Increase PCB track current capacity?

Discussion in 'General Electronics Chat' started by Crispin, Aug 8, 2011.

  1. Crispin

    Thread Starter Member

    Jul 4, 2011
    88
    2
    Hi Folks,

    One two very short tracks on my PCB I need to carry 25A continuously between battery and charger. According to the calculator I have, for a normal PCB (1oz copper) , I have to have a track width of 25mm.
    The track is very short, less than 5-6CM between posts.
    Is it considered “dirty” if I reduce the size slightly and put a large amount of solder along the track or solder a solid copper wire along the length of the track? If I had a 2.5mm solid strand along the length and up close to the spade post, the wire would be doing most of the work.
    Is this a real “dear gawd man what were you thinking!” or is it ok?


    Thanks
    Crispin
     
  2. kubeek

    AAC Fanatic!

    Sep 20, 2005
    4,670
    804
    I often soldered thick solid wire along traces and never had a problem with it.

    Btw 5-6cm is no short distance, 5-6mm is.
     
  3. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
    4,769
    969
    Its the width of that trace should be 25mm.. Not the length. They length is not part of the calculator.
    Also those calculators are based on a specific heat rise. If you can tolerate a higher temp rise you can decrease the width. A typical circuit board has a temperature rating of 105 or 130 deg C continuous. If your ambient is 25 deg C then you can easily tolerate a 50+ deg C temp rise.

    It is okay to just solder wire on the trace though for a one-off job.. I would NEVER do it for a real product but its fine for a DIY hobby project. Also traces don't have just just be a straight boring line.. I have made many intricate patterns to increase current capability. Neck down in some areas.. and increase over the required width in others..
     
  4. Crispin

    Thread Starter Member

    Jul 4, 2011
    88
    2
    Thanks folks,

    I've done it in the past on veroboard, but was not sure if there is some reason I should not do it on a real project.

    I don't think I can have much of a rise in temp as it will be in a small box so might get a bit uncomfortable in there...
     
  5. #12

    Expert

    Nov 30, 2010
    16,261
    6,770
    Add a wire, load the surface with solder, whatever. Maybe a nicer way would be to drill some holes and put jumper wires in parallel with the hot trace.

    25 amps is not a small amount of current. In American house wiring, that would require number 8 wire! There are calculators somewhere that calculate the heat generated on a circuit board. Personally, I over-do all my designs. You have my permission to get excessive today.

    and remember, two equal diameter wires in parallel results in 3 steps of American Wire Gauge numbering. Two 12 gauge wires in parallel is as good as a 9 gauge wire.
     
  6. SgtWookie

    Expert

    Jul 17, 2007
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    1,728
    Solder has about 5 times the resistance of copper, so adding more copper is going to help a lot more than adding solder. Try to have the copper in contact with the entire length of the trace when you are soldering it down.
     
  7. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
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    One-off its fine. In a real product that you intend to sell and make many of its a horrible solution as "properly" bonding a piece of wire along a trace is labor intensive.
     
  8. tom66

    Senior Member

    May 9, 2009
    2,613
    213
    On many PCBs I see the high current traces are plated. This is done by cutting a hole in the soldermask around these traces; the fab will then plate the bare copper. I am not sure if this helps with either heatsinking (because it is often not continuous traces of plating, usually 50% or so, in some pattern) or if it is actually used to enhance current carrying capability.
     
  9. yakuut

    New Member

    Sep 21, 2009
    7
    0
    Are you designing a PCB for your project?? If yes, then you can have identical solid copper regions on both the layers of PCB so that the current gets distributed equally.Make sure you make it plated through area when using SMD FETs.If they are thru hole the layers will be connected while soldering..
     
  10. THE_RB

    AAC Fanatic!

    Feb 11, 2008
    5,435
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    What!?

    I just checked using PCBtemp.exe, with a standard 1oz copper board at 25 amps a 0.5" thick trace has 1milliohm per inch of length. That's without any solder added.

    At 2oz copper thickness a 0.3" wide track has under 1 milliohm per inch.

    Either of those would be fine with a bit of solder on top, or if you are only making one just solder a copper wire on top of the track. There's no need for a track 1" wide!!
     
  11. Crispin

    Thread Starter Member

    Jul 4, 2011
    88
    2
    thanks guys,

    It is a once off project I am busy with, having a play last night with the PCB design and I should be ok with wide tracks, I'll still stick a piece of 2/2.5mm copper wire down track (noted SgtWookie about keeping it in contact) as well.

    It's a battery charger so 25A is the tops it will do but does it for about 3-4 hours initially then backs off for the rest of the day.

    I'll check PCBtemp.exe and compare to the calculator I have.:confused:

    Cheers,
    Crispin
     
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