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Problem on Ecigarette mod ( Voltage)

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zerostar

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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 1.2V-1.6V.

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

this is the schematic diagram:

mosfet2.JPG

Power source :[/B] 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 draw 3.7V and 0.98A
;but add into circuit, it only receive 1.2V-1.6V.
 

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The mosfet needs to be connected between the load and ground, not between the V+ and load.

The source on the mosfet goes to ground. The drain goes to the load. The other end of the load goes to the battery.

Finally, what voltage is your battery? A typical mosfet will not turn on completely like a switch unless its gate is about 10V positive relative to its source. It may work well enough at lower voltages, or you can get a "logic level" mosfet that will work with its gate at much lower voltages relative to its source.
 
The mosfet needs to be connected between the load and ground, not between the V+ and load.

The source on the mosfet goes to ground. The drain goes to the load. The other end of the load goes to the battery.

Finally, what voltage is your battery? A typical mosfet will not turn on completely like a switch unless its gate is about 10V positive relative to its source. It may work well enough at lower voltages, or you can get a "logic level" mosfet that will work with its gate at much lower voltages relative to its source.

Opps. you are right, both connection had already been tried but maintain the same.

Battery provides 3.7V, and i had tried a lot mosfet which have low Vgs, such as SSM3K123TU,FDC855N, but still failed to supply enough voltage to heater.

However, the circuit can provide 3.7V when using other component like 5V fan instead of heater.
 
Your new, animated drawing looks correct. Are you absolutely sure that is how it is connected. Are the connections correct to the mosfet? Does the PIC pin go high? Have you tried turning on the mosfet with just a 9-V battery between its source and gate? Have you tried testing the mosfets with an ohmmeter/diode tester? You can turn the gat one that way, then tests drain to source conduction.

Using mosfets in this manner is such well plowed earth that it is unlikely to be a design problem.

John
 
well.. the connection is correct since I follow you-tube video only:eek:
The pin output is high when press the switch then heater can operate.
 
The datasheet for the Mosfet you used shows a THRESHOLD Vgs voltage of 1V to 2.5V. That is when it is ALMOST TURNED OFF (not turned on) with a current of almost nothing (0.1mA).

The datasheet shows that it turns on very well with a Vgs of 10V and turns on fairly well with a Vgs of 4.5V.

We don't know the voltage from your battery when it is trying to heat the heater (it might be only 3.0V or less) and we do not know the current of the heater.
We also do not know how little current your motor uses.
 
That does not explain why the SSM3K123TU didn't work (post 3). I am not quite sure, however, what the OP has done, what devices he actually is using, and what this sentence really means:

The pin output is high when press the switch then heater can operate.

ssm3k123tu.png

John
 
His Mosfet is shown to be a follower. Then its gate voltage must be much higher than the supply voltage.
 
I pointed that out in post#2. He then revised his statements and claims to have done it with the mosfet on the low-side. His post was edited accordingly with the little animation. That is part of what is so confusing. We really don't know with certainty what schematic he is using. One interpretation of the sentence I quote is that it is working fine now.

Perhaps he can clarify things.

John
 
sorry about the confusion and lack of information about the case.

First, when it is trying to heat the heater , battery provides 3.7V and heater finally receive 1.4v -1.7V, and 0.5A only
 
In order for us to be of any help in solving this problem, you need to show the exact circuit you are using and component values, especially, but not limited to the part number for the mosfet you are using.

John
 
The part number of the "3.7V" lithium battery will help us determine if it can provide enough current. Does its voltage drop when it is trying to heat the heater?
Is the battery new or is it almost dead? Is it charged properly?
 
In order for us to be of any help in solving this problem, you need to show the exact circuit you are using and component values, especially, but not limited to the part number for the mosfet you are using.

John


This is the final circuit:
Mosfet_n-ch_circuit.2.png

Mosfet: irlr3114zpbf
Load : Heater
Battery : 3.7V Li polymer battery

----------------------------------------------



when operate, the atomizer only receive 2.2V but battery provide 3.7V, where is the rest going?internal resistance?
 
Battery : 3.7V Li polymer battery

----------------------------------------------

when operate, the atomizer only receive 2.2V but battery provide 3.7V, where is the rest going?internal resistance?
I have many worn out Li-po batteries that are 3.7V with no load but when loaded with 100mA their voltage drops to only 2V. Most are rated at 160mAh/25C so they conduct 4A when new and when fully charged.

That is why I asked a few times, "What is the battery voltage when the Mosfet tries to heat the heater?", but you did not answer.

The IRLR3114 Mosfet can typically conduct about 15A with a voltage drop of only 0.1V when its gate-source voltage is 3.7V.
You get 2.2V and 0.5A so your heater is (2.2V/0.5A=) 4.4 ohms. If the battery is 3.7V then the Mosfet turns on fairly well, the heater gets 3.7V and the current should be (3.7V/4.4 ohms=) 0.84A.

Maybe you are measuring the voltage across the heater when you have a current meter in series. But the resistance of the current meter might be reducing the voltage and reducing the current.
 
I have many worn out Li-po batteries that are 3.7V with no load but when loaded with 100mA their voltage drops to only 2V. Most are rated at 160mAh/25C so they conduct 4A when new and when fully charged.

That is why I asked a few times, "What is the battery voltage when the Mosfet tries to heat the heater?", but you did not answer.

The IRLR3114 Mosfet can typically conduct about 15A with a voltage drop of only 0.1V when its gate-source voltage is 3.7V.
You get 2.2V and 0.5A so your heater is (2.2V/0.5A=) 4.4 ohms. If the battery is 3.7V then the Mosfet turns on fairly well, the heater gets 3.7V and the current should be (3.7V/4.4 ohms=) 0.84A.

Maybe you are measuring the voltage across the heater when you have a current meter in series. But the resistance of the current meter might be reducing the voltage and reducing the current.

I test on Lipo and Li battery again and here is the result:

LI polymer battery:

Unload Voltage: 3.87V
Loaded Voltage: 3.56V
Current output: 0.99A

Heater:

Voltage receive: 2.68V
Current receive :0.98A

B]LI battery(18500)

Unload Voltage: 4.1V
Loaded Voltage: 3.33V
Current output: 0.99A

Heater:

Voltage receive: 2.34V
Current receive: 0.83A


I hope the heater can receive more than 3V , am I missed something?
 
I test on Lipo and Li battery again and here is the result:

LI polymer battery:

Unload Voltage: 3.87V
Loaded Voltage: 3.56V
Current output: 0.99A

OK, with a 1 A load, the battery voltage dropped, as expected. How did you apply the 1A load? Was that just the ecigarette directly across the battery?

Heater:

Voltage receive: 2.68V
Current receive :0.98A

How was this test done? Was that with the mosfet in circuit? Or, was this with the ecigarette directly across the battery?

B]LI battery(18500)

Unload Voltage: 4.1V
Loaded Voltage: 3.33V
Current output: 0.99A

Is this a new battery? Is it LiPo or lithium ion?

Heater:

Voltage receive: 2.34V
Current receive: 0.83A

This result, like the one above is unclear.

If you refer to Figures 1 and 2 of the datasheet for your mosfet, at a Vgs of 3.5V, which should be available under load based on your data, the mosfet will pass about 70A with a Vds of only 3V (equivalend Rds= 0.043Ω). Thus, at 1A, that would be a voltage drop of only 43 mV across the mosfet. Since the battery under load , according to your data, is at 3.5 volt, simple physics tells you that the voltage drop across the ecigarette is 3.5- 0.043 or 3.46V. The same calculation can be done using data in Figure 2 (tjs = 175°) and the results are similar.

There is something wrong with your data. Maybe you are not measuring the circuit at the correct points? What value is the resistor from gate to ground? You can use at least 10K there to minimize its effects.

Please give voltage and current data for the ecigarette directly across the battery.

How are you measuring current? Is it being done at the same time as you measure voltage (i.e., do you have two meters)?

John
 
I have many Li-Po battery cells. ALL of them are fully charged at exactly 4.20V. Why isn't your Li-Po battery fully charged?
The voltage is 3.2V when the battery charge is low and the load should be disconnected. Then the "average" voltage for a discharge is 3.7V.

Who is the manufacturer and what is the model number of your Li-Po battery? Can you post its spec sheet?
Some Chinese Li-Po battery cells cannot supply much current without the voltage collapsing.

Some of my American Li-Po cells are tiny (160mAh/25C) and the voltage barely drops with a load of 2A, except when they are swollen and are finished.
Here is the spec sheet for another American small battery cell:
 

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I see, btw, I figure out the problem finally:eek:

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

Once I move to PCB, the heater can receive 3.55V , thanks audio and John:)
 
Why is it that whenever somebody has trouble with a circuit it is their breadboard that causes the problem??

I found a tutorial about e-cigarettes. The LI battery is so small (about 200mAh) that the pushbutton has a 5 seconds timer. Then the battery charge might last one day. Day after day the battery gets weaker then needs replacement in one month.

The resistance of the heater is 2.2 ohms to 3.4 ohms. Then the current when the 4.2V battery drops to 4.1V is 1.2A to almost 1.9A.
 
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