hot mosfet

[Chegs]

I've just experimented with a FET from the incendiary device versus an old FET from my 1st build (90A miniature pita) and the larger FET was too hot to touch the instant I fired the 0.3 ohm atty, yet the 90A mini FET was still cool enough to hold even after a minute + of fire. This means I've got a drawer full of FET's I can only use on 8.4V mods, and I'll have to hunt out more of the physically larger FET if I want to resume 4.2V vaping which is going to be a bit of a pita.

 

[adam.]

I've just experimented with a FET from the incendiary device versus an old FET from my 1st build (90A miniature pita) and the larger FET was too hot to touch the instant I fired the 0.3 ohm atty, yet the 90A mini FET was still cool enough to hold even after a minute + of fire. This means I've got a drawer full of FET's I can only use on 8.4V mods, and I'll have to hunt out more of the physically larger FET if I want to resume 4.2V vaping which is going to be a bit of a pita.

Did you get them from modmaker? He said he would refund me if they are duff.

 

[SteveVapeStorm]

Hey adam. I have the same issue with my box mod build. I tested it before fitting in the box. I used a irlb3034pbf n channel fet and it was getting red hot within a secomd of firing a .1 ohm load. After some advice I tried firing again on a kayfun built at .65 and was getting warm but not excessivley. After completing the mod I used the same kayfun at 0.65 and got 2 minutes of vape time before it decided to fry the insulation and cause a battery to vent. Ive had a look on breaktru and seen the same build but with Parallel mosfets, if you can make it, come down to the yorkshire terrier pub in york city centre next sunday (21st) at 2pm for the vape meet, be great to see you there and chat mods.

 

[Chegs]

Did you get them from modmaker? He said he would refund me if they are duff.

I can't recall where I got them unfortunately.

 

[fasteddie600]

I've just experimented with a FET from the incendiary device versus an old FET from my 1st build (90A miniature pita) and the larger FET was too hot to touch the instant I fired the 0.3 ohm atty, yet the 90A mini FET was still cool enough to hold even after a minute + of fire. This means I've got a drawer full of FET's I can only use on 8.4V mods, and I'll have to hunt out more of the physically larger FET if I want to resume 4.2V vaping which is going to be a bit of a pita.

Hey adam. I have the same issue with my box mod build. I tested it before fitting in the box. I used a irlb3034pbf n channel fet and it was getting red hot within a secomd of firing a .1 ohm load. After some advice I tried firing again on a kayfun built at .65 and was getting warm but not excessivley. After completing the mod I used the same kayfun at 0.65 and got 2 minutes of vape time before it decided to fry the insulation and cause a battery to vent. Ive had a look on breaktru and seen the same build but with Parallel mosfets, if you can make it, come down to the yorkshire terrier pub in york city centre next sunday (21st) at 2pm for the vape meet, be great to see you there and chat mods.

Did you get them from modmaker? He said he would refund me if they are duff.

Certainly all sounds like an issue with the MOSFET specs, I have done loads of testing with FET's and 3.7V builds but unfortunately this isn't a FET I have tried.

I have had the same issues running a 3711 FET under high load with round cells due to high volt drop. If the Gate-Source voltage is not sufficient (more than the Vgs MAX of the FET) the FET will get hot and full current will not pass to the 510. The characteristics of different FET's varies quite dramatically, I am no expert but have spent a lot of time playing with and testing FET builds.

From what I have played with-
I would recommend the IRLB8748 FET for use with standard round cell 3.7V parallel builds. I have tested plenty and these are my preferred one for standard round cells at 3.7V. These still get warm running 60-70W+

The IRF3711pbf is great for LiPo builds as it starts to cut off around 3.0V under load which helps protect the batteries from over discharge.

I am sure there are better ones out there (please share if you find them!), but I know these work and have a good idea how they will react.

Remember- 2 FET's are better than 1, Heat Sinks are cheaper than chips and are very helpful.

Don't forget FET's will generate heat and you need to allow that out so wrapping in insulation is not ideal for dealing with high loads/more heat.

Hope that helps

 

[adam.]

Certainly all sounds like an issue with the MOSFET specs, I have done loads of testing with FET's and 3.7V builds but unfortunately this isn't a FET I have tried.

I have had the same issues running a 3711 FET under high load with round cells due to high volt drop. If the Gate-Source voltage is not sufficient (more than the Vgs MAX of the FET) the FET will get hot and full current will not pass to the 510. The characteristics of different FET's varies quite dramatically, I am no expert but have spent a lot of time playing with and testing FET builds.

From what I have played with-
I would recommend the IRLB8748 FET for use with standard round cell 3.7V parallel builds. I have tested plenty and these are my preferred one for standard round cells at 3.7V. These still get warm running 60-70W+

The IRF3711pbf is great for LiPo builds as it starts to cut off around 3.0V under load which helps protect the batteries from over discharge.

I am sure there are better ones out there (please share if you find them!), but I know these work and have a good idea how they will react.

Remember- 2 FET's are better than 1, Heat Sinks are cheaper than chips and are very helpful.

Don't forget FET's will generate heat and you need to allow that out so wrapping in insulation is not ideal for dealing with high loads/more heat.

Hope that helps

Cheers for all the help.being new to this forum I didnt expect such a good response.
I ordered a couple of 8748s today so hopefully these will do the trick.ill keep you posted.

 

[adam.]

Hey adam. I have the same issue with my box mod build. I tested it before fitting in the box. I used a irlb3034pbf n channel fet and it was getting red hot within a secomd of firing a .1 ohm load. After some advice I tried firing again on a kayfun built at .65 and was getting warm but not excessivley. After completing the mod I used the same kayfun at 0.65 and got 2 minutes of vape time before it decided to fry the insulation and cause a battery to vent. Ive had a look on breaktru and seen the same build but with Parallel mosfets, if you can make it, come down to the yorkshire terrier pub in york city centre next sunday (21st) at 2pm for the vape meet, be great to see you there and chat mods.

Hey buddy. Im afraid ill be away with work then. Is there info on the meet anywhere ? Id be well up for this in the future.

 

[SteveVapeStorm]

Hey buddy. Im afraid ill be away with work then. Is there info on the meet anywhere ? Id be well up for this in the future.

facebook.com/yorkvapemeet
Last sunday of every month, apart from this month because of xmas.
2pm till pissed lol

 

[adam.]

So i got the new fets.
Its better, but still not perfect. With batteries at 4v and a build of 0.7 ohms im getting 3.8v under load and the mosfet is cool.
With a 0.15 ohm build the mosfet is still getting warm and im getting 2.7v under load.

 

[Loco]

This seems the right thread to ask..........


If using fets in parallel, wouldn't you need to use a fet with half the vgs as you would if using one?