Problem on Ecigarette mod - Voltage Problem

[dstone]

Hi,

I am trying to build a E cigarette mod
but having the voltage problem. The heater do not receive enough voltage to operate and only receive 2.2V

Heater required to receive 3V to operate properly, do you know how to fulfil it?

this is the schematic diagram:




Power source : Li polymer 1000maH 3.7V battery,

Mosfets: IRLR3114/FDN357N.

- I tried at least 6 mosfet which have low VGS (1-2V), but still can not solve the problem)

Heater: atomizer in ecig

- when it directly connect to power source, it can operate properly and it got 2.8Ohm ,draw 3.7V and 0.98A ;but add into circuit, it only receive 2.2V

Also, when heater is alternated by other component like 5Vfan, it receive 3.7V ... why?

 

[bapgood]

I will start by saying I'm no expert....but you could use the MOSFET to switch to ground instead of switching the voltage.

I have had similar issues with a MOSFET and I'm not sure why either, but I do know you can use it to switch to ground....it just has to hooked up a little different if memory serves.

 

[dstone]

I find the diagram from other post and people said it work.
Just wondering how they said it..

I will start by saying I'm no expert....but you could use the MOSFET to switch to ground instead of switching the voltage.

I have had similar issues with a MOSFET and I'm not sure why either, but I do know you can use it to switch to ground....it just has to hooked up a little different if memory serves.

 

[DrMA]

You need to use a P-mosfet on the high side of the circuit (like your drawing) or, move the N-mos to switch the low side (ground). I'm surprised it works at all the way you've got it wired.

 

[WillyB]

Heater: atomizer in ecig

- when it directly connect to power source, it can operate properly and it got 2.8Ohm ,draw 3.7V and 0.98A ;but add into circuit, it only receive 1.2V-1.6

Do it like that.

I can't figure out what you are trying to accomplish with that design. Get a decent switch and forget about the mosfet.

Here's some basic diagrams using an N-MOS if you feel you want one.

 

[dstone]

Do it like that.

I can't figure out what you are trying to accomplish with that design. Get a decent switch and forget about the mosfet.

Here's some basic diagrams using an N-MOS if you feel you want one.

Finally it work, thanks. however,
the atomizer only receive 2.2V but battery provide 3.7V, where is the rest going?internal resistance?

btw, seem only me got the voltage problem like this, do I missing something?

 

[dstone]

hope someone can solve my problem

 

[bapgood]

Finally it work, thanks. however,
the atomizer only receive 2.2V but battery provide 3.7V, where is the rest going?internal resistance?

btw, seem only me got the voltage problem like this, do I missing something?

Are you using the same mosfet as the people/person you are trying to emulate?

I know there are tons! of varieties of mosfet designed for slightly different things. Typically switching power very quickly, unlike this application.

Sorry not really an answer....But if there is a thread where someone got it to work the way you are trying, they may have better incite.

 

[dstone]

Are you using the same mosfet as the people/person you are trying to emulate?

I know there are tons! of varieties of mosfet designed for slightly different things. Typically switching power very quickly, unlike this application.

Sorry not really an answer....But if there is a thread where someone got it to work the way you are trying, they may have better incite.

I just reference from this design:



In this design ,IRLR3114 is used

 

[WillyB]

Wells here's an easier to see pic.

She went to the mosfet approach because those little ball tact switches were burning out on their own.

As you can see she is following the same route as the pics I posted, switching the neg lead.

She gave no real reason but on her later builds she dropped both the switch and the mosfet and opted for a direct wired horn switch.

however,
the atomizer only receive 2.2V but battery provide 3.7V, where is the rest going?internal resistance?

I would expect some loss, both voltage and efficiency but not nearly that much.

That seems to be the same mosfet that Nuck used in his fistpack, from his tutorial. I imagine that's why she chose it.

IRLU3114ZPBF International Rectifier | IRLU3114ZPBF-ND | DigiKey

If you look at his schematic (trace just the mosfet) you see it is also following the same negative, N-MOS, switching path. A little bit of voltage loss here is no big deal as the regulator will easily compensate.

FWIW is your Lipo coming off the charger at a full 4.2V?

 

[DrMA]

Finally it work, thanks. however,
the atomizer only receive 2.2V but battery provide 3.7V, where is the rest going?internal resistance?

btw, seem only me got the voltage problem like this, do I missing something?

I think there's a compounding problem here:
1) your LiPo may be too weak to carry the load and drops voltage when turned on.
2) the MOSFET you're using has a Vgs(th) of 2.5V @ 100µA. So, if your battery voltage drops too low, that means it won't be turned on all the way. When Vgs approaches Vgs(th), Rds(ON) increases dramatically as well as Id (the forward current thru the fet), causing further voltage drop to your atty.

Test the voltage at the atty connector without an atty installed and see if it's 3.7V. If it is, but then drops to 2.2V when you have an atty installed, you'll know it's your battery being unable to carry the load. Get a new IMR battery.

 

[dstone]

Wells here's an easier to see pic.

She went to the mosfet approach because those little ball tact switches were burning out on their own.

As you can see she is following the same route as the pics I posted, switching the neg lead.

She gave no real reason but on her later builds she dropped both the switch and the mosfet and opted for a direct wired horn switch.


I would expect some loss, both voltage and efficiency but not nearly that much.

That seems to be the same mosfet that Nuck used in his fistpack, from his tutorial. I imagine that's why she chose it.

IRLU3114ZPBF International Rectifier | IRLU3114ZPBF-ND | DigiKey

If you look at his schematic (trace just the mosfet) you see it is also following the same negative, N-MOS, switching path. A little bit of voltage loss here is no big deal as the regulator will easily compensate.

FWIW is your Lipo coming off the charger at a full 4.2V?

YEs, fully charged,

 

[dstone]

I think there's a compounding problem here:
1) your LiPo may be too weak to carry the load and drops voltage when turned on.
2) the MOSFET you're using has a Vgs(th) of 2.5V @ 100µA. So, if your battery voltage drops too low, that means it won't be turned on all the way. When Vgs approaches Vgs(th), Rds(ON) increases dramatically as well as Id (the forward current thru the fet), causing further voltage drop to your atty.

Test the voltage at the atty connector without an atty installed and see if it's 3.7V. If it is, but then drops to 2.2V when you have an atty installed, you'll know it's your battery being unable to carry the load. Get a new IMR battery.

Absolutely like this, however, same result when using 18500 Li battery, is that the battery problem too?

 

[dstone]

You guy do not have such problem like this?
All of your atomizer recieve certain voltage as battery provided?
Can you share the circuit?

 

[DrMA]

Absolutely like this, however, same result when using 18500 Li battery, is that the battery problem too?

Sure sounds like it. If you don't have a battery capable of handling 2-3A continuous discharge, it's gonna drop really low under load. Use IMR round cells, or RC hobby-grade flat LiPo cells.

Remember capacity (mAh) x C-rating = continuous current rating.

For example:
flat LiPo 1000 mAh x 15C = 15000mA = 15A current rating
18650 LiPo 3000 mAh x 0.5C = 1.5A current rating
18650 IMR 1300 mAh x 8C = 10.4A

 

[dstone]

i see. but what happen when i use the same battery in v2? it also provide the same voltage .


But it performs very well in v2(original circuits , so is that my circuit problem?

 

[WillyB]

Sure sounds like it. If you don't have a battery capable of handling 2-3A continuous discharge, it's gonna drop really low under load. Use IMR round cells, or RC hobby-grade flat LiPo cells.

Yea OK. Folks have being using mosfets, for dinky switches or touch switches, in their mods long before IMRs came onto the scene.

And you need neither 'IMR round cells, or RC hobby-grade flat LiPo cells' to get a a piddling 2-3A, nor does it have to be continuous even. A decent 2600 Li-Ion can easily provide ~6A in short bursts (like vaping).

Even this TrustFire can easily handle a 5A continuous drain.

If it's a battery problem it's not cuz of "IMR round cells, or RC hobby-grade flat LiPo cells"

 

[dstone]

I see, btw, I figure out the problem finally

It is due to the internal resistant since I test on breadboard.

Once I move to PCB, the heater can receive 3.55V ,

 

[WillyB]

Good catch, good work.

 

[DrMA]

I see, btw, I figure out the problem finally

It is due to the internal resistant since I test on breadboard.

Once I move to PCB, the heater can receive 3.55V ,

makes sense. I'm glad you figured it out.