleeders discharge them.
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4. Test the watchdog: stop toggling GPIO21, and the HV must drop within about 1 s.
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5. Map the panel's power connector against the measured rails. Get a second check (photo/label).
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6. First power-up with the panel: 1 kΩ in series with each HV rail and a running test pattern.
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Measure the current per rail, then remove the series resistors.
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