From our experience in the JT topic, high permeability ferrite appears to work the best so far.

Bill

Quote from: Pirate88179 on May 14, 2010, 11:05:36 PM
From our experience in the JT topic, high permeability ferrite appears to work the best so far.

Bill

Ferrite has a high permeability that is true,  but my concern is with magnetic flux density which is I believe more important than permeability in this case(NS coil) because of the low amount of power in the primary.

I dont know much about the joule thief,  i have seen them power leds from nearly dead batteries, but how does it "step-up" dc?

@alchemist
Thanks for that description of Nickel Iron materials. That cleared things up for me.

@Jeanna
It's a good thing I didn't buy that Permalloy rod, eh?

Quote from: alchemist123 on May 15, 2010, 12:09:51 AM
Ferrite has a high permeability that is true,  but my concern is with magnetic flux density which is I believe more important than permeability in this case(NS coil) because of the low amount of power in the primary.

I dont know much about the joule thief,  i have seen them power leds from nearly dead batteries, but how does it "step-up" dc?

Well, I don't pretend to know everything there is to know about the JT circuit here.  I do know that you are correct, they can operate on nearly dead batteries at low volt and very low power levels.

The basic JT is a bifilar wound ferrite toroid using a small transistor like the 2n3904.  We have moved on to the more advanced designs, such as Jeanna's Circuit, which has a collector coil, a base coil and an emitter coil all wound on the same toroid.

Anyway, the Stubblefield coil is basically a JT.  You hit it with pulses and out of the secondary comes AC.  For the best spikes of BEMF we can get from either the JT or the NS coil, I believe we want core material that can handle having a magnetic field, and then not having one, many thousands of time/second, with a very fast collapse.  The ferrite cores we have been using operate easily up in the 20-30 KHz range.

This will be an experiment or a series of experiments that I will do.  I am not really suggesting that others buy ferrite for the core as, to my knowledge, it has never been tried.  I am also going to try a very similar transistor like the 2n3904.  This may not work, it may not work at all.  Or.....?

Bill

Quote from: Pirate88179 on May 15, 2010, 02:21:33 AM
Well, I don't pretend to know everything there is to know about the JT circuit here.  I do know that you are correct, they can operate on nearly dead batteries at low volt and very low power levels.

The basic JT is a bifilar wound ferrite toroid using a small transistor like the 2n3904.  We have moved on to the more advanced designs, such as Jeanna's Circuit, which has a collector coil, a base coil and an emitter coil all wound on the same toroid.

Anyway, the Stubblefield coil is basically a JT.  You hit it with pulses and out of the secondary comes AC.  For the best spikes of BEMF we can get from either the JT or the NS coil, I believe we want core material that can handle having a magnetic field, and then not having one, many thousands of time/second, with a very fast collapse.  The ferrite cores we have been using operate easily up in the 20-30 KHz range.

This will be an experiment or a series of experiments that I will do.  I am not really suggesting that others buy ferrite for the core as, to my knowledge, it has never been tried.  I am also going to try a very similar transistor like the 2n3904.  This may not work, it may not work at all.  Or.....?

Bill

I agree.  Rapid demagnetization after the break is essential.  Coercivity i think its called.   Oddly enough, the iron-nickel alloys have low coercivity.   However thats at a trade-off for low saturation points ( example: permalloy ).    Core choice seems to be key.  Cost wise  iron or silicon iron/steel  are the cheapest, and are pretty good overall, with low coercivity and low retentivity.  However the extent that some of these "neo" alloys can enhance output is ridiculous,  i was reading about Hiperco A50,  high permeability and really high flux density.  Flux density determines how many ampere-turns is needed to generate a certain strength magnetic field.    The higher the flux density of the core the less amount of current is needed to generate a strong magnetic field.

I have a question for you, how do you know what transistor to use?  i dont understand the codes, why 2n3904?

Ferrite, Iron, Silicon Iron  can all be scrapped from various appliances.