Posted by Chris Bussell on 14th Jan 2015
We have a ton of our customers that are veteran rebuilders. We also have many people who are just starting out or considering the move to open systems. So, this week's Fog Blog is dedicated to resistance and how to find it. Many will already know this information, but if not- hopefully it will help you build or become a better coil builder.
Via our Friends at WVS (Content Edited):
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 an ohm meter. 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 rebuild, 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 one of these meters. They are a vital tool for your safety.
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. If you'd like detailed information on the precise resistance of Kanthal, TEMCO - the manufacturer of Kanthal A1 - provides an excellent chart.
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.
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.
If you enjoy talking vape, testing, and writing/recording product reviews give us a shout if you are interested in becoming a contributor.
(About the author: Chris Bussell is a vape enthusiast, owner/partner in several vape shops, eLiquid Manufacturer, and daily blower of clouds. He is an Active Army National Guard Warrant Officer, holds a Master’s of Strategic Intelligence, and gets to plan satellite networks for a living.)
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