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Tue, 15 Apr 2014 12:25:55 -0700 (PDT) | |
In-Reply-To: | <20140415195425.37808583@richard-laptop> |
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Date: | Tue, 15 Apr 2014 15:25:55 -0400 |
Message-ID: | <CAOFvGD7y3a85_8O3HVuMhDe=kQfY+S1ADUBbtS+tYU3q47TSqA@mail.gmail.com> |
Subject: | Re: [geda-user] printed meter shunts |
From: | Jason White <whitewaterssoftwareinfo AT gmail DOT com> |
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A quick Google for "PCB trace resistance calculator" shows many nifty calculators like http://circuitcalculator.com/wordpress/2006/01/24/trace-resistance-calculator. But that does not take into account temperature rise form the high currents, so a better calculator exists in this case the author called it a "PCB Trace Width Calculator." It follows the IPC-2221 technical standard for calculating current capacities of PCB traces. For your task this will should be sufficent as it gives both the required trace width and trace resistance for a specific current. If it is not accurate enough I would recommend taking the data directly IPC-2221 to figure it out mathematically. Make sure to leave room for a >10% manufacturing tolerance in copper thickness (and thus resistance). I have a feeling that a *lot* of trimming will be required. Make sure the trace is wide enough so that is doesn't heat up significantly as resistance changes with temperature http://circuitcalculator.com/wordpress/2006/01/31/pcb-trace-width-calculator/ Good Luck! Jason White On Tue, Apr 15, 2014 at 2:54 PM, Richard Bown <richard AT g8jvm DOT com> wrote: > Hi, > I thinking of playing with the LTC1645 using its for over current shut > down, > it requires only 50mV across a shunt resistor to trip, at 10A thats > 5milli ohm. > And those resistors in TO-220 packages are expensive, so I was thinking > why use a length of wide track, needs to wide as handling up to 10A . > Are there any tables to give track resistance if the thickness , width > and length are known. > In practice its better to go for a lossier track and tap the voltage > across it with a potential divider, so target around 10 - 20 milli ohms, > cant use anything bigger as the board will get hot, 10A through 0.02 R > is 2 W, so better around 0.01 R > > Thanks > > -- > -- > Best wishes /73 > Richard Bown > Email : richard AT g8jvm DOT com > HTTP : http://www.g8jvm.com > nil carborundum a illegitemis > ################################################################################## > Ham Call G8JVM . OS Linux Mint 16 x86_64 on a Dell Inspiron N5030 laptop > Maidenhead QRA: IO82SP38, LAT. 52 39.720' N LONG. 2 28.171 W > QRV VHF 6mtrs 200W, 4 mtrs 150W, 2mtrs 400W, 70cms 200W > Microwave 23 cms 140W, 13 cms 100W, 6 cms 0W & 3cms 5W > ################################################################################## > -- Jason White
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