12V lighting track ghost voltage?

[ELA]

I am seeing a 32V p-p signal. -17 to +17V or 12V RMS if a sine wave. The high frequency pulsing appears to be amplitude modulated to approx. what 60Hz amplitude values would be.
Scope triggering is tricky with this type of signal and needs to be addressed in order to get better plots.

If you set the scope as Gar requested also see if you can turn on the "MEASURE" function and select RMS ( if available).

 

[synchro]

I am seeing a 32V p-p signal. -17 to +17V or 12V RMS if a sine wave. The high frequency pulsing appears to be amplitude modulated to approx. 60Hz.
Scope triggering is tricky with this type of signal and needs to be addressed in order to get better plots.

Choosing "Line" as the trigger source as gar suggested should provide more reliable triggering if the waveform envelope is coming from the 60 Hz AC supply.

 

[gar]

220427-2027 EDT

tortuga:

Assuming the light strip you are working on is not in your own home, then there are various experiments you can perform at home with the scope to learn how to use it.

You need to become familiar with various sweep trigger modes, sources of trigger, various types of X-axis time based sweeps, use of different probes, AC vs DC coupling, and a lot of other capabilities.

If you are interested, then I suggest you start playing with some single shot experiments. These are easy to create with lots of variability.

.

 

[tortuga]

220427-2027 EDT

tortuga:

Assuming the light strip you are working on is not in your own home, then there are various experiments you can perform at home with the scope to learn how to use it.

Thanks Gar!
Our customer is a general contractor and he provided the light and is providing a replacement.
When this has happened in the past they usually say to toss the old light, rather than ship it back somewhere.
When the new light comes in, Ill take the defective one back to my home bench along with the Rigol DS1054 so i can learn about scopes.
I also have an old analog BK Precision I'll dust off.
I'll also take some line voltage measurements when I go back to the problem house so see if they have higher than normal voltage.
I kinda wonder if the whole problem might be solved by adding a dimmer.

 

[hbiss]

I'll also take some line voltage measurements when I go back to the problem house so see if they have higher than normal voltage

I kinda wonder if the whole problem might be solved by adding a dimmer.

No. A dimmer will not work with that power supply. The power supply should also be able to compensate for voltage variations.

When the new light comes in, Ill take the defective one back to my home bench along with the Rigol DS1054 so i can learn about scopes.
I also have an old analog BK Precision I'll dust off.

I suggest you start by looking at a simple sine wave from a regular low voltage transformer like a door bell transformer on the B&K. When you are able to understand how the controls work and, most importantly, what you should be seeing then you can move on. As I said above, the Rigol provides a 1volt peak to peak 1000Hz square wave at the calibrate terminals on the bottom right. You can use the B&K to look at that also. Your goal should be to obtain a clear stable one cycle display of the 60Hz sine wave and the 1Khz square wave on the screen positioned so that you can read the voltage using the vert setting and the lines in the graticule.

I wouldn't bother with the Rigol or the power supply until you find a good source of instruction. Simply pushing the auto button IS NOT the way to go.

You are not going to get all this by osmosis.

how to use an analog oscilloscope - Search Videos

www.bing.com

-Hal

 

[gar]

220429-2038 EDT

tortuga;

I am going to make a suggestion or more of some simple experiments you can do to get a little familiar with your scope.

My first experiment suggestion is to look at the exponential curve that occurs from the discharge of an initially charged capacitor thru a resistor. This will be a single shot experiment.

I suggest a 12 V DC battery source, a lantern battery with two binding posts. This is way bigger than needed, but it has an easy way to connect to it, and an adequate amount of voltage.

A 10,000 ohm 1/2 w resistor. Possibly a 27,000 and 47,000 as well. A 1 mfd paper or Mylar capacitor. As this point I would not go less than 0.1 mfd. Any available voltage above 20 V is fine.

I believe you have used no scope probe, or possibly one with a times 1 ratio. That is OK for these experiments. A 10 times would be OK.

The capacitor is connected in parallel with the Y axis input channel you are going to use. The battery negative is connected to the scope common ( that is the outer shell of the scope BNC input connector ). And of course the other end of the capacitor is to the center pin of the BNC. The charging or discharge resistor is in parallel with the capacitor.

What we are going to do is charge the capacitor from the battery to + 12 V, and then allow the capacitor to discharge thru the resistor. This will be an exponential curve. As a starting point set the time base to 10 mS per major division. Assuming you have the equivalent of a 1 to 1 probe put the Y axis at 2 V / division.

Set trigger mode to AUTO, then select MENU. Select EDGE triggering, for the channel you are using, and select negative slope triggering.

Go to Y-axis and put it in DC coupling.

With no battery voltage applied adjust the horizontal trace to be 1 major division above the screen bottom. Connect the Y input to +12 and that horizontal line should jump up about 6 major divisions. You may see momentarily a curve in the trace during this transition.

You should see a marker at the top middle of the screen. This indicates the trigger time point.

If you turn off the right hand menu, then there should be a pointer on the right side that indicates the trigger point. Sometimes this is way off the screen. There should be a numeric display at the screen top that tells you the trigger level point. Adjust the trigger level to be in the middle of the screen vertically.

Next connect the battery 12 V + to the hot end of the capacitor. Switch trigger to single shot, and push the single button. Nothing will happen until you remove the 12 V supply. Then an exponential decay occurs, and when the trigger point is crossed this triggers the single trace capture.

Is this something you can try?

.

 

[gar]

220430-0616 EDT

Something very important to understand is ----
The scope BNC commons ( the outer shell of the BNC connectors ) are all connected together, and to the EGC pin of the AC supply. The impedance of this path is very low. Much lower than on a Tektronix scope. But in any case for any scope never connect the common of the scope signal inputs to any signal source that will connect back to any AC EGC, common, or hot lead, This connection could cause great damage to the scope.

You can isolate the scope common from a problem for small voltages between the scope common and AC common or EGC by use of an AC adapter at the scope AC cord plug for two wire ( hot and common ) to the AC cord plug by NOT connecting the adapter's EGC wire to anything. But you still do not want to work with a large difference voltage between the scope common and AC common or EGC. A 10 to 20 V difference might be OK.

This whole common problem is something you always need to be aware of.

.

 

[gar]

220430-1535 EDT

The next experiment to tries ....

Get a small bell transformer, and put its 120 V primary in parallel with the 1 mfd capacitor at the Y input. Pick a resistor than will produce a 20 to 50 mA current from your DC source. 50 mA at 12 V is 0.6 W. So use at least a 1W resistor.

Keep the scope in single shot mode, and try a 10 mS / div time base. Connect the battery and resistor to run the charging current thru the inductor. Apply and hold the charging current. Now push the single shot button, then release the charging current and you will see a damped oscillation of about a period of 40 mS. This damps very quickly.

.

 

[hbiss]

But in any case for any scope never connect the common of the scope signal inputs to any signal source that will connect back to any AC EGC, common, or hot lead, This connection could cause great damage to the scope.

Very good advice. Never connect a scopes input to a receptacle or power like you would with a meter. Not sure if anybody uses an isolation transformer to power the scope but I imagine it would be a good idea if you frequently need to do such measurements. Much like servicing old hot chassis radios and TVs.

Also, observe the maximum voltage ratings of the inputs. If you are working with tube type equipment the B+ voltage can fry an input.

-Hal

 

[gar]

220430-2200 EDT

tortuga:

My next experiment for you is to use two Y channels.

Channel 1 has the parallel 10 k and 1 mfd combination as before. You will continue to use channel 1 as the sync source. Start with 10 or 20 mS per division as the time base. Continue with the 12 V battery. And make both Y channels 2 V per division with 1 X probes.

Connect a 1 mfd capacitor across the channel 2 input. Put a 10 k resistor between the hot inputs of channels 1 and 2. Make channel 2 active as well as 1.

As before apply 12 V across channel 1 to charge both capacitors. Activate single cycle button, then remove the 12 V excitation. Obviously the sync trigger point had to be within 0 to 12 V, and is still from channel 1..

The result is two similar decay curves. The channel 1 is nearly the same as when the second capacitor was not present. The channel 2 curve is similar to the channel 1 curve, but somewhat slower decay, a slightly changed shape, and slightly rounded near t = 0.

.

 

[tortuga]

Thanks for this gar, I am going to give this a try next week when i got some free time.