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Date: Tue, 15 Apr 2014 21:13:39 +0100
From: Richard Bown <richard AT g8jvm DOT com>
To: geda-user AT delorie DOT com
Subject: Re: [geda-user] printed meter shunts
Message-ID: <20140415211339.6003d054@richard-laptop>
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On Tue, 15 Apr 2014 15:25:55 -0400
Jason White <whitewaterssoftwareinfo AT gmail DOT com> wrote:

> 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



Thanks Jason
Luckily as long as I can get 50mV drop across it with 10A flowing , I
can use a potential divider , ( two resistors ) to get the right
results..
> 
> 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
> > ##################################################################################
> >
> 
> 
> 



-- 
-- 
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
##################################################################################