Need help undestanding battery limits

Discussion in 'Ask An Expert' started by Big E Joose, Aug 30, 2018.

  1. Big E Joose

    Big E Joose New Member

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    I have an LG 18650 3.7V 3000mAh 20a battery. I have a build in my RDA and it ohms out to .20 exactly. I want to run this on my nemesis mech mod that I recently received in the mail. with 3.7V the math adds up too 18.5 amps ad at 4.2V its 21.0. I this safe to use like that all? or should I go with a higher ohm. Also it takes ridiculous amount of time for anything higher than that to start firing.
     
  2. Kitsune

    Kitsune New Member

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    In all honesty, a mech is never completely safe and personally I would never run a setup at its limits.
    We can only try to make it as safe as possible and that also (and especially) means batteries.

    I would get a Sony VTC5a or Samsung 20S if I were you. Never risk your health for 10 bucks. :)

    .2 with a VTC5a is well within its limits, but if you are new to mech, do yourself a favor and be extra precise and check your hardware frequently. A short or overheating will destroy even the best battery and you certainly don't want something exploding right in front of your face.
     
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  3. Big E Joose

    Big E Joose New Member

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    I went ahead and knocked my ohms up to be safe for sure, an thank you so much <3
     
  4. Carambrda

    Carambrda Gold Contributor Member For 2 Years

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  5. Ralph_K

    Ralph_K Silver Contributor Member For 1 Year

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    If you watch the video above the take away is you're not going to actually get the 4.2v because of voltage drop just a safety margin and 3.7 is closer to the actual voltage but then he says not to tell others that even though he is doing just that in the video.
     
  6. Carambrda

    Carambrda Gold Contributor Member For 2 Years

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    Yeah, but the reason why he mindfucks you like that is simply because there will always be those who use that as a starting point to see how much farther they can take it without first doing proper research or who think the research they did is proper when the reality is that it isn't. And he does have a point about unknown factors such as ohms readers that aren't sufficiently accurate and whatnot so basically we don't want the FDA to ban mechs and external batteries as a result from dumbasses who can't seem to figure out the difference between true facts based knowledge and widespread jackassery.
     
  7. Ralph_K

    Ralph_K Silver Contributor Member For 1 Year

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    Some people will just use 4.2v in ohms law then push it by adding a few extra amps above cdr when they could have used 3.7v and stayed within the cdr.
     
  8. Carambrda

    Carambrda Gold Contributor Member For 2 Years

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    But then you lose part of the idea of keeping a big enough safety margin to also account for unknown factors. My own personal approach is to turn unknown factors into known factors and still end up having enough safety margin for me to be capable to disarm my mech mod in a safe fashion and without panic in the rare event that the mod starts to auto-fire on me unexpectedly, and to always avoid any and all accidental button presses the same way you can always avoid driving yourself off a cliff. On a "faux hybrid" (i.e. direct-to-battery) mech, the battery can get pressed against the inside of the top of the mod if, before you unscrew the button, you unscrew the atomizer... thereby potentially causing a hard short followed by a battery explosion. But this can always be avoided by simply always remembering to unscrew the button instead. But if the mod starts to auto-fire and then you panic as a result from that, you might not remember this. So either you have to be sure that you won't panic or else you can get a mech that uses a 510 pin such as the Broadside. Only if you're the type of person who easily starts to panic or who has trouble remembering important stuff, like, for example, trouble remembering that you should never ever screw on an atomizer that doesn't have a protruding center pin excepting only if your mech mod isn't a faux hybrid, you should probably stay away from mechs in general. I mean, going above the CDR makes the battery heat up faster so you'll have less time to react in case something goes wrong with the mod. But not everyone knows how to react correctly, and not everyone knows how to always stay alert and to always notice it on time so therein lies part of the culprit.

    Another surefire way to make accidents happen by going above the CDR are people who don't understand when it's time to put the mod down and give it a rest. The higher you go above the CDR, the faster the battery heats up. But for reasons that are obvious, immediately as soon as you let go of the fire button, the battery cools back down again. If you're not familiar with the relationship between how fast a given battery heats up and how many amps you draw from this same battery for how many seconds, just pull out the battery each time when in doubt. Feel how warm it gets. As long as you don't immediately build to ridiculously low ohms, as long as your coil build is stable and your ohms reader is sufficiently accurate, if you can understand everything I have been explaining so far, you can familiarize yourself with all these factors. Using a .11 ohms build on a single Sony VTC5A is way above the CDR of 25A for this battery. Does that make it so unsafe that you'd have to be a jackass? Hell no, it doesn't. Even after you take like 5 hits in a row each one of which lasts almost 2 seconds, the Sony VTC5A in a single battery mech at .11 ohms gets barely even lukewarm. Above 45 degrees Celsius is where a battery starts aging faster than normal. 35A is not the CDR of the Sony VTC5A. Instead, it is only 25A. Despite this, the VTC5A is rated by Sony to 35A Maximum Continuous Discharge Current IF you make absolutely perfectly sure that it stays below 80 degrees Celsius. You do get an increased risk of the battery venting if you go above the CDR. You really do, but my question is, does it take to be a rocket scientist to make the battery always stay below 45 degrees Celsius so that you still have time to react appropriately before it can ever get to 80 degrees Celsius? You be the judge. Finally, because the Samsung 20S has a CDR of 30A and because it is hitting so much harder than the VTC5A... well, you get the picture.
     

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