300amp PCB continuous

Discussion in 'General Electronics Chat' started by trdracing1, Sep 23, 2016.

  1. trdracing1

    Thread Starter New Member

    Sep 23, 2016
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    Hi all,


    im designing a battery shut off switch using mosfets in a pack size of 2.5in width and 5in length i have in mind 4 layer pcb with 2 inner power plane one power plane connected to drain of the mosfet and the second power plain connected to source of the mosfet each power plane is 15 oz of copper and the external layer (Top.Bottom) 4 oz copper. is this sufficient for 300amp continuous with these copper sizes
     
  2. kubeek

    AAC Fanatic!

    Sep 20, 2005
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    I am not sure where do you plan to get a pcb with 15oz copper, that is roughly half a milimeter. Typically you would do such these connections for such current using a sheet of copper instead of a pcb, or use transistors that are suited to being connected to cables instead of a pcb.
     
  3. jpanhalt

    AAC Fanatic!

    Jan 18, 2008
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    Temperature it the limiting factor. It seems counter intuitive to insulate the power layers inside a board. I constructed a high current motor drive using mosfets soldered to 0.025 copper strips (about 0.6 mm) on a heat sink. No problems over the years, but it is to continuous duty.

    John
     
  4. Kermit2

    AAC Fanatic!

    Feb 5, 2010
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    It is poor design to rely on PCB traces for anything over 50 amp continuous duty, unless the runs are VERY short and increased in size with suitable wire soldered in place. Even at or near the 50 amp range reinforced traces using soldered copper wire are desired.
    Fiberglass board has this nasty habit of charring when temperature reaches 250 centigrade and above. The resulting remnants then become capabe of attracting moisture and it just goes all to hell from there.
    Make your design to include well heatsinked active devices and use oversized wire to carry high currents to minimize heating.

    Avoid mechanical connections in high current carriers by any means necessary.
     
  5. tcmtech

    Well-Known Member

    Nov 4, 2013
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    For a 300 amp load on what I am assuming is a mid sized brick module device use normal copper cable with copper lugs and bolt it directly to the device. You will be time and money ahead that way.
     
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  6. trdracing1

    Thread Starter New Member

    Sep 23, 2016
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    i dont quite understand that when you say that... Most PCB manufacturer are capable of producing board with individual copper layer any thickness required for any application epectec is one manufacturer thats capable. With that being said my application is automotive basically im going to have a custom battery terminal it will go on the positive side of the battery the PCB itself will attach to the battery terminal and then a power clamp Terminal pressed in to feed power going out to fusebox,starter,ect.. Im using IPLU300N04S4-R8 mosfet (6) of them and one mosfet dedicated for engine starter and one more for reverse battery polarity my questions are. (i do not want to solder wire to assist my pcb)

    1.Can my 15oz copper each power plane support this 300amp current instead of trace can i use polygon pour on top and bottom to cool my internal planes while i use 2mm vias to link layers together ill only use trace to link vias and mosfet driver?
    2.My Ambient temp going to around 130F and rise of 20F cause its going in the engine bay can my board survive this temp constantly?
    3.Can Polygon pour be used on my top and bottom layer be used to assist my inner layer but if i link them with microvias 2mm hole size on my yes i know quite big?
    3.How many Layer you guys think i need to support this massive project 4 layers,6 layers,ect?
    4.Can i used top layer (3oz copper) and first power plane(15oz copper) link them with vias connect that to drain of the moset while last power plane and bottom layer link them with vias will this be a better option?
    5. what can i do to maintain temp with out heatsinks?
     
    Last edited: Sep 23, 2016
  7. tcmtech

    Well-Known Member

    Nov 4, 2013
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    Why!? What do you imagine you could possibly gain from such s ridiculous concept? o_O

    Putting the circuit board directly on the battery is going to destroy in no time simply due to the unavoidable sulfur exposure. Sulfur loves copper and there is no ways to keep it out of a direct battery terminal connection.

    Also if your solid state starter solenoid shorts out, which with a 40 volt rating and sulfur vapor exposure in a hot engine compartment environment it's almost guaranteed to do so in short order,

    Most likely it would short while driving putting it in an unloaded state where the vehicle alternator can keep it spinning until it either goes to bits or burns down assuming it doesn't take your alternator and wiring with it from excessive overload plus there is the high chance it will be trying engage the ring gear and would be chewing that to bits while you drive as well being it will be constantly trying to mesh while both gears are already spinning.

    Just because something can be done with all solid state components does not make it a better or even good idea. :oops:
     
    Last edited: Sep 23, 2016
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  8. GopherT

    AAC Fanatic!

    Nov 23, 2012
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    Rather than etching, It would be easier to cut 15 ounce copper with a band saw or laser and glue it to a piece of fr4.
     
  9. AnalogKid

    Distinguished Member

    Aug 1, 2013
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    No, they aren't. 15 oz thickness presents major plating and etching challenges. Plus, if the high current traces are on internal layers, all of that current has to get there through vias. I did a VME backplane with 1000 A of 5 V, 50 A x 20 slots on 0.8" pitch. For Vcc and GND distribution we machined copper and aluminum plates to augment the multi-layers of 4 oz copper. The maximum voltage difference between any two slots was less than 15 mV, but it took some effort to get there.
    ? ? ? ? ?

    ak
     
  10. trdracing1

    Thread Starter New Member

    Sep 23, 2016
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    Infineon already prototype a smart battery shut off using these mosfet with zero issues only difference with my design and there is mines is beefed up on the component side...;) also if anything shorts out i have reverse battery polarity on the circuit which will PREVENT a disaster from even occurring . Also corrosive elements and moisture must be present for creep corrosion to occur (Sulfur) my board will be protected waterproof also my surface finish will be immersion gold with high temp resin poured over it so basically the board will be sealed.



    CAN 300amp Be Achieveable through thick 15 oz on the planes and 4-5 oz copper on top and bottom total cooper oz used on the board is 40oz so your telling me this still not enough? I ask these questions cause im not the only one who want high current design so many others want the same but never ask the questions for clarity

    FYI i dont think this a ridiculous concept its achievable with the right steps and guide
     
  11. trdracing1

    Thread Starter New Member

    Sep 23, 2016
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    im not asking for handouts ive been around this forums 5 years it just i never joined because i never had questions to ask until now i believe this post will set clarity for true high current design for others
     
  12. #12

    Expert

    Nov 30, 2010
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    Lots of less than optimum designs are achievable with enough effort and expense. They are still less than optimum designs.
    We see lots of people who come here trying to re-invent something that has been done better and cheaper a million times before.
    A lot of them learn a better, cheaper, more reliable way to do it.
    You have the right to refuse those methods.
     
  13. trdracing1

    Thread Starter New Member

    Sep 23, 2016
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    i understand you 100%. i dont want to re-invent the wheel i just want my own electronic fuse which is this battery smart switch my problem is the pcb layout i understand layers and trace width and temp rise but can polygon pours replace trace width? can i have thermal vias and lots of microvias to link my layers? Alot of people say 15 oz of copper is hard to come by with pcb manufacturer but the true is it is not i can throw out some names right now epectec,amitroncorp,omegcircuits,4pcb,saturnelectronic all company i contacted that tell me 15 oz copper not a problem each layer.
     
  14. trdracing1

    Thread Starter New Member

    Sep 23, 2016
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  15. jpanhalt

    AAC Fanatic!

    Jan 18, 2008
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    Connecting the drain of your N-channel mosfets to the battery positive, as shown in your link, will complicate the gate driver. It will need to produce batter potential + gate voltage (10 V). What will your battery voltage be?

    John
     
  16. tcmtech

    Well-Known Member

    Nov 4, 2013
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    What does reverse polarity protection have to do with anything in the event of the the switching devices shorting out full on permanently?

    For that matter, why do you think you even need it? How often do you change batteries in your vehicle or jump start it and get the battery in backwards? o_O

    As for the gold plating guess again.
    Ever look at the gold plated battery connectors on high wattage audio systems? They corrode just like everything else. Slower than plated copper but they still corrode just the same. The sulfur compounds in the battery may not directly react with the gold but it does just fine at electrolytically dissolving pinholes in it to where it can then attack the underlying copper. :rolleyes:

    If it was me I Would be building it into its own box and attaching it remotely on a firewall or some location away from the battery like is done with any other vehicle primary electrical distribution point. There's a reason all manufactures of anything that uses large batteries try to design their systems to only have one large cable and single connector on a battery and all other components located away from the battery.


    Also Infineon has high levels of experience in analyzing the practicality of application, design and fabrication of their products. Pretty sure you don't given the questions being asked here and attitude regarding our numerous reason to doubt your design and overall point and purpose of your design.

    You can build it and no one here will try and stop you. Heck I am wanting you to build it now just see what possible levels and costs of damage this thing causes when it does fail. :D

    Just because something can be achieved doesn't mean it can be achieved as applicably practical and reliable as imagined. :oops:
     
    Last edited: Sep 24, 2016
  17. trdracing1

    Thread Starter New Member

    Sep 23, 2016
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    13.5v when vehicle on and 12.5v when off
     
  18. tcmtech

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    Nov 4, 2013
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    It should be around 14.4 when running unless you have done other 'improvements' to your electrical system. :rolleyes:
     
  19. nsaspook

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    Aug 27, 2009
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  20. trdracing1

    Thread Starter New Member

    Sep 23, 2016
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