210Views16Replies

# What are the effects of Henrys in the use of inductors? Answered

I'm looking for information that might help me find a reactor for my variac setup. I noticed that almost every inductor I looked at has a Henry rating, I'm curious as to how this effects the circuit. After reading up on what a Henry is, I'm not sure I understand what it is exactly.

I have also heard of people referring to inductors by their inductance, would they be referring to their Henry rating or their voltage/amperage rating?

P.S. My variac is a 125/260v 11A military surplus, for all those interested.

Tags:

The forums are retiring in 2021 and are now closed for new topics and comments.

Henrys is just the measure of inductance. Inductors resist changes in the current flowing through them, and the higher the inductance, the more so they resist.

Say the current through an inductor is steady DC, the voltage dropped across one will be zero (ignoring resistance). However, if, say we were to steadily increase the current flowing by 1 amp per second, across a 1 henry inductor, the inductor would have one volt across it. In more mathy terms, the voltage across an inductor is proportional to the derivative of the current or how fast the current changes over time. It makes sense to say that an inductor resist changes in current because if the current starts changing, the inductor will have a voltage developed across it that works against the current.

Inductors also tend to allow DC current to pass, while blocking AC. (the opposite of capacitors) Because Alternating Current is, well, Alternating. and the inductor ends up dropping the voltage like a sorta like a resistor. In fact, there is a term, known as "inductive reactance" which describes exactly this "resistance-ish" property. Technically, it is not resistance, it is impedance. It is a bit more complicated because of phase shift between the current and voltage that occurs, though that is a bit more advanced.

Because of what they do, Inductors find uses in filtering certain frequencies, in limiting AC current for things like fluorescent and HID lamps, in radios as part of a tuner, and in power supplies to help remove ripple current and smooth out DC voltage rails.

this is rather informative, thank you for dumbing this down for me. i read the definition elsewhere and didn't understand it whatsoever.

Inductance is measured in Henrys, the same way resistance is measured in Ohms and capacitance in Farads ( or, more likely, in one of the very small sub-units)

Electrically, Inductors impede the flow of AC. As the frequency increases the impedance increases. The impedance is NOT resistive, so although there is a reduction in the current passed, for a given frequency, nothing gets hot.

Why do you need a reactor with your variac ?

I would like to both protect and isolate the variac, i know that inductors limit the current flow and if possible i would like to prevent my variac from ever seeing 11 amps. And unless im mistaken (which if i am this is the place to be corrected) isolation transformer and inductors are very similar and therefore the inductor should be able to isolate the variacc while i am at it.

if you think there is a better/easier way to do this im more than willing to listen to your suggestions.

No, the inductor will NOT isolate the variac !

Playing with mains, and mains feeding high voltage transformers requires great care, and preferably experience.

I do have some experience "playing" with high voltage and mains but any circuit I have ever made was rather simple and every circuit built for me had little to no explanation despite my every attempt to get one. So I guess my next question is: what is the difference between an inductor and an isolation transformer?

Well, in words, and inductor provides self-induction, but an isolation transformer relies on MUTUAL induction.

An isolation transformer "floats the electricity", so there is no common ground across the transformer.

so, would having an isolation transformer before my variac and an inductor after my variac would have a power supply that would be both isolated and not able to pull more than 10 amps?

personally, I'd run the isolation transformer - variac- MOT in that order, and protect the variac with a fuse on its output to the MOT

or, rather, this is a possibility with this configuration.

I can't link it to you now, But I think I've seen GreatScott make a video on that on YouTube, You might want to check that out

ill look it up, thanks

Lets just talk for a little while about why an inductor has this property called reactance.

A coil of wire (an inductor) has property that when an electric current is passed through it a magnetic field builds up, this emminated from the centre of the coil so as the field gets bigger it will cross many coils of the inductor, Faraday discovered that when a magnetic field crosses a conductor it generate an electrical current in that conductor.

It just so happens that in this case the electrical current generated is opposite to the current causing the magnetic field, so it opposes the flow of current, this causes the field to build more slowly. The opposition to the electrical current is seen as resistance (called reactance in an inductor )

This isn't quite the same as resistance as eventually the field will reach maximum size and the generation of the opposing current will effectively stop.

so - the reactance of an inductor is highest when the initial current is applied falling off as the magnetic field is established. A capacitor exhibits reactance but in the opposite way to an inductor.

Effectivly energy is store in the inductor because when the applied current is turned off the magnetic fiield collapses and of course the collapsing field generates a current in the coil tending to maintain the applied current so slowing down the appearance of turning off.

Generally inductor and capicitors are used a filters to reduce noise or as timing components to generate a resonate circuit that will react to a specific frequency.