Help! Having problem with Mosfet/Charger

[sparkyjuice]

No, I've not got that many but would you have a look at the specs and tell me where I went wrong pretty please? Thanks fella.
N-Channel MOSFET 80A/55V

section marked gate threshold voltage bud 2 to 4v

 

[RicModMaker]

section marked gate threshold voltage bud 2 to 4v

Thanks fella. What sort of value should I be looking for?

 

[sparkyjuice]

Thanks fella. What sort of value should I be looking for?

like I said the ones fasteddie600 linked to are fine
gate threshold 1 to 3v I believe
20v max VDS and 110A

 

[RicModMaker]

like I said the ones fasteddie600 linked to are fine
gate threshold 1 to 3v I believe
20v max VDS and 110A

Much appreciated fella. Sparky to the rescue again ;-) [emoji106]

 

[sparkyjuice]

actually fasteddie600 have you thought about making a regulated mod using a variable mark/space ratio
clock triggering the FET ?

 

[fasteddie600]

No, I've not got that many but would you have a look at the specs and tell me where I went wrong pretty please? Thanks fella.
N-Channel MOSFET 80A/55V

The problem with the ones you have is that they are too high on the Vgs(th). Which is 2.1-4.0V. This refers voltage we need to apply to the gate(G) for operation.
We need to be running a bit above the maximum to achieve fully on state.
I think ideally we would like Vgs(th) max 2.0-3.0V so that fully on can be achieved using 3.7. Lower should be better.
The Vgs refers to the maximum they can handle so yours are plenty over, 16-20V would be plenty. It's more the Amp limit we are interested in.

I hope that makes a little more sense than my earlier post. I am just getting my head around it.

I will order some new ones tonight and let you know how that works out.

 

[fasteddie600]

actually @fasteddie600 have you thought about making a regulated mod using a variable mark/space ratio
clock triggering the FET ?

Funnily enough that had occurred to me as I started to recall some of my understanding of FET's. I would need to get my hands onto a circuit printer to make that sensible on space though.

Probably just be easier to use the cheap LM board I have in my box if was going to run 7.5V.

I will finish this one first!

 

[sparkyjuice]

Funnily enough that had occurred to me as I started to recall some of my understanding of FET's. I would need to get my hands onto a circuit printer to make that sensible on space though.

Probably just be easier to use the cheap LM board I have in my box if was going to run 7.5V.

I will finish this one first!

i'll have a look round for 4v version.....

 

[fasteddie600]

Thanks fella. What sort of value should I be looking for?

I just found this from info from another vaper which may be useful.-

You need a mosfet with a low Vgs(He means Vgs(th)Max). 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.

 

[RicModMaker]

Good info fella. Thanks.