Electronics > Beginners
Need somebody to talk to about AC concept
<< < (6/11) > >>
CatalinaWOW:
At the risk of damaging your growing understanding I want to point out a coupe of things.

1.  Even though the secondary circuit of the transformer is a single piece of wire, there is EMF along that wire.  Each turn of the transformer has induced current in changing magnetic field and thus voltage.  The turns are series connected so voltage increases as you go farther from your reference point.  This voltage across a conductor is the essence of the difference between DC and AC circuits.  The time varying fields and currents do things that don't happen in the static case.

2.  You might want to experiment with a resistor across the secondary of your transformer.  How does the AC voltage vary with resistance.  This is actually a dangerous experiment (not physically dangerous, but dangerous to a fragile understanding), because over a range of resistance values there is a simple relationship, but if you go outside of that range more complicated explanations of what is going on are required.

3.  One way to help your understanding of the artificial nature of ground is to take the secondary of your transformer.  Connect one lead to the negative terminal of a nine volt battery.  If you connect a DMM across that battery it will read nine volts, just as you expect.  If you use that DMM to measure the DC volts across the the secondary you will get zero volts.  But if you measure AC volts across the battery you will get nothing, and if you measure AC volts across the secondary you will get an appropriate value.  If you look at the voltage with an oscilloscope you will see the other end of the coil going up and down with respect to the negative lead of the battery.

Another dangerous experiment - hook the battery up across the secondary.  This one can be physically dangerous also so be sure to think about it before you do it, and take appropriate precautions in case your understanding is not sufficient to protect you.  It will take a fair understanding of both the transformer and the battery to predict what will happen in this case.
tester43:
Very interesting. Thank you. so....

ad1. it's related to transformer ratio - each next cycle of wire over the core gives linear increase of voltage (without load)
ad2. I would expect to see voltage drop due to limits of transformer - Without load I have Peak of 17V - with normal load it would get lowered to typical 12.
ad3. I know what would be the multimeter result - need to read how MM are measuring the actual AC
ad4. this one I can't imagine for the moment - will need to do the actual test
tester43:
let me elaborate pt 3:

--- Quote ---Connect one lead to the negative terminal of a nine volt battery.  If you connect a DMM across that battery it will read nine volts, just as you expect.
--- End quote ---
Because it's potential difference between two points.

 
--- Quote --- If you use that DMM to measure the DC volts across the the secondary you will get zero volts.
--- End quote ---
Because there is no DC bias in output of transformer.

 
--- Quote ---But if you measure AC volts across the battery you will get nothing,
--- End quote ---
Because battery is not the part of AC circuit, it's not "in the loop".


--- Quote --- and if you measure AC volts across the secondary you will get an appropriate value.
--- End quote ---

ok


--- Quote --- If you look at the voltage with an oscilloscope you will see the other end of the coil going up and down with respect to the negative lead of the battery.
--- End quote ---
I think it's not relative to the battery - or did you mean one probe on battery + and second on transformer output?
tester43:
For battery (DC) coil is just w wire.
At the first moment it will generate single spike of change in magnetic field.
Then it will consume as much current as possible from battery considering wire gauge, because resistance of this wire for DC is small or near zero.
Basically like a heater for the vacuum tube.

But.... did you mean to connect the battery with primary connected to mains?
tpowell1830:
Spoiler alert....

Ground is not ground or negative side of DC.

In most cars, the negative side of the battery is connected to the chassis and is often referred to as 'ground'. In the 1950s, there were 2 cars that I knew of that had the positive side of the battery attached to the chassis 'ground'.   :popcorn:
Navigation
Message Index
Next page
Previous page
There was an error while thanking
Thanking...

Go to full version
Powered by SMFPacks Advanced Attachments Uploader Mod