Replacing my Mosfet (fried)

Ok ladies, stop what you're doing, I need all your focus here. Not because the topic is very complicated, but because I know close to nothing about it.

So I have bought the ABS Box Mod from Big here ABS BOX MOD W/MOSFET | Thailand Vapers

After 10min vaping a 0.6ohms, using the new LG HE4 fully charged, the Mosfet got really hot inside than... nothing.. "Ground Control to Major Tom, Your circuit's dead, there's something wrong"

Well it has been a hell of a ride !

So I contacted @Big by-pass , told him what happened, he immediately told me to send it back so big thanks to him for that. However, I want to know what happened and why it happen so fast. A Mosfet is dirt cheap (around 150thb) so I did not really mind frying it. I mind not to know why.

I have read long ago that a standard/commonly used Mosfet won't handle lower than .5ohms. So let's say I misread my res in the atty or had a short, the res went down and fried the chip.

Now my options are simple :

1. Get an exchange from Big
Pros: well, I get a new box
Cons: 50% chance to have the same issue

2. Replace the Mosfet by one that I am sure would handle subohming.
Pros: I would know how low I can go
Cons: I need to build it... I mean you should see what my Legos looked like..

So I remember my grand grand grand grand father, Napoleon (I dare you to prove me wrong) who said : "Impossible is a word only to be found in the dictionary of fools".

I decided to rebuild it by myself. Make a case out of it. Change my life. Take the risk. #YOLO #BRINGITON #ITSFRIEDANYWAY

Like most of you would do, I did my research. Like few of you would, I understand almost nothing.

So, a simple reminder, to find out who's worthy to keep read this thread :


Now that we all agree, here is where I stand :

1. I need to seek for a Mosfet that will allow me subhoming. My target is one that handle .2 or .3 at least (anything higher than .5 on a mech and I really dislike the ramp up).

2. I read the following :
You need a mosfet with a low Vgs. It needs to be below the lowest voltage (including drop) that you will vape at, otherwise the mosfet acts as a resistor and you don't want that as it will get very hot.

The 2-4V Vgs are no good that's too high, look at the 1-2.5V Vgs ones. Lower Rds is better, but also look at the data sheet to see what the current limitations of the package are.

Basically the mosfet is acting as a switch between the source and the drain. When the voltage at the gate is below Vgs(min) it is off, between Vgs(min) and Vgs(max) it works as a variable resistor depending on Vgs (you want to avoid this state), when Vgs >= Vgs(max) it is fully on. The resistor pulls the gate back down to 0V when you let go of the fire button.

From Doobedoobedo Need Help with n-Channel MOSFET Circuit


3. Big seems to have Mosfet 3034 in stock, and that is the specs I found on the net
http://www.irf.com/product-info/datasheets/data/irlb3034pbf.pdf

This model IRLB3034PBF seem to have a high tolerance in wattage but I cannot find the ohms limitation, at least I cannot make sense out of this specs sheets, much too technical for me.

4. Should I add a resistor to avoid the Mosfet getting in that stage which made it overheat ? I read the 15k resistor is quite standard and it would allow me to use a more standard Mosfet as well. Here is a simple diagram including a 15k res :


Now my question is the following : what would you advise me ? Getting that 3034 Mosfet and install it or add the 15k res ?

Installation look quite easy in terms of soldering three legs, I'm up to it. But I have no idea how to test it once it is build.

Your expertise would be so appreciated as for now, my 10min old ABS box Mod is as useful as a rock..

 

Yeah I need the McGyvers on this one ^^

 

I'd go for option 1b

 

Thanks for the advice guys but actually I am willing to give it a try. I would like to make it myself, seems quite simple to mold, I really want to learn new things. I feel like it is a great introduction for me, as I can't really mess it up more and the schemes are pretty basics.

So I need your advices on where to buy the 15k resistor as Big already got the Mosfet 3034.

Thanks

 

Anything on here? http://www.es.co.th/index.asp

 

Hey Tibo, How in the hell would I know?

Im just an old broken down pensioner, with a gout attack today.

 

@cmbrstefan buit his own box mod, if I recall correctly. Any tips, man ?

Actually very useful, yes !! I found so many different Mosfet, I forward it to my brother in law who works in this field. @Rick O-Shea , ever ordered from that website ?

I need a soldering tool too..

 

No, I haven't but have looked at it a few times just in case I'd need to

 

So many Mosfet.. Big Shop will get a 3034 in few days, just need to find a 15k resistor. Big thanks, man.

 

Ive not looked into which are the best to use yet, so going with the replacement from Big would be the obvious starting point. Check out RS for any other components you need.

RS ประเทศไทย | ผู้จัดจำหน่ายอุปกรณ์สำหรับงานอิเล็กทรอนิกส์ เครื่องจักรกลไฟฟ้า และเครื่องมือสำหรับงานอุตสาหกรรมชั้นนำของโลก

 

I can recomend you this Groub ..they all doing Box Mods and for sure they can help you !
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Thank you Sammy, I asked to join them. I'll see what I can take form it.

 

I ordered two Mosfet which arrived today. So I decided to try my luck and removed the old fried one and see what's not.

First, remove the fried Mosfet






Just to realize that it wasn't a 3034 as recommended but a STPS30H100CT which from what I understood does not like anything below .5Ohms.

Once done, I was a bit tricky to attach each wire to the new Mosfet, definitively could have use another set of hands. Wires are 16ga so very thick and it is hard to apply a correct pressure. However I think I have done an OK job, not the cleanest but it will do the trick.


I cut the legs and put everything back together, inserted 2 Samsung 25R fully charged and place the TugBoat V2 on top with a .35ohms build.

Well guys, it fires !!!!

BUT.... It does not fires well AT ALL. It is quite weak. Too weak for a dual paralel. It's much weaker than a single 18650 with the SMPL. It's like firing a 0.5ohms with 10watts..

The 510 pin seems dogdy but working, it fires any atty I put on it. The ramp up is just endless

After couples of minutes, I checked the battery voltage. One reads 4.02volts, the other one...4.12volts... DAMN IT !

Ok so I doubt it has anything to do with the chip, but looking at the wiring, if the left battery was not connected, how the Moseft would even get the Gate open. So I looked at other diagram and realize the following :


On these diagrams, the positive from the battery is NOT going straight to the Mosfet Gate leg. The Gate is connected to the Switch. So it would mean that the build was wrong from the start...

Can anyone explain this to me please, @Mack or @cmbrstefan , could it be the issue ? And even if it is firing with only one battery, why is it so weak, weaker than a mech mod. Does the Mosfet limit the voltage so much ?

Thanks in advance guys.

**Updated**

Just looked into it again and this is the difference..


I think mine is wrong, I don't see why one battery should be going to Gate on the Mosfet. That would mean only one battery is firing the atty.