Comparing toroidal inductors of different core dimensions

I often see comparisons of toroidal inductors of different core dimensions with all other characteristics (eg turns, core type, frequency) held the same.

There seems an implicit assumption by many that the bigger the core, the larger the inductance. There are several failure in that thinking.

The ‘inductance’ of a toroidal inductor is µ*n^2*a/l where:

  • µ is complex permeability, µ0+µr;
  • n is the number of turns;
  • a is the cross section area; and
  • l is the effective magnetic path length.

Note that at RF, permeability may be a complex frequency dependent value, and therefore ‘inductance’ will be a complex value.

Many online calculators incorrectly calculate l from core dimensions using a simplistic formula.

Many online calculators treat permeability as a real number that is not frequency dependent, they use initial permeability (µi). Continue reading Comparing toroidal inductors of different core dimensions

Review of inexpensive Chinese thermostat – MH1230A

This is a review of an inexpensive MH1230A Chinese bang-bang  thermostat that was purchased on eBay for around A$15 complete with thermistor sensor and postage.

Above is the front view of the thermostat. There are many thermostats on the market with similar front panels, but they differ in internals and most importantly, performance and quality.

Above, the rating label is clear and informational, and it does give the sensor parameters.  Continue reading Review of inexpensive Chinese thermostat – MH1230A

A flexible test panel for microcontroller based power control projects – #2

This article expands on A flexible test panel for microcontroller based power control projects with some enhancements and accessories.

A LED power meter that I had ordered finally arrived (slow boat from China syndrome).

Above, the upper rail contains a RCD, the power meter which displays Volts, Amps, and kW, or pf, hours, and kWh, a DIN mount terminal block for mains, and a 40A SSR on a heatsink. A clip on CT can be used for oscilloscope observation of mains current. Continue reading A flexible test panel for microcontroller based power control projects – #2

Tuned Plate Tuned Grid oscillator – a simple, but complete explanation

A correspondent trying to get his head around old designs was challenged by the Tuned Plate Tuned Grid (TPTG) oscillator in common cathode configuration.

A superficial analysis is that the feedback to the grid from the anode via the anode to grid capacitance (Cag) is in phase with the anode voltage, which because of inversion in the valve means it is negative feed back. How can it cause self oscillation? Continue reading Tuned Plate Tuned Grid oscillator – a simple, but complete explanation

A flexible test panel for microcontroller based power control projects

I do a lot of experiments with microcontrollers switching mains powered equipment, and the test beds have always been improvised. It has always been my intention to formalise something for convenience but mainly for better safety.

The article describes a test panel to fill that need.

The panel is constructed on a piece of 3mm aluminium sheet, drilled and tapped to take two sections of 35mm DIN rail for flexible mounting of accessories.

Above is a pic of the test panel in use to test the generic heating / cooling controller (hcctl), a flexible bang-bang controller based on an ATTiny25. Continue reading A flexible test panel for microcontroller based power control projects

Fixes #1: magnetic stirrer with heating plate and digital display XB 85-2

Review: magnetic stirrer with heating plate and digital display XB 85-2 documented problems that prevented the device being very useful.

Attempts to tune the supplied PID controller above were frustrated by a lack of meaningful documentation supplied or found in searches on the ‘net, and the fact that the display is sometimes faked to appear that the temperature has stabilised. With any non-zero I term, it behaved badly and some observations suggest that it suffers from integral windup. It is truly a piece of Chinese junk and unusable.

Above is an independent logger capture of the temperature from switch on. There is a large overshoot, and then, no matter what the settings, it oscillates and the lowest amplitude obtained was 1°pp (above). The overshoot is almost as much as observed in manual warm up when power is cut at 40°. Continue reading Fixes #1: magnetic stirrer with heating plate and digital display XB 85-2