Mail Archives: geda-user/2014/04/15/16:31:18
On Tue, 15 Apr 2014 15:20:54 -0400
Nathan Stewart <therealnathanstewart AT gmail DOT com> wrote:
> Why does it need to be TO-220? 3W wire shunt is about 50 cents.
Have you tried measuring 0.005 Ohm with shunt wire ?
also its round, whereas the legs of a TO-220 device are flat, so you
can get a much better connection to a track, NOT thru hole, so the
surface area of the contact is higher, and the joint resistance is
lower.
Handling 10A on a track is difficult if you allow for fault conditions,
the LTC1645 or maybe the LTC4356-3 are fast at shutting down under
surge conditions , but in the few microseconds it takes to shut down ,
up to 200 A may flow, so joins must be low resistance otherwise they get
hot and the track will lift , I guess the trick is to get the track to
flex but not breakdown the adhesion to the board.
>
>
> 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
##################################################################################
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