Joule Thief

[kooler]

hey folks
i got a stupid question..
do any of you know how long a jt runs when it is pulling 104 ma's..
sorry to bother anyone .. i know i need to learn the math
the battery was from my wii and it had 1.2volts left in it..
so i thought at 104ma it should run down quick..
but 24 hours later it still has 0.79 volts and the led is still full brightness.. it's really to bright
i don't know the mah of this battery it is a cheap eastpower from china

thanks

ps.. stprue very nice video.. you have done alot with that circuit..

robbie

[jadaro2600]

stprue:

Nice circuit there.  Wow, that is a very low amp draw.  Can you adjust your pot to increase the frequency so the led "appears" on?  I realize this may/will increase the amp draw but maybe by not all that much.  This circuit would run for a year on a 10F cap I believe.

Great job.

Bill

Actually, this low an amp draw: the supercap would bleed faster than the circuit.

stprue, can you repost or link to a schematic?

[jadaro2600]

hey folks
i got a stupid question..
do any of you know how long a jt runs when it is pulling 104 ma's..
sorry to bother anyone .. i know i need to learn the math
the battery was from my wii and it had 1.2volts left in it..
so i thought at 104ma it should run down quick..
but 24 hours later it still has 0.79 volts and the led is still full brightness.. it's really to bright
i don't know the mah of this battery it is a cheap eastpower from china

thanks

ps.. stprue very nice video.. you have done alot with that circuit..

robbie

This isn't a stupid question.  Depending upon the 'state' of the source voltage, a joule thief circuit may in fact use more milliamps when it's close to its death. ..the cut on voltage for the transistor has a lot to do with this, but I've noticed on my models that when there's no load on the device, it uses more current than when there is.  So...

Bearing that in mind, it's a good idea to keep a load on ( the secondary ) or off the collector or somewhere in this circuit.

Also, you'll want to keep in mind that batteries have a tendency to regain their charge voltage wise after a sudden discharge, so a joule thief might cut off, then cycle on and off again before it's really 'dead'.

The math is relatively simple, if you have a 2450mAh battery, then you have 2.45 amps or 2450 miliamps at your disposal for one hour.  Batteries, again, can be somewhat deceptive, as it may in fact be capable of supplying 3 or 4 amps over the life of a complete slow drain.

Sticking to the basics:  using 100mA your circuit will run for 24.5 hours it just a matter of turning mAh into mA.

Depending on your configuration, there will come a voltage point that the transistor will stop turning completely on and the current will simple bleed through to ground via the base-emitter path.  This is when the device may consume more milliamps that when it would loaded and the battery will become depleted for the duration of it being connected.

The only way to know is to compare the battery's performance to one which you know the properties of - this would be rather difficult because of the differing properties of manufactured AA cells (or what have you) and the various 'states' the circuit source finds itself in.

[innovation_station]

has anyone ever recharged an aa with a cam board ..

the reason i ask is this   i want to use a aa fuji cam board  to recharge a rechargeable aa  it STILL NEEDS A TRIGGER SYSTEM .....

and the aa is only ment to maintain 1.5 vdc out put there bouts ..  this then becomes the feed for 2 caps and i drive the other 2 cap pumps off the first one .. now im down to 3 aa's to power my power ring

and they only need to be pulsed to top up the aa .. or could be run constant .. 

i have not tryed a cam board on a aa or any other battery other than a 12vdc gel and it recharged it ...

W

[detrix42]

Hello folks.  I have built my second JTC.  Pictures below with schematic.

The third pic is about my question.  I want the output of the JTC to go into the transfomer in pic #3.  All I know about the transformer is the ohms of the windings. I am not sure how to do this.  Can some one supply a schematic or some guidance?

I am very happy with this JTC.  The input voltage is only 6.5v, and I am getting 100+v on the output across the capacitor.  I am a Newman motor advocate, and want a JTC to supply the voltage to my Newman motor. 

For those here I will post a link t my Newman motors.  Just in case any here are interested. 

http://www.youtube.com/watch?v=F6qLiAeyPng
http://www.youtube.com/watch?v=fdw3DAVuLbA
http://www.youtube.com/watch?v=EnLqEeO7Af4

I want my JTC to supply power to my large motor.  Motor #3