Li-Ion(or any 18650 battery) discharge current vs safety concerns?

Hello.

First I will explain what situation this is regarding and it might not be of any interest for some, so if you don't want to read all that scroll down until a Bold statement comes, after that it is the electronic stuff.

I don't know how many of you are smokers/nicotine addicts, not that you have to be that to know what "vaping" is.

But for anyone who don't know about vaping, it's the use of technologies to evaporate a mixture of nicotine diluted in PG and/or VG.

PG = Propylene Glycol also called propane-1,2-diol or α-propylene glycol(an organic compound with chemical formula C3H8O2, amongst other uses it is used in food processing as the E-number E1520, farmers are known to dilute the cattles water supply with Propylene Glycol during winters to keep it from freezing)

VG = Vegetable Glycerin or propane-1,2,3-triol(is used in a lot of food and cosmetic products as well as soaps and god knows what else)

Also you add flavor additives and then you "vape" it in a atomizer, there have been real academic research done about this quite extensively and it has been proven to be at least 95% less harmful than smoking tobacco, so I have switched all my tobacco usage to vaping instead and it's great.

The devices used to vaporize the liquid comes in many forms and I use the more serious so called MOD which is a device containing often extra batteries as opposed to e-cigarettes which has very weak batteries, but also have more firmware to control the wattage, temperature and other things. And the way I do it you have to wind your own coils to be used as the heat element(this is done with Kanthal, Stainless-steel, Nichrome or other metals), which is all a fun hobby, but enough about this.

Li-Ion Safety

Currently I have a setup on a device that is using 2 18650 Li-Ion 2100mA/h batteries in series and I generally use the device at a setting of 40W, in any case I have two use cases. One is drawing 17,7A and the other is drawing 14,7A, and with a battery with 2100mA/h I then get about 7 or 8,5 minutes of usage before the battery is drained.

I am using 2 Sony VTC4 IMR 18650 High Drain Flat top 2100mA/h batteries in series, if I am draining 17,7A how long will it last?
I am very unsure about how I got the following number but am I right that it should give me about 7 minutes?

I would like at least double that but the sites selling batteries for vaping MODs advices that only high quality batteries like these should be used.

What dangers could you see with using batteries from ebay with 6800mA/h (assuming there discharge rate is high enough)?

Regards

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Just to say, when I use the device I am activating it first for 10seconds after which I activate it for 3 seconfs each inhale, if the coils have cooled down then I activate it for 10 seconds again and then continue with 3 second activations, so those 7 minutes is spread out over a few hours.

yes if you are discharging Lithiums above 1C then generally you should be monitoring their temperature, and its when you get the sudden rise in temperature that thermal runaway is happening, and they could explode, and so you need to shut them off, i believe but may stand corrected by others here.
As you know, you shoudlnt discharge them below 3V per cell or something like that..but usually they are protected against this internally anyway.

David_ said:

What dangers could you see with using batteries from ebay

Click to expand...

Although the Li-ion type are supposed to have internal safeguards built-in, I saw a report (or perhaps a credible rumor) of far-East counterfeit battery makers who omit the safeguards. Ebay is to a large extent a marketplace for far-East vendors.

Have you seen news reports about Li-ion batteries causing fires and explosions? It makes me think twice about experimenting with them.

Most 18650 Li-ion cells do not have protection circuits built-in but some do. The protection circuit is usually in the laptop battery circuit, not in each cell.
ebay sells mostly fakes and manufacturer's rejects. Nobody makes an 18650 cell with as much as 6800mAh, it is probably 680.0mAh instead. One video of a fake shows a tiny 68mAh Li-Po inside the can of an 18650.
My radio controlled model airplanes use a 280mAh/30C Li-Po battery that has two cells in series. The airplanes use peaks of 5A and averages 4A for 4 minutes. The current is way more than 1C and the battery cell becomes warm, not hot.
I found a portable vacuum cleaner with a dead 5V (4 cells in series) Ni-Cad battery. I replaced the battery with four series/parallel 18650 Li-ion cells from an old laptop and the vacuum cleaner runs fine.

The stories of people being burned by their vaper's battery catching on fire usually have a vaper that was made poorly in a far east place. The battery contacts develop some resistance that causes the heat instead of the heating wire.