tag:blogger.com,1999:blog-2807403883562053852.post193872881214155893..comments2024-03-27T08:40:31.785-06:00Comments on Clayton Cramer.: Today's Electrical Engineering QuestionClayton Cramerhttp://www.blogger.com/profile/03258083387204776812noreply@blogger.comBlogger5125tag:blogger.com,1999:blog-2807403883562053852.post-75447899396760681422019-11-01T21:17:31.123-06:002019-11-01T21:17:31.123-06:00Short and wide has low resistance. Long and skinny...Short and wide has low resistance. Long and skinny has high resistance. While a simple rectangular sheet will have low resistance, you can get high resistance by cutting channels so the sheet becomes a long skinny trace that zig zags back and forthWhttps://www.blogger.com/profile/16464836634888906831noreply@blogger.comtag:blogger.com,1999:blog-2807403883562053852.post-35089654166717159922019-10-31T09:42:25.097-06:002019-10-31T09:42:25.097-06:00The point is that you need high resistance (and th...The point is that you need high resistance (and thus high bulk resistance) if you don't want to have to use insane amperage for a large conductor. Steel is way too good a conductor.<br /><br />To do what you want, you'd have to cut that steel down to a small wire - maybe a millimeter diameter (I'm too lazy to do the math).<br /><br />Your power in is P = E*I ( watts = amps * volts). Your amps is I = E / R ( amps = volts / ohms ).<br /><br />For most electrical power calculations, those two formulas will let you figure out anything you want, perhaps with a bit of trivial algebra. You can combine those and get P = E * E / R;<br /><br />E means electromotive force, which is measured in volts - i.e. the voltage.StormCchaserhttps://www.blogger.com/profile/02998174514362089471noreply@blogger.comtag:blogger.com,1999:blog-2807403883562053852.post-48525782471478329632019-10-31T07:42:11.844-06:002019-10-31T07:42:11.844-06:00Nichrome has a fairly high resistivity. It can als...Nichrome has a fairly high resistivity. It can also tolerate very high temperatures. That is also why heating elements have long, thin wires. Resistance increases linearly with the length and decreases linearly with cross-sectional area.<br /><br />Best of luck!Wayne Johnsonhttps://www.blogger.com/profile/07652553584958469329noreply@blogger.comtag:blogger.com,1999:blog-2807403883562053852.post-79968877542999296222019-10-31T07:31:21.601-06:002019-10-31T07:31:21.601-06:00So nichrome is used for heating because steel does...So nichrome is used for heating because steel does not produce enough heat until you get to very high amperage. To produce a high heat with durability (like cars passing over it) I would be better using nichrome under an electrically insulating sheet with the steel on top.Clayton Cramerhttps://www.blogger.com/profile/03258083387204776812noreply@blogger.comtag:blogger.com,1999:blog-2807403883562053852.post-81143522200612229282019-10-31T07:16:07.188-06:002019-10-31T07:16:07.188-06:00Clayton,
Those units are correct. Resistance of a...Clayton,<br /><br />Those units are correct. Resistance of a piece of metal is resistivity times length divided by cross-sectional area. All of the length units cancel, leaving only ohms.<br /><br />Based on <a href="http://www.endmemo.com/physics/resistance.php" rel="nofollow">this</a> resistance calculator, you are looking at about 0.4 milli-ohms for a piece of steel that size. You cannot put 12V into that sheet of steel and get 100W. Ohm's law states that for a fixed voltage, the power is P=V^2/R. Based on this, you would get a power of 360 kW for a 12V source providing 30,000 amps (think about welding for an example).<br /><br />To get 100W from that piece of steel, you need a power supply to deliver 500 amps at 0.2 volts (again, think of welding). At that resistance, the quality of your connections becomes an ENORMOUS problem. If each of four connections has only .1 milli-ohm of resistance, ONE HALF of your power is going into your connections.<br /><br />Honestly, this doesn't sound like a winning plan.Wayne Johnsonhttps://www.blogger.com/profile/07652553584958469329noreply@blogger.com