Ohms law

[Pinnie]

You asked a question that only matters to engineers.

Ah. The sheep wandered from the pasture.

If you can do basic Ohms law calcs and understand how a series and parallel circuit work that's all you need to get started.

This is good news

A good grasp of electrical theory is important to being an above average electrician, but I got to be a way better electrician by learning circuitry, hand/off/auto switches, remote start/stop, playing with relays and making some sense of schematics than I ever did learning obscure ohms and three phase calculations. You'll never need to calculate impedance to get through a day at work.

thank you that’s comforting.

 

[ptonsparky]

Not to sound lazy, but how much effort versus return do you think is there. I am maybe a third through mikes theory book and it feels like a lot of brain power to learn. Plus the theory well is deep, how much theory knowledge do I need? There’s only so many hours in the day. I’m more than capable of mastering theory, but I don’t think I want to be an engineer. I’m leaning towards focusing on studying business. I’m weak there.

Education only hurts while you're getting it.

You don't have to be an engineer to appreciate the nuances of theory and understanding business operations should be approached the same way.

I'm an electrician. I disliked the motor classes while in school. I never gave a thought to business.

I ended up being a business owner that worked with motors. Hindsight.

 

[LarryFine]

Got it. Just the properties of the physical components of the capacitor cause it to charge at a high rate at “lower” voltages correct?

Almost. The charging/discharging currents happen because the voltage is varying.

On a steady DC voltage, a capacitor blocks current passing through it, while an inductor passes current with little impedance. On AC, a capacitor's impedance drops as the frequency increases, while
an inductor's impedance rises as the frequency increases.

In power circuits, since we deal with a constant frequency, we only care about the impedances at 60Hz. The formulae for capacitance are reciprocals.

Is the capacitor stopping the flow current in a series circuit?

Yes, if the voltage is not varying, because its current must flow through every component in a series circuit.

This is the 90 degrees out of phase as you describe in a purely capacitive circuit.

Bingo.

Gotcha. The capacitor’s plates swap charge polarity during positive and negative parts of the cycle.

Bingo. Caps made for use on AC are called non-polarized.

 

[Pinnie]

Almost. The charging/discharging currents happen because the voltage is varying.

Is the wax paper rated to only for current to pass through at over a certain voltage?

On a steady DC voltage, a capacitor blocks current passing through it, while an inductor passes current with little impedance. On AC, a capacitor's impedance drops as the frequency increases, while
an inductor's impedance rises as the frequency increases.

So the rate of the cycle is what affects the ampacity of a capacitor.

Do caps and inductors do the opposite thing to each other, and switch roles on dc and ac?

Yes, if the voltage is not varying, because its current must flow through every component in a series circuit.

Is that because the voltage on both sides of the cap are the same?

 

[ggunn]

Is the wax paper rated to only for current to pass through at over a certain voltage?

The current does not actually pass through the wax paper, and the frequency of the AC, not the voltage, determines the apparent conductivity of a capacitor. At very high voltages the current may pass through the wax paper (or whatever the capacitive medium is), but that typically destroys it. Electrolytic caps may work differently.

So the rate of the cycle is what affects the ampacity of a capacitor.

Capacitors do not really have ampacity, but yes, the conductivity of a capacitor depends on frequency.

Do caps and inductors do the opposite thing to each other, and switch roles on dc and ac?

Capacitors and inductors do behave reciprocally in AC circuits, but they are inactive in DC circuits. An ideal inductor is just a conductor in DC and an ideal capacitor is an open circuit to DC.

 

[LarryFine]

Is the wax paper rated to only for current to pass through at over a certain voltage?

No, the paper layer is destroyed if the voltage exceeds its insulative capability.

So the rate of the cycle is what affects the ampacity of a capacitor.

No, the frequency determines the capacitors impedance.

Do caps and inductors do the opposite thing to each other, and switch roles on dc and ac?

Yes. The higher the frequency, the lower a capacitor's impedance and the greater an inductor's impedance, and vice versa.

Is that because the voltage on both sides of the cap are the same?

No, it's because once the capacitor has become charged, there is no more charging current.

A capacitor passes AC because it is constantly charging and discharging through the load.

A series capacitor's charging current and the circuit's load current are the same current.

 

[zooby]

is anyone here an electrician or are you all engineers?

there are a few of us but we try to lay low and not bring attention to ourselves....usually.

 

[kwired]

Allow me to try. Nothing as exotic as semiconductors. Physically, a capacitor is two sheets of aluminum foil separated by a sheet of waxed paper, rolled into a cylinder. Electrically, it behaves like a high-current rechargeable battery with a ridiculously short charge/discharge cycle.

That is the actual design of many "made capacitors".

You still get naturally occurring capacitance out of any conductors with insulating material between them. Even open conductors in free air will have some capacitance through the air and this can be more significant at medium and high voltages that POCO's use for transmission and distribution than it typically is for under 1000 volts.

 

[ggunn]

That is the actual design of many "made capacitors".

You still get naturally occurring capacitance out of any conductors with insulating material between them. Even open conductors in free air will have some capacitance through the air and this can be more significant at medium and high voltages that POCO's use for transmission and distribution than it typically is for under 1000 volts.

Tuning capacitors in AM radios used to be two sets of interleaved metal half discs where one set was fixed and the other set was on a shaft that would change the overlap area of the two sets when it was turned, The air between them was the dielectric.

 

[Strathead]

The current does not actually pass through the wax paper, and the frequency of the AC, not the voltage, determines the apparent conductivity of a capacitor. At very high voltages the current may pass through the wax paper (or whatever the capacitive medium is), but that typically destroys it. Electrolytic caps may work differently.

Capacitors do not really have ampacity, but yes, the conductivity of a capacitor depends on frequency.

Capacitors and inductors do behave reciprocally in AC circuits, but they are inactive in DC circuits. An ideal inductor is just a conductor in DC and an ideal capacitor is an open circuit to DC.

A couple things here. For the first thing, a little humor. When current passes through the wax paper, we generally call that "letting the smoke out."

For #3, they aren't actually inactive in my opinion, they just don't act as inductors and capacitors. Coils become electromagnets on DC. Capacitors become batteries on DC. Basically a capacitor draws current until it "saturates" and then it sits idle. If you then remove it from the source, it maintains the charge until it is shorted. This is a known danger for old Cathode Ray tube televisions, that the charge can be enough to injure or kill a person. With smaller ones, back in the day before everyone became a snowflake, we used to charge a capacitor and then toss it to someone and say catch. Little zap, lots of fun.

 

[roger]

With smaller ones, back in the day before everyone became a snowflake, we used to charge a capacitor and then toss it to someone and say catch. Little zap, lots of fun.

An elementary schoolmate would bring a small charged capacitor to school at times and we would get in a large circle touching hands then the two ends would touch the the leads.

 

[CoolWill]

An elementary schoolmate would bring a small charged capacitor to school at times and we would get in a large circle touching hands then the two ends would touch the the leads.

My dad had a story about connecting a charged points ignition condenser between a couple of metal chairs in a conference room when he was in the Army. It always got a good rise when someone would sit in a chair and then touch the chair next to them. It went over real well when a general was the accidental victim.

 

[kwired]

My dad had a story about connecting a charged points ignition condenser between a couple of metal chairs in a conference room when he was in the Army. It always got a good rise when someone would sit in a chair and then touch the chair next to them. It went over real well when a general was the accidental victim.

field phones that had a hand crank for making calls as well as M57 detonators (used to ignite blasting caps, particularly for Claymore mines) were fun to rig up for pranks as well.

 

[ggunn]

Basically a capacitor draws current until it "saturates" and then it sits idle. If you then remove it from the source, it maintains the charge until it is shorted. This is a known danger for old Cathode Ray tube televisions, that the charge can be enough to injure or kill a person.

The same is true for tube amplifiers. I have a wire wound resistor on a gator clip test wire that I use to discharge the HV points to the chassis before I start poking around in a guitar amp.

 

[Strathead]

The same is true for tube amplifiers. I have a wire wound resistor on a gator clip test wire that I use to discharge the HV points to the chassis before I start poking around in a guitar amp.

I guess I have been lucky. I am going to refurbish my Twin next. I will try to remember.

 

[ggunn]

I guess I have been lucky. I am going to refurbish my Twin next. I will try to remember.

I just finished working on my old Super a little while ago, Mostly cleanup and cosmetic stuff, as well as reseating all the tubes with Deoxit.