Amps vs Voltage

[Aal_]

Hi Guys,

So what is the relation between the voltage and the amps a battery delivers? I know batteries have the voltage (3.3, 3.7, 4.2 ...) and the capacity (650 mah, 1000 mah ...). The atomizers have the resistance (1.5, 2.5 ...). So if i calculate the amps by dividing the voltage by the resistance is that enough? I read somewhere that for example and ego-c battery 3.3 v is too weak for 1.5 ohms DCT. Does this mean that V/R gives a current that is greater than the battery can deliver? How can i know what is the maximum amps a battery can deliver? it is never mentioned.

 

[yanivriz]

technically? that the right way to calculate according to Ohms law.
in reality, the heat of the coil/atomizer, significantly effects its resistance, meaning the hotter the coil goes, the higher it will resist.
so when vaping on PG-that's quite the right amperage your getting, on VG your going to get a lower effective current.

 

[yanivriz]

the MAh is the amp's per current voltage per hour.

 

[DaveP]

A 3.7v battery actually charges to 4.1v-4.2v. When you add the load of an atomizer, that voltage settles to around 3.7 quickly as the top off charge stabilizes at the working voltage.

Just for example, say you have a battery rated at 500mah. That means a load that pulls 1/2 amp will work on that battery for an hour, then the battery will quickly die. We don't vape the entire hour at once. We hit the ecig frequently, but intermittently, not constantly, so we get hours out of a battery charge. That, and the battery will recover slightly between vapes on an intermittent load as opposed to a constant test load.

A 2 ohm carto will pull about 1.85 amps from a 3.7v batt when you draw. That's over 3 times the amount used during the MAH rating test. A 3 ohm carto will draw about 1.23A from that same battery. We generally estimate from collective experience that a battery will give the average of about an hour of vaping for every 100mah of rating. That's just the way it seems to work and is a good rule of thumb. LR = less charge life, SR = more vapes. When you screw on a 1.7 ohm dual coil, you are sucking battery power at an extremely high rate. If you work the numbers, you will see that a 3 ohm carto pulls a similar wattage, but significantly lower amperage from the same battery. It's just the way the plotted curves work out from the formulas.

The bigger the better when it comes to buying batteries, especially when you are using LR cartos. I can vape all day and frequently into the next on a 2000mah 18650 IMR using 3 ohm cartos at 4.2v on my Provari.

 

[Aal_]

That's over 3 times the amount used during the MAH rating test.

Excuse my ignorance but how do you know that? What is MAH rating test? how do I know that 1.85 amps is too much.

If you work the numbers, you will see that a 3 ohm carto pulls a similar wattage, but significantly lower amperage from the same battery. It's just the way the plotted curves work out from the formulas.

Isn't the wattage different since power = voltage x current?

 

[AttyPops]

Watts (basically the same as Power) = Volts * Amps. Or Voltage * Voltage / Resistance (a derivation from Ohms law).

The # amps from a battery are variable... a particular battery only puts out so many amps. In fact, max amps stresses them. That's one reason the mini cig-sized e-cigs only put out so current and you don't use 1.5 ohm LRs on them. Also the reason that they make high-drain IMR batteries.

Many mod users have put LR or DCC stuff on their e-cigs and found that they don't get what they expect. The units are amp-starved and the voltage drops under load as a result.

Think of voltage as water pressure (like PSI) whereas amps = flow rate (diameter of the water hose, not the pressure within).

Stated yet another way, a given battery can only release so many electrons per second.

How do you know the amps? You have to check the specs for a given battery. You're right it isn't always stated. Check the "C-Rating" and google that. Also google "Battery University".

 

[DaveP]

Excuse my ignorance but how do you know that? What is MAH rating test? how do I know that 1.85 amps is too much.

Isn't the wattage different since power = voltage x current?

I was just saying that battery life can vary with the resistance of the carto and the voltage you supply. Higher resistances can work more efficiently at not much more voltage. For example, I get good vapes from 4.2v with a 3 ohm carto that are roughly equivalent in taste and vapor as a 2 ohm at 3.7v.

I was comparing 2 ohm to 3 ohm carto amp draw on the same battery and should have clarified that. With one calculation at V/R and the other at V^2 / R, the resultant lines on a graph rise linearly for amperage and as a result of the square of the voltage in watts, but there's a sweet spot that provides good vaping at lower current drain.

Here's a simple graph that shows current rise on higher and lower resistance as voltage rises. Lower resistance experience rapid rise as voltage goes up. Higher resistances, not so much.
http://en.wikipedia.org/wiki/Current–voltage_characteristic

 

[vdrum4250]

i suggest you download ohms law app on the iphone to make it easier and get meter to help you get readings

 

[RickHerron]

So what wattage and amperage should I be shooting for in a perfect world? Using a Boge Leo 800 mAh at 3.7 volts and a 1.5 ohm DC clear-o-mizer. That's about 9 watts and 2.5 amps. What's the "sweet spot" supposed to be, because I think the amperage is kinda high, based on what I've read.

 

[Sev00]

Excuse my ignorance but how do you know that? What is MAH rating test? how do I know that 1.85 amps is too much.



Isn't the wattage different since power = voltage x current?

See my post at http://www.e-cigarette-forum.com/fo...96135-volts-amps-ohms-battery-life-oh-my.html

volts-amps-ohms-battery-life-oh-my

Most ecigs will handle 3 amps or less. So this really come into play with a varitable volt battery mod. You don't want to drive over 3 amps or you will kick in the protection on the batteries, or worst case fry a momentary switch. But a LR 1.5 works well with an eGo 1000 mAh battery. Although it drains it more quickly than a RR would. This is because it uses more wattage. A eGo 650 just runs down to fast in my opinion for a LR. But see my post for more info.

mAh is milliampere-hour. Its a measurement of how long a battery will last. But not a 1 for 1. It does give you a comparison point between different brand batteries though.

From Wikipedia, the free encyclopedia

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An ampere-hour or amp-hour (symbol Ah, AHr, A·h, A h) is a unit of electric charge, with sub-units milliampere-hour (mAh) and milliampere second (mAs). One ampere-hour is equal to 3600 coulombs (ampere-seconds), the electric charge transferred by a steady current of one ampere for one hour.^[1] The ampere-hour is frequently used in measurements of electrochemical systems such as electroplating and electrical batteries. The commonly seen milliampere-hour (mAh or mA·h) is one-thousandth of an ampere-hour (3.6 coulombs).

Sev