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Why does it need to be TO-220? 3W wire shunt is about 50 cents.


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
>
> ##################################################################################
>
>

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<div dir=3D"ltr">Why does it need to be TO-220? 3W wire shunt is about 50 c=
ents. <br></div><div class=3D"gmail_extra"><br><br><div class=3D"gmail_quot=
e">On Tue, Apr 15, 2014 at 2:54 PM, Richard Bown <span dir=3D"ltr">&lt;<a h=
ref=3D"mailto:richard AT g8jvm DOT com" target=3D"_blank">richard AT g8jvm DOT com</a>&gt=
;</span> wrote:<br>
<blockquote class=3D"gmail_quote" style=3D"margin:0 0 0 .8ex;border-left:1p=
x #ccc solid;padding-left:1ex">Hi,<br>
I thinking of playing with the LTC1645 using its for over current shut<br>
down,<br>
it requires only 50mV across a shunt resistor to trip, at 10A thats<br>
5milli ohm.<br>
And those resistors in TO-220 packages are expensive, so I was thinking<br>
why use a length of wide track, needs to wide as handling up to 10A .<br>
Are there any tables to give track resistance if the thickness , width<br>
and length are known.<br>
In practice its better to go for a lossier track and tap the voltage<br>
across it with a potential divider, so target around 10 - 20 milli ohms,<br=
>
cant use anything bigger as the board will get hot, 10A through 0.02 R<br>
is 2 W, so better around 0.01 R<br>
<br>
Thanks<br>
<span class=3D"HOEnZb"><font color=3D"#888888"><br>
--<br>
--<br>
Best wishes /73<br>
Richard Bown<br>
Email : <a href=3D"mailto:richard AT g8jvm DOT com">richard AT g8jvm DOT com</a><br>
HTTP =A0: =A0<a href=3D"http://www.g8jvm.com" target=3D"_blank">http://www.=
g8jvm.com</a><br>
nil carborundum a illegitemis<br>
###########################################################################=
#######<br>
Ham Call G8JVM . OS Linux Mint 16 x86_64 on a Dell Inspiron N5030 laptop<br=
>
Maidenhead QRA: IO82SP38, LAT. 52 39.720&#39; N LONG. 2 28.171 W<br>
QRV VHF 6mtrs 200W, 4 mtrs 150W, 2mtrs 400W, 70cms 200W<br>
Microwave 23 cms 140W, 13 cms 100W, 6 cms 0W &amp; 3cms 5W<br>
###########################################################################=
#######<br>
<br>
</font></span></blockquote></div><br></div>

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