Do N channel Mosfets have a current requirement?

[Buk]

That's the insulation I was meaning, thought it was called ceramic.

The same people have several other types including one called no-irritation ceramic.

BTW. Is the 1/4" copper tube you are using 22 gauge brake pipe? And when you say '1.5" diameter', is that OD, ID or centerline?

(I've been running a few sims to see if I could verify/demonstrate the skin effect:

Turns out the math is rather complex.

 

[gary350]

Have you considered Silica High-Temperature Sleeving its good to at least 1800°F.
View attachment 134061

I tried to buy some of that fiberglass insulation it is $10 per foot.

 

[gary350]

The same people have several other types including one called no-irritation ceramic.

BTW. Is the 1/4" copper tube you are using 22 gauge brake pipe? And when you say '1.5" diameter', is that OD, ID or centerline?

(I've been running a few sims to see if I could verify/demonstrate the skin effect:
View attachment 134064
Turns out the math is rather complex.

I used refrigeration copper tubing metal thickness is 50% thinner than copper tubing for water lines and very easy to bend.

1.5" is outside diameter of the coil. Center line to center line is 1.250"

 

[Buk]

I tried to buy some of that fiberglass insulation it is $10 per foot.

Seemed fairly reasonable to me. If you buy a size large enough to fit the largest gauge coil you think you'll use, you can slide it onto whichever coil you are using. It'll pretty much last forever.

At least they'll sell you 1ft. Most places I looked will only sell you a 15m reel for £160.

 

[Buk]

I used refrigeration copper tubing metal thickness is 50% thinner than copper tubing for water lines and very easy to bend.

1.5" is outside diameter of the coil. Center line to center line is 1.250"

Do you know the actual thickness?

 

[ChrisP58]

....
I also need dry sand to fill tubing so I can bend it with no kinks. I use to have sand but don't know what happened to it.
....

Salt might work.

 

[Buk]

Salt might work.

It does.
So does water if you seal the ends with something reasonably strong -- ie. solder ring or compression cap -- or just freeze it.
The best filler -- at least theoretically -- is a non-newtonian liquid -- eg. cornflour slaked with enough water to make it just flow.

But a bending spring is best of all.

 

[shortbus=]

Unless he has some kind of strange refrigeration tubing it probably won't need any type of filler to bend it, refrigeration tubing is called dead soft for a reason. It's the 1/2 hard and hard copper like water lines, that needs a filler.

 

[Buk]

Unless he has some kind of strange refrigeration tubing it probably won't need any type of filler to bend it, refrigeration tubing is called dead soft for a reason.

When I did this (40+ years ago) I was working for a car manufacturer, so we used copper brake pipe which is also soft annealled. Whilst putting the kind of bends used in routing brake pipes is easy to do without filler, we found it was very difficult to make tight coils without it kinking. Hence we tried the various methods I listed above.

We were using 3/16" pipe which has a 3mm ID and found using an internal spring difficult to remove once you've formed a coil. The best result we got was using ice.
Plug one end with wax, fill with water, plug the other and put it in the freezer. Once frozen, you have maybe 10 minutes to form your coil before the ice melts.

 

[shortbus=]

so we used copper brake pipe which is also soft annealled.

What country was that? Here in the USA copper of any kind isn't allowed for brake lines. Even though they look like copper they are steel that is copper plated. But now they do have and allow a nickle-copper line, but I haven used any of it. https://brakesystems.autopartsu.com/2020/08/24/nickel-copper-pros-and-cons/

 

[Buk]

Here in the USA copper of any kind isn't allowed for brake lines.

How very strange.

You can get cupro-nickel here(uk) also, but pure copper annealed to BS EN 12449 C106 is the norm, and is regarded as far superior to steel tube for this:

If you go to ddg and set the country code to UK, you'll see it is ubiquitous here.

 

[billybob]

MOSFET Gate current is typically uA. or even less. What part?

What is your circuit built to do? It looks like the MOSFET will get very hot.

I’m wondering the same thing, what is this?

 

[shortbus=]

I’m wondering the same thing, what is this?

It's a induction heater. Don't understand why he has to build one from scratch though. I used a module for mine and it works good.

 

[shortbus=]

How very strange.

Might have something to due with we used double flaring on connections unlike the "bubble" flare of metric country's. Also always hear it was because copper work hardens over time, from vibration. I have tried to double flare copper and it usually splits in the flare.

 

[morrissel311]

This was very helpful and informative.. Thank you so much for sharing this.

 

[unclejed613]

Also always hear it was because copper work hardens over time, from vibration.

that plus with the amount of salt used on roads here in the winter, copper corrodes quickly where it comes into contact with dissimilar metals.

 

[gary350]

I’m wondering the same thing, what is this?

Induction heater testing circuit for a better H circuit. It runs good with 21v 34a. It is tricky to run it at 25v 34a current wants to suddenly jump to 52a then mosfets go BOOM. I have not had time yet to make a 8mh choke. Several other projects are top priority. I was sick 2 days now I am alive again, almost.

8 year old computer finally died a few days ago. New 5G computer with window 11 arrived. Set up was easy. Typing in user name & password took a while for several plants Old notes were not good had to make new password for several places. YouTube has no option to recover password or change password and keeps telling me, that email has already been used. I am glad if I type MY computer password wrong 5 times I don't get a message that telling me I need to wait 24 hours to try again.

 

[gary350]

Life happens. Been too busy with other things to work on this project. New parts arrived in the mail a week ago. Eye doctor & dentist tomorrow. Wife had surgery Monday. Every day is something else it never ends.

 

[gary350]

Today I was able to test circuit a little bit before taking wife to doctor. The IRFP4310 mosfets work better than the P55NF06. The 8 turn RF coil does not over heat just setting there with no load. I have no problem running the circuit on 20vdc 40a. Circuit runs good on 25vdc 40a & 2uh choke but if amps goes up to 45a the amp meter suddenly pegs out above 60a loud hum sound it must be pulling 150a when both mosfets explode. This circuit needs some type of safety over load current limiting??? I tried all the choke coils 8uh lowers the general overall current but circuit can still peg the meter at maximum amps and explode the mosfets. I think I need to solve this over load problem before building the H circuit. I had no volt meter on the PS so I don't know if 25vdc PS dropped lower when the circuit over loads, it probably did.

 

[ChrisP58]

It sounds to me like you're reaching a point where one mosfet is not fully of when the other turns on. At that point you've got a dead short through the mosfets.

What do the waveforms look like for the two mosfet drain terminals as you raise the current to the point of failure?