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Is there a more robust alternative to IRF3205 MOSFET?

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LAN_403

Tesla Fan

Mon Nov 22 2010, 07:34PM

Registered Member #3353 Joined: Sat Oct 23 2010, 11:21PM
Location: Greece
Posts: 90

If a wire is connected to the ground, and at the same time gives you a shock when you touch it, that it bad news. At best it shows your ground does not work (open circuit).

Also, my IRFP240 is not insulated, they need the mica insulator seen in photo

Please keep in mind that evething i say may be wrong, as i am only familiar with "low" 50Hz voltage and not >10.000 volts or RF power

Steve Hobley

Mon Nov 22 2010, 07:54PM

Registered Member #1731 Joined: Thu Oct 02 2008, 02:22PM
Location: Indiana
Posts: 52

Yes I will definitely be checking the ground connection. I think my house was built in a hurry, and little details like grounding connections seem to have escaped the builders - as they rode off into the sunset on their horses... :D

Actually where do you get those Mica insulators from? Jameco don't include them with the Mosfets so I have to improvise...

Tesla Fan

Mon Nov 22 2010, 08:09PM

Registered Member #3353 Joined: Sat Oct 23 2010, 11:21PM
Location: Greece
Posts: 90

!amazed No grounding in your house !!!

That is Extremely Dangerous and possibly illegal!

I hope at least you have a safety relay.

The electrician that signed the papers for your house should be shot!

I suggest -before anything else- you check your ground if you can, or buy one of these quick-and-easy testers (less than $15)

, or (and) call an electrician to check / fix the grounding at your house and if you do not already have one, please install a safety relay. These are not things to play with, we are talking about real lethal dangers!

OK, now that i have calmed myself, here is a link for TO-247 mica insulators

. But please, take care the grounding problem and then fine-tune your coil.

Adam Munich

Mon Nov 22 2010, 10:18PM

Registered Member #2893 Joined: Tue Jun 01 2010, 09:25PM
Location: Cali-forn. i. a.
Posts: 2242

You can get those insulating pads, along with a giant heatsink and plenty of passives in a stereo receiver!

Tesla Fan

Mon Nov 22 2010, 10:45PM

Registered Member #3353 Joined: Sat Oct 23 2010, 11:21PM
Location: Greece
Posts: 90

Hi Grenadier,

you mention stereo receivers a lot, you must have got (is that correct syntax?) plenty of good parts from these.
But i doubt you found a "giant heatsink", i have one here as big as a receiver and i do not concider that giant!

(too tired to get a photo, it is 12:39 in the night now over here...)

To get back to the subject, i think most of the eshops that sells electronic parts, must have mica insulators, maybe that is not the name commonly used.

PS. Grenadier i LOVED your "F#ck my government." link, too bad there is not one for mine...

Adam Munich

Mon Nov 22 2010, 11:10PM

Registered Member #2893 Joined: Tue Jun 01 2010, 09:25PM
Location: Cali-forn. i. a.
Posts: 2242

I meant these old ones that can be found for five bux on Craigslist.

They have some beefy heatsinks, a beefy multi-voltage transformer, some really big filter caps, plus a whole bunch of useful passive components. The last one I took apart had a heatsink that was 1.2 feet long, 6 inches high with 4 inch fins. I'd consider that giant.

Oh and aren't politicians great. You do have one, but it's not nearly as detailed.

dingo27

Mon Nov 22 2010, 11:46PM

Registered Member #890 Joined: Tue Jul 10 2007, 10:06PM
Location: Slovakia
Posts: 180

I never trusted mica insulators, are they beter than silicon ones?

Tesla Fan

Mon Nov 22 2010, 11:58PM

Registered Member #3353 Joined: Sat Oct 23 2010, 11:21PM
Location: Greece
Posts: 90

That radio looks nice, Pioneer right?

Although i hear "off topic" and "thread hijack" bells ringing, i will risk one more reply:

Found some old photos, this is a quite big heatsink

that a friend would help me make into an amplifier.We (he) made the plans, we found a saw to cut the heatsink in half

and we got to about 60% of the project (4 years ago).

I have another one just like it, another one about 70% of this, and many many more...
Thanks for the link

I 'll send you a PM because i think we are abusing this thread...

dingo27,

I have not ever used anything like this, this is from "junk" i have and only thing i made is a simple driver for an ignition coil (blown some 2N3055, NE555, a multimeter, and finaly disassemble the thing to cut my losses...). So i do not have an opinion on the matter, just found lots of those transparent things...

Adam Munich

Tue Nov 23 2010, 12:06AM

Registered Member #2893 Joined: Tue Jun 01 2010, 09:25PM
Location: Cali-forn. i. a.
Posts: 2242

dingo27 wrote ...

I never trusted mica insulators, are they beter than silicon ones?

Well I'm pretty sure silicon would make a pretty delicate insulator.

If you meant silicone, I never saw any difference. Put it this way, if manufacturers trust those mica pads to not fail, I'm pretty sure they've done their research as to whether or not they're a safe bet.

Weston

Tue Nov 23 2010, 12:35AM

Registered Member #1316 Joined: Thu Feb 14 2008, 03:35AM
Location: Cambridge, MA
Posts: 365

The plastic pads "silicone" have a greater thermal resistance then mica pads. They do not need thermal grease however, as they are plastic enough to spread and fill in thermal gaps. Because of this it is not recommended to reuse or salvage them, as they are already molded to the shape of one transistor and will not remold to the shape of another transistor well. Mica is reusable, but needs a thermal paste on both sides to preform well. if you have small separate heatsinks best of all would be to use no thermal pads and float the heatsinks. be sure to isolate the heatsinks well then though. You could get a bad shock.

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