The wiper in a variac

Started by Robert Roland in sci.electronics.basics3 months 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...


A balanced 12AX7 based buffer

Started by Les Cargill in sci.electronics.basics3 months ago 10 replies

I'd like to "design" and implement a simple 12AX7-based buffer for musical instrument DI purposes. I'd like the output to be balanced for ... no...

I'd like to "design" and implement a simple 12AX7-based buffer for musical instrument DI purposes. I'd like the output to be balanced for ... no good reason at all beyond having balanced inputs to play with. My questions are: - Do I really need 300V for this? What's the trade here? - Is there a nice single-package, preferably switchmode power supply that does 300V and 12.6V heater, or ...


A question about relays

Started by default in sci.electronics.basics3 months ago 21 replies

I was poking around in my truck the other day and had cause to open up the starter relay. (not the solenoid, the relay that energizes...

I was poking around in my truck the other day and had cause to open up the starter relay. (not the solenoid, the relay that energizes the solenoid) I was amazed at the size of the contacts. They were under 1/8" in diameter yet the relay is rated at 40 amps. The AC clutch relay- ditto, tiny contacts. In the case of the clutch relay I know for a fact the inductive kick must be > 100 volts


Trickle charge C-type NiMh?

Started by Terry Pinnell in sci.electronics.basics3 months ago 6 replies

I have some inexpensive 220 mAH C-type Ni-Mh batteries, https://www.amazon.co.uk/gp/product/B07BJ85NNZ The equivalent 3300 mAh C-Types I bought...

I have some inexpensive 220 mAH C-type Ni-Mh batteries, https://www.amazon.co.uk/gp/product/B07BJ85NNZ The equivalent 3300 mAh C-Types I bought a couple of years ago specified charging with 330 mA for 16 hours, but these new ones have no charging data. I have three soldered together and obviously charge in series. I've been using a trickle charge of 25 mA in the circuit of my curtain contr...


Using a TO-220 heat sink

Started by Adam Funk in sci.electronics.basics3 months ago 41 replies

Hi, To attach an LM317 (for example) in the TO-220 format to the corresponding heat sink (see link below), is it useful to apply any thermal...

Hi, To attach an LM317 (for example) in the TO-220 format to the corresponding heat sink (see link below), is it useful to apply any thermal paste in addition to the flexible mat that comes with the heat sink? Thanks. -- XML combines


Anyone here know BLDC motors well? Hobby ones particularly?

Started by Anonymous in sci.electronics.basics3 months ago 5 replies

I want to use a hobby BLDC motor to power a compact high speed spindle to be used for engraving and the like. Mainly because they are so...

I want to use a hobby BLDC motor to power a compact high speed spindle to be used for engraving and the like. Mainly because they are so compact for the power and speed. I cannot find, for a price I can justify, a 24,000 to 40,000 RPM spindle that will fit in the space I want to put it. Looking at some hobby BLDC motors and then buying some to experiment with leads me to think that on...


Psu for valves

Started by Peter Percival in sci.electronics.basics4 months ago 20 replies

I wish to experiment with valves (or tubes, if you prefer) and I shall begin by building a power supply. What voltages (at what currents)...

I wish to experiment with valves (or tubes, if you prefer) and I shall begin by building a power supply. What voltages (at what currents) should it supply? Where may I find circuits? Naturally, the devices used should be easily obtainable.


(plastic) optical fibre

Started by kristoff in sci.electronics.basics4 months ago 11 replies

Hi, I want to learn a more and experiment with optical fibre, especially for communication. Does somebody here have any experience with...

Hi, I want to learn a more and experiment with optical fibre, especially for communication. Does somebody here have any experience with this (at a hobbyist level)? There seams to exist a kit called FO-30K, that just uses LEDs, optotransistors and plastic fibre. So it looks like this is a technology for hobbyies to play with. Concering fibre, I found something called "POF" (pla...


Torque Vs Speed curve of the Stepper motor

Started by Anonymous in sci.electronics.basics4 months ago 7 replies

Hi, Does torque vs speed curve tell anything about the acceleration and deceleration characteristics of a stepper motor? Farah

Hi, Does torque vs speed curve tell anything about the acceleration and deceleration characteristics of a stepper motor? Farah


Power for DC motor controller

Started by Bob Engelhardt in sci.electronics.basics5 months ago 10 replies

I bought one of these 24v DC motor controllers: https://www.ebay.com/itm/311703088756 It came with zero documentation. I found the basic...

I bought one of these 24v DC motor controllers: https://www.ebay.com/itm/311703088756 It came with zero documentation. I found the basic connections on the web, but nothing else. My question here is: it takes 12-24v DC in and with just a variac and bridge rectifier, it works. But would it work better with a regulated supply? I'm guessing not because of its own big cap and PWM output....


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