Oscilloscope Question

[jacobi]

When I hook up my oscilloscope to a 12 volt battery charger which is half wave why do I get a full wave
on the scope? It should show dc pulses only.

 

[duke37]

A simple battery charger is not half wave, it contains a bridge rectifier which will show two half waves side by side, one from the positive half cycle and one from the negative half cycle.

The waveform will have a DC component and also a AC component. If charging a battery, current will pass in pulses when the charger volts exceed the battery volts.

If you are getting AC sine wave out, then the rectifier is shorted.

 

[K9WG]

If you are getting a full wave AC signal then there are a couple possibilities.
1. As duke37 said, the rectifier is bad.
2. The battery charger is not grounded and you are seeing the AC from the floating ground.
Make sure both charger and scope are grounded. Posting a picture might help.

 

[duke37]

Battery chargers have floating output so just connect the scope to the charger output leads. No need to bother about grounding.

If the rectifier is working properly and you have a load such as a low value resistance or bulb, then you should see rectified AC which will look like a chain of inverted Us. Very different from a sine wave.

Post a picture of the scope screen.

 

[jacobi]

Battery chargers have floating output so just connect the scope to the charger output leads. No need to bother about grounding.

If the rectifier is working properly and you have a load such as a low value resistance or bulb, then you should see rectified AC which will look like a chain of inverted Us. Very different from a sine wave.

Post a picture of the scope screen.

I've hooked this up before and it had all positive pulses.All I did was hook up positive lead from oscilloscope to positive lead to battery chger. I tried 2 different bat chgers. I'm not sure how to grd the oscilloscope. I gue3ss I'm a novice at this but am interested in it. Thanks for the input.

 

[Ylli]

You will need to connect the charger negative lead to the scope ground.

 

[duke37]

Voltages are measured between two points. If you only connect to one point (the positive) then the other connection is floating and may be up to the full mains sine voltage, so masking the much smaller charger output.

 

[(*steve*)]

Is it also possible that the input to the scope is set to AC coupled causing the trace to centre itself around 0?

 

[jacobi]

Is it also possible that the input to the scope is set to AC coupled causing the trace to centre itself around 0?

I don't have a place to grd my oscilloscope. It just has a positive outlet that I know of.
Where do I grd it then on the case?

 

[BobK]

The probe should have a ground clip attached to it. If not, it is missing.

Bob