Joule Thief

[poynt99]

Measurements and claims discussion on all forms of the JT.

This is a rebuild of the JT topic after Stefan messed up and merged this original thread and one that was started afterward because I did not allow the whining and BS for which Wilby is famous and evidently has a real knack for.

.99

[poynt99]

Stefan,

How will you measure this GJT to ensure at least 1W of power is being supplied by its output?

I would not rely on the specification of an LED. LED's can run on a wide range of voltage and current inputs, above its minimum. You can run a LED off 20mW or so (i.e. 10mA @ 2V).

I would suggest dispensing with LED's as an output power indication in favor of a 0.5W or 1W suitable value* carbon resistor. Do a control test with a DC supply and see what temperature the resistor is at with 1W input power. Then monitor the resistor's temperature for the DUT test to ensure it remains at that temperature, or higher. *A value that results in a temperature rise of say 20 to 40ºC above ambient.

As a side note, the applicant would be wise to tweak the submitted device to put out the amount of power he thinks will make the device last the 3 months and still maintain the minimum 1W output.

An AA battery should be able to source 1W of power for about 3.75 hours (assumed 1.5V output). This control test being with a standard Ohmic load, for example a 1.5 Ohm resistor. At this point, the battery would have fallen to a certain percentage of its full charge voltage. The battery however is not fully depleted of its energy.

It should be noted that using this same battery in a step-up circuit such as the JT, the time duration of this 1W output power can be extended quite a lot for two reasons:

1) The average load current on the battery is lower than with the control test, and

2) The JT facilitates access to more of the battery's stored energy, depleting it far beyond what the control test will while still being able to maintain the 1W power output.

I estimate therefore, that the AA battery would be able to charge the 650F cap from 0V to 2.6V about 8 to 10 times using the JT to charge it.

So I would suggest the temperature monitored resistor as the output power indicator (use a thermistor attached to the resistor), and see how long the GJT can keep the heat on. This will require some tweaking of the switching circuit which dumps some of the cap's energy back into the battery, such that it does so before the resistor's temperature drops below the required minimum.

For a 1W constant load, I will be surprised if this circuit (powered by a 2500mA AA battery) lasts more than 10 hours, which is a little shy of 3 months.

.99

[poynt99]

Poynt:

The issue about "recharging" the AA battery from the charged ultracapacitor.

The poor AA battery gets fried for a few seconds, I don't remember how many.  The ultracap forces 2.6 volts across the battery and discharges through it at quite a high amperage.  The amperage could be checked with a variable power supply.

I have to assume that at least 4/5 of that energy becomes heat and less than 1/5 charges the battery.  I also assume that the battery will manifest a higher voltage for a few minutes after that extremely stressful event.  If you do this for too long something in the poor battery would start to boil.

Therefore when the battery voltage is measured after this event, the voltage is a bit higher from when you started charging the ultracapacitor due to the "shock treatment."  Hence there is a "victory" claim - but in reality what you just did was dissipate some stored battery energy as heat energy - back through the initial source battery.

I am not going to crunch the numbers but if you assume 10 amps for 10 seconds you probably only get a tiny voltage drop across the incredibly humongous 360 farad cap.  For all practical intents and purposes, the battery becomes a resistor dissipating 20+ watts of power for 10 seconds.  That should make it toasty warm.

These are my opinions and I approved this posting.  lol

On the capacitor front, I tried to explain how a "regular" capacitor, a supercapacitor, and ultracapacitors are all fundamentally the same thing - capacitors.  This was fiercely objected to by Pirate88179 and I got vaporized in seconds like steel wool hugging an ultracapacitor.  I even extended a polite invitation to discuss it here.  Apparently the truth about the differences between different types of capacitors is to be found in the Joule Thief ten-thousand posting archive.  The invite is still open Bill.

MileHigh

[poynt99]

MH,

I agree with most of what you're saying.

Back to the cap. Yes, the now infamous Mr. Gadget doesn't quite understand the implications of what he is doing by discharging that huge cap into that poor AA battery. Not only is he stressing Mr. AA to pieces, but he's wasting a great deal of energy by doing so. But alas, it will only end speculation that much sooner, and as I said before, I give the GJT device less than 10 hours of operation at 1W. But then again, the entry for the OU prize won't be official until Stefan receives one to test. Will it make it to that stage? I am doubtful.

.99

[poynt99]

Experiment, observation and measurement. Now that is where the wheat must really be separated from the chaff. Indeed I'll be pleased when I see some appropriate and well-executed measurements taking place in some of the threads at this forum.

.99