calculation · Misc · computed
Scotchn's 20YI-style SCR ladder build: why it latched (inductive P:S primary ~0.83 H freewheels through the bridge; ~31 µs valley window; dimmer parts may be TRIACs)
Build (Scotchn, Discord #neuralstan20-testing 2026-11-04): tap ladder on his nanocrystalline C-core; P:S step-up 200:1000 T on toroid B (20x20 mm section); "SCRs" salvaged from light dimmers (no part numbers); 240 V AC 60 Hz in as he stated (my notes elsewhere assume NZ 230 V 50 Hz; unconfirmed), no variac; load = his tiny tube cell (WFC_Behave basis, gap < 1.5 mm, C not recalled). He had to add a bleed to unlatch. My calculations: (1) Lp(200 T) = 20.74 µH/T² (his 10-turn small-signal AL, 10 kHz, #3432) x 200² = 0.83 H. With a diode bridge feeding an SCR into that primary, the bridge is a freewheel path at about 1.4 V, so di/dt = 1.4/0.83 = 1.7 A/s, a drop of only about 14 mA over an 8.3 ms valley: continuous conduction, the SCR cannot unlatch. A bleed across the primary diverts that current, which is consistent with what he saw. (2) Even with a resistive load, an SCR after a diode bridge never sees reverse voltage; the rail is under 2 V for only about 31 µs per valley at 340 V peak, 60 Hz, which is marginal against phase-control t_q with zero reverse bias. (3) Unchopped humps on the P:S: 1.8 V·s per hump / (200 T x 4 cm²) gives about 22 T, far past saturation, if no chopper sat between SCR and primary. (4) Dimmer devices are usually TRIACs; a gate held on (20YI drives the opto LEDs from DC) makes a TRIAC conduct both ways. Implication for FIG. 20YI: Q9 chopping primary 41 is probably the intended commutation and the volt-second limiter. The simulator has no thyristor part and caps sources at 24 V, so none of this is simulated. Open: device marking, Q9/chopper present?, bridge before ladder or AC direct, 50 vs 60 Hz.
Basis
- Method
- unversioned-legacy
- Recorded
- Published
- 4 Nov 2026
- Stanbot
- v3
- Source Ref
- Scotchn Discord 2026-11-04; notebook #3432 (toroid B AL), #3515-#3517; vic_calc expression
- Notebook Id
- 3518
- Device Slug Unmapped
- hgg
20YI SCR TRIAC commutation saturation scotchn