Joule Thief 101

[minnie]

  I've found the way to test AA cell is to set on the 10 amp setting, voltage doesn't
  tell you much.
            John.

[tinman]

  I've found the way to test AA cell is to set on the 10 amp setting, voltage doesn't
  tell you much.
            John.

Such a delight to have your insightful input minnie


Brad

[tinman]

  I've found the way to test AA cell is to set on the 10 amp setting, voltage doesn't
  tell you much.
            John.

Actually,you will need a known value resistor in there as well as your amp meter 

[tinman]

 author=MileHigh link=topic=8341.msg488309#msg488309 date=1468308406]

And you can be such a complete bimbo sometimes, can't you Brad?

Bimbo-->an attractive but unintelligent or frivolous young woman.   

Forget about locking yourself up in a room for one month with four electronics books, how about much longer?

And continue to learn the past?

Even if the unloaded voltage of the battery decreases somewhat, this is pretty much junk data and it can be safely ignored.

Lol-ok

The simple battery model works just fine.

Well mine will,yours will not,as the battery voltage will not remain the same as it dose with your model. Your model will show the same voltage across the inductor at T=0 for all time,where as mine will show the actual battery voltage drop at T=0.
If you did some bench work,you would see the error of your ways.

Presumably you might indeed find differences between the absolute and the differential output impedance of a battery at a given operating point, I haven't really read in major depth about batteries.

"Déjà Vu" hit.

However, I am figuring that if there were major differences in the absolute and differential impedance, I would have heard of it.

Like you would of heard about a J/FET

For sure there are much more complex battery models, but we aren't going there.

Nope.
The battery model to suit our purpose is quite simple.

What do you think the "battery tester" function is there for on your multimeter?  It's because just measuring the open-circuit battery voltage with the voltmeter is no good.  You have to switch to battery tester mode to put a moderate load on the battery to get a better picture of the voltage drop/state of charge of the battery.

Indeed MH--now your learning

Now,what voltage will we see at T=0 across the inductor ?
Will it be A-the open voltage of the battery?
Or B-the loaded voltage of the battery,as per what the multimeter will show?

I know that you must know this, and yet you still stated what was quoted above.  It's like Neuron A can't talk to Neuron B sometimes.

Perhaps a little peak in the mirror would be a good choice at this point in time MH.


Now,are you sure you want TK to carry out the measurements again,using your idea of a simulated battery?,where you have a power supply supplying 1.5v,and a VR in series with that power supply to imitate battery impedance.
Perhaps you should look back at some of the earlier measurements,where TK used the PSU,where for some !!odd!! reason,circuit 2 was more efficient at producing more light per Mw.
Have you even stopped to think as to why,when TK used the PSU,that circuit 2 was more efficient than circuit 1,and then by some miracle,when TK swapped over to a capacitor as the power supply,circuit 1 all of a sudden became more efficient than circuit 2

So, shall we do as you request,and use the power supply at a set voltage of 1.5v(or any voltage you wish),and have that series resistor to simulate the impedance of the battery as you stated ?.

What will we get if TK comes back with results like that of his first test using the PSU

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.
A second set of results at a lower input voltage of 1.52V:
Circuit 1 gave 49.3 Lux at an average input power of 54.6 mW for an efficiency of 903 Lux/Watt.
Circuit 2 gave 26.1 Lux at an average input power of 28 mW for an efficiency of 932 Lux/Watt.
Operating frequency is between 10 and 11 kHz.

Will your responce then be much like it was when you fist seen those result's ?

Well, I can easily see Brad having a braingasm from TK's posting

Perhaps MH,you could tell us exactly what type of efficiency you would want to see--that way we can just keep testing until we get the results you want,and screw actually looking for the correct answer--like,why was there a swap around in efficiency between the two circuits ,when TK went from a power supply,to a battery?
Would you like to have a go at explaining that maybe?

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.

Brad

[minnie]

Actually,you will need a known value resistor in there as well as your amp meter 

Rubbish,I've done it for years.