X-Authentication-Warning: delorie.com: mail set sender to geda-user-bounces using -f X-Recipient: geda-user AT delorie DOT com Date: Tue, 15 Apr 2014 21:31:02 +0100 From: Richard Bown To: geda-user AT delorie DOT com Subject: Re: [geda-user] printed meter shunts Message-ID: <20140415213102.7714447a@richard-laptop> In-Reply-To: References: <20140415195425 DOT 37808583 AT richard-laptop> Organization: Ham radio X-Mailer: Claws Mail 3.8.1 (GTK+ 2.24.20; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-Provags-ID: V02:K0:v9sLodJlt7BmWgISwukCYzzGOgu9XYjBtqIQFfZ59Zq mHeD6eQS+9DZHlf9y7eEgkqis+pUqTcA7HCRCMEA2v6IQmLB1Y 4op79Qx/YNrlMAk+Mk1eqgzKr3Pi6QKoN9IYUVYwzN/tRRYMWx nsgArq5gsHZ5jNZlF7ppRqZffzqtKlK1VIhgDIEOv/MsS+uIOC W1/k3A3Eo1BaHpSheH5t80M8AIOVELLOathDzWDpKDAkIdog07 Kfelz+fxCs562mc5CTvFQBaGT3gS8Gpu0oL7zPoAtAdM/tCZjr QC6TL6R8xoQbeIdQBdcDc4F7mEhYAb2ssT+zMRvUCf52SazIYK XG9nUxaShsrwHl8gTyyUSm7sWapHT3W3sEDjnz08P Reply-To: geda-user AT delorie DOT com Errors-To: nobody AT delorie DOT com X-Mailing-List: geda-user AT delorie DOT com X-Unsubscribes-To: listserv AT delorie DOT com Precedence: bulk On Tue, 15 Apr 2014 15:20:54 -0400 Nathan Stewart 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 > 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 ##################################################################################