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Voltage drop

Discussion in 'New Members Forum' started by VapeRock, Sep 15, 2015.

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  1. VapeRock

    VapeRock Full Member

    Sep 15, 2015
    I just built a series dual 18650 box mod. It's unregulated with a MOSFET setup. Without Adam miser it's around 8.5 volts. With a .7 build on it the voltage drops to around 5.9v and steadily drops. I'm using brand-new VTC4 fully charged. Any ideas?
     
  2. Bunnykiller

    Bunnykiller ECF Guru Verified Member ECF Veteran

    Nov 17, 2013
    New Orleans La.
    Yup I have an idea.... run the batteries in parallel for 4.2 and increased amps with a matched/married set... unregulated series can be an issue waiting to happen at low ohms.. and, when a mosfet fails, it fails closed normally....
     
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  3. Mooch

    Mooch Electron Wrangler Verified Member ECF Veteran

    Supporting member
    May 13, 2015
    Welcome to ECF! @Bunnykiller brings up some good points.

    What coil resistance are you running at? An immediate drop to 3.0V per battery right away either means you are severely overstressing the batteries or they are damaged/worn out/counterfeit. Or a big mod voltage drop.

    Arrrggghhh....completely missed that you said it was a 0.7 ohm build. Those batteries shouldn't be dropping much below 7.5V at the start, if that.
     
    • Like Like x 1
  4. edyle

    edyle ECF Guru Verified Member ECF Veteran

    sounds to me like you have about 0.3 ohms contact resistance somewhere.
    maybe on the centerpin


    btw
    most times unregulated boxes are made in parallel
     
    • Like Like x 2
  5. Ryedan

    Ryedan ECF Guru Verified Member ECF Veteran

    Mar 31, 2012
    Ontario, Canada
    A voltage reading of 8.5 with no atty is 4.25V each batt after the mosfet. I don't know mosfets well, but I know there is some V-drop through one, which means either your batts are noticeably overcharged or your voltmeter is off. What voltage are your batts after being charged?

    Good VTC4's in series will handle the 0.7 ohm resistance with way less than your reported V-drop without a mosfet.

    How do the batteries perform in single battery mods?
     
    • Like Like x 2
  6. VapeRock

    VapeRock Full Member

    Sep 15, 2015
    Thank
    thank you! I'll look into that.
     
  7. VapeRock

    VapeRock Full Member

    Sep 15, 2015
    Batt
    I'm charging the batteries now and I will check what the full charge voltage is and get back to you. I appreciate your help.
     
    • Like Like x 1
  8. AzPlumber

    AzPlumber Vaping Master Verified Member ECF Veteran

    Aug 28, 2011
    Arizona
    Is the mosfet getting hot when powered?
     
    • Like Like x 1
  9. dc99

    dc99 Ultra Member Verified Member ECF Veteran

    Aug 17, 2014
    earth
    What mosfet are you using? Most of mine drop to around 7.5 at first on a fully charged set of batteries. It will sound dumb but check all you solder connections for good connection.
     
    • Like Like x 1
  10. VapeRock

    VapeRock Full Member

    Sep 15, 2015
    Okay just charged my LG DBHE4 they are new. I'm at 8.3V.yea
    yes it is getting hot
     
    • Like Like x 1
  11. VapeRock

    VapeRock Full Member

    Sep 15, 2015
     
  12. VapeRock

    VapeRock Full Member

    Sep 15, 2015
     

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  13. VapeRock

    VapeRock Full Member

    Sep 15, 2015
    Okay... I a noob at this haha. When answering a question can I reply to one person and everyone will see it, or do I respond and answer each question to its own?if that makes sense.
     
  14. Mooch

    Mooch Electron Wrangler Verified Member ECF Veteran

    Supporting member
    May 13, 2015
    No disrespect intended but that's a very bad MOSFET to use. The Rds-on spec is 0.2 ohms. Compare that to the popular IRLB3034 MOSFET which has a Rds-on of 0.002 ohms. This Rds-on number is its internal resistance and determines how hot it gets when current passes through it.

    You can probably only run about 3A through that NTE2390 before it gets hot enough to burn out.
     
    • Like Like x 1
  15. Mooch

    Mooch Electron Wrangler Verified Member ECF Veteran

    Supporting member
    May 13, 2015
    Not sure if I understand but everyone can read each reply to any person. You could just do one post with multiple replies on its own paragraph. Just start each with the person's name with a "@" in front of it. You'll see a box popup with names you can pick from. Pick the right name and that creates an alert to the person so they know you have posted something with their name in it.

    For example... @VapeRock
     
    • Like Like x 1
  16. VapeRock

    VapeRock Full Member

    Sep 15, 2015
    Thanks for letting me know. This is my first build and I would like to make it as safe as possible. I'll get that switched out. Thanks again
     
    • Like Like x 1
  17. Mooch

    Mooch Electron Wrangler Verified Member ECF Veteran

    Supporting member
    May 13, 2015
    The IRLB3034 is good to about 25A max. Parallel them for higher current.
     
    • Like Like x 1
  18. VapeRock

    VapeRock Full Member

    Sep 15, 2015
    Okay cool, I'll pick up that MOSFET and switch over to parallel. I'll let you know how it reads after. Going to order them so I'll give it a shot when it come in. Thank you all, it's been a big help.
     
    • Like Like x 1
  19. dc99

    dc99 Ultra Member Verified Member ECF Veteran

    Aug 17, 2014
    earth
    • Like Like x 2
  20. VapeRock

    VapeRock Full Member

    Sep 15, 2015
    Good looking out, that would go between the 510 and switch right? If anyone has a wiring diagram for series and parallel with volt meter that would be great. I think I have it down but would like to double check. Thank you
     
    • Like Like x 1
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