Joule Thief

[Pirate88179]

@ kooler

5 LEDs x 3V = 15V across coil. That is not from the battery, so there must be some bemf there.

It would be between the emitter and the negative terminal of battery with positive at the battery. Maybe the positive spike is just getting sucked into the battery negative terminal.

Possibly, a way to isolate what is happening is to use a supercap instead of a bat.  I did some experiments a while back with a 2.7 volt 10 F supercap that showed some additional anomalies.  It is documented on my videos but, when the ultra bright leds went out, all I had to do was to touch the top of the transistor (2n2094) and they lit up again.

If a supercap (a small one) is charged up with a 1.5 battery, I think this will expose any bemf in the system.  It won't be any rebound from the battery or anything like that, just the cap and the JT and the leds.

This may help, it may not.  I am just tossing this out there based upon what I have observed.

Bill

[kooler]

thanks bill
i will check it
i didn't think to stick a cap across the battery and see what happens
i am also going to put a bridge on my secondarys to see what is really going on there.. cause my scope isn't showing the spikes.. it just show a small wave form with 4 volts

robbie

[jadaro2600]

thanks bill
i will check it
i didn't think to stick a cap across the battery and see what happens
i am also going to put a bridge on my secondarys to see what is really going on there.. cause my scope isn't showing the spikes.. it just show a small wave form with 4 volts

robbie

I've found it beneficial to put a small electrolytic cap across the + - terminals of the battery when checking for current usage - otherwise most of my circuits don't operate with the ammeter inserted.

[xee2]

@ kooler

scope isn't showing the spikes.. it just show a small A form with 4 volts

How  can 4 volts light up 9 LEDs in series? 9x3=27 volts would be required.

Maybe there is something wrong with the scope. However, the spikes might just be too fast for the scope to capture them.

[xee2]

@ kooler

If you put a capacitor across the 9 LEDs it should charge up to about 27 volts and you should be able to measure that with a DMM set to read DC voltage and then you can check to see if the scope agrees.