Akula0083 30 Watt Self Running Generator.

[dllabarre]

Trollin trollin where's your troll buddy's
I have a novel idea maybe try and make it work, wow who would of ever thought.

HA HA

[lost_bro]

Dear All.

I can confirm your suspicions as regards the transistor getting hot. It get's REALLY hot!!

I have spent the greater part of this evening trying various frequencies and m/s ratios whilst dumping the output through a super fast FWBR. In fact I got better results connected the other way round !!This was accidental on my part but the results were definitely interesting. Even with a step down ratio the scope was seeing 50 V pulses and a ringdown. Holding the circuit run for up to a couple of seconds.

May I courteously suggest that you guys should make the transformer and try driving with a PWM device as per T-1000's earlier post. A few more stabs with different coil configurations might just see a breakthrough??!!

Cheers Grum.

Good evening Grumage:

OK, in relation to the really HOT!!! MOSFET; this is some info that I use when winding GDT's:

Saturation flux density is how much magnetic flux the magnetic core can handle before becoming saturated and not able to hold any more. This depends on several factors including ferrite type, temperature and electrical and magnetic conditions on the transformer.

When the ferrite saturates, the transformer no longer acts like an inductor with a linear increase in current over time. Rather, the magnetic field cannot increase further and current is limited by the source impedance of the power supply and the resistance of the transformer wire.

This leads to very large currents- Very HOT MOSFETs and blown devices. This is a Bad Thing.

Ferrite typically saturates at a flux density (B) about 0.3 Tesla but this depends on temperature and the ferrite type. A typical design might have as a target a B = 0.25T at 125ºC which gives plenty of operating margin to the limits.

The formula for flux density is

B = ( V x t ) / ( N x Ae )

where:
B = flux denstiy in Tesla
V = applied Voltage to the winding in Volts
t = time that Volts V is applied for in seconds
Ae = cross sectional area of the core in m^2 - obtainable from the core datasheet

If this were an inductor carrying a DC component, the DC current would play a significant part in calculating the saturation.

I usually use a DC blocking capacitor in the primary side of the GDT to eliminate the DC component and thus avoid alot of the issues involved (flux walking).

The main thing to take from this equation is that for a given core and frequency there is a minimum number of turns that can be used without saturating the core. So, to avoid saturation, use more than the minimum number of turns.

So I have wound many GDTs that have overheated the driver circuit just for the above mentioned fact:  When the core saturates, it acts as a DEAD short and MOSFETS don't like that..... yes it is a balancing act between minimizing the leakage inductance, the minimum number of windings permitted and core saturation and of course maintaining an acceptable wave form...

So looking at the plan for the winds on the XFMR, could be that for the type of Ferrite involved, you don't have sufficient windings on it to avoid saturation.

Just a thought.

Take care, peace
lost_bro

[verpies]

Come on guys I could fake that video easy !

So could I.
I was merely translating what the author was saying.

Without scopeshots it is not possible to analyze the credibility of this video nor its MO.

[4Tesla]

This leads to very large currents- Very HOT MOSFETs and blown devices. This is a Bad Thing.

The main thing to take from this equation is that for a given core and frequency there is a minimum number of turns that can be used without saturating the core. So, to avoid saturation, use more than the minimum number of turns.

So I have wound many GDTs that have overheated the driver circuit just for the above mentioned fact:  When the core saturates, it acts as a DEAD short and MOSFETS don't like that..... yes it is a balancing act between minimizing the leakage inductance, the minimum number of windings permitted and core saturation and of course maintaining an acceptable wave form...

Thank you so much!  A lot of good and helpful info there.  So do you think having a higher amp rating won't make a difference since it is this shorting that is causing it to over heat?  Is it possible that saturation of the core is what makes this thing work?  How about the 1W toroid transformer.. do we know if it had a ferrite core?

Thanks

[lost_bro]

Thank you so much!  A lot of good and helpful info there.  So do you think having a higher amp rating won't make a difference since it is this shorting that is causing it to over heat?  Is it possible that saturation of the core is what makes this thing work?  How about the 1W toroid transformer.. do we know if it had a ferrite core?

Thanks

I guess the short answer is related to the actual problem>    If it is related to saturation of the core, it is directly related to the core permeability, core size and winding ratios .....  and the core permeablility can be changed by changing the core material.

All the ETD cores that I have here now are PC40 TDK material.
I do not know what Grumage used for the core material, I would have to pull out the charts to see how that all works out...

take care, peace
lost_bro