The wiper in a variac

Started by Robert Roland in sci.electronics.basics2 years ago 7 replies

I have been thinking about the way a variac works. One thing that puzzles me, is the wiper design: If the wiper is too narrow, the output...

I have been thinking about the way a variac works. One thing that puzzles me, is the wiper design: If the wiper is too narrow, the output voltage will cut out when the wiper is between two turns of the coil. If the wiper is too wide, it will bridge two contact points, causing one turn of the transformer to be directly shorted. Although it is not a lot of voltage, it is also not a long pi...


printed inductors

Started by Tom Del Rosso in sci.electronics.basics7 years ago 44 replies

When an inductor is printed on a PCB in the shape of a 'square wave' or square zigzag, each time it zags the trace doubles back on itself. ...

When an inductor is printed on a PCB in the shape of a 'square wave' or square zigzag, each time it zags the trace doubles back on itself. Doesn't this cancel the magnetic field to an extent? How much does the coil structure matter to a coiled inductor, or would the straight wire have the same inductance? -- Reply in group, but if emailing remove the last word.


Strange LO Oscillator won't oscillate

Started by Bill Bowden in sci.electronics.basics5 years ago 4 replies

It's a Autodyne converter in a small AM Radio. DC voltages look ok but doesn't oscillate. Originally, the problem was a weak transistor with a...

It's a Autodyne converter in a small AM Radio. DC voltages look ok but doesn't oscillate. Originally, the problem was a weak transistor with a hFE of 4. I replaced the tranny with a 2N2222A and it worked fine for a couple weeks and then died. Now the DC voltages look ok with about 1.5 volts on the emitter. Usually, this type of oscillator has the coil tap connected to the emitter throu...


Major Differences In Small Engine Coils

Started by Bret Cahill in sci.electronics.basics8 years ago 7 replies

Maybe the voltages vary somewhat for different point and plug gaps but is it enough to make any difference? . Supposedly Honda no longer...

Maybe the voltages vary somewhat for different point and plug gaps but is it enough to make any difference? . Supposedly Honda no longer makes the coils for their 100 outboard, a 2 cylinder 4 stroke engine. Isn't it likely that other small engines, say from riding lawnmowers, use coils that are pretty much the same? For that matter couldn't a motor vehicle coil work? Bret Cahill ...


MCU reset during relay switches ON

Started by Niresh in sci.electronics.basics1 week ago 7 replies

Hi, Could any please suggest how to avoid MCU reset with voltage glitches/noise during relay switches ON. I have protected the relay coil with...

Hi, Could any please suggest how to avoid MCU reset with voltage glitches/noise during relay switches ON. I have protected the relay coil with free wheeling diode and MCU with 2x10uF parallel with 100nF near VDD of MCU and 1uF across RESET pin. Regards, NiK


Permeability in a DC Motor

Started by Anonymous in sci.electronics.basics4 years ago 15 replies

Two motors were evaluated to find the ratio of the speed of the rotor over the speed of the electron in the coil. ratio = speed(rotor) /...

Two motors were evaluated to find the ratio of the speed of the rotor over the speed of the electron in the coil. ratio = speed(rotor) / speed(electron) ratio = 8 meters per second / 10 microns per second Some calculations show that DC electric motors rotate thousands of times faster than the electrons move in the drive current. For example, the Mabuchi RE 280RA motor has a c