mAh (milliamp-hour) - The run-time capacity of a battery.
One mAh is equivalent to 1/1000th of an amp hour, 1000 milliamps is equal to one amp. So for example a 3000 mAh battery has 3 amp hours, meaning that it can provide 3 amps for 1 hour, 6 amps for half an hour etc. A real world example might be more in the region of 15 amps being drawn from the battery, giving approximately 10 minutes of use, equivalent to about 120 puffs.
Voltage (volts) - The charge state of the battery.
A fully charged 18650 will have 4.2 volts, and will usually be considered discharged at around 3.2 volts. 18650s should not be discharged below 2.5 volts as this distresses the battery. Below 2.0 volts the internal copper electrodes start to dissolve. Then when the battery is recharged this free copper will 'plate' to the internal components damaging the battery and creating the possibility of a short-circuit. Battery's discharged below 2.5 volts should be considered potentially unsafe, with recycling being a cheap and safe option.
18650s often display a value of 3.7 volts on the wrapper. This is a 'nominal' value, meaning that over the battery discharge curve the majority of the charge life is in the 3.7 volt range.
CDR (Continuous Discharge Rate) - The number of amps that a battery can safely deliver, continuously.
As well as creating a ‘green’ safe usage zone and an effective amp limit, it is highly relevant in the event that your mod auto fires or the button on the device is actuated when it is unattended. If your devices power demands are within the CDR of your battery, it will discharge until it is flat without being damaged or reaching unsafe internal temperatures. If your setups power demands grossly exceed CDR, your battery will be damaged and in extreme cases vent or explode. Beware of 'pulse' ratings.
There is no need to exceed CDR. Should your atomizer require more than one battery can provide, then the amp load should be split/shared using a multi-battery mod.
Mooch's test data should be consulted for a reliable CDR value for any given battery.
List of Battery Tests | E-Cigarette Forum
Pulse Rating - Amp capability of a battery over an undefined short period of time.
There are no standards or clear definitions for this value, and it should be discounted as a factor when choosing a battery. Some vapers choose to exceed the CDR of a battery, but at the low end this will reduce the lifespan of the battery, and at the higher end this can result in a venting or exploding battery.
Voltage Sag (voltage under load) - The transient drop in available voltage under load caused by the battery's internal resistance.
Some batteries have less voltage sag than others often leading them to be described as 'hard hitting'. On a regulated device voltage sag can be responsible for your mod displaying a 'weak/low battery' message even though there appears to be charge remaining.
What is battery internal resistance? | E-Cigarette Forum
The relationship between capacity (mAh) and the amp limit (CDR)
This can be thought of as akin to a seesaw. The higher the amp limit is the lower the mAh value will be, that's just how battery chemistry works.
So if your vaping style requires a battery with a high amp limit, a battery capable of delivering this will have a relatively low mAh value.
eg. The LG HB6 - 30 amp CDR, 1500 mAh
Conversely if your amp requirements are lower, then you could use a battery with an accordingly higher mAh value.
eg. The Samsung 30Q - 20 amp CDR, 3000 mAh
If your setup requires less than 10 amps it might seem attractive to use a high capacity battery in the 3100 mAh to 3600 mAh range. Unfortunately these batteries have very high internal resistances meaning that you will actually get longer run times using a good quality 3000 mAh battery.
As a rule of thumb there is no 18650 on the market that has:
A genuine CDR rating of over 30 amps
A genuine CDR of 20 amps capable of more than 3000 mAh
A genuine CDR of 10 amps capable of more than 3100mAh-3600mAh
There are no 18650s capable of over 3600mAh
Lies, more lies and re-wraps
It's worth mentioning that just because a battery has 50 amps written on the wrapper, it does not mean it is capable of it. I've been lied to to, How is this possible?!
There are only a few companies in the world with sufficient manufacturing power to actually produce batteries, those companies being Sony, LG, Samsung and Panasonic. All other batteries you see on the market are B or C grade castoffs from these companies that have been bought in bulk and 're-wrapped'. A new re-branded plastic wrap is placed on the battery before being resold at an inflated price. Inevitably the specifications shown on these re-wrapped batteries will also be inflated, usually with pulse ratings being passed off as CDR.
In my opinion re-wraps should be completely avoided, and only genuine battery's from Sony LG Samsung and Panasonic should be used purchased from reputable vendors.
List of Battery Tests | E-Cigarette Forum
There are a number of reasons why your tank atomizer might leak, so it's helpful to understand the mechanics of how a tank works.
The content of the tank is a column of juice suspended above a wick, which acts as a conduit to the coil. The flow resistance of the wick material and the negative pressure above the liquid at the top of the tank are the forces that prevent the juice from simply pouring out the bottom.
This explains why having the top of the tank open for too long while filling can result in leaking: there's no negative pressure "holding it in".
This also explains why bubbles are sometimes seen rising in the tank during use: atmospheric pressure is attempting to equalize the lower pressure in this area above the juice.
If you are using a tank with factory made coil heads (or an RTA) then the steps below can be used to minimize or eliminate leaking ~
Don't overfill your tank. Do leave a small air space at the top
Close the airflow/juice control when filling
Avoid leaving your mod in anything other than a vertical position
Check your o-rings are well fitted and not damaged or worn
Check all the tank components are fitted firmly together
Check that none of the components are cross threaded
Check for cracks or chips in tank glass
Check for bends or distortions in any of the tank components
Keep the chimney clear of gunk and excess juice
Clean your tank inside and out regularly
If you are using an RTA (Rebuildable Tank Atomizer) then there are additional steps you can take to prevent leaking:
Tank choice - Some tanks are just more prone to leaking then others and all tanks require a unique wicking technique particular to that device.
Wick position - Wicks should be well situated ensuring that juice channels are completely filled.
Wick length - Short wicks will provide a short distance from the juice to the coil, but may not provide sufficient flow resistance to the pressure of the juice above it: the wicks are then overwhelmed and leaking can occur. A long wick may have enough resistance, but be too long to wick efficiently creating dry hits.
It's a balancing act!
The density of the wicking, airflow, wattage and juice viscosity (PG/VG ratio) are all also pertinent variables in creating a successful leak free build.
The simple answer:
Too much juice on your coil.
Then when the coil is heated (crackle) bubbles of superheated vapor will violently expand outwards (pop) and in the process throw hot droplets of liquid into your mouth hole (spit).
What do I do about it?
The simple answer:
Reduce the amount of juice on the coil using one or a selection of the steps below.
Increase the density of your wicking. Tighter wicking through the coil will restrict the flow of juice being delivered to it.
Increase the viscosity of your juice. Using a juice with a higher proportion of VG will make the juice thicker and less of it will end up on your coil.
Check your coils for hot-spots on your coil. This can produce produce excessive popping and spitting along with other nasty symptoms
Hit the power before you put the drip tip to your mouth.
Reduce your wattage. Less power will decrease the violence of said pops and crackles.
If you use premade factory coils, then choices 1 and 3 and possibly 2 are not an option. This might be a good time to move to a rebuildable system like an RDA or an RTA.
Bear in mind that some popping/crackling/spitting is a part of many atomizers normal operation especially at higher power levels.
A much asked question amoung new users specifically of regulated devices (variable wattage) is "what coil do I need" or "what resistance is best for wattage X, and what wire should I use?".
The answer to the first question is, whatever coil works best for you as long as your device can supply enough power to get it up to heat. The answer to the second, is that that coil resistance is essentially unimportant on a regulated device, use whatever wire you like.
The key to understanding this is to think of the chosen power level dictating the wire guage and end resistance, rather than the other way around.
If you want to use a lot of wattage, then you need a heavier gauge of wire to be able handle this power. Heavier wire, more mass, with an intrinsically lower electrical resistance.
If you want to use a far lower power level, then you need a much thinner wire with less mass, or your power level will not be sufficient to light it up. Thinner wire, less mass, with an intrinsically higher electrical resistance.
On a unregulated device this takes care of itself, as the relationship between resistance and power is fixed. Using thicker wire produces lower resistance coils, which draw more amps and produce more wattage as per Ohms law - P=V²/R
There are practical limits to how low a resistance coil you can due to battery voltage sag, and voltage drop within the mod which increases exponentially as amp draw increases. Also very high mass coils have undesirably long ramp/down times. There are also safety issues with using extremely low resistance builds.
On a regulated device the relationship between resistance and power is not fixed, you can apply any power level you like to any coil regardless of it's resistance. Coils can be chosen to suit the desired power level, not the other way around.
The resistance of the coil becomes irrelevant, other than limitations set by the mod's own regulator chip. Now the important factors become the relationship between coil mass, surface area and the selected power level. Generally for maximum vapor production and battery efficiency one should choose a coil with the greatest surface area and the least possible mass.
Karl puts 12 watts through a 0.25 ohm dual 24AWG coil. He gets barely any vapor and the ramp up time of his coils is measured in hours.
Frank puts 70 watts through a single 6 wrap 30AWG 1.8 ohm coil. The vape is hideously harsh and his coil turns to a pool of molten slag in the bottom of his atomizer.
This is not based on any kind of research, it is an educated guess based on circumstantial evidence and some science.
As you pulse heat your coils, a layer of insulating oxide forms on the outside of the wire. This stops the electricity from taking a shorter path across any given loop where it makes contact with another. However there will initially be points of contact that are snug enough to prevent this oxidization process, causing electrical shorts.
These short circuited partial loops will be hotter, and deprive other areas of electricity which will be cooler. This uneven heating will lead to inefficiency, and hotspots which can scorch the cotton or juice.
Strumming, tapping or squeezing the coils disturbs these unwanted points of contact enough for oxidization to occur there too, allowing an uninterrupted even flow of current down the length of the wire. A properly setup coil should heat from the center of the coil out.
Contact coils should always be pre-heated and tested this way as it also removes any machine oil or impurities from the surface of the wire.
1. Only buy quality batteries of known CDR (continuous discharge rate) and correct chemistry from reputable vendors. The CDR represents the number of amps that a battery can deliver continuously without safety issues. As well as creating a ‘green’ usage band, it is relevant in the case that your mod auto fires or the button on a mechanical device is actuated when it is unattended.
|Link to Mooch's blog describing battery chemistry suitable for vaping|
Li-Ion Battery Chemistries - What are the differences in their safety? | E-Cigarette Forum
2. Be aware of your batteries CDR amp limit and don’t exceed it. Beware, some vendors are known to put exaggerated amp limits on their batteries.
|Link to Mooch's list of batteries with verified CDR|
18650 Safety Grades -- Picking a Safe Battery to Vape With | E-Cigarette Forum
3. NEVER carry unprotected batteries in a bag or pocket. Cases and protectors for 18650s are cheap and easy to obtain.
4. Inspect the wraps of your batteries regularly for damage, repair or replace if they are. The outer shell of a battery is the negative terminal, the wrap is the only thing preventing it from making an electrical connection with your mod or loose change, causing the mod to auto fire or to short circuit leading to thermal runaway and an all-round bad day.
|Link to re-wrapping instructions|
Tutorial: Re-wrapping a battery
5. Whenever possible charge using a good quality external charger, and don't leave charging batteries unattended especially over night.
6. Replace batteries when they reach 300 cycles or one year of use, which ever comes first. The CDR of a battery will decrease with age, so even if they appear to perform OK replacement is a cheap way to be safe.
7. Always test a new coil build before use to ensure target resistance has been met, and most importantly that’s there is not a short.
8. If you are using a hybrid style 510 connector on an unregulated device, ensure the positive pin on the atomizer protrudes at least 1mm and is not sprung loaded or uses rubber bushes. If the positive pole of the battery comes into contact with both the positive and negative connections of the 510 it will result in a dead short and the battery will vent. The positive connector on your battery will become slightly concave with regular use increasing the chances of this occurring, so do not become complacent.
Ohms law can be confusing or even intimidating for those of us who are less than comfortable with maths. The good news is there are only three equations that are pertinent to vaping either mechanical or regulated devices.
It is vital to how many amps your device and setup is drawing from your battery, and to choose a battery or batteries capable of safely delivering this.
All these checks can be modeled using Steam Engine main page, but it's wise to understand the maths that drive it, for instance in the unlikely event that you had no internet access.
On a regulated device
The resistance of the coil is irrelevant. Regulated mods separate the input and output voltage, in other words they separate the battery from the atomizer. The only relevant values are the wattage, and the remaining voltage in the battery.
As the battery voltage falls, the mod will increase the amp draw to maintain the selected wattage. You need to know the amp draw at full charge, and when the battery is discharged as this value will be the highest. Most regulated mods are about 90% efficient, so you will also need to factor this loss into your calculations as it will marginally increase the amount of amperage pulled from the battery.
To find the amp draw use I=P/V (-10%)
50w divided by 4.2v equals 11.9 divided by 0.9 = 13.22 amps
50w divided by 3.2v equals 15.6 divided by 0.9 = 17.33 amps
With multi battery devices, simply calculate the amp draw then divide by the number of batteries.
On a mechanical device
The resistance of the coil controls the amount of amperage drawn from the battery, and therefore the wattage delivered to it. Calculate the maximum amps used, based on a fully charged battery at 4.2 volts. As the charge decreases, so will the amount of power and amperage used.
I = amps V = volts R = resistance P = watts
To find the amp draw use I=V/R
Eg. divide 4.2v by 0.5Ω = 8.4 amps
To find the wattage use P=V²/R
Eg. 4.2v multiplied by 4.2v divided by 0.5Ω = 35 watts
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