A few more questions about sub-ohming, batteries, and electricity.

[TheBiloi]

So far this forum's been a great help but I just want to completely hammer out my understanding of this all before my mech mod and rda arrive from Focalecig.

I guess first off I've had a question about my charger itself. It has a toggle switch that can be pointed in two positions: 3.0v and 3.6v. My assumption is that it will only charge the batteries to those voltages and then stop charging, which is fine by me for now. Am I correct in this? I'll probably look into purchasing a higher quality charger that can fit more batteries and charge to 3.7v.

I'm also wondering about the dangers involved here. If I understand correctly the main danger involved is in drawing a current greater than the battery's design capacity causing it to go into breakdown. Now I'm wondering what would happen IF this were to occur in an IMR battery? Would it explode? Immediately dissolve into a pile of goo and seep out the vent holes? Or would it just get hot first, cueing me in on the fact that I should get it out of my device and into a safe area?

Last question for now, how likely is it that I'll have an issue with these batteries? I intend to run them at 3.6v, on a 0.8 - 1.0 ohm coil, which should generate 3.6 - 4.5 amps on these batteries which have a rating of 10 amps. IF a short were to occur, which I'm confident it won't, how many amps could it potentially generate beyond it's design capacity?

I really appreciate the help everyone. This forum's been awesome so far and I'm just trying to make sure I know everything I can.

 

[TheBiloi]

Here's a picture of the switch on that charger.

 

[dwarfcat]

This intrigued me so I looked up some stuff. This seems like it might be helpful to people. Dont know if its accurate or even useful for this stuff but interesting

Watts - volts - amps - ohms conversion calculator

 

[LucentShadow]

Hi. I've heard of that type of charger mentioned before. My understanding is that the 3v setting is for a different chemistry battery that we don't use in e-cigs. The 3.6v setting should properly charge the battery to 4.1-4.2v. It would be a good idea to get a multimeter to monitor the voltage before and after charging, occasionally. You should not discharge to less than 3.1-3.2v, and the charger should never charge them to over 4.2v.

IMR chemistry cells are generally recognized as the best choice for an application such as this. They have good discharge current ratings, and much less-violent failures than ICR chemistry does. See this video for an example:

Callies Kustoms IMR Battery and AW short circuit observations - YouTube

Staying less than 50% of the rating seems pretty reasonable. They should be fine, as long as they remain in good condition. Keeping tabs on them with a miultimeter helps, in this regard. Keep in mind that a short circuit can theoretically pull unlimited amperage. Reality forces that down to a very high amperage due to the resistance of the cells, themselves, as well as the surrounding circuit. Rest assured that a short can easily damage the cells. A shorted coil may open before that point is reached, but I would not count on it. A multimeter is a good idea here, as you can check for that condition before using.

 

[TheBiloi]

Thanks, I appreciate the help. I was planning on using my iTaste SVD to read the coil resistance and check the battery voltage but it sounds like I'll just be better served to learn how to use a decent multimeter.

If my batteries are designed for 3.7 volts and my charger, as you say, is in a mode where it charges to 4.2 volts, could that have any negative effects? 4.2 volts and 3.7 volts are a pretty substantial difference in wattage.

Edit: I just checked and it sounds like a green light on my SVD indicates that my battery is above 3.8volts. What does the big "3.7v" printed on my batteries even mean then if they can take a charge greater than that?

 

[DKP#]

3.7 Volts is "nominal"
The battery goes from 4.2V fully charged to 3.2V discharged

 

[LucentShadow]

Thanks, I appreciate the help. I was planning on using my iTaste SVD to read the coil resistance and check the battery voltage but it sounds like I'll just be better served to learn how to use a decent multimeter.

If my batteries are designed for 3.7 volts and my charger, as you say, is in a mode where it charges to 4.2 volts, could that have any negative effects? 4.2 volts and 3.7 volts are a pretty substantial difference in wattage.

The '3.7v' batteries are actually charged to 4.2v. The nominal voltage, as they are discharged, is about 3.7v. Note that, by the numbers I mentioned above, they vary from 4.2v to about 3.2v when discharged. The electronics that they are used in should turn off at about 3.2v. If you are using a mechanical mod, then you need to stop using them before they go lower than that. Here is some more info on these types of batteries:

Lithium-based Batteries Information

It would be a good idea to read some of the other links on that site, too.

 

[jersey_emt]

3.7 volts is the nominal voltage for the batteries we use, but 4.2 volts is the maximum charge voltage. Yes, the wattage and the amp draw will drop as the battery discharges. What this means is that in order to verify if a coil is safe to use, you calculate the amp draw using the charge voltage of 4.2 volts, not the nominal 3.7 volts.

Amps = Voltage / Coil resistance in ohms
Watts = (Voltage x Voltage) / Coil resistance in ohms

A 1.0 ohm coil will fire at 17.6 watts and draw 4.2 amps on a fully charged battery.

Amps = 4.2 volts / 1.0 ohms = 4.2 amps
Watts = (4.2 volts x 4.2 volts) / 1.0 ohms = 17.64 watts

A 0.5 ohm coil will fire at 35.3 watts and 8.4 amps

Amps = 4.2 volts / 0.5 ohms = 8.4 amps
Watts = (4.2 volts x 4.2 volts) / 0.5 ohms = 35.28 watts

 

[LucentShadow]

Thought I'd drop some more e-cig-specific battery info, here. Baditude has some good blogs on the subject. Here's a link to his blog page:

E-Cigarette Forum - Baditude - Blogs

 

[TheBiloi]

This is starting to make a lot more sense. I really appreciate everyone's input, I think I'm understanding now. I'll go read more following that link.

The last question I'm most ashamed to ask is if the mech mod does indeed fire at whatever voltage the battery is at. I assume it does but all the China-based sites like FastTech and Focalecig list mechs with a voltage of 3.7. I assume that a fully charged battery at 4.2 volts will be sending a voltage of 4.2 volts to the coil, correct? Again, seems pretty obvious but I figure I might as well confirm.

Edit: I just checked and it looks like they aren't actually listed that way. Maybe it was another site or maybe I'm hallucinating.

 

[LucentShadow]

This is starting to make a lot more sense. I really appreciate everyone's input, I think I'm understanding now. I'll go read more following that link.

The last question I'm most ashamed to ask is if the mech mod does indeed fire at whatever voltage the battery is at. I assume it does but all the China-based sites like FastTech and Focalecig list mechs with a voltage of 3.7. I assume that a fully charged battery at 4.2 volts will be sending a voltage of 4.2 volts to the coil, correct? Again, seems pretty obvious but I figure I might as well confirm.

Never be ashamed to ask a question. Yes, mech mods will just send through the battery voltage. They will 'hit harder' on a fresh charge, and you'll likely notice the performance drop when they need to be recharged. I mentioned the fact that you need to stop using the batteries at about 3.2v, because they can become damaged due to discharging too low. This is especially important for mech mod users, who must monitor that themselves. Regulated mods will shut down at that voltage.

 

[Baditude]

I'm also wondering about the dangers involved here. If I understand correctly the main danger involved is in drawing a current greater than the battery's design capacity causing it to go into breakdown. Now I'm wondering what would happen IF this were to occur in an IMR battery? Would it explode? Immediately dissolve into a pile of goo and seep out the vent holes? Or would it just get hot first, cueing me in on the fact that I should get it out of my device and into a safe area?

Last question for now, how likely is it that I'll have an issue with these batteries?

IMR batteries, being safe-chemistry, are not likely to vent flames or explode, but merely vent gas rather gracefully. However, the following pic shows an AW 18490 IMR battery which vented in a book bag's pocket (likely coming into contact with metal to complete the circuit and over-discharge).



The high pressure of the hot gas forced the battery's "innards" out of the battery casing. Imagine this occuring in a metal tube mechanical mod whose vent holes were blocked off by the battery swelling in size. Can you say "pipe bomb"?

The below pic is also of an AW IMR battery that went into thermal runaway. These things can get hot enough to cause a fire even if they do not vent flames.




This has nothing to do with the above batteries being from AW. AW is probably the safest battery that you can purchase. In fact, our forum administrator and resident battery expert Rolygate recommends them as the safest battery available to us.

http://www.e-cigarette-forum.com/forum/ecf-library/129569-rechargeable-batteries.html - "Our advice is that the best and the safer choice of battery for APVs is the AW IMR Li-Mn rechargeable."


Respect the power that are in these batteries at all times, and practice safe battery habits even more. Even the safest of batteries can go into thermal runaway.

 

[TheBiloi]

Thanks, that's good to know. Sounds like knowing how to check for shorts, knowing that my build is generating a current within my battery's limits, and making sure everything's stowed away safely will ensure no accidents happen.

Thanks for the help everyone.