Which MOSFET to use?

[WoodEs]

I am still confused on which mosfet to put in my box mod.. any recommendations? I will be using a 3.7 v 18650 battery, with a nautilus mini tank. I understand I need to put a 15k resistor across the mosfet, but I am not entirely sure why that is. I understand the basic principle that a mosfet is for relaying the current from the switch so that it doesn't fuse across and cause a short.

When going on Mouser, there are so many options to refine my search for a mosfet I can't figure it out

Thanks for the help guys/gals

 

[caramel]

Something like this

IRLB8743PBF International Rectifier | IRLB8743PBF-ND | DigiKey

 

[TheRac25]

low Drain-to-Source On-Resistance, (several milliohms)
Gate Threshold Voltage < depleted battery voltage
Drain Current > battery pulse current rating

 

[Dusty_D]

Thread moved to Modding Forum

 

[tehdarkaura]

15pcs 30V 150A Logic Level N Channel MOSFET HEXFET to 220 IRLB8743PBF US Seller | eBay

I just picked up some of these for a non-mod project but this is a good price and are well suited for mods too...

 

[Visus]

The 15k resistor stops the mod from firing it pulls the mosfet down to ground with a low level voltage. Once you open the mosfet it would be more than happy to never close again, you gotta slap it around a bit, ya see, if you slap the fat off its back hitting it a million times, you can make it so sensitive that you can use a touch switch...

This is another really good MOSFET
IRLB3034PbF

There are others out there that are better but you have to board them. Check out David's post if your building a box mech, he makes that easy for us and best optioned everything. You can buy his awesome helpful board $4.50 and he includes parts list so its uber fun and easy..

http://www.e-cigarette-forum.com/forum/battery-mods/655784-triple-parallel-mosfets-pcb.html

 

[Jtterrible]

would this mosfet work
AUIRFB8409 International Rectifier | Mouser
or
AUIRFB8405 International Rectifier | Mouser

 

[Visus]

would this mosfet work
AUIRFB8409 International Rectifier | Mouser
or
AUIRFB8405 International Rectifier | Mouser

8409:
The turn on is to high for a 1s 4.2v take a look at fig 16 on the data sheet, 1s you want that to turn on at least 2.5v..
That one is ~5v if your using a 2s 7.4v mod its fine but not optimal..
I did not check the other but you can, just go to the data sheet go to this spec and check it...

 

[Kaana]

is this good for paralel samsung 25r ?

MOSFET, N, 40V, 280A, TO-220
Transistor Polarity:N Channel
Continuous Drain Current Id:280A
Drain Source Voltage Vds:40V
On Resistance Rds(on):2mohm
Rds(on) Test Voltage Vgs:10V
Threshold Voltage Vgs Typ:4V
Power Dissipation Pd:330W
Transistor Case Style:TO-220AB
No. of Pins:3
SVHC:No SVHC (18-Jun-2012)
Current Id Max:270A
Device Marking:IRF2804PBF
Junction to Case Thermal Resistance A:0.45°C/W
On State resistance @ Vgs = 10V:2.3ohm
Package / Case:TO-220AB
Power Dissipation Pd:330W
Power Dissipation Pd:330W
Pulse Current Idm:1080A
Voltage Vds Typ:40V
Voltage Vgs Max:4V
Voltage Vgs Rds on Measurement:10V

 

[WoodEs]

Okay I am still confused about MOSFETS.. is there a resource anyone has that will show me how to understand the charts and graphs? I see the recommendations and I appreciate them, but is there multiple mosfets that would work for me? I tried IRF510 from radioshack but it didn't work for some reason

 

[david4500]

Here is what you'll want:

ID continuous - As high as possible, say around 100 amps or greater. This is the maximum continuous current rating of the mosfet. Select one with a high value to give plenty of buffer room.

VGS TH - Around 2.5 volts or less. This value is when the mosfet will BEGIN to turn on. You want the value to be less than the low end range of your batteries. Being that the range of a single battery/parallel batteries is 4.2-3 volts, 2.5v is an appropriate.

RDS ON - Around 2 milliamps or less. This value is basically the on state resistance of the mosfet. A higher value will cause excessive voltage drop.


As far as looking at the charts, I typically look at one if it is available. The same chart Visus posted which shows the relationship between the RDS ON (on state resistance) and VGS V (voltage supplied to the gate).

Take a look at this mosfet's data sheet: PSMN1R9-40PLQ NXP Semiconductors | Mouser

Page 6, Figure 7 will show the chart mentioned. Horizontally the chart is showing the voltage to the gate (VGS V), look at the 3-4.2v range. Now look vertically and you can see that the resistance (RDS ON) is around 2 milliamps. You can see below 2.5v, the resistance increases dramatically. That is ok since you should be charging your battery/batteries before or as they approach 3 volts.

Here is a link to the data sheet for the mosfet you tried to use and wasn't suitable: http://www.vishay.com/docs/91015/sihf510.pdf

ID continuous is 5.6a (too low), VGS TH is 4v (too high), and RDS ON is .54 ohm (540 milliohms! too high).