Mosfet question.

[Jgmathis]

Anybody know what would happen, when you fired your mod, if you used the wrong polarity mosfet?

 

[Mooch]

I think it would start firing as soon as you put the batteries in.

 

[Jgmathis]

Really? The momentary switch wouldnt break the circut?

 

[Mooch]

Really? The momentary switch wouldnt break the circut?

Either the switch would be non functional, because the MOSFET would already be on when the switch wasn't pressed, or the "body diode" of the MOSFET would allow current to flow freely through the MOSFET because it was installed "backwards" for its polarity.

But it's an easy test to do if you have the wrong polarity MOSFET. Just hook it up with a 6V light bulb as the load. It will only draw a little current and you won't fry the MOSFET.

 

[Jgmathis]

Is that the only way? I was hoping you wold be able to tell by the item code on the fet.

 

[Mooch]

Is that the only way? I was hoping you wold be able to tell by the item code on the fet.

You have the FET? Why didn't you post the model in your first post?
I thought you were asking a FET theory question.

Heck yea, I can tell you if you have the number...what is it?

 

[Jgmathis]

IRLB3034
IORP511y

Thanks =)

 

[K3nn0Q]

I wired one up backwards on accident once... insta-fried the tact switch.
Seemed fine until I hit the button

 

[Mooch]

IRLB3034
IORP511y

Thanks =)

The IRLB3034 is a very good N-channel MOSFET. You can use it up to about 25A if chain vaping, higher if you take draws less often.

 

[AzPlumber]

How is it wired?

 

[Jgmathis]

Well, now i wonder if that was ALL that was wrong. I went though the box pretty well and the fact i was using an nfet when i shoild be using a pfet. However, nothing happened at all once i got it wired up and tried to fire it

 

[Jgmathis]

How is it wired?

Wired like a pfet on an okl2 build

 

[Mooch]

U will want to use a irlb3034pbf 40v 195 amp

That's a great MOSFET but that 195A number is only for use when it's mounted to a heat sink that keeps its surface directly under the MOSFET at 25°C, a very, very tough thing to do. Using the junction-to-ambient thermal resistance spec and the Rds-on resistance when the junction is hot, you're abke to calculate that the IRLB3034 can handle about 28A continuous before reaching its max rated junction temperature of 175°C. And that's if it's not wrapped in heat shrink inside a closed box near warm batteries.

Of course, since vaping only pulses the current we can pass more than 28A through it. But certainly not 195A.

 

[Nightly_Paradox]

If you wire up a P channel mosfet as if it was a N channel it would just fire consistently like if you had a fire switch that has welded contacts in the on position.

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