Change of capacitor capacitance in a circuit

[StillTrying]

LOL
Why don't you simulate the circuit, that's bit safer way as well.

[timb]

I have a small halogen desk lamp with 2 metal bars going up from the base to the bulb, clipping on to the metal bars provides a useful 12 VAC 50Hz for testing purposes, it's a bit safer than using live mains as a signal generator!

Thanks for your suggestion, but I think that the voltage divider indicated in the experiment, made just with one 470k resistor and one 1k resistor, is a very easy, cheap and safe way to reduce mains electricity to a very safe level.

Ugh... You have no clue what we're trying to tell you. The way the circuit is constructed is inherently unsafe. You could learn the same thing, a lot safer, by using the output of a 12 or 24VAC transformer. You don't need to use raw 240VAC mains! Those protoboards are unsafe at that voltage for a variety of reasons.

That book was written 40+ years ago, before inexpensive function generators or simulation were available. There's absolutely no reason not to just use a function gen or transformer or LTspice to learn about impedance and AC dividers today.

[tggzzz]

That experiment looks like it was designed (I use that word loosely) by an academic that has little practical experience. You know, just like the PhD that tries to use a multimeter to measure the impedance of the mains!

That book was published by Philips, likely the largest electronics manufacturer in Europe. You can immagine how many engineers it had at the time of the publishing, so that book likely was throughly checked before and after publishing.

Ah. You must be young. I have more than one book describing fun things to do with your X-Ray machine; aimed at kids, and with a warning that you probably shouldn't let your skin get too red.

I've no intention of wasting my life trying to work out the quality of an arbitrary book nor of the context in which that circuit was discussed - but my comment stands unchanged.

[tggzzz]

I have a small halogen desk lamp with 2 metal bars going up from the base to the bulb, clipping on to the metal bars provides a useful 12 VAC 50Hz for testing purposes, it's a bit safer than using live mains as a signal generator!

Thanks for your suggestion, but I think that the voltage divider indicated in the experiment, made just with one 470k resistor and one 1k resistor, is a very easy, cheap and safe way to reduce mains electricity to a very safe level.

Given the number of times you have been warned and actively refused to understand/listen, that's definitely a good example of the Dunning-Kruger effect in action.

I really don't care if you endanger yourself; that's your business. I do care if other people might be encouraged to follow your example.

[Nerull]

I have a small halogen desk lamp with 2 metal bars going up from the base to the bulb, clipping on to the metal bars provides a useful 12 VAC 50Hz for testing purposes, it's a bit safer than using live mains as a signal generator!

Thanks for your suggestion, but I think that the voltage divider indicated in the experiment, made just with one 470k resistor and one 1k resistor, is a very easy, cheap and safe way to reduce mains electricity to a very safe level.

But it's not doing that. You're working with directly exposed mains, there is nothing protecting you from that. It doesn't matter what's going on partway through the circuit, it's the most dangerous exposed part that will get you - and you've got plug wires coming directly out of the wall outlet exposed.

Each of the circuits also has failure modes that will pass 325V directly to your scope. (Did you bother to learn what RMS means?) This is above the maximum voltage rating of your analog scope and waaay above the maximum voltage rating of your digital scope, so you were risking destroying both.

[tggzzz]

I have a small halogen desk lamp with 2 metal bars going up from the base to the bulb, clipping on to the metal bars provides a useful 12 VAC 50Hz for testing purposes, it's a bit safer than using live mains as a signal generator!

Thanks for your suggestion, but I think that the voltage divider indicated in the experiment, made just with one 470k resistor and one 1k resistor, is a very easy, cheap and safe way to reduce mains electricity to a very safe level.

But it's not doing that. You're working with directly exposed mains, there is nothing protecting you from that. It doesn't matter what's going on partway through the circuit, it's the most dangerous exposed part that will get you - and you've got plug wires coming directly out of the wall outlet exposed.

Each of the circuits also has failure modes that will pass 325V directly to your scope. (Did you bother to learn what RMS means?) This is above the maximum voltage rating of your analog scope and waaay above the maximum voltage rating of your digital scope, so you were risking destroying both.

Just so, but I fear your points will fall on deaf ears.

The OP has repeatedly been introduced to the concept of working out how things fail, and so far as can see has chosen not to apply the concept to his experiment. He has even failed to consider how he could achieve the same results and understanding much more safely simply by using a lower voltage.

[StillTrying]

Anything blown up yet? 

[j57H8I4]

But it's not doing that. You're working with directly exposed mains, there is nothing protecting you from that. It doesn't matter what's going on partway through the circuit, it's the most dangerous exposed part that will get you - and you've got plug wires coming directly out of the wall outlet exposed.

Of course the circuit will go into an enclosure, although I do not know yet what type of PCB to use to rebuild it and I still have to calculate what wattage the resistor should have.

Each of the circuits also has failure modes that will pass 325V directly to your scope. (Did you bother to learn what RMS means?) This is above the maximum voltage rating of your analog scope and waaay above the maximum voltage rating of your digital scope, so you were risking destroying both.

Anyway I do not keep the probe in my hand when I do this experiment, I hook it and then i put the plug in the socket.

[j57H8I4]

Anything blown up yet? 

I do not have much time for doing experiments during weekdays.

[tggzzz]

But it's not doing that. You're working with directly exposed mains, there is nothing protecting you from that. It doesn't matter what's going on partway through the circuit, it's the most dangerous exposed part that will get you - and you've got plug wires coming directly out of the wall outlet exposed.

Of course the circuit will go into an enclosure, although I do not know yet what type of PCB to use to rebuild it and I still have to calculate what wattage the resistor should have.

Each of the circuits also has failure modes that will pass 325V directly to your scope. (Did you bother to learn what RMS means?) This is above the maximum voltage rating of your analog scope and waaay above the maximum voltage rating of your digital scope, so you were risking destroying both.

Anyway I do not keep the probe in my hand when I do this experiment, I hook it and then i put the plug in the socket.

And with those two statements you demonstrate (again) that you do not understand what anybody has been telling you.

Is there any reason why you don't just use a safe voltage, but persist in using dangerous voltages? What benefit does using dangerous voltages give you?

[Neilm]

Can your components take the surge you will get on a mains supply? Normal transients are spikes that are several thousand volts

[j57H8I4]

Is there any reason why you don't just use a safe voltage, but persist in using dangerous voltages? What benefit does using dangerous voltages give you?

I am interested in seeing how is the mains wave.

[j57H8I4]

Can your components take the surge you will get on a mains supply? Normal transients are spikes that are several thousand volts

Can an hairdryer stand spikes that are several thousand volts?

[tggzzz]

Is there any reason why you don't just use a safe voltage, but persist in using dangerous voltages? What benefit does using dangerous voltages give you?

I am interested in seeing how is the mains wave.

So, since you can do that with a transformer at safe voltages, the answer is that there is no benefit. Hence fiddling with high voltages and failure mechanisms that you don't understand is being wilfully and perversely dangerous.

But I thought your circuit has capacitors and resistors, so your statement confuses me.

[tggzzz]

Can your components take the surge you will get on a mains supply? Normal transients are spikes that are several thousand volts

Can an hairdryer stand spikes that are several thousand volts?

Irrelevant.

Stop avoiding the important points and issues.

[Tac Eht Xilef]

I trust what Albert Einstein said: “If a person studies a subject for 15 minutes a day in a year he will be an expert. In 5 years he will be a national expert”.

I'd trust my own common sense, calibrated against the advice of reasonably knowledgeable others, more than an alleged Einstein quote that appears to have been made up years after he died...

"I never said half the crap the Internet says I did" - Albert Einstein.
"Dear Albert, on Facebook it's more like 3/4" - Mark Twain.

[Zero999]

Can your components take the surge you will get on a mains supply? Normal transients are spikes that are several thousand volts

Can an hairdryer stand spikes that are several thousand volts?

Yes, a correctly designed hair drier can withstand short voltage spikes over several thousand volts and even if the voltage spike goes on for long enough to destroy the hair dryer, it will still not pose a safety hazard to the user.

But it's not doing that. You're working with directly exposed mains, there is nothing protecting you from that. It doesn't matter what's going on partway through the circuit, it's the most dangerous exposed part that will get you - and you've got plug wires coming directly out of the wall outlet exposed.

Of course the circuit will go into an enclosure, although I do not know yet what type of PCB to use to rebuild it and I still have to calculate what wattage the resistor should have.

You don't understand. As long as the circuit involves exposed parts which are directly connected to the mains, then it isn't safe. The correct way to assemble a circuit like this is to use an isolation transformer. A 24VAC transformer is perfect, since all the voltages will be divided by 10.

[StillTrying]

Can an hairdryer stand spikes that are several thousand volts?

They try to direct any mains or switch on spikes back to neutral or earth, not out to the user!
 

[Nerull]

Can your components take the surge you will get on a mains supply? Normal transients are spikes that are several thousand volts

Can an hairdryer stand spikes that are several thousand volts?

Yes, it can, because it was designed by someone who understands what they are doing. Anything connected to mains needs to be designed to handle voltage spikes.
An electronic device that blew up every few weeks wouldn't be very popular.

[j57H8I4]

Yes, it can, because it was designed by someone who understands what they are doing. Anything connected to mains needs to be designed to handle voltage spikes.
An electronic device that blew up every few weeks wouldn't be very popular.

Well, then this circuit can be improved to handle voltage spikes too.

[tggzzz]

Yes, it can, because it was designed by someone who understands what they are doing. Anything connected to mains needs to be designed to handle voltage spikes.
An electronic device that blew up every few weeks wouldn't be very popular.

Well, then this circuit can be improved to handle voltage spikes too.

Give up, guys; we're wasting our breath.

There's an English proverb: "You can lead a horse to water, but you can't make it drink". For why that is relevant, I refer you to most of the posts in this thread!

[beenosam]

I think we should really implement a new rule here. If someone is doing something inherently dangerous and refuses to listen to advice of experienced professionals, then that thread ought to be locked. We really don't need more beginners reading these kinds of threads and think that level of ignorance is acceptable. Nor do we need to continue advising these people further.

[Gyro]

...and while you're at it, delete those stupid photo's too in case they encourage copying. 

[tggzzz]

I think we should really implement a new rule here. If someone is doing something inherently dangerous and refuses to listen to advice of experienced professionals, then that thread ought to be locked. We really don't need more beginners reading these kinds of threads and think that level of ignorance is acceptable. Nor do we need to continue advising these people further.

It is difficult, but I am biassed against locking threads.

Beginners need to be exposed to practices that have poorly-understood dangers, then to realise that the dangers are subtle, and that some people will persist in dangerous practices. Learning to recognise such people and behaviour is a valuable part of learning about life and the intertubes

In this case the OP will only harm himself and/or his equipment. I'm not too worried about that, it is his problem.

OTOH, sometimes people advocate practices that could harm them and/or random strangers in the vicinity. Classic examples involve buying 400mW/1W lasers for cutting things and imagining they are safe, or misusing chemicals. That does get me angry, and such threads should probably be locked with a statement as to why they are locked.

[Zbig]

Give up, guys; we're wasting our breath.

There's an English proverb: "You can lead a horse to water, but you can't make it drink". For why that is relevant, I refer you to most of the posts in this thread!

Yes, you're all wasting your time. Just click the guy's username and take a peek at his other past threads. That's the troll who argued to death that isolation transformers are useless (apparently because there are fewer of them than the scopes on the market) and that DSO's don't stand any chance to analog scope (because he's just learned what A/D conversion is). He first admits he doesn't know shit in his first post and then proceeds to fight everyone who actually does. Plus, he exhibits some unhealthy fascination with learning electronics by sticking probes to mains stuff. He's a lost cause.