DIY Box Unregulated Box Mod - 450W Build Log

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AzPlumber

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    A few questions

    What are you using to measure a resistance of .03?

    What happens if one mosfet fails at .03 ohms?

    What happens if one mosfet lags at .03 ohms?

    What happens if one battery fails at .03 ohms?

    What happens if one battery is weaker at .03 ohms?

    eta: 4.2 volts at .03 ohms is 140 amps and 588 watts
     
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    WKS01

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      The N-Channel Mosfets, in this build, can handle 375 watts max each - there are two in this build in parallel

      The maximum power dissipation is rated with additional heat sinks not the standalone package. At 123A and an RDSon of 0.001 ohm (due to parallel) each MOSFET needs to dissipate around 7.5W. Much more than the 2W or so the package can handle. Additionally 123A is double what the theoretical amp limit that parallel VTC5s can handle and is above the amp limit you should put through 12 AWG wire.
       
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      rhelton

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        I agree with WKS01, I am just learning about alot of that. BWoodruff I think you have a great build there everything looks top notch. Its really up to you what you build but just be safe and have fun. People think they have to build with heavy guage wire with super low ohm's and tailpipe their atty's to be cool at the vape shop in my neighborhood. I girl in her teens that goes in there took a trip to the hospital after her Flip came apart and cut her hand and burnt it some.

        I think your mod will be great, whats done so far is nice.

        Be safe
         
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        bwoodroof

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          I have fluke multimeters that can measure that low
          If a Mosfet fails at .03 ohms then you would have magic smoke rolling out of your mod and possible loud pop.
          If a Mosfet is slower than the other one, then you are gonna get a one mosfet that will get warmer than another, but we are talking in ms, it wont make that much difference.
          If one battery fails then you will not get that high of wattage, because of voltage drop, and you will strain the other battery (downside to any dual battery unreg box) VTC5s are rated for 150A @ >3 Sec (Dangerous Load, but i do not know anyone who could vape @450W)
          And when you pull 450w of current the batteries would stay at 4.2V i measured at 3.7 to account for voltage drop under load

          Basically this box is capable of delivering high power. It is over built I don't plan on using it at is limits
           
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          WKS01

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            Two VTC5s can handle the 123A (80 amp for 8 sec per battery). 12AWG wire can handle that amount of current @ 4 ~6" (with 3.5% voltage drop) if it were feet it would be different. I am aware of the thermal limits of MOSFETS.

            No, VTCs should not be used above their maximum continuous discharge rating of 30A. The chart everyone refers to does not mean what they think it means. Notice the chart is in a section talking about an over protection circuit. The chart is not referring to an unprotected single cell, but rather when the cells are being used as they were manufactured for, in a pack with protection circuitry. With the lack of information by Sony and that clip from that data sheet that does not truly explain anything, I would not go over the continuous maximum discharge for the battery. Personally I would not use over 80-90A with 12AWG. Also, if you are aware of the thermal limits of MOSFETs you would not be attempting to dissipate 7-8W in a package that can handle ~2W and risking having a MOSFET fail. They usually fail closed by the way.
             

            bwoodroof

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              What are you basing your opinion on about wiring standards??? 14 AWG is safe for that amount of current, I just chose 12 because there is less loss in it. Have you personally load tested these batteries? And seriously, do you possibly think that I am going to vape at 450?
               
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              bwoodroof

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                Check me on this WSK01

                RDS (each) = 0.0017 ohms
                RDS (2 in Parallel) = 0.00085 ohms
                RDS (4 in Parallel) = 0.000425 ohms

                I = 123 A
                I^2 = 15129 A

                P = I^2 * RDS

                P(2 in Parallel) = 15129*0.00085 = 12.85W (6.43 Watts Per Mosfet)
                P(4 in Parallel) = 15129*0.000425 = 6.43W (1.61 Watts Per Mosfet)
                 

                bwoodroof

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                  The Mosfet's "on" resistance (Rds) will increase as it's temperature rises so parallel Mosfets will "self balance". If you have four FETs in parallel, the one that conducts the most current will also be the one that runs the hottest; therefore it's Rds(on) resistance will rise and the other three FETs will conduct more current and balance the current load.
                   
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