9VAC wallwart says 11.29VAC???

[AcousticBruce]

I posted 2 pictures just to make it easy.

The wall wart says Input 120VAC output 9VAC.

why is my multimeter saying 11.29VAC?
Also why, even on new 9V batteries is it always around 7.5V?


**broken link removed**

**broken link removed**

 

[ericgibbs]

hi,
Is it reading 11.29Vac Off load or On load.

Unloaded, most low cost adaptors read high.

What type of 9V battery is it.?

 

[AcousticBruce]

hi,
Is it reading 11.29Vac Off load or On load.

Unloaded, most low cost adaptors read high.

What type of 9V battery is it.?

The wall wart had zero load. Should I not use this to make a power supply. I do not have one and 9v batts are annoying!

The 9v batt. is a cheap ultralast. Maybe because I spent a dollar on it?

 

[mvs sarma]

I posted 2 pictures just to make it easy.

The wall wart says Input 120VAC output 9VAC.

why is my multimeter saying 11.29VAC?
Also why, even on new 9V batteries is it always around 7.5V?
the specification means that for the standard input, and at the 750mA load, the output would be 9V AC

try to put a 100 Ohms 1 or 2 watts acoross secondary and them measure again.

 

[ericgibbs]

The wall wart had zero load. Should I not use this to make a power supply. I do not have one and 9v batts are annoying!

The 9v batt. is a cheap ultralast. Maybe because I spent a dollar on it?

Use a 100R 2Watt resistor as a load and measure the voltage.

BTW the wall wart is 'ac' not 'dc' so its NOT suitable to use as a DC power supply.

 

[mvs sarma]

Battery being read as 7.5V

we experience fresh stocks of batteries showing 9.8V DC.
even though the battery may be new for you, it might be date expired stock or a bad supply.
Next you DMM FLUKE 83 III ( a Nice make and Model though)might have developed a fault in the DC Voltage ranges. the best is to use a standard reference of say 1.25V from LM317 by wiring it properly and have a cross check.

 

[AcousticBruce]

Use a 100R 2Watt resistor as a load and measure the voltage.

BTW the wall wart is 'ac' not 'dc' so its NOT suitable to use as a DC power supply.

Hmmm... could I not just make a diode rectifier with added filter and create a nice DC power supply from this? Also Before the rectifier I can splice an AC power supply also?

It seems to be rare to have an AC power supply... why is this? Is this what a signal gen is for?

 

[ericgibbs]

Hmmm... could I not just make a diode rectifier with added filter and create a nice DC power supply from this? Also Before the rectifier I can splice an AC power supply also?

It seems to be rare to have an AC power supply... why is this? Is this what a signal gen is for?

You could use a full wave rectifier with a smoothing capacitor, on a light load that would give about 12Vdc.

Use a low voltage drop out 9V reg, lightly loaded you should get just about 9Vdc.

Using a low voltage 8V or 5V reg would be better, give you a higher current capability.

 

[mvs sarma]

Hmmm... could I not just make a diode rectifier with added filter and create a nice DC power supply from this? Also Before the rectifier I can splice an AC power supply also?

It seems to be rare to have an AC power supply... why is this? Is this what a signal gen is for?

As you see the electronics world initially every thing seems strange and odd.
step down transformer type wall warts ate very much around. this would help other equipment 's size small.

If I were to be in your poition, i would notry to assemble the entire supply use a 9V regulator chip with suitable heat sink and get my needed 9V DC instead of doing arbitrary research and wondering for things that I did not know earlier.

Try to keep to your goal and we hope , if you have few components and proper schematic and a soldering iron and associated items, (to burn your fingers !!!)
you will finish making your PSU with the same wall wart.

All the best

 

[AcousticBruce]

....
Try to keep to your goal and we hope , if you have few components and proper schematic and a soldering iron and associated items, (to burn your fingers !!!)
you will finish making your PSU with the same wall wart.

I really appreciate that. Basically it doesn't matter what I do.. as long as I do something. How would I learn otherwise


OK so here is some questions... I didnt want to make a new thread for this either.

I have made a full wave rectifier I think?! And hooked it to the scope (this is the first time I have used the scope for any other reason than learning the buttons!!!!!) And I have the AC wave on top and the DC wave on the bottom.

My question is... Why does it seem on the scope that the wave bottoms out at 0 for a while... Seems like its missing the other inverted half? I understand that a cap will smooth this... just seems to me its a half wave rec.
Whats going on?

Scope settings
.5 V/div
2ms sec/div
didnt really mess with anything else other than moving the waves for better viewing.


**broken link removed**

**broken link removed**

This is what I am trying to emulate...

**broken link removed**

 

[ericgibbs]

What I can see of your scope probes you appear to be measuring on the wrong place on the 4 diode bridge.

You should measure on the opposite 'corners' of the bridge that are not connected to the ac input.

Do you follow.?

 

[AcousticBruce]

What I can see of your scope probes you appear to be measuring on the wrong place on the 4 diode bridge.

You should measure on the opposite 'corners' of the bridge that are not connected to the ac input.

Do you follow.?

At the bottom left of the breadboard you can see the AC adapter hooked into the breadboard.
Blue wire leads to bottom corner of rectifier.
Brown Wire leads to top corner of rectifier (This is where channel 1 is plugged)
The left side of rectifier is plugged into negative... the right side is positive.
I have channel 2 of scope plugged into the right side of rectifier.

Im not sure how else to plug it in. When I switch corners from right to left on channel 2 than the wave just inverts.

For the AC (channel 1) i didnt think it mattered which end was connected.

I took off the gator clip and it was just a bit more rough of a wave. So I kept it on.

Channel 1 is at top of scope (AC)
Channel 2 is at bottom (DC)

I also uploaded a new picture of this awsome free program that is helping me understand electronics. And I am trying to emulate the scope on the program.

 

[ericgibbs]

This is how would expect the connections.

You should get the neg going fullwave on #1 and a sine wave on #2

 

[AcousticBruce]

This is how would expect the connections.

You should get the neg going fullwave on #1 and a sine wave on #2

Here is the latest... now I really dont understand?



**broken link removed**

**broken link removed**

**broken link removed**

 

[audioguru]

You could use a full wave rectifier with a smoothing capacitor, on a light load that would give about 12Vdc.

No.
The peak voltage of 11.29VAC is 16V and the full wave bridge rectifier would drop it to 14.8V.

BTW, a very cheap Chinese 9V battery might have spent one year on a boat then a few years in a store. The chemicals in it are who knows??
A name-brand battery is reliable and is stamped with a best-before date.

 

[ericgibbs]

Try connecting a 100R thru 330R across the bridge + and - outputs, give it a load.

 

[Willbe]

It's 9v when supplying 780 mA. Therefore the internal resistance of this transformer is (11.29-9)/0.78 = 2.9Ω.

With 10w in and 9(0.78) = 7w out the efficiency is 7/10 = 70%.

 

[AcousticBruce]

I used a 250Ω and a 300kΩ and a 2MΩ Resistor.

Nothing changed really... just got a little more smooth.

 

[ericgibbs]

No.
The peak voltage of 11.29VAC is 16V and the full wave bridge rectifier would drop it to 14.8V.

Read the post properly.

Its lightly loaded in my explanation in order to bring it closer to 9Vac.!

 

[ericgibbs]

I used a 250Ω and a 300kΩ and a 2MΩ Resistor.

Nothing changed really... just got a little more smooth.

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.?