Joule Thief

[nul-points]

Hello,  Can someone help me with a very simple circuit...

This is what I want it to do...  starting with a 4v solar panel then charging a small super cap up to about 
1.5 ~ 2.0v  with a red LED showing it charging, and when the super cap reaches the desired voltage 1.5 ~ 2.0
then the same red LED light will go out and no more charge will come through !

Is this possible ?

hi freepow

maybe you misunderstood my post above where i gave you a circuit to charge your supercap in this way?

the supercap stops charging when its voltage reaches the limit set by the zener (minus the default volt drops in the diode & transistor) - ie. it will charge to around 3.2 - 1.4 = 1.8V

the supercap voltage will not increase above this

(even tho' the sun may be shining, the circuit will just keep it at that voltage)

this is what you want, isn't it?

i also pointed out that you could try putting your red LED across the series 'surge protection' resistor to give some indication of charging - the LED would start brighter when the supercap is emptier and then the LED would dim & go out when charging had completed

i recommended experimenting with slightly higher values of series resistor if the LED is too dim whilst charging - you could also try connecting the LED across both the series resistor AND diode, if necessary
(LED polarity has to be same as polarity of series diode)

hope i've explained the operation better?

anyway, good luck with your solar energy project
np


http://docsfreelunch.blogspot.com

[dasimpson]

hi all im back just been thru a messy break up and no internet for awhile. but things look to be getting better thank god.

while i been away i been messing with batterys and run times.
what i cont seem to understand is i have some aa at 2500mah rechargable batterys.
by my maths 3 of these in series to get 3.6 volt should run a led with current draw at 25mah for about 100 hours but i dont seem to get anyware near that maybe 10 befor it starts to drop of in voltage.

now am i right in thinking to get the full 2500mah the battery would have to run down to 0volts to get the full rating
or am i missing something.

and i dont know how some of you have manage to have your jt run for years months or weeks i seem to be only able to manage a couple of days if that.
just a basic jt with 2n3904 1k resister and a 1doller goldmine toriod with 11 turns bifoler only gives me maybe a nights worth of like what am i doing wrong lol 42ma draw

[Pirate88179]

hi all im back just been thru a messy break up and no internet for awhile. but things look to be getting better thank god.

while i been away i been messing with batterys and run times.
what i cont seem to understand is i have some aa at 2500mah rechargable batterys.
by my maths 3 of these in series to get 3.6 volt should run a led with current draw at 25mah for about 100 hours but i dont seem to get anyware near that maybe 10 befor it starts to drop of in voltage.

now am i right in thinking to get the full 2500mah the battery would have to run down to 0volts to get the full rating
or am i missing something.

and i dont know how some of you have manage to have your jt run for years months or weeks i seem to be only able to manage a couple of days if that.
just a basic jt with 2n3904 1k resister and a 1doller goldmine toriod with 11 turns bifoler only gives me maybe a nights worth of like what am i doing wrong lol 42ma draw

Good to see you.

Check out Dr. Jones's topic on his possible 8x OU JT.  XEE2 posted a circuit there that lights an led but draws less than 5 micro watts!  Very little energy going in.  42 mA's is very high, I don't think my Fuji's putting out 400-500 volts draw that much.  Try substituting a VR of 5k or 10k value and then you can tune for lowest possible draw vs having it light up.  It helps to find the sweet spot.  Plus, as the battery drains, you can retweak it as it drifts off resonance.

None of the circuits I have built draw anything near as low as Dr. Jones's or XEE2's.  That is a whole new ball game over there.  I hope to be able to replicate some of those circuits soon.

Bill

[dasimpson]

i just tried some of the circuits with compnents i have and no luck i have very limited parts so try to stay true to the joule thief parts list.
you are corect the current draw is very high compares to what my other draw the yellow and white ones out of psu dont draw that much with the same number of windings

[dasimpson]

here is my latest joule thief found the toriod on a motherboard with 7 bifoler winds on allready so just used it.
had to use 5x5k resisters to make a 1k resister the current draw is 25 to 30 ma thay is also a 100uf cap on the battery terminals to help
putting a fresh battery on now and the voltage reading is 1.48v and the time is 18.24 on the 24/06/2011 lets see how long it lasts btw this is lighting a room 13x13 feet to a lvl that can be moved around in easy wish i knew away to test lumans here are a couple of pictures