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Using Arduino => Project Guidance => Topic started by: rclark43 on Mar 19, 2019, 02:55 am

Title: Using 120V AC through a Breadboard (good or terrible idea?)
Post by: rclark43 on Mar 19, 2019, 02:55 am
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?
Title: Re: Using 120V AC through a Breadboard (good or terrible idea?)
Post by: alesam on Mar 19, 2019, 03:11 am
Please don't do it till you get much better knowledge of the subject.
Title: Re: Using 120V AC through a Breadboard (good or terrible idea?)
Post by: Wawa on Mar 19, 2019, 03:30 am
Very bad idea, because ground of the circuit will always be connected to mains power.
Leo..

Title: Re: Using 120V AC through a Breadboard (good or terrible idea?)
Post by: jremington on Mar 19, 2019, 03:36 am
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.
Title: Re: Using 120V AC through a Breadboard (good or terrible idea?)
Post by: rclark43 on Mar 19, 2019, 04:17 am
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?
Title: Re: Using 120V AC through a Breadboard (good or terrible idea?)
Post by: TomGeorge on Mar 19, 2019, 09:31 am
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  (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.. :)
Title: Re: Using 120V AC through a Breadboard (good or terrible idea?)
Post by: PerryBebbington on Mar 19, 2019, 09:43 am
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.
Title: Re: Using 120V AC through a Breadboard (good or terrible idea?)
Post by: dave-in-nj on Mar 19, 2019, 11:16 am
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.
Title: Re: Using 120V AC through a Breadboard (good or terrible idea?)
Post by: rclark43 on Mar 19, 2019, 02:31 pm
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
Title: Re: Using 120V AC through a Breadboard (good or terrible idea?)
Post by: PerryBebbington on Mar 19, 2019, 02:56 pm

Quote
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.


Quote
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.


Quote
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.


Quote
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.
Title: Re: Using 120V AC through a Breadboard (good or terrible idea?)
Post by: Paul__B on Mar 19, 2019, 04:46 pm
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 (http://www.powerswitchtail.com/)" to do so.
Title: Re: Using 120V AC through a Breadboard (good or terrible idea?)
Post by: rclark43 on Mar 19, 2019, 05:31 pm
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.
Title: Re: Using 120V AC through a Breadboard (good or terrible idea?)
Post by: Paul__B on Mar 19, 2019, 06:23 pm
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 (http://xyproblem.info/)".  Only if you specify your real task can we begin to explain what you will need versus something you happen to have lying about.
Title: Re: Using 120V AC through a Breadboard (good or terrible idea?)
Post by: rclark43 on Mar 19, 2019, 06:43 pm
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.

Title: Re: Using 120V AC through a Breadboard (good or terrible idea?)
Post by: PerryBebbington on Mar 19, 2019, 07:35 pm
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:

Quote
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.


Quote
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.


Quote
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.




Title: Re: Using 120V AC through a Breadboard (good or terrible idea?)
Post by: rclark43 on Mar 19, 2019, 08:55 pm
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.





If the responses here told me it was okay (which I kinda expected it wasn't going to be), then I would have used 120V AC. But now that I know its a really bad idea, emphasized by pretty much everybody, I will use my step down transformer: 120V AC to 24V DC.

Now, since I am using this transformer, what precautions would you advise? Is it okay to wire the transformer into the breadboard? Or is that equally a bad idea?

Thanks
Title: Re: Using 120V AC through a Breadboard (good or terrible idea?)
Post by: PerryBebbington on Mar 19, 2019, 09:03 pm

Quote
Now, since I am using this transformer, what precautions would you advise? Is it okay to wire the transformer into the breadboard? Or is that equally a bad idea?
If the transformer provides isolation from the mains (which I cannot confirm) then it is OK to wire the low voltage side to the breadboard. My concern remains that you will still have to connect the mains side to the mains and based on what I think you know about mains safety I am concerned about you doing that.

You should also connect the DC output of the rectifier (not the AC input for the same reasons I have already given) to ground as an extra precaution, usually the -ve side as that is the most common configuration for most electronics. Am I correct that you are in the US? Despite 2 visits to the US I do not know if your mains supplies have ground connections, I imagine they must....
Title: Re: Using 120V AC through a Breadboard (good or terrible idea?)
Post by: Paul__B on Mar 19, 2019, 10:19 pm
My other point was that you at least need a fuse - about 1A - securely wired in series with the secondary of the transformer in order to prevent a fire when something goes wrong.  I am presuming that the transformer already comes mounted in a case to protect the AC wiring and the case is grounded with a 3 pin plug fitted.  A picture or Web link would have been reassuring.
Title: Re: Using 120V AC through a Breadboard (good or terrible idea?)
Post by: rclark43 on Mar 19, 2019, 10:25 pm
If the transformer provides isolation from the mains (which I cannot confirm) then it is OK to wire the low voltage side to the breadboard. My concern remains that you will still have to connect the mains side to the mains and based on what I think you know about mains safety I am concerned about you doing that.

You should also connect the DC output of the rectifier (not the AC input for the same reasons I have already given) to ground as an extra precaution, usually the -ve side as that is the most common configuration for most electronics. Am I correct that you are in the US? Despite 2 visits to the US I do not know if your mains supplies have ground connections, I imagine they must....
Yes they do have grounds connections, but the 120V AC side of my transformer only has hot and COM (neutral) connections. The plug I can wire it to does have a ground connection.

So, do you advise that I connect a wire from the DC output into the connection on the plug that is for ground? Or should I also connect the DC - side to the COM AND the ground at the plug? In theory would this mean that my grounded wire will always have 24V DC going through it? If so, will that cause my breaker to trip?

Thanks
Title: Re: Using 120V AC through a Breadboard (good or terrible idea?)
Post by: rclark43 on Mar 19, 2019, 10:30 pm
My other point was that you at least need a fuse - about 1A - securely wired in series with the secondary of the transformer in order to prevent a fire when something goes wrong.  I am presuming that the transformer already comes mounted in a case to protect the AC wiring and the case is grounded with a 3 pin plug fitted.  A picture or Web link would have been reassuring.
Link to the transformer I have, it is the 90-T40F3:

https://www.alliedelec.com/product/white-rodgers/90-t40f1/70101870/?gclid=Cj0KCQjwpsLkBRDpARIsAKoYI8zonaQBFHKDQyC-sBfpX_p-z5E8GeZkhP34PTEuVBt78q5mtlJNJWsaArm1EALw_wcB&gclsrc=aw.ds
Title: Re: Using 120V AC through a Breadboard (good or terrible idea?)
Post by: Bringamosa on Mar 19, 2019, 10:52 pm
Oh no that's not having a ground....
Title: Re: Using 120V AC through a Breadboard (good or terrible idea?)
Post by: PerryBebbington on Mar 20, 2019, 08:37 am

Quote
Yes they do have grounds connections, but the 120V AC side of my transformer only has hot and COM (neutral) connections. The plug I can wire it to does have a ground connection.

So, do you advise that I connect a wire from the DC output into the connection on the plug that is for ground? Or should I also connect the DC - side to the COM AND the ground at the plug? In theory would this mean that my grounded wire will always have 24V DC going through it? If so, will that cause my breaker to trip?
To the input side of the transformer you connect hot (live) to the mains live and COM (neutral) to the mains neutral. Nothing else.

You connect an earth / ground wire from the plug to the negative (-ve) output of the rectifier, not to the transformer. At no point do you connect the hot (live) or the COM (neutral) to anything on the low voltage side of anything, nor should you connect them to earth / ground or to anything that is connected to earth / ground.

The use of the term 'COM' for neutral slightly concerns me but it might be just the difference between US and UK terminology. Are you sure this connection is the one intended to go to neutral? I can't tell from the photo and description.


Quote
In theory would this mean that my grounded wire will always have 24V DC going through it?
You might think this a pedantic point about language but it's important because it's about how electricity works. The phrase 'have 24V DC going through it' has no meaning because contrary to frequent inaccurate artistic representation, voltage does not go through anything, voltage is between 2 points, not through. Current goes through.


Title: Re: Using 120V AC through a Breadboard (good or terrible idea?)
Post by: rclark43 on Mar 20, 2019, 11:59 am
I will draw it out and send a picture thanks Perry. I believe here in the US neutral can also be referred to as the common line that is connected to ground. Our neutral line provides a common connection to ground. We also have the third ground part of the plug, which only ever has current going through it if there is a ground fault, and a lot of our appliances only use hot and neutral without the third ground part.
Title: Re: Using 120V AC through a Breadboard (good or terrible idea?)
Post by: rclark43 on Mar 20, 2019, 01:58 pm
Perry, please see my attached drawing. I highlighted in pink what I interpreted as you telling me to connect the DC out to the ground at the wall. Please let me know if this setup will work and if not how to fix it. I also added the Arduino in there with a relay (which I'll do after making sure it is good without the relay. I use a switch to turn everything on and off. The Arduino is physically isolated from the high power side and has its own separate 9V power supply.

I find it odd to connect the 24V DC out to the ground at the wall. This wont trip my breaker?

In response to your previous post, our 'neutral' wire is connected to the ground at the transformer outside. It has a ground conductor that brings it back to the transformer. It is at or near ground potential even when it is live. As far as I know the ground part of our plug is actually connected to the ground.

Thanks
Title: Re: Using 120V AC through a Breadboard (good or terrible idea?)
Post by: rclark43 on Mar 20, 2019, 02:03 pm
Picture size was too big, had to resize.
Title: Re: Using 120V AC through a Breadboard (good or terrible idea?)
Post by: PerryBebbington on Mar 20, 2019, 02:44 pm
(http://forum.arduino.cc/index.php?action=dlattach;topic=604493.0;attach=300219)
Title: Re: Using 120V AC through a Breadboard (good or terrible idea?)
Post by: PerryBebbington on Mar 20, 2019, 02:54 pm
Perry, please see my attached drawing. I highlighted in pink what I interpreted as you telling me to connect the DC out to the ground at the wall. Please let me know if this setup will work and if not how to fix it. I also added the Arduino in there with a relay (which I'll do after making sure it is good without the relay. I use a switch to turn everything on and off. The Arduino is physically isolated from the high power side and has its own separate 9V power supply.

I find it odd to connect the 24V DC out to the ground at the wall. This wont trip my breaker?

In response to your previous post, our 'neutral' wire is connected to the ground at the transformer outside. It has a ground conductor that brings it back to the transformer. It is at or near ground potential even when it is live. As far as I know the ground part of our plug is actually connected to the ground.

Thanks
As far as I can see that's fine.


Quote
I find it odd to connect the 24V DC out to the ground at the wall. This won't trip my breaker?
Correct, it won't. There is no circuit that the breaker is involved in to trip anything. Doing this is for safety, in the event that, for example, the transformer insulation breaks down then any resulting leakage will be grounded and your breaker should trip. You should connect the 0V of the Arduino circuit to ground for the same reason. If you project ends up in a metal case you should connect the case to ground as well.


Quote
In response to your previous post, our 'neutral' wire is connected to the ground at the transformer outside. It has a ground conductor that brings it back to the transformer. It is at or near ground potential even when it is live. As far as I know the ground part of our plug is actually connected to the ground.
I would expect neutral and ground to be connected somewhere, that's what makes neutral neutral. That does not mean neutral can be used as a ground connection for at least 2 reasons:

1. Assuming you have earth leakage protection (I think you have from what you said) the leakage current needs to bypass the earth leakage breaker in order to trigger it. The neutral goes through the earth leakage breaker so any leakage back through the neutral won't trigger the breaker.
2. The neutral in the return path for current in the live wire after it has gone through whatever you are powering, so the neutral is connected to live via lights, heaters, TVs, whatever. In the event that the neutral becomes disconnected, maybe because of a loose connection, then the neutral becomes live and it no longer safe.

Title: Re: Using 120V AC through a Breadboard (good or terrible idea?)
Post by: rclark43 on Mar 20, 2019, 03:03 pm
2. The neutral in the return path for current in the live wire after it has gone through whatever you are powering, so the neutral is connected to live via lights, heaters, TVs, whatever. In the event that the neutral becomes disconnected, maybe because of a loose connection, then the neutral becomes live and it no longer safe.


Perry could you please explain your second point here? When the electrical AC path is going from the load to the neutral, is the neutral not at ground potential? And, when the current reverses direction and goes from the neutral to the load, is it also not at ground potential? Could you also please explain what you mean by the neutral becoming disconnected? Disconnected in between the wall outlet and the load? Or between the wall outlet and breaker? Or between the breaker and the transformer outside?

Here in the US we have tons of plugs for appliances that do not have a ground prong, which is probably much less safer than what y'all have in the UK.
Title: Re: Using 120V AC through a Breadboard (good or terrible idea?)
Post by: PerryBebbington on Mar 20, 2019, 04:08 pm
Perry could you please explain your second point here? When the electrical AC path is going from the load to the neutral, is the neutral not at ground potential? And, when the current reverses direction and goes from the neutral to the load, is it also not at ground potential? Could you also please explain what you mean by the neutral becoming disconnected? Disconnected in between the wall outlet and the load? Or between the wall outlet and breaker? Or between the breaker and the transformer outside?

Here in the US we have tons of plugs for appliances that do not have a ground prong, which is probably much less safer than what y'all have in the UK.
Quote
Could you also please explain what you mean by the neutral becoming disconnected? Disconnected in between the wall outlet and the load? Or between the wall outlet and breaker? Or between the breaker and the transformer outside?
Disconnected anywhere due to a fault or damage. In order to draw power an appliance has to be connected to both live and neutral. Under normal working conditions the neutral wire is at or very close to ground potential all the time. However, it is also connected via whatever appliances you have to live. If, due to a fault or whatever, the neutral becomes disconnected at some point then after that point the neutral will be at or close to live potential, and so not safe to touch. For this reason you cannot consider the neutral and earth to be the same, even though they are at the same potential under normal working conditions. If you unplug something then you disconnect both the live and the neutral so the neutral being disconnected doesn't matter, as the live is also disconnected.

In the UK it is OK for appliances that have insulating cases, which usually means made of plastic, not to have an earth connection as there is nothing to earth. The actual terminology is double insulated (look it up), which come down to the equipment inside the case is insulated and the case itself is insulating, so there are 2 insulating barriers between you and the tickley stuff.

The US 120V supply, while not completely safe, is a lot safer than our 230V supply (the voltage at my house is usually around 250V).
Title: Re: Using 120V AC through a Breadboard (good or terrible idea?)
Post by: rclark43 on Mar 20, 2019, 06:01 pm
Perry, I'm still a little confused. If the neutral becomes disconnected then how is the power transmitted? Doesn't the circuit break open? Wouldn't any power stored between the live (hot) wire and the load be forced to ground from that? Perhaps either through a ground cable, or something else?

What I don't get is how the neutral becomes live if it breaks off. Do you have a video link or article?

Thanks
Title: Re: Using 120V AC through a Breadboard (good or terrible idea?)
Post by: Paul__B on Mar 20, 2019, 06:11 pm
"Double insulated" - the requirement for not having an earth wire - also means that the transformer itself must have two defined layers of insulation between primary and secondary (and that does not include the enamel coating on the wire).  If this is the case, there is no need to ground the secondary in any way.

Perry, I'm still a little confused. If the neutral becomes disconnected then how is the power transmitted? Doesn't the circuit break open? Wouldn't any power stored between the live (hot) wire and the load be forced to ground from that? Perhaps either through a ground cable, or something else?
If the neutral becomes disconnected, then any and all appliances connected to that neutral will form a connection to the live.  Power will not be transmitted because the circuit has been broken, it will be obvious that something is wrong, but until action is taken, those non-functioning appliances will be holding the neutral to live and contact with the neutral will be dangerous.

(http://www.electrical101.com/wpimages/open-neutral1.png)
Title: Re: Using 120V AC through a Breadboard (good or terrible idea?)
Post by: PerryBebbington on Mar 20, 2019, 06:38 pm
Perry, I'm still a little confused. If the neutral becomes disconnected then how is the power transmitted? Doesn't the circuit break open? Wouldn't any power stored between the live (hot) wire and the load be forced to ground from that? Perhaps either through a ground cable, or something else?

What I don't get is how the neutral becomes live if it breaks off. Do you have a video link or article?

Thanks
I'm struggling to find new ways to say this but I'll try.

You understand that the live is dangerous, yes? You understand that there is a connection from the live to, for example, an electric heater, yes? And a connection from the other side of the heater to neutral, yes? So there is a connection from the live via the heater to the neutral, yes? As long as the neutral is connected as it should be, through the wiring back to the local distribution transformer then all is fine. If the neutral becomes disconnected, maybe because of a loose connection, at, for the sake of argument, where it comes into the house, then from that point onwards the neutral in the house is not connected to the distribution transformer but it is connected, via the heater (an anything else) to live. The neutral wire is now live (hot) and therefore dangerous. If you touch it you will get a shock.
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Do you have a video link or article?
No, I have the training I did in college, I have what my dad taught me when I was a boy and I have 50 years experience. If my explanation doesn't work for you then I'm sorry but I out of ideas for explaining any more clearly. I invite someone else to try and I invite you to search elsewhere. Sorry, I've done my best.

Edit: I didn't see Paul__B's diagram until after I had posted the above. I hope his diagram makes it clear.
Title: Re: Using 120V AC through a Breadboard (good or terrible idea?)
Post by: Paul__B on Mar 20, 2019, 06:51 pm
Edit: I didn't see Paul__B's diagram until after I had posted the above.
That is because it wasn't there!  :smiley-lol:
Title: Re: Using 120V AC through a Breadboard (good or terrible idea?)
Post by: rclark43 on Mar 20, 2019, 07:04 pm
I think I get it now and I appreciate your explanations. After setting everything up I'll come back and let y'all know how it went.

You're probably tired of me but I do have another question about the control aspect of this. Will PWM on the relay be effective control? Should the snubber capacitor  be placed before or after the relay?

I just realized that in the drawing I posted the capacitor comes before the relay and will therefore always have DC going through. Any thoughts?
Title: Re: Using 120V AC through a Breadboard (good or terrible idea?)
Post by: PerryBebbington on Mar 20, 2019, 07:20 pm
That is because it wasn't there!  :smiley-lol:
DAMN! I gave you Karma for that. --Karma doesn't seem to work :smiley-confuse:
Title: Re: Using 120V AC through a Breadboard (good or terrible idea?)
Post by: PerryBebbington on Mar 20, 2019, 07:27 pm
I think I get it now and I appreciate your explanations. After setting everything up I'll come back and let y'all know how it went.

You're probably tired of me but I do have another question about the control aspect of this. Will PWM on the relay be effective control? Should the snubber capacitor  be placed before or after the relay?

I just realized that in the drawing I posted the capacitor comes before the relay and will therefore always have DC going through. Any thoughts?
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The capacitor comes before the relay and will therefore always have DC going through. Any thoughts?
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Should the snubber capacitor  be placed before or after the relay?
Yes, DC doesn't go through capacitors. The capacitor is in the right place as far as I can tell. It's job is to smooth the output from the rectifier and it should always be connected. Unless we are talking about different capacitors it's called a smoothing capacitor.


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Will PWM on the relay be effective control?
I was so focused on how you were supplying power I didn't notice PWM to the relay. No, you can't do that, a relay cannot switch anything like fast enough for normal PWM. There is an exception, which I am pretty sure does not apply here. For a heating load you might want PWM running very slowly. My heating controller uses PWM but the time for 1 cycle is 12 minutes. That is unusual for PWM.





Title: Re: Using 120V AC through a Breadboard (good or terrible idea?)
Post by: rclark43 on Mar 20, 2019, 08:51 pm
Yes, DC doesn't go through capacitors. The capacitor is in the right place as far as I can tell. It's job is to smooth the output from the rectifier and it should always be connected. Unless we are talking about different capacitors it's called a smoothing capacitor.

I was so focused on how you were supplying power I didn't notice PWM to the relay. No, you can't do that, a relay cannot switch anything like fast enough for normal PWM. There is an exception, which I am pretty sure does not apply here. For a heating load you might want PWM running very slowly. My heating controller uses PWM but the time for 1 cycle is 12 minutes. That is unusual for PWM.






Hmm not even if I use a solid state relay? Any recommendations besides PWM? In this instance I was going to start with an incandescent light bulb. I've done triac control on a bulb but I wanted to see if DC is generally better and easier to control. I'll be using a potentiometer to check but I eventually want to be able to program my own PID controllers for various things like temperature, motor speed, etc.
Title: Re: Using 120V AC through a Breadboard (good or terrible idea?)
Post by: paulwece on Mar 20, 2019, 10:30 pm
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.


Actually, I plan to do this for one of my project that needs a reliable source of power, so I don't want to use batteries. I plan to use a phone charger that plugs into the wall outlet and outputs 5V which I can connect a USB cable to.

But this thread is making me have second thought...

I don't want to risk anything. How risky is my approach? Perhaps I should stick to batteries.

Thanks
Title: Re: Using 120V AC through a Breadboard (good or terrible idea?)
Post by: lastchancename on Mar 20, 2019, 11:14 pm
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PWM... you can't do that, a relay cannot switch anything like fast enough for nor
Not that it has any real purpose in this project, but you can... for a different reason.
In some larger, more complex relay/solenoid projects, it is common use 100% PWM for a few milliseconds - to pull the armature in, then drop back to 20-30% to hold the armature 'on'.
In the datasheet this is referenced as 'pull-in' and 'hold' current, which can be related to how you drive the relay.  Saves current in a tight budget.
Title: Re: Using 120V AC through a Breadboard (good or terrible idea?)
Post by: rclark43 on Mar 21, 2019, 04:18 am
Actually, I plan to do this for one of my project that needs a reliable source of power, so I don't want to use batteries. I plan to use a phone charger that plugs into the wall outlet and outputs 5V which I can connect a USB cable to.

But this thread is making me have second thought...

I don't want to risk anything. How risky is my approach? Perhaps I should stick to batteries.

Thanks
Personally I'd prefer being crafty with the phone charger because I feel there's more to learn that way. Same reason I'm asking experienced people questions though so I don't end up having an accident.

If the charger outputs DC then I imagine all you'd have to do is cut the wire and connect. Then again, better to let more experienced people than me tell you if it's safe.
Title: Re: Using 120V AC through a Breadboard (good or terrible idea?)
Post by: lastchancename on Mar 21, 2019, 04:22 am
 This is a good chance to learn about power supplies - voltage current and indeed the result of that - power.
Because you're using mixed voltages and you'll also need isolation - if you're touching any mains. 
Title: Re: Using 120V AC through a Breadboard (good or terrible idea?)
Post by: PerryBebbington on Mar 21, 2019, 08:41 am
Actually, I plan to do this for one of my project that needs a reliable source of power, so I don't want to use batteries. I plan to use a phone charger that plugs into the wall outlet and outputs 5V which I can connect a USB cable to.

But this thread is making me have second thought...

I don't want to risk anything. How risky is my approach? Perhaps I should stick to batteries.

Thanks
The issue at the heart of this discussion is connecting stuff to the mains when you don't understand the risks. I you just use a commercially made power supply and connect to the output then you'll be fine (well, you will if it's not some cheap knock off that's not been manufactured to proper standards!).

I collect old power supplies from discarded equipment. I'll never use most of them, but I'm never short of a power supply when I need one. I suggest you do the same.
Title: Re: Using 120V AC through a Breadboard (good or terrible idea?)
Post by: dave-in-nj on Mar 21, 2019, 12:12 pm
just to toss in a note about grounding to the AC mains.

the AC mains here in the US is on a common electrical buss in the breaker panel.
there is a wire that exits the building and is connected to a rod that is driven into the ground.  Earth Ground..
there is also a shield ground wire from the main feed from the utility company.

every ground wire for the premises and every neutral wire are landed on the buss.
therefore every ground at every receptacle is mechanically connected to every Neutral wire.

if you connect your project to the ground wire in your AC wiring, you have a path to the AC neutral.

if the AC neutral fails between the panel and the receptcle, then there is no completed circuit.
if, the ground fails for the entire panel, so there is no connection to any external ground, then any and every other path to ground becomes a viable path.  if your project for basement water detecion shared the AC common, and there is water, a path might be made.
if you touch any plumbing and your device, and the water can carry to a ground, then a path is available.

We are not talking likely, but rather possible.

if, on the other hand, you never connect your project to the AC mains by any means other than the transformer secondary, then any loss of power means there is no path.

As a rule, there is no need to connect a project to an Earth Ground.   The small phone-charger power supplies offer both power and isolation and keep us all out of trouble.

As a note,  even those who can do this sort of thing, add AC to a board, chose not to because of all the requirements and risks and because a wall-wart is so common, cheap and easy.

A simple phone charger is often all that is needed and you can get double insulated power supplies with a regulatory label for a few dollars if you do not already have a box of them.








Title: Re: Using 120V AC through a Breadboard (good or terrible idea?)
Post by: paulwece on Mar 29, 2019, 03:26 pm
The small phone-charger power supplies offer both power and isolation and keep us all out of trouble.


Can you define isolation a bit more in the electrical sense? Heard that term a few times in this thread.

thx
Title: Re: Using 120V AC through a Breadboard (good or terrible idea?)
Post by: lastchancename on Mar 29, 2019, 08:20 pm
The complete physical & electrical separation of electrical paths to eliminate crossover of electrical potential between those paths.
(You could be one of those circuits)

This for both safety and electrical integrity of the associated circuits.
Title: Re: Using 120V AC through a Breadboard (good or terrible idea?)
Post by: paulwece on Mar 30, 2019, 12:52 pm
Thanks,

But what is it about a phone charger that provides "physical & electrical separation" though? Ultimately power from 120VAC still gets transformed into 5VDC inside the phone charger so one can still consider the charger as part of an larger "overall" circuit. Just curious.
Title: Re: Using 120V AC through a Breadboard (good or terrible idea?)
Post by: lastchancename on Mar 30, 2019, 02:14 pm
In an approved transformer/plug pack/adapter, the separate windings of the transformer provide electrical isolation, the plastic case and it's design create physical protection, the low voltage output is obvious (in conjunction with the physical & electrical isolation)
Proper grounding may also be needed if the reference or earth potential is required  in your project.
Title: Re: Using 120V AC through a Breadboard (good or terrible idea?)
Post by: Paul__B on Mar 30, 2019, 11:53 pm
the separate windings of the transformer provide electrical isolation
Specifically, there is the requirement that there be two separate and distinct layers of insulation between the primary winding and the secondary winding - in every direction - thus double-insulated".