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Lets talk safety!!!

Discussion in 'APV and Mods Discussion' started by bebeau25, Jul 19, 2013.

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  1. bebeau25

    bebeau25 Senior Member Verified Member ECF Veteran

    Jun 17, 2012
    Tulsa OK
    I'm posting this for my own reassurance and for others interested in coil building. I recently got an RBA, started playing around with it, and have had decent results. I did some research and found other people talking about their setups and decided it was safe to go ahead and pretty much copy what they are doing. Probably not the safest way of doing things. It kind of bothered me that I didn't know, with some kind of hard evidence, that what I am doing is safe, so back to ECF and youtube I go. This will be old news for a lot of you, but feel free to chime in with any info that you would like to add. It didn't take long and I came across the ohms law calculator. Wonderful little tool. Did some research on the batteries I'm using and this is what I came up with.

    AW IMR 18350 700mAh 3.7 V specs

    Nominal Voltage: 3.7 V
    Capacity: 700mAh
    Lowest Discharge Voltage: 2.50V
    Standard Charge: CC/CV (max. charging rate 2A)
    Cycle Life: > 500 cycles
    Max. Continuous Discharge Rate: 6A

    Using Ohms Law Calculator, Ohm's Law Calculator Here are the results,

    Voltage: 4 (freshly charged battery)
    Current: 5.71429
    Resistance: 0.7
    Power: 22.85714

    Voltage: 3.7
    Current: 5.28571
    Resistance: 0.7
    Power: 19.55714

    So according to these numbers (and please correct me if I'm wrong) the battery has a 6A discharge rate, and the numbers come to 5.7 @ 4V and 5.2 @ 3.7V which makes this setup a "safe vape".

    AW IMR 18650 3.7V 2000mAh specs

    Nominal Voltage: 3.7 V
    Capacity: 2000mAh
    Lowest Discharge Voltage: 2.50V
    Standard Charge: CC/CV (max. charging rate 2A)
    Cycle Life: > 500 cycles
    Max. Continuous Discharge Rate: 10A

    With a 10A discharge rate these batteries would be safe with this setup as well.

    To anyone that has a better understanding of all this, please correct anything that I've done wrong and add any helpful information to keep all of us safe while diving into this new found hobby. :)
     
  2. CloudZ

    CloudZ Super Member Verified Member ECF Veteran

    Nov 21, 2012
    Minneapolis, MN
    Yep, you got it right. If you stay under the safe amperage with theoretical calculations, there should be no problem due to voltage drop. So the actual voltage the battery is putting out will be lower than what you measure with a multimeter because the mod and battery itself have some small internal resistance. Thus, lower amps. Its not as safe when you actually factor in the voltage drop and try to push right up to the amp limit with even lower resistance.

    So lets say my battery comes off the charger reading 4.2V and my coil is 0.5 ohms. Theoretically, that is 35 Watts at 8.5 amps. My batteries can handle up to 10A. So in theoretical fantasy land, even that is safe. Now, if you consider that I am getting 0.4V drop at that current draw (its probably considerably more than that with my cheap mechs), I am actually operating at 3.8V, which is only 29W at 7.6A. Lets say I measure my voltage drop and decide to play with fire. I drop my resistance down to 0.4 ohms, and assuming the drop is still the same (it would actually be a bit more), now I am at 9.5A. That's how sensitive it is, 0.1 ohms less and you're pushing the limit.

    So be safe, know exactly what the electricity is doing with a decent multimeter, and use theoretical calcs to stay under the battery limitations.
     
  3. Ryedan

    Ryedan ECF Guru Verified Member ECF Veteran

    Mar 31, 2012
    Ontario, Canada
    I agree you are on the right track bebeau. One thing that is incorrect - a freshly charged battery will run between 4.15 and 4.25 volts. Most chargers will stop charging very close to 4.2. At 4.25 volts and 0.7 ohms, you will be drawing 6.07 amps, a bit over your smaller batteries capacity. A short will make the resistance go down, taking the amps way above what these batteries can handle. This is not safe.

    I run a mech mod and AGA T with 0.7 ohm coils drawing the 6.07 amps we already established for these numbers. I use batteries rated for 10 amps and this has been safe for me since February this year. I regularly check battery volts and coil resistance with a multimeter. Vape safe and enjoy!
     
  4. bebeau25

    bebeau25 Senior Member Verified Member ECF Veteran

    Jun 17, 2012
    Tulsa OK
    Thanks guys...all good information here. Ryedan I appreciate the correction on a freshly charged battery. I'm kind of a numbers guy, so I love having the information so readily available using ohms law calculator.

    Sent from my DROID RAZR using Tapatalk 2
     
  5. classwife

    classwife Admin Admin Verified Member ECF Veteran

    Supporting member
    Good !
    Adding a calculator to your thread !

    Online Conversion - Ohm's Law Calculator


    Ok...gonna go get more coffee !
    I see it is in the first post ! :facepalm:
     
  6. bebeau25

    bebeau25 Senior Member Verified Member ECF Veteran

    Jun 17, 2012
    Tulsa OK
    Lol...I can't think straight without a few cups of coffee either.

    Sent from my DROID RAZR using Tapatalk 2
     
  7. Steam Turbine

    Steam Turbine Ultra Member ECF Veteran

    Correct me if i'm wrong but I believe that firing your battery at exactly or a little under it's amp limit will reduce the overall life of your battery.
     
  8. Ryedan

    Ryedan ECF Guru Verified Member ECF Veteran

    Mar 31, 2012
    Ontario, Canada
    I believe you are correct ST. Actually, pushing a battery to any limit will stress it and shorten it's life. Fast charge, over charging, running to almost empty and running hot all come to mind. It's amazing how few people know this.
     
  9. Baditude

    Baditude ECF Guru ECF Veteran

    Apr 8, 2012
    Ridgeway, Ohio
    And users come here wondering why they are only getting 2 hours time on their battery. :facepalm:
     
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