18650 LiFePO4 cells and variable wattage systems--do they get along?

[JuiceIsLoose]

Sorry to take up space!

I'm new to the E cig concept, switched over 22 days ago and really enjoy it. After a few false starts with cheezy
stuff, I am putting together in my mind the perfect E gadget. Metal body, metal threads, smart chargers and variable
wattage heads. I've used LiFePO4 batteries in my DeWalt 36V power tool system, it handled everything from cold,
being dropped and 6 months in Afghanistan--after 6 years the batteries are still kicking .....

Using an 18650 LiFePO4 cell with a variable wattage head (or variable voltage if I have to) it is my quest. Since LiFePO4
or Lithium Iron Phosphate has a nominal voltage of 3.2 volts--that might create havoc with the low voltage warnings from
E vape devices. Are there any devices that allow programming the device for the 3.2V nominal battery voltage? If so,
can anyone tell me where to find such a device?

Any help is appreciated! Vape on!

 

[fabricator4]

Lithium Iron Phosphate is a very safe technology and is not susceptible to thermal runaway. It has a low internal resistance and good specific energy ratings, but its specific power delivery is only classified as "moderate". You would need to charge it more often than the current ecig battery technologies, weight/power. Other problems include reduced current at lower temperatures, and short self discharge times which gets worse with higher temperatures.

A good, safe technology, however the main problem here is the the nominal battery voltage is 3.3V, with an end point of about 2.2V. Most PV delivery devices (atomisers) are designed to work at about 3.7V nominal, giving a power output of about 6-7 watts. A fresh LiFePo4 battery will only give about 4.5 watts on this resistance, dropping off to about 2 watts. In other words, it's not going to run many of the off-the-shelve delivery systems very successfully at all - you'd need to look for low resistance coils. I'd suggest you'd probably find a disposable e-cig more satisfying.

It's possible that you would be able to redesign the coils in these devices to be more suitable, but this is going to present a few other challenges, requiring much thinner gauge kanthal wire and associated reduced longevity of the coil.

Similarly, most of the APVs available are designed to run at the higher voltages, and have cut-out protection circuits that shut down at 3.2 V to prevent battery damage. There are no APV devices available that I know of that can be altered to run at lower voltages, however a few of them can use stacked batteries with a voltage range of 6.4Vto8.4v (eg Vamo V2) and automatically detect when stacked batteries are being used.

My recommendation would be to stay with the commercially available systems since you can get (for example) and Ego-C twist VV battery with Ego threads for around $20 or less. I'd recommend the VV (variable voltage) as the starting point for someone interesting in experimenting with different power outputs and finding out how this affects the vaping experience. Something tells me you might fit this category.

Many vapers start off with fixed voltage systems but progress to VV before too long. As well as the twist, the spinner is also a very similar low cost entry level VV battery this is suggested as an alternative.

 

[JuiceIsLoose]

Thank you, Chris

My experience with LiFePO4 has been the A123 Systems cells--they are rated 30C of discharge! The 2300mAH cells can and do
punch out in excess of 60 amps without flinching. The DeWalt battery management system board only allows a surge of 19 amps (8.2C) but that is still 26 watts.

Maybe in the future the high discharge LiFePO4 cells will show up, but not now. I'll punt and go with LiMn 3.7 volt cells, not as safe or durable but available at this point in time. I guess the VAMO with the 18650 body and LiMn cell to match is about my best bet. A123 does make an 18650 1100mAH cell that easily could deal with 15 watt heads but they have always been oddballs about their stuff.

Thanks again for your help, it narrows down my quest by quite a bit.

 

[Ryedan]

The Vamo and Zmax can use one 3.7 IMR 18650 cell or two 18350. I don't know if this means they can be one voltage or the other (3.7 or 7.4 nominal) or anything in between. Just a thought.

I know of no mods where the battery voltage settings are adjustable.

 

[fabricator4]

Thank you, Chris

My experience with LiFePO4 has been the A123 Systems cells--they are rated 30C of discharge! The 2300mAH cells can and do
punch out in excess of 60 amps without flinching. The DeWalt battery management system board only allows a surge of 19 amps (8.2C) but that is still 26 watts.

Yes, that's the "specific energy" rating. LiFePO4 is very good in this regard. The "specific power" is basically mAh/weight. Yes, it seems back to front but those are the industry definitions.

I'll punt and go with LiMn 3.7 volt cells, not as safe or durable but available at this point in time. I guess the VAMO with the 18650 body and LiMn cell to match is about my best bet.

Yes, LiMn batteries are fairly safe technology that will easily handle high power demands. They are usually labelled "IMR". "ICR" batteries are LiCoO2 and while they may be cheaper or higher capacity, they need to be protected against short circuit and overcharging when being used in the e-cig environment. The one safety tip to take away if you can, is not to take any of these batteries off charge and immediately start using it in your PV. A cool-down period will definately reduce your chance of serious mishap, perhaps by an order of magnitude or two (in an already very low probability set).

Thanks again for your help, it narrows down my quest by quite a bit.

I see a Vamo V2 in your future...