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9VAC wallwart says 11.29VAC???

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I have relooked at all your pictures, its puzzling?

I assume the probes are set to divide by 10.

Disconnect the scope and use your DMM to measure the ac into the bridge and the fullwave rectified voltage on the output of the bridge.??

Lets know.?

They are 10x probes your right. As for it being puzzling... did you mean you are puzzled or you couldnt understand why I am puzzled? I was puzzled because it still seems like a half wave rectifier with the scope.


I did some tests with a 220µf 16v cap. and a 12V 250mA Fan

With no cap or fan
AC=11.34V
DC=9.76V

With Fan only
AC=10.97V
DC=8.58V

With Fan and Capacitor
AC=10.84V
DC=11.62V

Maybe this might help. This is all new to me. I am having a blast in the process though ;)
 
They are 10x probes your right. As for it being puzzling... did you mean you are puzzled or you couldnt understand why I am puzzled? I was puzzled because it still seems like a half wave rectifier with the scope.
Maybe this might help. This is all new to me. I am having a blast in the process though ;)

hi Bruce,
I'm puzzled :confused: why you dont see the full wave, only half wave.
Have you got an open circuit diode in the bridge.????
Or a poor/non connection on one of the diodes.?
 
Bruce, you should turn the "var" knobs fully clockwise for calibrated reading on the Tek scope.

That way the > sign will disappear and we will know the exact voltage levels.

Those 'scopes recognise the x10 probes and show the scale in volts at the probe tip, not at the 'scope input.
 
With all the probes and clips in the two pics I can't be sure just where the ac & dc leads are connected.
 
hi Bruce,
I'm puzzled :confused: why you dont see the full wave, only half wave.
Have you got an open circuit diode in the bridge.????
Or a poor/non connection on one of the diodes.?

I checked all the diodes.. only to find they are all ok.

Bruce, you should turn the "var" knobs fully clockwise for calibrated reading on the Tek scope.....

I now have them set correctly. Now it seems more accurate.

Can you tell me why the full rectified wave is there if I use both channels (One probe on negative and one probe on positive)?

Shouldn't I get this with just the positive end on channel 1?

Also when I click invert I am able to match both channels to form a full rectified wave so what is this for?

Am I just testing this wrong?

here is some pics to help.

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You should apply the AC wires to the top (no lead clips) and bottom (with the black alligator clip) nodes in the diode bridge in the picture. The far left node is your ground, and the far right node is your V+. You should see full wave rectified AC across those two nodes. Strap a capacitor across it and you have rectified filtered DC.
 
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You should apply the AC wires to the top (no lead clips) and bottom (with the black alligator clip) nodes in the diode bridge in the picture. The far left node is your ground, and the far right node is your V+. You should see full wave rectified AC across those two nodes. Strap a capacitor across it and you have rectified filtered DC.



Wouldnt that just show me the AC full wave?

I am looking for the rectified DC current. If I take off one channel then you only see this as half wave?!? Why is this? So I hooked up the channel 2 into the negative and I see the other half of the wave. Why is this? Couldnt I just do one channel and see a full rectified wave?
 
Your ground clip is in the wrong place. It should be at the far left junction in the bottom picture in your post above. The positive terminal is at the far right.
 
Your ground clip is in the wrong place. It should be at the far left junction in the bottom picture in your post above. The positive terminal is at the far right.


It seems to me that it looks cleanest the "wrong way" but again I am new and dont know what to look for.


This is with the ground clip on negative DC (far left junction)


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This is with it in the ground clip on the AC bottom junction (the one you said was wrong)

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This is with no ground clip at all.


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Diode rectifier on scope questions...

I have been playing with this java based circuit sim and was studying the "full wave diode rectifier"
So I made this diode rectifier from a 9V AC wallwart.

The scopes in the program show a nice AC sine wave and a nice full rectified wave on DC.

I really wanted make my scope of use and test it out. I just cant get it to act the same.

The first thing I did was set the scope to 2 channels. I put channel 1 as AC and hooked it to the top junction. Then I put channel 2 as DC and put it on the right hand junction (DC+). Where do I put ground?

-Why would I need 2 probes to make the full rectified wave? Shouldn't I be able to do this with one?
-If both channels are working on the same circuit... do you need to use both grounds?




This is what I would like to accomplish... notice the AC wave on one prob and the full rectified wave on another probe...

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This is the scope without ground

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This is the scope with gound on bottom junction (AC)

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This is the scope with DC positive on CH1 and DC negative on CH2

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Just inverted the CH2 wave and now its starting to look like a full rectified wave. But why do I need 2 probes for this?

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Just in case this helps... this is with a 220µF cap added across DC- and DC+

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Hey Bruce, it looke like u're workin pretty good on this. ur circuit is right. First of all u need to connect a resistive load just like in the program's picture around 1Kohm load or watever. connect one probe across on the right terminal of the load and the ground across the left terminal, i belive u'll get a full rectified signal. the position of the ground is very important in an oscilliscope because it measures the voltage between the probe and the ground and in this experiement u need the voltage acorss a load.

Regards,
Ahmad Jamjoom
 
Why did you start this new thread and duplicate your other thread?

Connect the 'scope like this to view the full-wave rectified waveform.
The 'scope must be connected differently to view the AC waveform.
 

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Hey Bruce, it looke like u're workin pretty good on this. ur circuit is right. First of all u need to connect a resistive load just like in the program's picture around 1Kohm load or watever. connect one probe across on the right terminal of the load and the ground across the left terminal, i belive u'll get a full rectified signal. the position of the ground is very important in an oscilliscope because it measures the voltage between the probe and the ground and in this experiement u need the voltage acorss a load.

Regards,
Ahmad Jamjoom


Well I hooked it up the way you said. Looks like you were right. So I see the full wave rectified wave on channel 1!!! Thanks so much....but

A new question arose, the AC sine wave is acting weird?!?
look at the pics.


Half of the bottom wave (Ch.2) is disappearing. And, if I hook the ground (on channel 2) it sparks... and messes up the other wave also (the last pic). So I left the ground out of the Ch2 Probe. I can hook them in the same spot (both grounds) but nothing changes.

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Where is the bottom half of the AC wave? The scope is set on AC.

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Well I hooked it up the way you said. Looks like you were right. So I see the full wave rectified wave on channel 1!!! Thanks so much....but

A new question arose, the AC sine wave is acting weird?!?
look at the pics.


Half of the bottom wave (Ch.2) is disappearing. And, if I hook the ground (on channel 2) it sparks... and messes up the other wave also (the last pic). So I left the ground out of the Ch2 Probe. I can hook them in the same spot (both grounds) but nothing changes.

You may think the scope as being a pair of voltmeters, but with both black leads joined together (tose black leads are the scope's ground).

A bridge rectifier has no "common ground" between the AC and the DC sides.

So you can't look at both the AC and DC waves at the same time with the same scope, unless you have a 4 channel scope or a differential probe.

With a 4 channel scope you use channel 1 and channel 2 to measure the AC sides (just both sides, no ground) and adjust the scope to display the difference between them (1-2). Then channel 3 is free to meassure the DC side, putting the scope's ground at the DC ground (minus).

A differential probe accesory (rather pricey and so not a common thing) has two input probes and one output that connects to a single scope's channel, displaying the diference between both inputs.

EDIT: Safety notice

The scope's ground is ussually tied to the safety ground (PE).
There are many ways to meassure a "live" circuit (one that is not isolated from the power line), some of them are rather safe and some are downright dangerous.:eek::eek:

Probably one of the safest ways to measure a live circuit is with a diferential probe. That's what they are made for.
 
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Why did you start this new thread and duplicate your other thread?

Connect the 'scope like this to view the full-wave rectified waveform.
The 'scope must be connected differently to view the AC waveform.

Well i figured it was so far away from what the thread originally intended. I figured I should make a new one... :eek:

Thank you audioguru that was exactly the issue :)
Also trying to read an AC wave as well as DC in the first 2 channels might not work as ecerfoglio says.

You may think the scope as being a pair of voltmeters, but with both black leads joined together (tose black leads are the scope's ground).

A bridge rectifier has no "common ground" between the AC and the DC sides.
...

Wow looks like i need to learn a bit more about my scope. Thanks so much!
Ill have to learn more about my scopes channels.

It is a 4 channel scope. Techtronics 2465 300Mhz. I have 4 of those 10x probes you see in the picture. and about 4 more of these really weird ones. They say 100Mhz on them and look older.
 
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No.
The peak voltage of 11.29VAC is 16V and the full wave bridge rectifier would drop it to 14.8V.
I think you missed out that they he said a low droput regulator.

If it has a dropout of just 500mV it would be more than good enough for light loads.
 
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