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Author Topic: To be deleted  (Read 14528 times)

Offline Void

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Re: To be deleted
« Reply #60 on: December 08, 2018, 07:21:00 PM »
Hi Itsu. OK, I see. Maybe using an appropriate CSR and using a voltage probe would
give more stable current readings.


Free Energy | searching for free energy and discussing free energy

Re: To be deleted
« Reply #60 on: December 08, 2018, 07:21:00 PM »

Offline Void

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Re: To be deleted
« Reply #61 on: December 08, 2018, 07:43:35 PM »
Pot, caps and Inductor power dissipation.

Hi Hoppy. Well, in my estimation those would not account for the approx. 5 mW discrepency
as their power consumption would be fairly low, but Itsu has pointed out that his current probe
may not be giving consistent readings (at those low current values). All the best.

Offline itsu

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Re: To be deleted
« Reply #62 on: December 08, 2018, 08:38:58 PM »
Hi Itsu. OK, I see. Maybe using an appropriate CSR and using a voltage probe would
give more stable current readings.

I did use a 10 Ohm 1% inductionfree csr (1 Ohm is to noisy) in the beginning and compared the values with the current probe
and found them to be very similar, but they might influence the working of the whole circuit.

So therefor i opted for the current probe as it is much more convenient to use on a fixed PCB circuit.

I think i will be very close to accurate measurements when averaging like 10 measurements or so.


itsu

Free Energy | searching for free energy and discussing free energy

Re: To be deleted
« Reply #62 on: December 08, 2018, 08:38:58 PM »
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Offline Void

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Re: To be deleted
« Reply #63 on: December 08, 2018, 09:11:07 PM »
Yes, sounds good Itsu.

Offline itsu

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Re: To be deleted
« Reply #64 on: December 09, 2018, 03:14:52 PM »

Collected measurement data up till now:


Itsu

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Re: To be deleted
« Reply #64 on: December 09, 2018, 03:14:52 PM »
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Offline Void

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Re: To be deleted
« Reply #65 on: December 09, 2018, 06:52:24 PM »
Looks good Itsu.

My Siglent SDS1204X-E scope can do the same sort of math calculations
that you are using to compute the power consumption, so I tried a power measurement
comparison test with two test circuits using the exact same type of white LEDs in both test
circuits. One test circuit is DC, so the power measurement is straight forward. The other
test circuit is using a 10% duty cycle pulse train to power the LED. The LEDs in both circuits
were adjusted to be approximately the same brightness, but that is very hard to do by eye,
so their brightness is probably not a really close match, but they were in the same ballpark of
brightness anyway. :) The frequency of the pulse waveform was set to 10 kHz.

See the attached test circuit diagrams which I used in this test.
The LED power consumption in the DC test circuit came out to: 2.71V x 5.2 mA = 14.1 mW
The LED power consumption in my AC test circuit was measured using a product math function
and then taking the mean of the resulting waveform (White trace).
(mean of the product of the voltage and current waveforms), and is: 1.67W /100 = 16.7 mW

The difference between the two power measurements may be largely due to my eye not being able
to accurately compare the brighness of the white LEDs in the two test circuits. There may be other factors
in there that are affecting the power measurement a bit as well. The 100 Ohm CSR resistor value is close
enough to 100 Ohms, but off by a few Ohms. So using the scope product Math function and taking the
mean of the resulting waveform seems to give a reasonable result, in this test setup anyway.

Notice that in the attached Scope screenshot that the measured scope RMS values for the LED voltage and
LED current are not useful in doing any power measurements when measuring asymmetrical AC waveforms.
The current is being measured across a 100 Ohm CSR, so current must be divided by 100.

Ch 1 - Yellow trace - LED Voltage waveform
Ch 2 - Pink trace - LED current x100 (Set to Inverted)
White trace - Power waveform - Product of Ch1 x Ch2, with the Mean of this waveform indicated.

P.S. No jokes about Channel 2 having a pink trace. :D That's the way the scope is configured, and I don't
see any way to change the trace color. Why they chose pink instead of orange or red is beyond me. ;D


Offline itsu

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Re: To be deleted
« Reply #66 on: December 09, 2018, 07:30:37 PM »

Very nice Void,

yes, eyeballing a led (pulsed or steady) is almost impossible, you need a black box / lux meter to measure properly, but still you came very close.

Indeed, it again shows that the measured scope RMS values for the LED voltage and LED current are not useful in doing any power measurements
when measuring asymmetrical AC waveforms.

 
 
Strange colors indeed, most scopes i know have fixed colors, so nothing to do about that i guess.


Itsu

Free Energy | searching for free energy and discussing free energy

Re: To be deleted
« Reply #66 on: December 09, 2018, 07:30:37 PM »
Sponsored links:




Offline Void

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Re: To be deleted
« Reply #67 on: December 09, 2018, 08:45:49 PM »
Hi Itsu. A few things I don't really understand with my scope is how the scope
is computing those RMS values. I would have thought the RMS values would come out
a lot lower considering I was only using a 10% duty cycle. My scope indicated 9.54 V RMS
for the voltage waveform and 12.8 mA RMS (1.28 / 100) for the current waveform. Not sure
how my scope is arriving at those values. The actual RMS voltage across the LED should be
around 2.7 V to 2.8 V, and the actual RMS LED current should be around 6 mA.  :o
All my scope's manual says for the RMS measurement is: "RMS: Root mean square of all data values."

Another thing that I think is odd is both Channel 1 and 2 were set to have the traces centered
vertically in the screen, but channel 1 has the waveform sunk down to its average DC value,
which I think is normal when displaying this kind of waveform on a scope using DC coupling, but
the waveform for channel 2 is displaying with the lower part of the waveform in the center of the screen.
Channel 2 is also set to DC coupling. I am not sure why channel 1 displays as sunk down to the average
while channel 2 is not. Can anyone explain why the 2 channels are displaying differently?

The scope is a fairly new scope, so it could have bugs I suppose. Not sure if the above mentioned results
are what should be expected, but they seem odd to me anyway. :)


Offline itsu

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Re: To be deleted
« Reply #68 on: December 09, 2018, 09:28:01 PM »

Void,

i have the same (down offset) yellow voltage trace when using an AC pulse.
When using a DC pulse its like normal.

Also, do you use a grounded Signal Generator?  If so then the (grounded) black lead will short out
the 100 Ohm  resistor as very probably the both scope ground leads are also grounded.

Itsu

Free Energy | searching for free energy and discussing free energy

Re: To be deleted
« Reply #68 on: December 09, 2018, 09:28:01 PM »
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Offline Void

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Re: To be deleted
« Reply #69 on: December 09, 2018, 09:42:55 PM »
Hi Itsu. Yes, I guess because the current is rectified by the LED,
the current waveform shows differently than the voltage waveform, which was AC with 0V DC offset. 

I was using a portable signal generator that was powered from my bench power supply.
I used my DMM and measured the resistance between the scope ground and the signal
generator ground across the 100 Ohm resistor, and it measures as 103 Ohms, so the
signal generator ground was isolated from the scope ground. If it was a short,
I wouldn't have measured any current across the 100 Ohm resistor.

Also, I think I may know why the scope is calculating the RMS values the way it is, by I am
still reviewing that. I will post something here if I figure it out. :)



Offline itsu

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Re: To be deleted
« Reply #70 on: December 09, 2018, 09:51:06 PM »

I used a battery operated SG, but it has only 10Vpp output, see white trace when unloaded (10Khz, 10% duty, AC)


The setup used is the same as your right diagram above, white led, 100 Ohm resistor, probes setup the same.

Yellow is the (sunken) voltage across the led
blue is the current through the 100 Ohm csr (rms value adjusted to show correct value, so no /100 needed).
red is the math trace yellow x blue = power of the led.

So nothing wrong with your scope, its probably the led (diode) doing this.


Itsu 

Free Energy | searching for free energy and discussing free energy

Re: To be deleted
« Reply #70 on: December 09, 2018, 09:51:06 PM »
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Offline Void

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Re: To be deleted
« Reply #71 on: December 09, 2018, 09:55:46 PM »
Thanks for that Itsu. Yes, the LED is rectifying the current waveform, so it
shows differently than the AC voltage waveform. Thanks for confirming that!


Offline Void

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Re: To be deleted
« Reply #72 on: December 09, 2018, 10:25:51 PM »
For the current waveform in my AC test, it is a DC pulse waveform with a 10% duty cycle,
so I believe the correct RMS formula for that type of waveform is: Vp x sqrt (duty cycle ratio).
Based on the current waveform in my scope screen shot, this would give:
4 x sqrt (0.1) = 1.26
The scope calculated the current RMS as 1.28, so that is pretty close. :)
1.28 /100 = 12.8 mA
However, the actual RMS current for the LED should be around 6 mA (estimated), so we can't
use that calculated RMS value by the scope.

For the voltage waveform, we have an AC pulse waveform which the scope is offsetting
with a negative offset. The RMS voltage value calculated by the scope is also not correct for our circuit,
because the LED is only conducting for 10% of the time, but the scope is calculating the RMS value for
the entire waveform cycle. I am still fiddling to see if I can figure out how the scope calculates that 9.54V RMS
value for the voltage waveform. :) The actual RMS voltage across the LED was probably about 2.75 V (estimated).

At any rate, the RMS values calculated by my scope obviously can't be used to calculate the power consumption
of the LED with a pulse type waveform being applied to the LED. :)

P.S.
After thinking about it, I guess the way the scope calculates RMS values is to square all the measured sample
values taken over a period of time, then calculate the mean of those squared values, and then take the square root
of the calculated mean. I am feeling too lazy right now to save waveform samples to a CSV file and compute it
all out using Excel, but I might try it at some point to confirm if that is how the scope calculates the RMS values.  ;D

P.P.S.
Since the voltage and current waveforms are pretty close to being a nice rectangular shape in my test setup,
another way to do a sanity check on the measurement of the power consumption of the LED in my AC test circuit
is to use the actual scope measured values (as shown in the scope screen shot I posted above).

If we do it this way we get (I think this is right, but maybe I am overlooking something :) ):
We are only concerned about the voltage waveform when the LED is conducting,
so, V measured = 0.65 divisions x 5 volts per division = 3.25V
I measured = ( 4  x 1 A per division) / 100 = 40 mA
Duty cycle is 10%, so the duty cycle ratio is 0.1
3.25V x 40 mA x 0.1 = 13 mW
The scope's measured/calculated value for the LED power consumption (using the Math function) was 16.7 mW.
Ballpark, but not exactly really close. Maybe this method of estimating the power consumption of the
LED is not right, or maybe it is not so accurate. Or maybe the power calculated using the Math function was off a bit.

I think this only works out (roughly) because the waveforms are quite clean rectangular waveforms.
However, thinking about it, that should actually be what the LED is doing. According to the scope measurements,
the LED has 3.25V across it and conducts 40 mA during its On time, which is 10% of the time.
That very possibly may not be so good for the LED however, if left running for a long time.  :D

This is why it is way easier to try to self-loop a circuit that you think might be OU, and see
if it will self-sustain itself.  No measurements or calculations required, and much less chance of
making an error somewhere.  ;D


Offline itsu

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Re: To be deleted
« Reply #73 on: December 10, 2018, 11:31:38 AM »

Hi Void,

on this wiki there is some info on rms values / waveform:
https://en.wikipedia.org/wiki/Crest_factor

So every waveform needs its specific calculation to arrive at the correct rms value.
I can not see how a scope does that, so probably there is some generic way.

But i agree, (power) measurements are no easy task and marginal cop > 1 values should be treated with causion.


Itsu

Offline nul-points

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Re: To be deleted
« Reply #74 on: December 10, 2018, 12:16:34 PM »

Therefor i am planning to take daily measurements and take the average after some time.

Today i did a second measurement and put the results in a spreadsheet, see below.
There you see that the difference between input and the power users is much smaller (about 1mW)

Itsu


interesting observation, thanks Itsu - i'll look forward to seeing how those readings develop


np

 

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