Spehro, You made my mistake obvious. I mis-calculated I2R losses to be 1/2 watt! Now referring to http://www.rencousa.com/wiretable.htm I see that the 12AWG wire already in the system will be perfect for what I'm trying to accomplish! Thank you so much!! Andy Spehro Pefhany on 03/27/2000 10:21:41 AM Please respond to pic microcontroller discussion list To: PICLIST@MITVMA.MIT.EDU cc: (bcc: Andrew Kunz/TDI_NOTES) Subject: Re: [OT] Resistance At 01:52 PM 3/27/00 +0100, you wrote: > You could use a block of aluminium alloy which would certainly be >much lighter, but the temp co. wouldn't be very good. Mike -----Original The main problem is that his power dissipation will be 50W to 5W depending on the resistance, so that requires something physically fairly large, as you say, to keep it from getting too hot. At the lower end of the scale, 5W isn't too bad if not much accuracy is required, and/or if a heatsink surface is available. Maganin has a relative resistivity of 26, tempco is about 20ppm/K IIRC Brass has a relative resistivity of 3.9, tempco is about terrible, about 2000ppm/K Constantan has a relative resistivity of 28.45, tempco is about 200ppm/K The above resistivities are relative to copper at 1.72 E-6 ohm-cm Assume you have a 6 mm diameter wire of maganin (strip would be better), to get 0.0005 ohm would require: L = 0.0005 * (.3 * .3 * 3.141)/(26 * 1.72E-6) = 3.2 cm (If I didn't make a mistake!) That has a volume of 0.9 cm^3 , specific gravity is about 8, so weight should be about 7 grams. I'll leave working out the temperature rise of a 6mm diameter x 32 mm rod dissipating 5W as a (necessary) exercise. It will get rather hot without heatsinking, I think. Hope this helps. Best regards, =-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-= Spehro Pefhany --"it's the network..." "The Journey is the reward" speff@interlog.com Info for manufacturers: http://www.trexon.com Embedded software/hardware/analog Info for designers: http://www.speff.com =-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=