Battery Safety and Ohm’s Law

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tofed

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Jul 16, 2015
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So you recently purchased your first mechanical mod and then realized you had no idea that it took batteries or had no idea which batteries were going to be safe with it? First of all, congratulations on your first mech mod but, read this first: A Basic Guide for Mechanical Mods and Safety.

Already read it? Great, you’re definitely on the right track now and we’ll teach you as much as we can about batteries, battery safety, ohm’s law, and how to determine how safe your coil or atomizer/clearomizer/cartomizer is for the battery you are using.

With regards to vaping, the battery is the most important item, far more important than your coil, or multiple coils if you have them. Batteries are even more important than the debate over the superiority of wick materials (cotton, organic cotton, silica, mermaid hair – whatever). So if you are looking to get into mechanical mods, or thinking about pushing the limits of your current set-up, or are completely unaware of what your battery can even handle – then this article is definitely for you.

Battery Safety Basics
Do not overcharge or over-discharge.

To combat this, do not leave your batteries in any charger without supervision. Make sure that you are able to see or check on the charger every 15-30 minutes. This way when the charger indicates that the batteries have been fully charged, you can remove them from the charger. Leaving batteries in a charger all night long or longer can cause them to be overcharged, which can result in battery failure. Charging your battery over 4.25 volts can shorten its life-cycle and going over 4.5 volts can cause it to burst. Cease using your charger if this ever happens.

Our recommendation on a good charger: Nitecore D2 Charger (2 Bay) or Nitecore D4 Charger (4 Bay)

Recharge batteries with a resting voltage below 3.6V as soon as possible.

Leaving LiIon batteries in a discharged state will incur irreversible damage – creating a loss in capacity and a loss in cycles.

Determining the exact voltage can be tricky, unless you have a multimeter. If you are delving into the world of mechanical mods and RBAs (ReBuildable Atomizers), or making your own coils, a multimeter is a must have device because you can use it to test your coils and your batteries. Sure, you can always use a battery tester, but the majority of battery testers are not equipped for the types of batteries that are used in mods, or even test batteries under load condition.

Do not short circuit your batteries.

Short circuiting can cause a huge surge of current that will potentially burn out your battery, damage your mod, or even your face!

Short circuits happen when the voltage from a battery is discharged through a low resistance wire at a discharge rate that exceeds the battery’s upper amp limit. Short circuiting a battery is very close to what a mechanical mod with a sub-ohm coil is doing, except you are trying to keep the resistance under the upper amp limit – there’s a fine line that you have to be careful of when sub-ohming.

Do not let your batteries touch each other or other metallic items.

Keeping your batteries loose, such as in your pockets, is a good way to have your batteries fail and seriously harm you. There are battery holders and covers to keep your batteries safe. Get some – now.

Do not dispose any battery in a fire.

This is just common sense people. There are dangerous chemicals in batteries. If you try to burn your batteries they’ll release dangerous fumes and will probably explode. Do yourself, and the rest of the world, a favor by taking your old batteries to a battery recycling center.

What’s In a Name?
Let’s take a look at the specifications of AW IMR batteries for a moment:

IMR16340 Specifications:

Nominal Voltage : 3.7V
Capacity : 550mAH
Lowest Discharge Voltage : 2.50V
Standard Charge : CC/CV ( max. charging rate 1.5A )
Cycle Life : > 500 cycles
Max. continuous discharge rate : 4A
Operating Discharge Temperature : -10 – 60 Degree Celsius

IMR14500 Specifications:

Nominal Voltage : 3.7V
Capacity : 600mAH
Lowest Discharge Voltage : 2.50V
Standard Charge : CC/CV ( max. charging rate 1.5A )
Cycle Life : > 500 cycles
Max. continuous discharge rate : 4A
Operating Discharge Temperature : -10 – 60 Degree Celsius

IMR18350 Specifications:

Nominal Voltage : 3.7V
Capacity : 700mAH
Lowest Discharge Voltage : 2.50V
Standard Charge : CC/CV ( max. charging rate 2A )
Cycle Life : > 500 cycles
Max. continuous discharge rate : 6A
Operating Discharge Temperature : -10 – 60 Degree Celsius

IMR18490 Specifications:
Nominal Voltage : 3.7V
Capacity : 1100mAH
Lowest Discharge Voltage : 2.50V
Standard Charge : CC/CV ( max. charging rate 3A )
Cycle Life : > 500 cycles
Max. continuous discharge rate : 15C
Operating Discharge Temperature : -10 – 60 Degree Celsius


IMR18650-1600 Specifications:

Nominal Voltage : 3.7V
Capacity : 1600mAH
Lowest Discharge Voltage : 2.50V
Standard Charge : CC/CV ( max. charging rate 4.5A )
Cycle Life : > 500 cycles
Max. continuous discharge rate : 15C
Operating Discharge Temperature : -10 – 60 Degree Celsius


IMR18650 -2000 Specifications:

Nominal Voltage : 3.7V
Capacity : 2000mAH
Lowest Discharge Voltage : 2.50V
Standard Charge : CC/CV ( max. charging rate 2A )
Cycle Life : > 500 cycles
Max. continuous discharge rate : 10A
Operating Discharge Temperature : -10 – 60 Degree Celsius


Determining Your Maximum Discharge Rate

The most important specification to pay attention to is the “Max. continuous discharge rate” for each battery. Each battery has a number and a letter, either measured as A or C (30 Amps or 15C). Look at the IMR18650-1600 for example. If your battery has a maximum continuous discharge rate of 15C, this means the battery is rated for 15 times the capacity of the battery measured in amps. So a battery that sits at 1600mAh, which equals 1.6Ah will have a max continuous discharge rate of 15 X 1.6 = 24A. There is a chart below which has the max continuous discharge rate in Amps of some common batteries.

You should always determine what your max continuous discharge rate is in Amps (which many of the new and popular batteries have already) to keep your math consistent and mind at ease.

How To Use This Information Effectively

Knowing the max discharge rate in amps is only half the battle.

How do you know if your coil or atomizer/clearomizer/cartomizer won’t short circuit your battery? Simple, use this equation: battery volts / the ohms resistance of your coil = your actual discharge rate.

If your actual discharge rate is less than the maximum discharge rate you calculated earlier, you’re in the clear. If it’s not, you need to suck it up and rebuild a higher resistance coil.

Let’s take a closer look using the 18650 1600mAh battery again (for the sake of continuity). If you took a freshly charged 18650 1600mAh battery and tossed it in your mechanical mod with a very limited voltage drop, and put a .2 Ohm coil on top, you’d be running at 20 amps. To figure out this math you take the voltage running to your coil from your battery, which lets say after a full charge, the multimeter shows that the battery is sitting at 4 volts. Now, divide by the ohms of your coil. The number you get is your total amps. In this case our math is 4/0.2 = 20. So we now know that running this exact setup will push our battery to 20 amps, just 4 amps under its max discharge rate. If you were using a different battery capable of less power under the same circumstances, you would be asking for complete battery failure and the chance of possibly hurting yourself.

Safety PSA: Resistance in coils can have a variance of 0.2 Ohms in either direction, or +/- .2 Ohms. This means that if you build a 0.2 Ohm coil, you have to account for that +/- 0.2 Ohm variance. The coil in the above example at .2 Ohms is an incredibly unsafe coil, and I would not use nor suggest that anyone use such a coil. Because of this, I would not recommend anything lower than a 0.4 Ohm coil for 18650 1600mAh battery.

Equation Recap

Let’s take a look at everything you’ll have to calculate in order to determine your coils safety in order.

1. Calculate your battery’s capacity in amps: capacity in mAh / 1000 = capacity in amps

2. Calculate the maximum discharge rate if measured in C: maximum discharge rate = (battery capacity in amps) x (continuous discharge rate)

2. Measure your battery’s volts with a multimeter.

3. Measure the Ohms of your coil and subtract .2 to account for the +/- .2 variance.

3. Calculate the discharge rate you’ll have with the coil you’ve built: battery volts / Ohms = your actual discharge rate

4. Check to make sure that the actual discharge rate is LOWER than your battery’s maximum discharge rate.


But What About Other Batteries?


Below, I have listed out the commonly used batteries by brand with their max continuous discharge rate in amps, to make your math a little easier. However, remember that you’ll need to test the battery’s volts before AND during use in order to make sure that the coil you used is safe.

The best batteries for sub-ohm vaping are generally Sony VTC 4 or Sony VTC 5, although they are often out of stock. In that event I usually use an 18650 STARING 45A.


Battery name and mAh Continuous Discharge Amps

STARING IMR

STARING 14500 700 mah 8 amp

STARING 16340 600 mah 6 amp

STARING 18350 900 mah 10 amp

STARING 18490 1400 mah 15 amp

STARING 18650 2500 mah 45 amp

STARING 26650 3500 mah 65 amp

Efest IMR

Efest 10440 350 mah 1.4 amp

Efest 14500 700 mah 5.6 amp

Efest 16340 700 mah 5.6 amp

Efest 18350 800 mah 6.4 amp

Efest 18490 1100 mah 11 amp

Efest 18650 1600 mah 30 amp

Efest 18650 2000 mah 10 amp

Efest 18650 2250 mah 10 amp

EH IMR

EH 14500 600 mah 4.8 amp

EH 15270 400 mah 3.2 amp

EH 18350 800 mah 6.4 amp

EH 18500 1100 mah 8.8 amp

EH 18650 2000 mah 16 amp

EH 18650 NP 1600 mah 30 amp

MNKE IMR

MNKE 18650 20 amp

MNKE 26650 15 amp

Samsung ICR INR

Samsung ICR18650-22P 2200 mah 10 amp

Samsung ICR18650- 30A 3000 mah 6 amp

Samsung INR18650-20R 2000 mah 22 amp

Samsung Samsung INR18650-15mm 1500 mah 23 amp

Sony

Sony US18650v3 2150 mah 10 amp

Sony US18650VTC3 1600 mah 30 amp

Sony 18650VTC4 2100mah 30 amp

Trustfire IMR

Trustfire 14500 700 mah 2 amp

Trustfire 16340 700 mah 2 amp

Trustfire 18350 800 mah 4 amp

Trustfire 18500 1300 maah 6.5 amp

Trustfire 18650 1500 mah 7.5 amp


Panasonic


NCR18650B 18650 NP 3400 mah 6.8 amp

NCR18650PF 18650 2900 mah 10 amp

NCR18650PD 18650 2900 mah 10 amp

CGR18650CH 18650 2250 mah 10 amp

Orbtronic

Orbtronic 18650 2900 mAh 10 amp

Orbtronic 18650 SX22 2000 mAh 22 amp

 
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Mooch

Electron Wrangler
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  • May 13, 2015
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    Good post! Very comprehensive. You should make a blog post for this though. Like this: (18) Baditude's Blogs | E-Cigarette Forum

    i agree, great recommendation. A blog will allow you to update your data as you get new imformation about cetain cells, as old cells are no longer available, and to include new cells. @tofed, after a couple of days you won't be able to edit your post.
     
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