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Author Topic: Safe practice for sub-Ohm coils  (Read 14897 times)

Offline danwldr

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Safe practice for sub-Ohm coils
« on: March 16, 2014, 08:08:08 PM »
So after reading Ean's thread - https://www.thevapersden.com/index.php?topic=7406.msg182626#msg182626

I thought it may be an idea to do a quick guide on how to Sub-Ohm carefully

We are always seeing new guy's coming on here and seeing all the huge clouds we are blowing out, it looks great, but it is not safe to do it just casually.

If you are new to rebuilding, or experienced with the higher resistance stuff, then please take a few minutes to read this quick guide.

Some of it is from experience, and some more important stuff has been taken from the experience of others.



Batteries

1.Use this guide to select batteries that are suitable for the resistances you are building - https://docs.google.com/spreadsheet/lv?key=0AhCCsGn6F0QLdDJxNzV2c0dSc01mUkl6RXNnM2o2R1E&usp=drive_web&pli=1

2.Don’t use a cheap multimeter to measure sub-ohm resistances – the measurement might be much higher than the actual value of your resistance. Low-resistance measurements require dedicated equipment! Do not experiment with super-low-resistance builds unless you can accurately measure your resistances. Once you have the necessary experience, you will be able to rebuild the same setup in a repeatable way even without measurement tools.

3.Check the condition of your batteries often. Stressed batteries will gradually discharge very fast and show a higher voltage drop on their internal resistance. Don’t use batteries for sub-ohm vaping unless you are monitoring their condition.

4.There is also a good, simple calculator here to work out Watts, Volts and Amps - http://vapecalc.com/

The Mod

1.Just like with batteries, you need to be able to monitor the condition of your mod by measuring voltage drop using a battery that you know. When you notice an abnormally high voltage drop, immediately inspect all connections, starting with the atomizer-to-mod contacts and with the battery-to-mod contacts. It may take time to find the bottleneck, but it will save you from other headaches. If necessary disassemble all fixed contacts of the mod and clean all threads and connections individually.

2.Avoid spring-loaded contacts for sub-ohm vaping, or use harder and preferably plated springs. With use, springs tend to lose their flex, which weakens contact at both ends, resulting in voltage drop and overheating. If you have to use a spring, stretch it often to ensure firm contact at both ends.

3.The collapsible springs used in some mods are a sacrifice of performance in favour of safety. In most cases, you can remove them, though. If you have such a mod and have damaged more than a few of those springs, you shouldn’t be using a mech mod in the first place.

4.Keep all parts tight and clean and, as a rule of thumb, prefer simpler mods with fewer connections. If that means sacrificing things like air-flow control, extensions or other gimmicks, so be it. Keep things simple, especially at the lower end of the sub-ohm range.

5.Keep a list of all connections from the positive battery terminal to the atomizer resistance, and from the negative battery terminal to the atomizer resistance. You need to know which of these connections are the most sensitive, handle them properly and inspect them often.

Mod Switches

1.Handle the switch properly and keep it in top shape to ensure that it is able to conduct the high current without overheating.

2.Proper maintenance and prevention is important. Wipe the contacts of the switch with alcohol every week, blow all parts with compressed air and avoid touching them with bare hands.

3.At lower resistances, remember to operate the switch firmly, especially if it’s a double-break design (all top-firing mods).

4.Very light, accidental presses of the switch can be catastrophic at high currents. Always lock your mod when carrying it and avoid throwing it in dusty pockets.

5.When sub-ohming, you will have to re-plate the contacts of your mods at least every few months. The more serious you are with vaping, the more you must be informed and prepared to do what’s necessary to enjoy it when pushing the limits.

6.With regular maintenance and proper use, the contacts of your mod are very unlikely to suffer from overheating incidents, but if any black spots appear on them, they should be cleaned with “silver wipes” or a non-corrosive cream suitable for silver/brass/ss-ware as soon as possible.

7.Some mods use thermoplastic materials designed to handle temperatures up to 300*C. This means that they are – by design – able to operate in overheated switch conditions that can possibly be an issue for battery safety. Although that means that the mod won’t break easily, don’t take the matter lightly – just because the switch can be operated in unsafe conditions doesn’t mean that you should neglect its maintenance. Industrial switches at these ranges are built to be operated well below the 80*C threshold — high temperature always translates into rapid contact damage, high voltage drop and compromised safety. Monitoring the voltage drop of your mod is the best way to ensure that the switch is in mint condition


5th vapersary 23/12/2016


Offline CraigHB

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Re: Safe practice for sub-Ohm coils
« Reply #1 on: March 16, 2014, 08:56:13 PM »
Very nice, you hit well on all points.  Some I wouldn't have thought of myself.

Just to reiterate, voltage drop is probably the best overall thing to monitor in terms of the health of your mod and battery.  Just about any breakdown will show up as excessive voltage drop whether that's a battery that's getting worn or dirty switch contacts.  As you said, parts of the circuit that cause big drops are heating points which can result in damage to the mod that is not repairable or in the worst case, battery failure.

Offline danwldr

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Re: Safe practice for sub-Ohm coils
« Reply #2 on: March 16, 2014, 08:58:36 PM »
Thanks Craig

TBH some of them wern't mine either  #T#

But I spent a couple of days researching this one as it was quite important to get it right.

The internet has some very interesting idea's.
5th vapersary 23/12/2016


Offline CraigHB

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Re: Safe practice for sub-Ohm coils
« Reply #3 on: March 16, 2014, 09:14:21 PM »
Whatever the case, that's some good info to have all in one place.  I'm sure there are some not so helpful ideas out there and you did a good job of filtering those.

Offline vapingfool

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Re: Safe practice for sub-Ohm coils
« Reply #4 on: March 19, 2014, 03:31:14 AM »
Very good, Dan.

Resistances occurring anywhere except in the coil are always a concern. The lower the resistance of the coil, the greater the concern about all the other resistances.

Here is a basic mathematical treatment:

Those that get dizzy when exposed to math may wish to skip the rest of this.

Assume we have a battery that is in good condition and fully charged to 4.2 volts. We will ignore the internal battery resistance in this example, except to include it in the miscellaneous circuit resistances. The misc resistances will include all except the resistance of the coil. To simplify the example, we will assume that the coil does not change resistance when heated. We will also assume misc circuit resistances of 0.1 ohm, which can easily occur with dirty/poor contacts.

There are two conditions to consider - coils with normal vaping resistances and those used for sub-ohm vaping.

For normal vaping - assume the coil has a resistance of 1.5 ohms and the misc circuit resistances are 0.1 ohm. So the total circuit resistance is 1.6 ohms. With the applied 4.2 volts, the current flowing is 2.625 amps (I = V/R). The total power dissipated is 11.025 watts (P=V*I). The power dissipated in the coil is 10.336 watts (I2R) and in the rest of the circuit 0.689 watts. So a little over 6% of the power is dissipated in the misc circuit resistances. That is not good, but would probably be tolerable - at least intermittently.

For sub-ohm vaping, assume everything is identical except the coil resistance is 0.5 ohms. The total circuit resistance is 0.6 ohms and the current flowing is 7 amps. The total power dissipated is 29.4 watts. The power dissipated in the coil is 24.5 watts and in the rest of the circuit 4.9 watts. 16.67% of the total power is being dissipated in undesirable places. If that is at a contact somewhere, it can quickly overheat and burn. If it is in the battery, then the battery can overheat.

As the coil resistance is decreased even further, the percentage of the total power that is dissipated outside the coil increases as well. In our example, if the coil resistance was 0.1 ohm (equal to the rest of the circuit resistance), then the current would be 21 amps, the total power dissipated would be 88.2 watts and 50% of the power (44.1 watts) would be dissipated somewhere besides in the coil.

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Offline ckim111

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Re: Safe practice for sub-Ohm coils
« Reply #5 on: July 10, 2014, 02:40:02 PM »
So what is the range of resistance for the coils to be considered sub ohm?  Is it anything lower than 1 ohm?  Or is it 1.2?  I just wanted to be sure what the official response was.  Thanks!

Offline danwldr

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Re: Safe practice for sub-Ohm coils
« Reply #6 on: July 10, 2014, 02:46:17 PM »
So what is the range of resistance for the coils to be considered sub ohm?  Is it anything lower than 1 ohm?  Or is it 1.2?  I just wanted to be sure what the official response was.  Thanks!

Anything below 1Ohm....so 0.9Ohm downwards

Welcome to the Den :)+1
5th vapersary 23/12/2016


Offline ckim111

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Re: Safe practice for sub-Ohm coils
« Reply #7 on: July 10, 2014, 02:51:02 PM »
Thank you SIR!

Offline ODG420

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Re: Safe practice for sub-Ohm coils
« Reply #8 on: November 13, 2014, 03:46:37 PM »
I looked at the battery list for your link and I use the LG HE2 2500mAH and noticed that the Efest purple with all the same amps ect. has a .3 difference in safe ohms. Can you explain why this is?

Offline Jerry

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Re: Safe practice for sub-Ohm coils
« Reply #9 on: March 16, 2015, 10:46:40 PM »
Thanks a lot for this guide. This is very helpful especially to the new users.

 


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