Go Down

Topic: Using 120V AC through a Breadboard (good or terrible idea?) (Read 1 time) previous topic - next topic

Paul__B

"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.


PerryBebbington

#31
Mar 20, 2019, 06:38 pm Last Edit: Mar 20, 2019, 06:48 pm by PerryBebbington
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.
Quote
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.

Paul__B

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:

rclark43

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?

PerryBebbington

That is because it wasn't there!  :smiley-lol:
DAMN! I gave you Karma for that. --Karma doesn't seem to work :smiley-confuse:

PerryBebbington

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?
Quote
The capacitor comes before the relay and will therefore always have DC going through. Any thoughts?
Quote
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.


Quote
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.






rclark43

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.

paulwece

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

lastchancename

#38
Mar 20, 2019, 11:14 pm Last Edit: Mar 20, 2019, 11:14 pm by lastchancename
Quote
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.
Experienced responders have a nose for laziness, (they were beginners once)... Sure, there are trolls, chest-beaters, and pretenders - but the help you'll get here is about as good as it gets - if you try to help youself!.

rclark43

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.

lastchancename

 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. 
Experienced responders have a nose for laziness, (they were beginners once)... Sure, there are trolls, chest-beaters, and pretenders - but the help you'll get here is about as good as it gets - if you try to help youself!.

PerryBebbington

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.

dave-in-nj

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.









paulwece

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

lastchancename

#44
Mar 29, 2019, 08:20 pm Last Edit: Mar 29, 2019, 08:21 pm by lastchancename
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.
Experienced responders have a nose for laziness, (they were beginners once)... Sure, there are trolls, chest-beaters, and pretenders - but the help you'll get here is about as good as it gets - if you try to help youself!.

Go Up