Joule Thief is not working

[IanB]

Your T50-7 toroid is made of type 7 material and is designed to operate most efficiently in the 1-25 MHz range. This is far too high for a joule thief.

Looking at the table at the bottom of your link the type 42 compound would be best, but type 3 or type 8 could be OK too.

All the toroids in that table are designed for creating radio frequency inductors and this is a different application than the joule thief circuit.

The reason you need a lower value resistor is that you don't have enough voltage on the feedback winding to drive the base current into the transistor. With the toroid you are using you need many more turns of wire on both primary and secondary windings to get good operation.

You will get better results with the circuit if you can find a toroid that is being used as a filter. You may find such a toroid in an old switch mode power supply, or in a failed CFL.

[T3sl4co1l]

I actually learned something from your post: that toroids have different inductance values. Thank you.
Except in the specs it shows the letter AL. Can you help me understand what that letter stands for?
Here are the specs I'm looking at: http://kitsandparts.com/mtoroids.html

A_L is the inductivity, measured in inductance per squared turn.

Every time a wire passes through the center of the core, counts as a turn.  So a straight wire with the toroid hanging like a bead, counts as one turn.

Each turn contributes an amp-turn of magnetization: two turns at 1A looks the same as one turn at 2A, and so on.

Each turn picks up the voltage induced in the core's flux, so voltage goes up as turns.

Both together means the inductance goes as turns squared.  So, L = A_L * N^2, for N turns.

A_L is given in different units.  Sometimes uH for a single turn, sometimes nH.  These are obvious enough, just a shift of the decimal point.  Sometimes the figure is given for 100 turns, in which case you have to divide by 10,000 (= 100^2) to get the correct (normalized) value.  Follow the rules of dimensional analysis.

The Micrometals parts specify units of nH/t^2, so after multiplying by turns squared, you will get nH.

Also can you clarify what Rbb and Cbyp is? I'm new to electronics and don't quite know all components and abbreviations yet.

I posted this on the previous page...

Oops, meant to say Rbias, not Rbb, and Cbb, not Cbyp.

Tim

[geratheg]

I'm placed an order from this ebay seller that sells Joule Thief kits. Upon contact, he told me my toroid may have too low inductivity.

I believe these are the toroids he used:
http://www.ebay.com/itm/8-pcs-10x6mm-ESD-EMI-ferrite-cores-toroid-cores-18mm-outer-dia-/141281353212

Also looking at his store, he sells toroidless Joule Thief kits. Interesting. I have a whole lot of learning to do.

Everything else is one of the cheapest I've seen such as the metal film resistors he sells.

[geratheg]

The toroids that I linked to in the previous post work amazingly well. 6 wraps of wire, could probably use less wraps, but with 6 wraps the LED lit up brightly. As far as resistor values, used various up to 10K into the base and the LED was still pretty bright.

Also for experimental purposes, I tried something else. If I plugged the negative lead of the LED into the base of the transistor, it would still light up though not as bright.