Using 120V AC through a Breadboard (good or terrible idea?)

[rclark43]

I'm interested in taking 120V AC and running it through a full bridge rectifier to try and get DC current so I can use PWM to control the voltage and drop down as needed for different components.

Is it a bad idea to hook up the 120V AC into the breadboard and run it through a series of diodes to achieve something more like DC? If it is a bad idea then what other options do I have to do this besides using a breadboard?

Also, what size capacitors and diodes do y'all recommend to use to try and get the flattest DC line possible, while also making sure that the components are rated for handling the 120V AC?

[alesam]

Please don't do it till you get much better knowledge of the subject.

[Wawa]

Very bad idea, because ground of the circuit will always be connected to mains power.
Leo..

[jremington]

There are literally millions of different types of AC power supplies that will safely provide DC for your motors and other equipment.

If you don't want to spend much money, visit nearby thrift stores or computer recycling outfits for $3 bargains of all imaginable shapes and sizes.

[rclark43]

Guys,

Thank you for the feedback, I appreciate your experience to keep me safe.

Is there an alternative for a breadboard where I can assemble higher voltage components for prototyping? What specifically can I use instead of a breadboard to make sure I don't hurt myself?

[TomGeorge]

Hi,
Welcome to the forum.


Please read the first post in any forum entitled how to use this forum.
http://forum.arduino.cc/index.php/topic,148850.0.html . 


Can you tell us what your application is?

Do you need 0 to 120 * 1.414 = 170Vdc
How much current?

Thanks.. Tom..

[PerryBebbington]

I'm interested in taking 120V AC and running it through a full bridge rectifier to try and get DC current so I can use PWM to control the voltage and drop down as needed for different components.

Is it a bad idea to hook up the 120V AC into the breadboard and run it through a series of diodes to achieve something more like DC? If it is a bad idea then what other options do I have to do this besides using a breadboard?

It's not just a bad idea to connect your mains supply to breadboard for the reasons people have given, even if you use a more appropriate medium for testing your circuits you are still left with a direct, un-isolated connection from the mains to whatever you are working on. While for some specialist projects this might be appropriate, doing so carries a great deal of risk and you have to know what you are doing to mitigate those risks. For most general low voltage projects this is not just a bad idea, it is a very dangerous idea.

I'm not sure from your question if you realise this, but if you connect a bridge rectifier directly to mains the DC side does not have a 0V or ground connection. Neither the +ve or -ve terminal is at ground voltage because both are connect to live 50% of the time.

 I'm afraid the saying "if you have to ask then you shouldn't be doing it" comes to mind.

[dave-in-nj]

Here in the US, everything inside of the enclosure needs to be rated for the highest voltage.
when you start wiring 120 volts into the enclosure, you have to make everything rated for 120 volts.

google dual voltage gang box to see how they put 120 volts and phone or data lines behind the same wall plate.

that said, you can buy a phone charger that is smaller than your capacitors, inductor, regulator and diodes.
you can put that into the box and connect 5v USB out the end.
it is cheaper than making your own.


With mains power, the simple rule of thumb is that if you have no experience and have no training, you have no business.   as a rule, even those on here who are completely qualified to do such a thing do not bother because of the inherent risks and problems.   it really is one of those things that is just much cheaper and simpler to buy.

[rclark43]

All,

I am only prototyping at the moment and have no intention of keeping anything running unless it is for testing.

PerryBebbington, I have a triac switch that I control for dimming. It has a bridge rectifier on it so would that also mean it doesn't have a 0V or ground connection?

This is what I'm thinking for the setup: https://cdn.instructables.com/FMT/P75C/I24LZHBT/FMTP75CI24LZHBT.LARGE.jpg

Perry, if I make a bridge rectifier as shown in the link above how does the DC side not have a ground connection? What specifically is +ve and -ve, the alternating current part? From my limited understanding wouldn't the DC part of the circuit always have a lower potential path to either the hot and neutral side of the socket? I can see how it wouldn't have a ground path as it passes electricity down the hot wire.

I understand that there are dangers with using 120V AC and I have no intention of doing anything dangerous. However, I do try my best to understand exactly what is happening with the things I build, 99% of the time in concept and thought experiment before even daring to attempt a test.

Guys please tell me:

1. How can I set up a full bridge rectifier (with or without a breadboard) to make DC-like current that I can step down as needed for other components and exercise appropriate control? (PWM or any other means)

2. How can I always ensure all parts of the circuit have a safe path to ground?

Tom, I only want to harness 120V but yes I suppose I can get up to 170V with a larger capacitor correct?

The reason I ask all this is because as an engineer (I'm a process engineer), I am not content with just using components others have already built, because my aim is to truly understand the internals of the circuit. I place more value in the process of building, designing, troubleshooting, and debugging; I place little value on the end product because I try to be a continuous learner.

Thanks everybody

[PerryBebbington]

Perry, if I make a bridge rectifier as shown in the link above how does the DC side not have a ground connection?

When the live wire into the rectifier is in the positive half cycle the positive output of the rectifier is connected to live and the negative output to neutral. When the mains reverses and the live wire is negative then the live wire is connected to to the negative output of the rectifier making it live. Neither output of the rectifier can be considered to be ground, by which I mean the same voltage at the environment. Both the positive and negative outputs are connected to live for half the time. This is very dangerous if you don't take a great deal of care and understand the consequences.

What specifically is +ve and -ve, the alternating current part?

Please PLEASE! If you have to ask that then you do not know enough about electricity to be doing this. Please stop.

I understand that there are dangers with using 120V AC and I have no intention of doing anything dangerous. However, I do try my best to understand exactly what is happening with the things I build, 99% of the time in concept and thought experiment before even daring to attempt a test.

If you want to learn then do so at save voltages. Use a mains isolating transformer with a low voltage output and experiment with that.

1. How can I set up a full bridge rectifier (with or without a breadboard) to make DC-like current that I can step down as needed for other components and exercise appropriate control? (PWM or any other means)

The bridge rectifier circuit is fine AS LONG AS IT IS NOT CONNECTED DIRECTLY TO THE MAINS! Use a transformer.

I appreciate you want to learn, that is good, but connecting stuff directly to the mains is dangerous and the questions you are asking clearly indicate that you don't yet know enough to do it safely. Experiment at low voltages (<50V) that won't kill you if you make a mistake.

[Paul__B]

I am only prototyping at the moment and have no intention of keeping anything running unless it is for testing.

Nevertheless ...

The reason I ask all this is because as an engineer (I'm a process engineer), I am not content with just using components others have already built, because my aim is to truly understand the internals of the circuit. I place more value in the process of building, designing, troubleshooting, and debugging; I place little value on the end product because I try to be a continuous learner.

All fine warm and fuzzies, happy kittens but the take-home message here is:  Do not attempt to do anything at power mains voltages until you know a lot more than it is evident you do now.

Use ready-made power supplies to generate your DC power, and if you must switch the mains, use a "powerswitch tail" to do so.

[rclark43]

Perry,

I have a White-rodgers Class 2 Transformer, 40 VA Rating step down transformer (120V AC to 24V AC). Not sure how to verify it is mains isolated without taking it apart first.

"Please PLEASE! If you have to ask that then you do not know enough about electricity to be doing this. Please stop."

-I get it, that's why I'm trying to learn; I haven't even tried wiring anything together. That's why I'm asking for help so I can gradually get a better understanding. At some point we all didn't know and had others help us along the way. That said, is +ve and -ve the hot and neutral AC (which would switch directions and signs), or is it the positive and negative side of the DC after the bridge rectifier?

I know I'm new to this but I have to start somewhere; it would be more helpful to tell me what to do or what not to do, instead of telling me to stop. I am here to learn and understand the dangers inside out instead of giving up.

[Paul__B]

We are simply saying do not attempt to do anything involving connecting to the power mains until you have much better understanding.

Even the transformer you cite can cause a lot of damage if you connect it to something incorrectly.

What you have not described - at least in this thread - is what you are actually trying to do.  Someone guessed "motors" but you have only said "components".  It becomes the "XY Problem".  Only if you specify your real task can we begin to explain what you will need versus something you happen to have lying about.

[rclark43]

Paul,

I want to learn how to convert AC to DC using a rectifying bridge with a snub capacitor. To begin I can use a lamp as a load.

1. Safely convert AC to DC and power a load (testing a lamp for example)
2. Connect the DC power to a solid state relay and use PWM to control the output to a load (lamp)
3. Compare this with triac control of a lamp (which I have already successfully done, though timing is a pain and harder to control than PWM on DC)
4. If all the above are successful I would like to connect the DC to a bus, where I can drop the voltage to any load that I need, and have relays controlling each load with PWM.

I figure this is easier to do than straight up AC control fed to a circuit. My goal is to able to find a way to harness 120V AC that we all have access to (in the US), and understand the components necessary to control any device or equipment that I may want to design. As specific issues come up for specific projects I'm working on, I will always consult the community to make sure I am safe before even putting wires together.

[PerryBebbington]

Perry,

I have a White-rodgers Class 2 Transformer, 40 VA Rating step down transformer (120V AC to 24V AC). Not sure how to verify it is mains isolated without taking it apart first.

"Please PLEASE! If you have to ask that then you do not know enough about electricity to be doing this. Please stop."

-I get it, that's why I'm trying to learn; I haven't even tried wiring anything together. That's why I'm asking for help so I can gradually get a better understanding. At some point we all didn't know and had others help us along the way. That said, is +ve and -ve the hot and neutral AC (which would switch directions and signs), or is it the positive and negative side of the DC after the bridge rectifier?

I know I'm new to this but I have to start somewhere; it would be more helpful to tell me what to do or what not to do, instead of telling me to stop. I am here to learn and understand the dangers inside out instead of giving up.

I cannot say that any specific transformer is safe for any particular application, only the manufacturer can tell you that. Even then, they will say the end application affects the safety. Having said that, reducing to 24V makes it a lot safer. Please remember where this discussion started, it started with you saying:

I'm interested in taking 120V AC and running it through a full bridge rectifier to try and get DC current

Which terrified me as doing so provides no isolation from the mains and is dangerous. Now you have mentioned a transformer I am a bit more relaxed.

My warnings might be a bit over the top but I am concerned not only for your safety but also for the safety of anyone else reading this who also doesn't understand the risks.

That said, is +ve and -ve the hot and neutral AC (which would switch directions and signs), or is it the positive and negative side of the DC after the bridge rectifier?

I'll try and explain again. The mains supply is AC, as I think you know. The 'hot' (as you call it, I'm guessing that is US terminology, we call it live) side swings between (for 120V supply) between +170V and -170V (about +320V and -320V in the UK and European countries), the neutral side is the same as or close to the ground. By ground I mean the environment including the muddy stuff under your feet. This is not the same as the +ve and -ve coming out of the rectifier in your diagram because the rectifier switches the incoming AC to the correct +ve and -ve output terminal of the rectifier, so, when the mains hot (live) wire is positive it it is connected to the +ve terminal of the output of the rectifier, when the hot (live) wire is negative it is connected to the -ve terminal of the rectifier. Thus neither the +ve or the -ve terminal of the rectifier can be considered to be at ground potential, both of them are at mains live potential for half the time, both of them are just as dangerous as the incoming mains. I hope that makes sense.

I know I'm new to this but I have to start somewhere; it would be more helpful to tell me what to do or what not to do, instead of telling me to stop. I am here to learn and understand the dangers inside out instead of giving up.

I appreciate that, but the way to start understanding is to start with voltages that won't kill you if you touch them, voltages below 50V. Once you understand those then you will have an understanding of what makes mains dangerous. You are trying to drive a racing car without an instructor sitting next you when you are yet to learn to ride a bike. Stick to the safe voltages from commercially produced power supplies.