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Stacked batteries and Amp Rating...

Discussion in 'Battery Issues' started by Andrew Freeman, Oct 3, 2013.

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  1. I have googled this, and have come up with nothing...

    So, i understand that running stacked batteries doubles the voltage, but what happens with the Amp discharge rating?

    I wanted to run stacked 18350 in a K100, but was curious after looking at rapidtables.com and realizing a .5 ohm coil at 3.7v will require 7.4amp...but the efest 800mah batteries are only rated to 6.4amp.

    Does this mean that I simply can not run below ~0.58ohm with these batteries?
     
  2. Rader2146

    Rader2146 Ultra Member Verified Member ECF Veteran

    Mar 11, 2012
    Waco, TX
    It means that you cannot run below ~.6Ω on a SINGLE battery.

    The max discharge rate of the batteries does not change when run in series (aka "stacked"). What does change is the voltage. Now you will have 7.4v (nominal) instead of 3.7v. Now toss 7.4v and .5Ω into ohms law and you get 14.8A.

    Stacked batteries are a thing of the past, and anyone with a mechanical mod just needs to forget the word "stacked" ever existed. With 18650 batteries capable of 30A discharge, there is NO EARTHLY REASON to try to stack batteries and do something dangerous.
     
  3. Switched

    Switched ECF Guru ECF Veteran

    Feb 18, 2010
    Dartmouth, NS Canada
    ^^ what he said^^

    ... .... I hate being an old timer. Thanks Rader... :)
     
  4. Switched

    Switched ECF Guru ECF Veteran

    Feb 18, 2010
    Dartmouth, NS Canada
  5. Ryedan

    Ryedan ECF Guru Verified Member ECF Veteran

    Mar 31, 2012
    Ontario, Canada
    Never stack batteries in a mechanical mod. It's not worth the pain you might have to endure.
     
  6. Gotcha...

    Thanks, everyone!

    Obviously I should read a little further into this...lol!

    I am very confident in my skills and competent, however, as with everything I do, I am always educated and confident enough to be VERY dangerous to myself...keeps it interesting, hahaha...
     
  7. Nikkel

    Nikkel Moved On

    Dec 16, 2013
    Southern, USA
    "Stacked batteries are a thing of the past, and anyone with a mechanical mod just needs to forget the word "stacked" ever existed."

    I've noticed when ecig peeps talk about batteries they almost always assume Li-Ion batteries. I'm currently considering stacking 3 NiMH batteries in a telescopic mechanical mod.

    2/3 A size 1.2 V, 1600 mAh rechargeable NiMH battery
    Dimension: Height 28 mm, Diameter 17 mm
    All-Battery.com:Tenergy 2/3A 1600mAh NiMH Rechargeable Battery
    NiMH Rechargeable Cell: 2/3A 1600 mAh NiMH Battery (1PC) - RoHS Compliant

    Private V2 Telescopic Mechanical Mod
    Maximum Supported Battery Length: 105.8 mm
    $12.71 Private V2 Telescopic Mechanical Mod - brass + aluminum at FastTech - Worldwide Free Shipping

    3 batteries stacked would be 3 x 28 = 84 mm long and produce 3.6 volts at 1600 mAh.
    The mod was designed for 18 mm diameter batteries, so a 17 mm diameter battery would fit loosely.
    On paper, it looks to me like this would work.
    Is there any reason I should not consider this configuration?
    Wouldn't this be safer, cheaper, and in general more groovy than using a single Li-Ion battery?
     
  8. Switched

    Switched ECF Guru ECF Veteran

    Feb 18, 2010
    Dartmouth, NS Canada
    Sorry sir, we don't do groovy when it comes to battery safety.
     
  9. Rader2146

    Rader2146 Ultra Member Verified Member ECF Veteran

    Mar 11, 2012
    Waco, TX
    I don't see any reason to attempt this other than curiosity.

    1) I'd be surprised if the max supported battery length is ACTUALLY ~105mm.

    2) You'd end up with 3.6V, 1600mAh and a 10C discharge rating...no better, actually worse, than a high quality, high drain, Li-Ion.

    3) It's an egregious violation of the KISS method. :D
     
  10. Nikkel

    Nikkel Moved On

    Dec 16, 2013
    Southern, USA
    "3) It's an egregious violation of the KISS method."
    Keep It Safe Stupid or Keep It Simple Stupid
    In my opinion, the three stacked NiMh batteries would be safer than one Li-Ion. I would relinquish a bit of simplicity for a bit of safety.
    Some NiMh can be fully recharged in 15 minutes. Not sure about these particular batteries.

    "1) I'd be surprised if the max supported battery length is ACTUALLY ~105mm."
    For my scheme of three, it only needs to support 84mm.
    Wish I could find a cheap mod that would support 4 batteries, 112mm. If you hear of one, please let me know. I checked the specs of most, if not all, the mods at Fasttech and didn't see one.
    I recall reading something about FAA restrictions on the weight of Li-Ion batteries allowed on planes. I wonder if 18650 mods would be allowed?
    I'm new to vaping and to this forum. I've noticed several posts from newbies saying they were terrified of their batteries. NiMh batteries might calm their nerves.
    The NiMh are one millimeter smaller in diameter than the 18xxx series batteries. I'm hoping that won't be a problem.
     
  11. Switched

    Switched ECF Guru ECF Veteran

    Feb 18, 2010
    Dartmouth, NS Canada
    ... and most of them only read what they want to hear, not what they need to hear. Separating the chaff from the wheat is a daunting task, no one will deny that. OTOH dissing the advice from the veterans only magnifies the problem now doesn't it?

    I have been vaping going on 4 yrs without incident. I do not fear my batteries I respect them, just like I respect electricity.

    Although many veterans are still around to help out the "newbies" many no longer respond to questions because of the ensuing argument that follows when the provided advice is not what they want to hear.

    Here we provide you with the short strokes, you fear batteries? Good! Now if ya want to get rid of your unfounded fear educate yourself with their intricacies. Basic to Advanced Battery Information from Battery University

    The groovy thing these days is sub-Ohm coils, there is no need for them and a dangerous practice at best especially with neophytes that simply are looking for clouds of vapour without understanding the fundamentals of their practice. A 2 week in vaper had a thermal runaway using a 0.6Ohm coil on a no name unmarked battery. These folks could very well become statistics :facepalm: Think about it.

    We are not here to pee on your parade, we are here to keep you away from cigarettes in a safe, not reckless manner. :)

    ETA: As my avatar states, I was vaping when vaping wasn't cool:) In closing, do you own a digital multi-meter? If you don't that should be your next purchase if you are serious about vaping and tinkering.
     
  12. Nikkel

    Nikkel Moved On

    Dec 16, 2013
    Southern, USA
    I am new to vaping, but not new to reasoning and arithmetic.
    I see that you are a vendor. You have a dog in this fight. Your opinions are apt to be biased.

    "Although many veterans are still around to help out the "newbies" many no longer respond to questions because of the ensuing argument that follows when the provided advice is not what they want to hear."
    Unlike the Pope, veteran vapers are not infallible. Critical thinking skills apply here as they apply everywhere.

    I have read and understood much of the info from Battery University. I have previously owned and used a multimeter. It is an arrogant mistake to assume peeps who favor NiMh and shun Li-Ion are ignorant.

    "A 2 week in vaper had a thermal runaway using a 0.6Ohm coil on a no name unmarked battery. These folks could very well become statistics Think about it."
    If NiMh batteries were predominately used in vaping rather than Li-Ion, thermal runaways and other battery mishaps would less hazardous and the probability of serious injuries would be less. Put that in your pipe and smoke it.
     
  13. MorpheusPA

    MorpheusPA Ultra Member ECF Veteran

    Sep 7, 2012
    Lehigh Valley, PA
    I see no reason not to use NiMH if it floats your boat. They're really safe, stackable, durable, easy to find, and fairly inexpensive. Any NiMH charger can be used to recharge them.

    The downside is that their energy density is much lower, about a third of that of lithium batteries--hence the reason you need to stack 3 to get near the voltage of a lithium, but don't get any more amp-hours out of it. For a box mod, that's not a severe consideration.

    Just make sure to choose batteries with mAh ratings high enough to make you happy (AAA doesn't usually go over 1,000 or so, D is up to 10,000), and that has the ability to output the amperage you need in the time you need it. Never overstep that, it makes the batteries unhappy--the voltage will droop and the vape will be bad.

    You may wish to buck/boost the voltage, just as it's done from a lithium and for the same reason. NiMH cells start around 1.4 volts fresh off the charger, maintain about 1.2 through most of their usable life, and drop rapidly when near full discharge. For best battery life, don't use your NiMH cells when they're below 1.0 volts each (some say down to 0.7, I tend toward the conservative, 0.8 or 0.9 is probably a good compromise).

    Update: Some quick research shows max discharge rates as 3C--so a 1,000 mAh battery should be able to output bursts of 3 amps for at least a short period of time (assuming a poor battery). A 10,000 mAh battery should be able to output an astounding 30 amps. I'd still test voltage under load, but a boost controller would take care of that problem quite handily.
     
  14. Nikkel

    Nikkel Moved On

    Dec 16, 2013
    Southern, USA
    I recall reading recently the relative energy density is more like half, and perhaps even a little more than that.
    For the 1.6A batteries I mentioned, the max C listed was 10.
    10 x 1.6 = 16A

    Seems like I recall reading that the capacity of NiMh is somewhat misleading when it comes to comparing the satisfactory vaping time with Li-Ion. For example, I recall seeing the claim that 1Ah of NiMh will provide more satisfactory vaping time than 1Ah of Li-Ion. I think it had something to do with NiMh maintaining its nominal voltage longer across the discharge time than Li-Ion.
     
  15. Switched

    Switched ECF Guru ECF Veteran

    Feb 18, 2010
    Dartmouth, NS Canada
  16. Nikkel

    Nikkel Moved On

    Dec 16, 2013
    Southern, USA
    The aluminum version of the Private V2 clone is the only mod I'm aware of that can accomodate three 2/3 A NiMh. I think most other (smoothly) telescopic mods could accomodate two of them.
    2.4/1 = 2.4, 2.4 x 2.4 = 5.6
    Using a 1 ohm atomizer at 2.4 volts would vape at 5.6 watts. Not too shabby. Might do in a pinch.
    The 2.4A draw on 1.6A batteries rated at 10C doesn't seem too outrageous.
    But, if I could find a cheap mod to contain four of the batteries, I would be a happy camper. At least, on paper.

    Dang! That peak load current on the BU page is listed at 5C. That doesn't jive with the 10C listed on the vendor sites.

    *******************************************************************
    "High capacity (1600 mAh) and high discharge rate (9C-12C)"

    *******************************************************************************************************
    "As high as 10 C discharge Rate. "

    It's possible the info at the BU site is outdated. It's also possible the info at the vendor site is inflated.

    Just as I would suspect a vendor, such as Switched, who sells Li-Ion batteries to be biased in favor of his wares, I would also suspect a vendor who sells NiMh to be biased in favor of his. But, when a vendor sells both, that moderates my suspicion.
     
  17. MorpheusPA

    MorpheusPA Ultra Member ECF Veteran

    Sep 7, 2012
    Lehigh Valley, PA
    Sure, it's possible...make sure to buy really good NiMH batteries for best energy supply. I find they're frequently overrated in terms of supply, even on my project designs (where, if I'm drawing 0.05C, that's actually quite a bit). They'll perform best at low discharge rates.

    That C rating seems really overinflated. Internal resistance on an NiMH is pretty high for an output of 10C. That might be a peak as opposed to a sustained current, so good for a few milliseconds to maybe a few tenths of a second, but not smart to extend to seconds and really not smart to extend to multiple-second bursts one after the other.

    LiMn batteries do have the advantage of lower internal resistance, so voltage drop isn't quite so much of an issue. Again, with a buck/boost circuit, it makes no real difference as long as the voltage stays high enough for the circuit to work with (and that's not hard to do).

    Warranted, when working with the extreme edge of battery supplies I'm not that experienced (my electronics designs tend to try to extend battery life as far as I can), but I'm seriously suspecting a high voltage drop.

    There's nothing wrong with testing at that level, but I'd check the output voltage to make sure it isn't drooping.

    That sounds likely. The NiMH discharge curve's a lot flatter than LiMn. If you buck/boost, it won't matter terribly much as the electronics will adjust the output voltage for you. In a manual mod, you'd get a more consistent vape for a longer time using NiMH.
     
  18. Switched

    Switched ECF Guru ECF Veteran

    Feb 18, 2010
    Dartmouth, NS Canada
    Let me be quite succinct here grasshopper: (sarcasm intended)
    • I am a person 1st
    • a vaper 2nd
    • and a vendor 3rd

    I do not have a dog in this fight, with the exception of providing advice in preventing you in becoming just another vaping statistic. Another thing you will learn as you mature in your new chosen lifestyle is that battery specs are more often than not inflated, to include but not ltd to the sites you have linked us to. Hey but then again, you know your stuff :)
     
  19. Nikkel

    Nikkel Moved On

    Dec 16, 2013
    Southern, USA
  20. MorpheusPA

    MorpheusPA Ultra Member ECF Veteran

    Sep 7, 2012
    Lehigh Valley, PA
    I'd be willing to bet that the specs are over-inflated. My best batteries, technically rated (reasonably new) at 2,500 mAh actually test out closer to 2,000 even under low load. And there's no way in heck I'd ever go anywhere near 10C constant discharge, the voltage is going to droop severely.

    Battery with internal resistance

    I'm going to guess the internal resistance at 25 mOhm (milliohm), you stated an 0.5 ohm coil.

    Using two stacked batteries, 2.4 volts, you're giving up 0.12 volts and about 1.1 watts to internal resistance. It actually gets worse at 3.6 volts (3 batteries stacked) with 2.4 watts being given up.

    Internal resistance = heat, which is a killer for most batteries, including NiMH. While 1.1 watts of heat (0.55 per cell) doesn't sound like a great deal (and it isn't), I managed to singe my hand on a large linear converter with a heat sink dissipating 3.5 watts after five seconds of use and about a half second of contact. It's not necessarily the heat amount, but how quickly it can leave the system--and it can't go anywhere very fast here.

    So the more I think about this, the less I like it. Eventually the system heats up, the internal vents open, and things get...interesting. Not nearly as interesting as with a lithium where fire and whatnot results, but the battery is headed for a fast and unlamented death.

    If they're actually correct on their specs, and I have no idea, internal resistance should be around 10 mOhms. While that makes the picture much rosier, I'd really want confirmation that they're not inflating the numbers.

    Edit: My gut response is to go with a lithium. They have very low internal resistance, we're certain of the C rating, know they're good actors under high rates of discharge, and simply aren't that dangerous. Of course, it's unwise to charge it unattended...but that's actually true of NiMH and NiCd as well.
     
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