Joule Thief 101

[picowatt]

Have a good hard think about it Poynt--about what drives the magnet oscillator,and how it could be possible to get the results shown. I will add that(although mentioned in the video),the input RMS value is kept at a constant throughout the test by the voltage regulation function of the FG--as can be seen in the scope shots below,where Ch1 is the voltage across the primary coil,and CH2 is the current flowing into the coil,measured by way of voltage drop across a 3 ohm CVR.

https://www.youtube.com/watch?v=mlb79xSh93w

Brad

What is this "voltage regulation function of the FG" you mentioned?  Isn't your FG output 50R?  Although a bit rare, I have seen some FG's with a very low Z output selection .  Perhaps yours has that function as well?

Is the scope CH1 actually across the primary or before the 3R CVR?  I thought CH1 was across the 5R secondary load.

A schematic of the setup with probe points would be helpful...

PW

[MileHigh]

Poynt, PW:

I suggest that you don't do anything yet with respect to Brad's question because it appears that Brad hasn't even done the work himself.  He believes his little experiment with the oscillating post that has a magnet on it, which is oscillating in front of a coil driven by the function generator, is showing "magical work coming from magnets" once again based on the two scope shots.  Now he is coming here asking for a spoon-feeding session and he is expecting, yet again, to see you guys do the work and validate his theory.  We all know how that one will end up.

Here is an earlier quote from Brad about his experiment:

Now,lets see your books and laws work that one out MH--and remember,this is a very simple setup that anyone can make,and verify my results-i think Mags already has--not sure on that though.

Your so happy to sit there and criticize my work--point out faults that don't exist ,dismiss PMs being able to do any work--then lets see your books explain the result's.

The P/in for each test-without and with the oscillating magnet are there in the scope shot's. Voltage and current is in phase--easy to calculate P/in.
P/out from the secondary is there in the video for both cases--so work it out MH-give ya books a good work over,and see what you come up with.
The change in inductance test was done in the video,and clearly shows that with the large laminated block increasing the inductance by a huge factor,still did not come close to the results of the oscillating magnet. So we can rule out any inductance increase. Then along with that fact,and there being no phase shift between voltage and current,or no change in frequency,and also the frequency being very low,and resistance staying the same,would take care of any sort of change in impedance or reactance.
So what else do your books have MH?

Well in fact in both of the scope shots there is a slight phase shift between the voltage and the current, and the two phase shifts are not the same.  That may or may not be significant in determining what is going on in the experiment.

I also explained to him that when he added the oscillating post and magnet to the system, the electro-mechanical impedance of the setup changed, and that's why he was getting different results.  From the quote above, he is saying that he disagrees that the impedance is changing.

So Brad adds the oscillating post and the current draw decreases and If I recall correctly there is also more power being dissipated in a five-ohm load resistor attached to the transformer secondary and the phase on the secondary voltage also changes.

I told Brad before he draws any conclusions to do a full power audit in both cases and see where the input power is going.  I also told him that he could use an optical system to understand the phase relationship between the oscillating post and the voltage from the function generator so he could understand what is going on there.

So at least it appears that Brad has done none of this.  All that he did was look at a kind of glorified "numbers in boxes" deal and arrive at a conclusion.

So there is no point in doing any kind of analysis for Brad until he actually tries to do the analysis himself first.

MileHigh

[tinman]

A schematic of the setup with probe points would be helpful...

PW

What is this "voltage regulation function of the FG" you mentioned?  Isn't your FG output 50R?  Although a bit rare, I have seen some FG's with a very low Z output selection .  Perhaps yours has that function as well?

Yes,mine has that selection--50R or !Z! as you call it,which in my case is 50R or 0-R.

Is the scope CH1 actually across the primary or before the 3R CVR?  I thought CH1 was across the 5R secondary load.

The posted scope shots are with ch1 across the coil/resistor combo,and CH2 across the CVR.
They were posted to show MH that there was no phase shift or voltage change(CH1) when the magnet was in play.

In the video,CH1 was across the load resistor on the secodnary,and CH2 across the CVR on the primary.

Brad

[poynt99]

What would need to change if a ferromagnetic material was bought close to the air core transformer in order for the impedance to change--E.G,inductance?

One would think inductance, yes.

Have a good hard think about it Poynt--about what drives the magnet oscillator,and how it could be possible to get the results shown. I will add that(although mentioned in the video),the input RMS value is kept at a constant throughout the test by the voltage regulation function of the FG--as can be seen in the scope shots below,where Ch1 is the voltage across the primary coil,and CH2 is the current flowing into the coil,measured by way of voltage drop across a 3 ohm CVR.

https://www.youtube.com/watch?v=mlb79xSh93w

Brad

I did watch the video a couple of days ago.

An increase in impedance would certainly cause a drop of input current and possibly an increase in output.

What other introduced element can cause the circuit to appear as though the impedance has increased (i.e. a decrease in current)? How about an opposing voltage, i.e. cemf?

The input current is determined by the potential difference across the primary impedance, with the assumption that the opposite end of the primary is at gnd potential (see "normal case"). In this case Vpri is Vfg=3V. Now what happens if another FG is connected to the bottom of the primary? See "cemf case". Now Vpri is Vfg1-Vfg2=2V.

Nothing was changed in terms of the transformer impedance, but the input current is clearly going to be lower in the case when cemf is introduced.

Is this happening here and in the rotor example (pretty much the same in concept)? Is the moving magnet also causing a higher output? I don't know for certain, I'm just speculating at the moment in an attempt to explain the reduced input current without changing the impedance.

[MileHigh]

Yes, increased in-phase CEMF is what I asked him to check for by rigging up a photocell to measure the phase of the vibrating post relative to the function generator EMF.  He could then simply move  the post in and out on the bare coil and determine the corresponding EMF polarity from the magnet.  The two EMFs together may explain the increased power in the load resistor but you have to know the phase.  You just have to do the work to find out what is going on.