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.
Try to think of the 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 (and possibly greater surface area), 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, higher 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.
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 chosen 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 one should choose a coil with the greatest surface area and the least possible mass.
You could put 12 watts through a 0.25 ohm dual 24G coil, but it would barely vape and the ramp up would be measured in minutes.
Alternately you could put 70 watts through a single 6 wrap 30G 1.8 ohm coil, it would produce a hideously harsh vape and probably melt the coil.
This is just my opinion, it is not based on any kind of research. It is an educated guess based on circumstantial evidence and what limited knowledge I have.
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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