A Perspective On The B Type EESD - Robert Murray-Smith - Any issues?

[MileHigh]

No need for that! Both circuits make the LED I'm using "blindingly bright" when viewed by eye. I'm barely able to see the difference in brightness, but the lightmeter tells the tale.

Phasers on blindingly bright....

[markdansie]

Take a look at a Joule Thief.   Are we talking about electrical power in vs. electrical power out efficiency like Poynt just stated?  Or are we talking about electrical power in vs. light power out like TK just stated?

What about the LED itself?  Are you doing your "burn" at the optimum efficiency point for the LED where you get the most light out per milliwatt in?

Hi MH
I had a recent experience that is very relevant to this. I was in China at a lighting manufacturer who we are having build some lighting technologies using our Hydra-Cell. I had with me a simple Dc to DC converter designed by the late Mark E , a water cell and a lux meter with 3 leds in a tube attached.
The Chinese engineers said they had designed a more efficient board according to the volts/amps in and volt/amps out. So we tested there using the water cell and the lux meter measuring light output. We measured 570 units of light. We then put in the Mark E board and measured 1270 units of light. They are still dumb founded. So measuring light output vs electrical sheds a whole ne light onto things.


The led we used has an efficiency of 180 lumens per watt in this case. It is always important to use the same led when testing and the optimum power that led has been designed for


We have also tested many variations of the Joule Thief and the closest was about 85% as efficient according to light output.
In the case I just explained the light output was what we wanted as it is being applied to a lighting product.
Many other variable can come into play.


The trick in this case was the circuit extracted the maximum energy available out of the cell by forcing it to operate at the optimum voltage we had established by power characterization testing.


I hope my experience helps to understand that there are many other variables in the equation when comparing light output to electrical output.


PS TK has some knowledge of what I am talking about


Kind Regards
Mark Dansie

[TinselKoala]

Well, I can easily see Brad having a braingasm from TK's posting so I will get a few words in edgewise.

One of the classic weaknesses on the forums is to use the term "efficiency" without even defining what it means.  Brad is someone that does this all the time.

Take a look at a Joule Thief.   Are we talking about electrical power in vs. electrical power out efficiency like Poynt just stated?  Or are we talking about electrical power in vs. light power out like TK just stated?

What about the LED itself?  Are you doing your "burn" at the optimum efficiency point for the LED where you get the most light out per milliwatt in?

How flat or sloped is the current discharge curve across the LED when you are doing a burn?  Does this have an impact on the power in to light out efficiency?

What about the flashing frequency and duty cycle and human perception of brightness?

What about the human perception of the light level?   How do you define an "adequate" level of light output from the Joule Thief?  Is it just bright enough to be a panel indicator light?  Or do you want a practical amount of light like a small night light?  Is there a sweet spot for human perception of the light output from a Joule Thief?

How you define efficiency for a Joule Thief is a big enough question for such a little circuit.  But it is what it is.

Just saying, "Wow, that looks like an efficient Joule Thief!" is essentially meaningless if you don't qualify it.

Oh my god I must be wrong based on TK's data!  Brad is going to have a braingasm!

Why did I say that circuit #1 might be more efficient?

My line of thinking was as follows:  In circuit #1 when the LED is lit it is based on a discharge of the LED in series with the battery.  So the EMF from the battery is a "helper" to keep the LED lit.  So, it suggests to me that circuit #1 may be able to extract more energy from a nearly dead battery because it looks like it will run at lower battery voltages than circuit #2.  That will likely translate into a longer run time from the same battery.

How did I define "efficiency" for the "most efficient Joule Thief?"

The answer was the most efficient Joule Thief by my definition would be the one that has the longest run time and extracts the most possible energy from the nearly-dead battery.

I stated this to Brad multiple times but it never sank in.

Now we can go back into the holding pattern waiting for Brad's expected tsunami braingasm.

Brad:  I still would like to see your "bench smarts" measurement procedure for your supercapacitor.

You bring up lots of valid points wrt "efficiency" of a JT type flashing/pulsing light. There are many many variables to be considered, both in the circuit itself (like number of turns, core material, impedance of power source, etc) and in the behaviour of the LED, the lightmeter, etc. As far as I can tell this lightmeter is doing a pretty good integrating of the 9-13 kHz flashing of the LED so I mostly believe in its readings. I don't have "threshold" operation levels yet, that is I don't know the low voltage limit of the two circuits. It seems to be the case that the supply impedance affects the efficiency (my definition, Lux/watt input power) but I'll have to do more testing to see how much. (Power supply vs battery have different impedances.) Then there is the matter of the turns ratio of the inductor. Then again, the different waveforms that the oscilloscope sees on the input current measured across the 0.1 ohm CSR in the two cases may be affecting the calculations of the average input power, although I've made the computation using DMM measurements and they agree with the scope measures to within 10 percent or so.

So nobody should take my measurements as "solving" the issue or supporting either side of the argument _at this point_. At best, I am trying to establish a reasonable testing protocol that can be used to track down the effects of the various variables in the experiment.

[ramset]

Poynt
Quote
Well there we have it Chet. It's a no-go.

MH and TM will just have to keep bickering at each other I guess...

end quote.

Well I commend you for your thoughtful input ,and it is quite obvious you can see a path towards this taking place
and I know itsu would be able to work hand in hand with MH to assist in the necessary bench test for dialing in his circuit.

itsu has done this "bench time" very well with Verpies and others.

However
There is definitely a high anxiety level ATM.
------------------
Compliments to Tinsel for his Input !!

we shall see??

Respectfully
Chet

[tinman]

While it is very amusing to see you mates arguing back and forth, it has been a long time since anyone has actually posted any real empirical results. Some of the arguing and conjecturing (hand-waving, or maybe ****-waving      ) has to do with the Joule Thief circuits and their efficiency. So I decided to make up a test bed and do some testing.

The results so far are to be considered preliminary, but it looks like Circuit 2 is the efficiency winner, by a thin margin. It produces less brilliant light but on a lux per watt basis it wins.

I am running short on suitable toroids so I wound the inductor on a small pot-core setup. This is probably even better than using a toroid, and a heck of a lot easier to wind. Both L1 and L2 are 20 turns of #34 magnet wire.

I couldn't get my power supply to set precisely at 1.5 volts; the voltage monitor showed 1.62 volts for the tests I have run. I checked input voltage and current both with DMMs and with oscilloscope and got essentially the same results. The output ran one LumiLed super-efficent LED in my lightbox, with the ExTech LT300 lightmeter, with sensor 18 inches away from the LED. As you can see from the image of the test circuit below, all I had to do to change between the circuits was to flip the LED connector over and attach it to the other output pins. The actual position of the LED in the lightbox is exactly the same in both cases, there is absolutely no difference in the two setups except how the LED is connected to the board.

So, Circuit 1 ran at an average input power of 90 mW and produced 63.9 lux at the sensor, for an efficiency of 710 lux per Watt.
Circuit 2 ran at an average input power of 40 mW and produced 30.0 lux at the sensor, for an efficiency of 750 lux per Watt.
By eye, there was little difference in the brightness of the LED, even though in real terms #2 was half as bright as #1. Both circuits ran at a little over 12 kHz, but with very different waveforms (Collector wrt Emitter). I'll show the waveforms later on, perhaps also with a video of the testing.

So the efficiency winner in these preliminary tests is Circuit 2, by a thin margin. Brightness winner is #1 but will definitely drain the battery much faster.

Great test TK,and of course the results are as expected.
As  i pointed out to MH,the second circuit eliminates the losses associated with charging the battery also,when a battery is used in place of your PSU. The battery will produce more waste heat,when being discharged and charged continuously,and also there are the internal resistive losses that grow as the battery voltage drops.


Brad