N Channel Mosfets

[Bradley]

I have a small Solid State Tesla Coil I'm working on I'm getting an output on my HV side but it's not what I'm looking for, very little break out at an input of 18v pulling between 2A and 6A. Anything higher than that and it's cooking up my Mosfets this is before the paralleling of the Mosfets... The set up in the picture is roughly my current setup with 2 like Fets in parellel.. I'm running 18v into the dual Fets and there still getting very hot, running as if it was still only 1 Fet. Affraid to go any higher on the inputs because I sure don't want to be going through twice as many Fets any suggestions or ideas to help with a higher input on my primary!!! D
Thank You

P.s. High frequency set up!!

 

[Colin Mitchell]

The problem is the back emf from the primary winding is entering the MOSFETS and killing the back emf you are expecting from the secondary.
You need a higher voltage MOSFET

 

[Bradley]

The problem is the back emf from the primary winding is entering the MOSFETS and killing the back emf you are expecting from the secondary.
You need a higher voltage MOSFET

I am getting back spike which I can't seem to stop, but I have grounded the heatsink to help prevent further failures, such as the 555 circuit.... So all this really boils down to are just bigger/better Mosfets? The power disapation is 208w per Fet and I don't believe I'm close to that... Especially with 2 parelled Fets???¿¿¿Any Fet suggestions? Like maybe the IRFP260n? Or any that can handle more than what I'm currently using?

 

[Colin Mitchell]

Try a 800v transistor

 

[Bradley]

Try a 800v transistor

I'v

Try a 800v transistor

If I were to use a transistor, which I do have some laying around.. Will I need to make any modifications to the circuit? Or should it work just the way the circuit is now? I'm still a newbie when it comes to circuitry.. I've come a long way but I've still got a ways to go.. just have a great understanding

 

[Arouse1973]

Hello
Is this 2-6 Amps what you are expecting as far as current goes. What is the primary resistance and inductance, do you know? Or can you give me the number of turns and dimension of the former it's wound on.
Thanks
Adam

 

[Bradley]

Hello
Is this 2-6 Amps what you are expecting as far as current goes. What is the primary resistance and inductance, do you know? Or can you give me the number of turns and dimension of the former it's wound on.
Thanks
Adam

No, the 2-6Amps is what im currently pulling.. 2A up to 6A when i pull an arc from the toroid.. Roughly between 16v and 18v from my DC power supply. I've got a power supply that can give me up to 90v DC but i can't even achieve 25v without burning up my Fets...

(Primary Form Dimensions)

Top Diameter= 4 1/2"
Bottom Diameter= 3 1/2"
Height= 5 1/2"
Primary runs 4" up from the bottom, with 14 Turns of 8Ga (Braided Wire)., Insulated wire with no turn spacing, Well besides the insulation and maybe what cant be seen by the eye...
There's also about a 1" Air Gap between the Primary and the Secondary.

If there's any other info you need let me know
I don't have proper tools to measure inductance nor do i have a scope to measure wave forms

Thank you!!

 

[Bradley]

Hello
Is this 2-6 Amps what you are expecting as far as current goes. What is the primary resistance and inductance, do you know? Or can you give me the number of turns and dimension of the former it's wound on.
Thanks
Adam

let me re-phrase that last sentence
I don't have the proper know how to get inductance...
The numbers I'm getting are:
1.5 Henrys
4.6 mF
but I'm not certain if this is even correct
BUT...
If this was all correct than my resonate frequency would be roughly .06 Hzs

 

[Arouse1973]

I make the inductance approx. 10.8 uH for an air core. (r^2 * N^2) / (9*r) + (10*l). r = radius of coil, N = Turns, l = length. What core material are you using?
Adam

 

[Bradley]

I make the inductance approx. 10.8 uH for an air core. (r^2 * N^2) / (9*r) + (10*l). r = radius of coil, N = Turns, l = length. What core material are you using?
Adam

The only material between the primary and the secondary would be the Tupperware container used for the mold and the 1 - 1 1/2 Airgap. The secondary is wound around a 2" piece of PVC Approx. 1200 times.

 

[Bradley]

I will upload a picture in a few..

 

[Bradley]

I make the inductance approx. 10.8 uH for an air core. (r^2 * N^2) / (9*r) + (10*l). r = radius of coil, N = Turns, l = length. What core material are you using?
Adam

Its messy right now but it's going through a lot lol

 

[Arouse1973]

Do you have the parts on a heat sink? if so what type is it?
Adam

 

[Colin Mitchell]

You are not going to get any energy transfer between the primary and secondary when you use AIR.
It has to be IRON or FERRITE.
It's nothing to do with back emf. It's just a matter of saturation and high current

 

[Arouse1973]

Its messy right now but it's going through a lot lol

Ok so the first thing to do is sort out the heating issue. The second issue is what Colin just mentioned, this won't work very well. Where did you get the coil design from?
Adam

 

[Bradley]

Ok so the first thing to do is sort out the heating issue. The second issue is what Colin just mentioned, this won't work very well. Where did you get the coil design from?
Adam

I didn't get it from any specific design honestly, I kinda of just put it together for fun at first.. and became intrigued with the whole aspect of it and wanted to take it farther. This is my first coil and it started out as a SGTC and I then wanted to build a solid state design which is what I'm working on now. Here's a picture of it as a SGTC. I have a video if I'm able to upload it.

 

[Arouse1973]

Do you have any heat sinks fitted to the MOSFETS?
Adam

 

[Bradley]

Do you have any heat sinks fitted to the MOSFETS?
Adam

Yes, there currently on nice size copper core, and alluminum heat sinks.

 

[Bradley]

The picture of the SGTC, is a coil driven by a flyback from an old tube TV where I was pushing close to 40kv through the primary

 

[Arouse1973]

When you have 5 mins, post a picture please.
Adam