MOSFET or something else?

[drmarble]

One advantage of the n-fet is the tab is connected to drain. Thus you can connect it to your case and thus the outside of the 510 connector without fear. It just gives you another switched current path and good heat dissipation. With an p-fet you need to isolate that tab.

 

[NaCl_H2O]

. SI7157DP-T1-GE3 Vishay / Siliconix | Mouser
Im tinkering with a few of these right now.

How the heck can you solder to that? You must be a VERY patient soul!!

The tab is electrically connected. Note for example, in the data sheet for the PP80P03P4L-04 it shows the drain as "pin2/Tab". "Tab" refers to the metal tab, so your heatsink either needs to be electrically isolated from the tab (there's kapton tape that gets used for this, used to be mica insulators) or the design needs to allow the heatsink to be connected to the drain.

You can solder directly to the leads of these parts; try to do it as quickly as possible (although parts like this aren't that sensitive to heat).

Got it, thanks!

 

[NaCl_H2O]

One advantage of the p-fet is the tab is connected to drain. Thus you can connect it to your case and thus the outside of the 510 connector without fear. It just gives you another switched current path and good heat dissipation. With an n-fet you need to isolate that tab.

Isn't this backwards?
n-fet tab/drain is negative, so connection of the tab to the case/510 case would be OK
p-pet tab/drain is positive, so need to isolate the tab from the case/510

 

[drmarble]

Isn't this backwards?
n-fet tab/drain is negative, so connection of the tab to the case/510 case would be OK
p-pet tab/drain is positive, so need to isolate the tab from the case/510

Thanks for catching that. I didn't mind my p's and n's. I edited the post to correct that. It is the n-fet that you can connect the tab to the box/510 outside/negative.

 

[twgbonehead]

Thanks for catching that. I didn't mind my p's and n's. I edited the post to correct that. It is the n-fet that you can connect the tab to the box/510 outside/negative.

Yes, but in that case you HAVE to be switching from the negative side of the battery (which is why that's now many of the MOSFET designs are done).

 

[dc99]

Small copper board. Just flow the solder to it. You can cut it with a dremel to separate the pads.

 

[NaCl_H2O]

Stupid (ok, probably really stupid) question:

Could a P-Fet be used in series with a relay (solid state) to switch the high side? I don't know squat about selecting relays, but in general they appear to be super expensive!!??

... never mind - see my next post ;-)

 

[NaCl_H2O]

You have all been very patient with my novice questions - I greatly appreciate that and also not being blasted ... yet!

I REALLY want to keep my design as-is which means I need to switch the high side. I searched Digikey & Mouser one more time. I found this one before at Digikey (above) but it was not stocked, but now I found it in-stock at Mouser!
IPP80P03P4L-04 Infineon Technologies | Mouser

If someone could look at this one closely and offer any advice, I would REALLY appreciate that?
It appears to support 80Amps with a RdsOn of 4.1 mOhms - not bad! Obviously I need to heat sink this, which I think is doable in my design (lots of Copper).
I don't understand the Vgs of +5/-16?
Gate threshold is -1 to -2 so that should be good?

Regarding what I am trying to build. Basically a box mod housing dual/parallel 18650s (VTC4/5). I am more of a woodworker than an electrical engineer (obviously!). I will have a wooden box holding the batteries, with Copper accents that carry the battery (-) to the atomizer.

I do intend this mod to be useful in sub-ohm builds, but I am ok if I need to limit that somewhat. With this 80A P-MOSFET, maybe I won't need to limit too much if I can get the heat sink right?

If this MOSFET looks reasonable, then what resistor (edited ) do I need? Pull-up/pull-down??

Thanks to all!

 

[NaCl_H2O]

Should have added
Targeting ~40A capable circuit, I like this MOSFET due to the margin of safety @ 80A