Hey guys...
I'm new to AC circuirts, but found a piece where i need some help from. It's from here actually, a 555timer ldr light switch(not important, can't use it).
Diagram:

Questions:
1) Am i right in assuming that the DC current will be close to 1Amp, due to 220V/220Ω(R1&2)
2) Am i right in assuming than the DC output voltage is whatever volt rating C3 is or will it stay aproximately 220V from mains?(lil less due to diode drops)..

i need some help.
thanx

 

I'm not sure mains circuits are an allowed topic or not. This may have changed.

Any time you rectify AC to DC and use an appropriate capacitor filter you have to multiply the final voltage by 1.414. So 220 X 1.414 is going to be 311VDC. If your capacitor is not rated for at least 33% above that value you run the risk of an exploding capacitor. If it doesn't explode it's likely going to swell and fail. In this case I'd use a cap rated AT LEAST for 400VDC. NOT 220VDC. At 300VDC the cap will not survive. You're well above the 10% tolerance most caps have. And if you get a tighter tolerance cap - you're even worse off.

As for your question about 1 amp - that, I'm not able to answer.

 

Working straight off of mains is dangerous. Use an appropriate power transformer.

 

This is a non isolated AC to DC "capacitor" supply. It is dangerous. Some forums do not allow this subject because people get hurt. (Non isolated) Do does not use it if a human can tough any part of this.
There is no 1A!
It is true current flows through R1,2. The current flows through C1,2. Together they look like a 0.5uF cap. Do the math 0.5uF at 60hz to find the impedance. I am too lazy to do the math for you. Often these supplies are good for 10mA.
Usually there is a Zener diode across C3 to limit the voltage. With out a load you will blow up C3 if there is no Zener. The Zener regulates the voltage which is usually in the 3 to12V range. Not 200 volts.

If you really want to know more, we can do that.

 

What would you want with 220 volts DC? Or in the case of a filtered source, 311 volts DC?

 

Z = 5305.16 ohms output voltage is little less then 14 volts dc probably a Zener after C3 the part the OP didn't think he needed.

 

If you need a low voltage DC supply, get a wall adapter. They are inexpensive from a second hand store.

 

It also appears there's more to the diagram than is shown. What are you working on? Again, what do you need with 300VDC?

 

C3 will be nowhere near 300 volts it be around 14 volts

 

Z = 5305.16 ohms output voltage is little less then 14 volts dc probably a Zener after C3 the part the OP didn't think he needed.

You aren't taking into account that C3 is on the other side of a full-wave bridge, thus (with no load and assuming no internal leakage), it can only charge, never discharge. So as long as there is ANY voltage across R1 and R2, that current will be routed so as to charge C3 even more. Thus, it will charge until it finally has the maximum voltage that ever appears across the AC source, less two diode drops (and, given long enough, not even those two drops since it will continue to charge with subthreshold voltages). That's going to be about 311 V for a 220 Vrms supply.

This is one of the reasons why these kinds of circuits are so dangerous -- people think that they know that the voltage across C3 will always be low and so they start poking around and find themselves getting tangled up with potentially lethal voltages.

 

My point is the OP is going to power something not just charge the C3 so he will never see 311 volts on C3 and never 1 amp

This part

[Zener after C3 the part the OP didn't think he needed./QUOTE]

This thing is only good for about .05 amps 50 mA The OP most likely left this off.

Thats the right side of the circuit
I can see people getting hurt making these. I wouldn't use one myself but it's still not going to get the OP a AMP at 300 plus volts if he going to
power something with it any load over 50 mA should drop it to like 14 volts or less.

I did a little math I tried to sim with LTspice but Im not to good with LTspice

 

Questions:
1) Am i right in assuming that the DC current will be close to 1Amp, due to 220V/220Ω(R1&2)
2) Am i right in assuming than the DC output voltage is whatever volt rating C3 is or will it stay aproximately 220V from mains?(lil less due to diode drops)..

1. how do you get 1A? R1 and R2 are in series so they alone are 440 Ohm 220V/440Ohm = 0.5A. but that is not it, current will be much lover because of capacitors. this type of "power supplies" are really only good for few mA.
2. that is also wrong. this thing does not have regulation. so without load voltage would rise to peak value of the mains (220*1.41 = 310V). and with load it would be less, normally significantly less.

this is just a very bad idea, use proper PSU as others have mentioned.

 

My point is the OP is going to power something not just charge the C3 so he will never see 311 volts on C3 and never 1 amp

This part

This thing is only good for about .05 amps 50 mA The OP most likely left this off.

View attachment 334066Thats the right side of the circuit
I can see people getting hurt making these. I wouldn't use one myself but it's still not going to get the OP a AMP at 300 plus volts if he going to
power something with it any load over 50 mA should drop it to like 14 volts or less.

I did a little math I tried to sim with LTspice but Im not to good with LTspice

I set up a sim in LTSpice, using diodes that has sufficient reverse voltage to avoid breakdown.



Here is the sim results with no load:


If the user powers up this circuit with no load, or removes the load at some point (both of which are very likely to happen), the voltage across the cap will head for 300 V within a matter of seconds and, if C3 isn't rated for it, bad things will happen. And that's probably the good news, because if the cap can handle it, the output is sitting there just waiting to deliver a nasty jolt to someone or something. I don't know off the top of my head if 300 V on 470 µF has enough energy to be a major safety concern to a human -- I doubt it, since it's only about 21 J of stored energy. IIRC, 300 V is in the vicinity of about half the voltage needed to punch through the skin, so that could be a concern for some fraction of situations and, if punch through does happen, the circuit may be able to sustain a very concerning current through the path.

With a 1 kΩ load, the voltage is reduced to about 33 V.



While this circuit is probably not going to kill anyone -- provided they ONLY get tangled with the output and provided none of the components on the supply side of the bridge fails in the wrong way -- it is an accident waiting to happen. If someone is messing around with this without an enclosure, their reaction to getting hit by the output when it is unloaded could cause them to make a movement that gets them tangled up with the high-voltage side.

 

Could you post the spice file please

 

Could you post the spice file please

Sure.

 

Here is the original circuit, still a very bad idea.



https://www.electroduino.com/automatic-night-light-using-ldr-and-ic-555/

 

WOW thank you all for your input. i learned a lot.. like i forgot the resistors are TECHNICALLY in series..
I did say im very new to AC circuits. infact this will be my first...

In the fact OF COURSE i want a load, i wanted to say "i suppose i need a load on my capacitor before i can start prodding around with my multimeter right?"

OK so the big thing is i want to make a bug zapper without a transformer. ive seen it done before, and i just dont have the space to step it down via transformer then using transister and transformer to step it up to about 1400V and then use volt multiplyer caps to get 6000V...

i needed to know if i can use this kind of input circuit from mains to safely run it (knowing full well mains AINT SAFE) and so in potential used to power other lower volt stuff like 24volt high current motors....

i WAS wondering about a zener. i was thinking of adding a few in parallel to slowly step down like 100v then 50 then 24. or something like that, i didn't think one can just add a single zener. My highest zener is 24v..

For a bug zapper a wall adaptor and transistor with transformer will do as i've done few times before.just never made it zap(lol) I just wanted to learn AC circuits also. and unfortunately all i have is MAINS and i want it safe(as possible) and need to learn. That is why i asked it here.

1) DOES C3 HAVE to be a polarized capacitor or can i add a 233je 2000v plate capacitor as C3?
2) Might a voltage divider after C3 work for lower voltages? i need to add lights.


this is my idea. with a potentiometer volt divider. any thoughts?
please i want to learn AC.

 

Here is the original circuit, still a very bad idea.

View attachment 334077

https://www.electroduino.com/automatic-night-light-using-ldr-and-ic-555/

YOU ARE VERY CORRECT. BUT LIKE I SAID I CAN'T USE THAT SO I DIDNT POST LINK. Thank you for sharing it the Mains AC caught my eye and wanted to learn.

 

I don't know off the top of my head if 300 V on 470 µF has enough energy to be a major safety concern to a human

I once lost a second or so from my life by inadvertently getting a 400V zap between both hands (i.e across the heart) from a 470uF cap. In that second I was thrown across the room and woke up to find myself on the floor.
I can't recommend the experience !

 

I once lost a second or so from my life by inadvertently getting a 400V zap between both hands (i.e across the heart) from a 470uF cap. In that second I was thrown across the room and woke up to find myself on the floor.
I can't recommend the experience !

Happened to me too. I was repairing a tube amp. The jolt pushed me and my chair across the room.