Finding the Resistance
We just talked about the importance of resistance when factoring amperage draw. This week we'll discuss resistance itself and how to find it. If you already know all this, that's excellent. If not, I hope you'll find it useful.
Resistance is the way we measure how difficult it is for current to pass through a given material. The unit of measurement is the ohm (Ω). Different factors that may come into play to affect the resistance of your coil include the wire material, amount of wire,gauge of the wire, temperature, and number of coils.
Tools of the Trade
To measure resistance, we recommend using a resistance checker or ohm meter (same thing). A volt meter with the proper settings can also be used but we recommend the former for their ease of use. All that is necessary is that you build your atomizer, and then screw in the 510 connector to the meter and flip a switch to display the resistance.
If you do not have ohm meters on hand and you sell rebuildables, they are a must-have item. I cannot stress this enough. If you do not have a method of reliably measuring resistance to the tenths place (0.19 for example), please get some of these meters. They are a vital tool for your safety and that of your customers.
The most widely-used type of wire used in rebuildables today is Kanthal A1. We can accurately determine it's resistance by length because composition of the metal alloys that go into making it. It has been tested, and is reliable from a resistance perspective.
Different wire types, due to the composition of materials that go into the wire, will measure different resistances per length than Kanthal. For example, there are a number of "competition" wires (Royal, Gplat, etc.) as well as standard wire types (Nichrome, Ni200) that are less common, but abide by the same principle.
Side note: always be aware that different types of wire, especially proprietary brands that do not disclose their compositions, may contain metals that when heated beyond a certain point may be hazardous to inhale. Do your research and make sure you feel comfortable vaping with a type of wire before using it.
The length of wire used will also factor into the resistance of your atomizers. The more wire you use in a singe coil, the higher the resistance will be because the current has to travel further from positive to ground. This will be the case no matter what type of wire is used for the build. Wrapping more and more loops in the coil will increase the amount of wire used, and raise the resistance with each loop.
The coils diameter will also come into play when determining the length of wire used. A 3mm diameter coil (usually the largest in precision screwdriver sets) will produce a higher resistance, with all other factors being the same, than a coil with a diameter of 2mm because more wire is required to wrap around the larger screwdriver.
Inside the United States, we have a system of measuring wire called American Wire Gauge (AWG). The thicker the wire is, the lower its gauge. Inversely, the thinner the wire, the higher the gauge. Thicker wire has lower resistance per length because there is more room for electricity to flow within the wire, which means that current can pass through it more easily. Using extremely low gauges may yield resistances that will stress your batteries.
Note: In many countries outside the United States, wire "gauge" is measured by the diameter of the wire. For example, 28AWG Kanthal may be described as 0.32mm wire. A good conversion chart can be found here.
Number of Coils
Depending on the configuration, additional coils are likely to reduce your resistance (serial coils will increase resistance, but these are uncommon setups). If you wrap a single coil that measures 1.8Ω, and then install an identical second coil, your resistance will drop to 0.9Ω. Doubling the number of coils again will reduce the resistance again to 0.45Ω. Seeing how quickly resistance plummets with additional coils, to install 4 or more coils, you'll want to make sure each coil is fairly high in resistance. This can be achieved, as we already covered, with more wraps, larger diameters, or higher wire gauges.
Your customers are probably going to hurt themselves. Scary, isn't it? All this talk about safety when they're using their mods and they may still very well get burned. I mean that literally. Like first-degree, going to the hospital burned.
But we've been talking about safety all this time!
We have been talking about safety when your customer is using his batteries. But what about when he's not using it? How about when he's just riding around in his car? Or standing at the bus stop? That's actually when most vaping-related injuries happen.
Yep. Your customer is more likely to be hurt by his vaping equipment when he isn't even holding his mod than when he's taking that massive super sub ohm pull for the cloud competition.
Because he's not paying attention. He's complacent, and not even thinking about battery safety because his vape isn't in front of him... it's in a pocket, or a purse, or a backpack.
"Oh, my mod has a recessed button!"
"I have a magic magnetic button that prevents auto-firing!"
"Oh, I only need to lock mine halfway for it not to fire!"
Have you heard the excuses that vapers make for not carrying their mods in a locked state? These are the same customers that are going to hurt themselves, given time.
If a mechanical mod has a locking ring, and the mod isn't being used, that locking ring should be engaged. Fully engaged. It doesn't matter if the button is recessed. It doesn't matter if it only needs to be halfway locked to avoid firing.
But not my mod!
"Oh, my mod has a recessed button!" Throw a recessed button mod into your pocket. Your pocket is not a flat surface, and it doesn't always stay the same shape. Given time, an unlocked mod with a recessed button WILL fire in your pocket.
"My mod has a magic magnetic button that prevents auto-fires!" This is nonsense If you can fire it with your finger, you can fire it with your leg.
"Oh, I only need to lock mine halfway for it not to fire!" Only need to lock it halfway? The manufacturer didn't give it the ability to lock further for kicks and giggles to frustrate you. Locking rings that aren't fully engaged can become unlocked again fairly easily, and again, will be happy to fire in your pocket.
So my battery will drain a little. No big deal.
If you aren't thinking about your battery firing, you likely won't hear it, depending on the atomizer. If the battery is firing for an extended length of time without your being aware of it, expect to get burned when you reach for it or it comes in contact with your leg.
The alternative is that you stress the battery out and it starts to vent. If a battery starts venting in your pocket and you aren't aware of it, you're now carrying tiny little grenade in your pocket, and I mean that literally. The pressure will increase inside the mod, until the weakest point is found, and now you've got a potentially explosive situation, complete with shrapnel (your former mod) for effect.
"Oh, my mod has vent holes. Won't happen to me."
Don't be fooled into a false sense of security. Vent holes almost never account for swelling of the battery during venting. If the battery swells in the tight tube, and the gasses can't escape, then you're in the same situation I just described above.
Last year there was an attendee at Vape Blast 2014 who had exactly this happen in a room with hundreds of people who were put at risk of serious injury or worse.
Here's what was left of the mod after it exploded in the middle of the event floor. He didn't think it would happen to him, either. Thankfully no one was hurt, but this story could have ended much differently.
Do you carry spare batteries with you? How do you carry them?
If the answer is "in my pocket," that answer needs to change. So many injuries have been caused by doing exactly this. Your batteries do not belong unprotected in your pocket. The most common response is likely to be "I keep them in their own pocket with nothing else." That doesn't make it better.
It only takes two seconds to mess up your day by tossing your keys, or the spare change from your last purchase, or the aluminum foil from your chewing gum into your special battery pocket. All these things are made of metal, and under the right circumstances (like shifting in your seat of leaning against something) can cause the battery to short if there's a continuous path of metal touching the positive and negative ends of the battery.
This can cause burns. You may experience anything from minor burns with a blister to severe, you're-leaving-to-go-to-the-hospital burns. Batteries that can get hot enough to cause these burns, damage your furniture, and melt carpeting on contact, and do not belong in your pocket unprotected.
When to Replace Batteries
Using a battery beyond its intended lifespan, or using a battery that has been damaged can cause the battery to fail. Depending on the type of battery being used and its application, the results of a catastrophic failure can be somewhat unpredictable.
We recommend the replacement of any battery meeting the following conditions. Batteries have a lifespan, and are meant to be replaced once their life has come to an end. It's always better to be safe than sorry.
There are several conditions under which a battery may be considered to be damaged. Once a battery is damaged, it should be replaced. Using damaged batteries may cause them to discharge unevenly, become hot, or to experience catastrophic failure.
Torn wrappers: If your battery's wrapper is torn, especially towards the positive contact, you'll want to make sure that you replace it ASAP. Torn wrappers can result in the battery shorting inside the device. Though batteries can be re-wrapped, it's not recommended unless being performed by someone trained to do so. Re-wrapping without knowing exactly what you're doing can injure you, so please leave it to the pros, or don't do it at all.
Moisture: When your battery has been the victim of unfortunate submersion in water, or is showing spots of mildew or mold on the wrapper, it's time for a replacement. If such spots are showing on or through the wrapper, there is likely moisture inside the battery, which may cause it to fail.
Dents: Sometimes the damage is exceptionally apparent. If a battery has been dropped on a hard surface and is showing dents, it should be replaced. The contents of the battery are not designed to move, and when the battery becomes dented, contents have to shift to the new shape of the battery. This may also occur if you have a habit of excessively tightening them into your mods and denting the contacts.
Aging batteries should also be replaced. If you've had the same battery in regular rotation for several months, it's time to replace them. I'm being deliberately vague on exact time frames because there are several factors that play into what causes batteries to "expire" more or less quickly.
Usage: If you constantly run the same batteries in a mechanical mod, with low resistance builds close to their limits, they will begin to die more quickly, because they've had a stressful life.
Rotation: The more batteries you keep in rotation, the less often you use any single battery, so those batteries that are used less often will survive longer.
Paired Batteries: These may not be old batteries, but if you pair your batteries in devices that use more than one at a time (which you should), and one becomes damaged or needs replacement for any other reason, you'll want to replace both batteries in the pair, no matter how old they are. If you can find another use for the battery that's left, like using it in a mechanical mod or a flashlight or other regulated device, go for it. It may not be dangerous, but do not switch out single batteries from a pair.
I've stopped using a battery. Now what?
Now that you know when batteries need to be replaced, what should you do with the old ones? I'd like to mention here that this applies to all batteries sold in a vape shop, from eGo batteries to devices with internal batteries that cannot be removed, like an MVP.
Don't throw them out: If a battery must be removed from service for any of the reasons above, please do not just chuck them into the trash can. Lithium batteries can wreak havoc on the environment, and can injure people that are near them. Imagine a battery shorting in a trash bag as you're taking the garbage to the dumpster, and being unaware of it until catastrophic failure.
Recycle: Any good shop will recycle batteries, and mods, so that they do not end up in landfills or cause hazards in other ways. You can also check out www.call2recycle.org to find a nearby organization happy to accept your rechargeable batteries FOR FREE
Current Discharge Rate
Last one on the subject, I promise. The last thing we have left to talk about is maximum current discharge ratings for your batteries. There are usually two different ratings listed either on the wrapper, the manufacturer website, or spec sheets available online.
Maximum Continuous Current Discharge
The continuous discharge rating is the most popular rating given. When someone says, “this is a __ amp battery” generally they are referring to the maximum continuous current discharge rating of the battery. What does that mean? We’ll use an MNKE 26650 battery for this example. It’s a “20 amp” battery. This means that the manufacturer has set a 20 amp discharge as the maximum current that can safely be discharged over a sustained period of time.
Another way to consider this is to compare it to driving. The continuous discharge rating is like looking at the tachometer (which measures RPMs on your dashboard). My car is happy to run at about 3,000 RPMs all day. If I forget to shift and I’m running it at 5-6,000 RPMs for 20 miles down the highway, I’m likely to be doing damage to my engine. 3,000 RPMs is similar to the max continuous discharge rate, because it’s the max power I can apply while driving at a constant speed for a sustained period of time before it has a negative impact on the performance of my vehicle.
Using your battery above its max continuous discharge for sustained periods of time, usually more than a few seconds, will take a toll on the battery’s performance, possibly damaging it or reducing its capacity over time.
Maximum Pulse Current Discharge
The other rating important to the battery is the pulse discharge rating. This is less commonly known or referenced by the average vaper with a mechanical or high-wattage device, and there’s much debate in the community as to whether it’s applicable to vapers. To keep in line with the MNKE 26650 above, this battery has a pulse rating of 60 amps. Pulse ratings are much higher (usually double to triple) than the max continuous discharge rate of a given battery.
Going back to our driving analogy, if the max continuous discharge is the maximum power you want to demand from a car while driving normally, the pulse rating is the amount of power available to you from 0-60mph. You wouldn’t hit the gas like that when driving down the highway for more than a few seconds at a time. Similarly, it’s the same situation with pulse ratings on batteries. This rating is meant to convey the very maximum current that is safe to discharge from your battery for a very short period of time.
The reason I use this analogy is because one of the most popular applications for the types of batteries that we use is remote control cars and planes. The pulse rating is used to get the car going to it’s top speed, and the continuous rating is for maintaining a sustainable speed.
Which one should I go by?
I don’t recommend relying on the pulse rating for one simple reason: accidents happen. Eventually, you are likely to forget to engage your locking ring on a mech, or a defect may cause a high wattage device to fire. These things do happen. If the build on your atomizer exceeds the continuous maximum discharge rating, and the device is firing for some time unnoticed, then there will likely be negative effects, ranging from over-discharging the battery to a point where it no longer works, to much more severe results like those we discussed the previous section.
If you rely on the pulse rating, you are doing so at your own risk, and we encourage you to use extreme caution. If you’d like to tuck your mod away in a bag with a super low resistance build that uses the pulse rating, it would be a good idea to remove the atomizer before stowing it, or removing the battery from the mod. This will prevent many of the accidents that can occur.
Doing the Math. Math? Really?
Last week we touched a little on the dangers of overdrawing current from your batteries and the events that might occur if you do. This week we will get into how to avoid doing so, with the awesome power of math. Not all of us excelled in it in school, but knowing the math is one of the most important things you can know about rebuildables. Besides, many of us have learned more about science through vaping than we ever did in school.
Down to Business
The formula, which will be explained below, to measure the amperage draw of your build is V / R = I where:
V = Voltage, measure in volts
R = Resistance of your atomizer, in ohms (Ω)
I = Current, measured in amps
Voltage is the voltage coming from the battery. On a fresh charge, battery voltage is 4.2 volts with a small tolerance one way or the other. There is a small amount of voltage drop that factors into the equation (especially in mechanical devices), but without testing that particular resistance and device combination, it’s nearly impossible to know exactly how much drop there is, so for safety we always assume you’re getting the full battery voltage to the atomizer.
Divide the battery voltage by the resistance of the atomizer (which you should have measured on an ohm meter beforehand). This will give you the amperage, or current draw. As an example, suppose you've built a coil measuring 0.4Ω that you’d like to use on your device. Plugging values into the equation you should have 4.2V / 0.4Ω = 10.5 amps. This is well within the limits of most of the IMR batteries that we carry.
Lower and Lower
Remember, going to lower resistances will cause the amperage draw to increase exponentially. Using the same formula, we find that a 0.2Ω coil will draw 21 amps, where battery ratings start becoming an issue for safety, and a 0.1Ω coil will draw 42 amps, which only a very few batteries available can handle safely.
Need a Cheat Sheet?
Everyone does. Even I do occasionally, either because I know the numbers will be close to my limitations if I'm trying mental math, or because I have a case of the lazies and want to make life a little easier.
There are calculators abound on the internet, but the one I go to myself and recommend for others is a nifty little site called Steam Engine. There's a link to it here. I like this one because it calculates almost anything you'd want to know about in vaping, from Ohm's Law to DIY e-liquid and some I think are exclusive to Steam Engine like expectations of battery runtime and sweet spots in resistance for specific devices based on their specs.
One more small perk is that if you have an Android device in the shop, "there's an app for that" in the Play Store.
Battery Safety - Types of Batteries
Knowing the different types of batteries is critical. Let's talk about about them now.
The vaping industry is changing faster and faster every day. To help you keep up on some of the latest tips, tricks, and information, we want to provide for our subscribers a weekly newsletter with information you may find useful.
For the first few issues of this newsletter, we're going to be discussing battery safety. Because of the vastness of this topic, we'll focus each week on a particular aspect of battery use. Join me this week as we discuss the different types of batteries used in vaping.
These are the high-drain lithium ion batteries that are the most recommended for vaping by manufacturers, and are widely considered to be the safest batteries available for the purposes of vapers. They will typically have a LiMn (lithium manganese) composition which makes them a safer chemistry battery than other varieties. These batteries are known for their ability to support withstand high current draw (measured in amps, or amperage). They come in a variety of colors and sizes, and are produced by several different manufacturers, including Sony, Panasonic, Efest, PVTSO, LG, and Samsung. When people refer to 20+ amp batteries, they are talking about IMR batteries.
These lithium ion batteries are less common, but we see them frequently sold in kits online or may come packaged with a device purchased through a third party or overseas vendor. These batteries are typically blue in color, and should never be used in mechanicals or high-wattage devices because they lack the current-bearing properties of IMR batteries. Also, in the event of catastrophic failure, these batteries can be quite dangerous to handle. WVS does not sell ICR batteries because anything an ICR can do, and IMR battery can do more safely.
Protected batteries may still be stocked by some shops, and they are designated as protected batteries because of a small protection circuit mounted on top of the battery under the wrapper. Though they may sound safer because of their “protected” name, this is a misnomer, and they are not recommended for use in high-powered or mechanical devices. There are two reasons for this. First, the added protection circuit nearly always makes the battery either too long or too wide to fit into most devices comfortably, if at all. Secondly, if the protection circuit is not functioning properly, the battery has similar failure risks to ICR batteries.