Interesting Higher Powered Joule Thief I just made - Part 2.

[Legalizeshemp420]

I just tried it on a fresh NiMH that read 1.30V and it over ranged my meter which has a maximum of 200ma.   Yeah, if I had money I would have a better meter, lol.

So, I had to put it on the 10A settings and it read 0.54  Well, OMG, that is 540ma I am draining from the battery for the 700ma LED.

Interesting.

[Legalizeshemp420]

With the 3 watt 700ma LED in the circuit (everything is as is in the video) I get a little over 2 volts with a battery at .57 volts.  The signal is as it is in the picture.

Now if I could only get it to put out 3 or 3.5 volts at .57vdc

[TinselKoala]

1. You can use a small resistor like 1 ohm or 0.1 ohm and hook the DMM Voltmeter across the resistor and look at the voltage drop. This will give you the current by Ohm's Law.
2. You have a load (the LED) that starts out looking like an open circuit, and then as the supplied voltage rises to the LED's rated "forward voltage" the LED turns on and starts looking like a low resistance load. So the voltage you are supplying can't go much over this value, since the LED is "shorting" it out when it turns on. This is why you get higher voltage when you put LEDs in series: the JT's spikes must rise higher before the LEDs turn on and limit the voltage rise. Try running your JT with no LED load and monitor it on the scope. You should see higher voltage peaks when it's oscillating with no load.
3. You talk about "20 mA" or "700 mA" LEDs as if you expect them always to draw this current. But the current the LED draws is determined by the voltage you supply to it. The more voltage you supply, the more current the LED will draw, until the LED's limits are exceeded and it fails. Try this: hook up your straight DC power supply, your milliammeter, and your "700 mA" LED all in series, and start bringing up the voltage. You will see that the LED gets pretty darn bright well before it is drawing 700 mA. However it will not draw 700 mA until you supply it with its normal rated voltage. When you do supply it with its rated voltage and it is drawing 700 mA, then you should be at the rated light output (and you will need a heatsink, because you will be trying to dump several Watts of heat power out of that tiny LED package.)

[Legalizeshemp420]

1. You can use a small resistor like 1 ohm or 0.1 ohm and hook the DMM Voltmeter across the resistor and look at the voltage drop. This will give you the current by Ohm's Law.
2. You have a load (the LED) that starts out looking like an open circuit, and then as the supplied voltage rises to the LED's rated "forward voltage" the LED turns on and starts looking like a low resistance load. So the voltage you are supplying can't go much over this value, since the LED is "shorting" it out when it turns on. This is why you get higher voltage when you put LEDs in series: the JT's spikes must rise higher before the LEDs turn on and limit the voltage rise. Try running your JT with no LED load and monitor it on the scope. You should see higher voltage peaks when it's oscillating with no load.
3. You talk about "20 mA" or "700 mA" LEDs as if you expect them always to draw this current. But the current the LED draws is determined by the voltage you supply to it. The more voltage you supply, the more current the LED will draw, until the LED's limits are exceeded and it fails. Try this: hook up your straight DC power supply, your milliammeter, and your "700 mA" LED all in series, and start bringing up the voltage. You will see that the LED gets pretty darn bright well before it is drawing 700 mA. However it will not draw 700 mA until you supply it with its normal rated voltage. When you do supply it with its rated voltage and it is drawing 700 mA, then you should be at the rated light output (and you will need a heatsink, because you will be trying to dump several Watts of heat power out of that tiny LED package.)

Nope, I don't always expect them to draw that since they really aren't a resistive load and why in the simulator I can't measure anything with it.  After using a .1ohm (I do not have that value irl) and the 1 ohm in the simulator I just discounted them irl too.

[MileHigh]

Note that commercial LED power supplies are rated in current out, not voltage.  They are current sources.  So you always hook the LEDs in series to an LED power supply.  The higher the wattage of the power supply, the more LEDs it can drive in series.