Help! Having problem with Mosfet/Charger

[fasteddie600]

Right, finally have an update! Sorry been away at a festival all weekend and only get chance to put the new one in last night so not had a full running.

I fitted this one as listed before-
http://uk.rs-online.com/web/p/mosfet-transistors/5432351/
These are 20V max 110A Gate Threshold Max 3V

These so far are performing very well indeed in my 4V set-up.

I am getting very low voltage drop with 2 x 18650 AW IMR's in. It fires like a beast, I currently running a 0.2ohm coil to put it under some stress which should be hitting about 70W given that I am getting 3.7V at the atty. Everything seems to be running nice and cool so far. I will have to wait for the battery voltage to drop before I can say definitively these work all the way down to charging time voltages but all signs look good!

I reckon I should be good for 120W+ with this FET and wiring (I have used 2.5mm wires for main conductors and they are very short lengths)

Anyone know how far I can go with the right batteries in here? From my reckoning 80Watts should be safe but I reckon the unit will take 150-200Watts theoretically?

 

[sparkyjuice]

Right, finally have an update! Sorry been away at a festival all weekend and only get chance to put the new one in last night so not had a full running.

I fitted this one as listed before-
Buy MOSFET Transistors IRF3711PBF, N-channel MOSFET Transistor, 110A 20V, 3-Pin TO-220AB International Rectifier IRF3711PBF online from RS for next day delivery.
These are 20V max 110A Gate Threshold Max 3V

These so far are performing very well indeed in my 4V set-up.

I am getting very low voltage drop with 2 x 18650 AW IMR's in. It fires like a beast, I currently running a 0.2ohm coil to put it under some stress which should be hitting about 70W given that I am getting 3.7V at the atty. Everything seems to be running nice and cool so far. I will have to wait for the battery voltage to drop before I can say definitively these work all the way down to charging time voltages but all signs look good!

I reckon I should be good for 120W+ with this FET and wiring (I have used 2.5mm wires for main conductors and they are very short lengths)

Anyone know how far I can go with the right batteries in here? From my reckoning 80Watts should be safe but I reckon the unit will take 150-200Watts theoretically?

couple vtc5 batts and 240W is possible, but pushing your cables......short bursts should be ok

 

[fasteddie600]

couple vtc5 batts and 240W is possible, but pushing your cables......short bursts should be ok

Thanks for confirming what I was thinking before I blew myself up due to miscalculation!, I was trying to decide on batteries and VTC5's seemed favourite as it looks like a complete lottery with the efest ratings.

I have been running 70W ish all evening and nothing gets warm, so I need to find a better ohm checker which gives 2 decimal places(both of my multi-meters only give to 1 decimal). Maybe that shall be my next project! Anyone know where I can get an OHM display?
I think i will need some practice to build 0.06ohm coilsto get anywhere near 200W!

USB charging now all working correctly having fitted an acrylic insert in the box to insulate charge slot.
Paint is all dry and once everything is final fixed and tested I will share photos.
All in all this seems to be a great little power house, and should be good for weekend long vaping on normal builds. For around £20 in parts, plus batteries and paint, I am a happy bunny!

 

[sparkyjuice]

don't forget pics.....hope to finish my mech. box one day......
then PWM mosfet project.....

 

[fasteddie600]

don't forget pics.....hope to finish my mech. box one day......
then PWM mosfet project.....

Yep pics will follow shortly, I like to make sure everything is working A1 before I show it off!

The mech's take much more work to put together and design but ultimately very satisfying!

You will have to float some PWM ideas around here, I have also been thinking along these lines but need to learn some more first. I was possibly thinking of making a large 12V hookah pipe box/topper with an air intake turbine (with a hall type sensor) still just ideas floating around though.

 

[fasteddie600]

Just as a final update to complete this thread really. I have run the box through a full charge and the new MOSFET has responded perfectly.

The gate looks to begin to move at around 3.35V.

In real terms this has meant with 2 x AW IMR 18650 2000mAH batteries-

A 0.2ohm coil was only running fully with 3.6V in the batteries(3.35 at the gate with V drop)

A 1.5ohm coil was running fully until 3.45(3.35 at the gate)

Once the gate voltage dropped to around 3.25V mark, voltage at the atty down to around 2.8V.

By the time the batteries were this low the vape had diminished significantly anyway and I would be charging, and it took me 3 days to get it down to 3.6!

So I would say these MOSFET's will be a good choice for anyone else wanting to try a 4V build.

 

[RicModMaker]

I got these IRF3711PBF. Hopefully they will do the job.

 

[fasteddie600]

I got these IRF3711PBF. Hopefully they will do the job.

Those one's are good to go unless the build is getting silly.

I now have two of those running parallel in my little big project and that is now good/tested for 0.08ohm at 160W and still only getting 0.5v drop from the lipos. which keeps it well over 3V under load.

I had one running in the 2 x 18650 box and was finding with very low res coils the volt drop(even on VTC5's) was taking the voltage too low for the gate(1V drop at 100W). I have now changed that out for a pair of the IRLB8748pbf ones as they have gate voltage max 2.35v and that suits normal IMR batteries better for high loads, but they get a bit warmer.

I hope that info helps.

 

[RicModMaker]

Those one's are good to go unless the build is getting silly.

I now have two of those running parallel in my little big project and that is now good/tested for 0.08ohm at 160W and still only getting 0.5v drop from the lipos. which keeps it well over 3V under load.

I had one running in the 2 x 18650 box and was finding with very low res coils the volt drop(even on VTC5's) was taking the voltage too low for the gate(1V drop at 100W). I have now changed that out for a pair of the IRLB8748pbf ones as they have gate voltage max 2.35v and that suits normal IMR batteries better for high loads, but they get a bit warmer.

I hope that info helps.

That is helpful thanks.
So what sort of build are these suitable for?
And also what sort of build is the IRLB8748pbf suitable for?
Ric

 

[fasteddie600]

That is helpful thanks.
So what sort of build are these suitable for?
And also what sort of build is the IRLB8748pbf suitable for?
Ric

Ok so this is only based on my own tests and using these FET's in my builds but I would say that either FET is good for builds unlikely to be used for more than 50W vaping, assuming a good battery source(2x18650, lipo packs etc).

If more than 50W vaping is desired I would use-

IRF3711pbf for LIPO builds/battery sources with low voltage drop

IRLB8748pbf for standard battery builds (18650 etc) with higher voltage drop.




I hope that makes it clearer, the problem is that it all depends on the voltage drop on the batteries under load.