tag:blogger.com,1999:blog-7590176649168185428.post5396264530765491192..comments2024-03-29T07:34:28.586-04:00Comments on SolderSmoke Daily News: Reverse Polarity Protection Bill Mearahttp://www.blogger.com/profile/07662500663603350847noreply@blogger.comBlogger3125tag:blogger.com,1999:blog-7590176649168185428.post-77930118275083468052016-11-15T11:31:44.148-05:002016-11-15T11:31:44.148-05:00Isn’t D7 already across the 12 volt power supply?Isn’t D7 already across the 12 volt power supply?Doug N8PYNhttps://www.qrz.com/db/N8PYNnoreply@blogger.comtag:blogger.com,1999:blog-7590176649168185428.post-20133417340696481002016-11-04T16:13:39.924-04:002016-11-04T16:13:39.924-04:00I have long used the reverse-biased diode across t...I have long used the reverse-biased diode across the supply in conjunction with series-wired PTC (self-resetting) fuses. These devices look like a disk ceramic capacitor (usually yellow, can be round or square/rectangular), are available with current ratings from a few 10s of mA to 10s of amps, with available maximum voltage ratings to 60-75 volts - and they are pretty cheap! Best of all once the "oops" is corrected, life goes on without incident.<br /><br />If one accidentally connects the power leads backwards (I have!) then *nothing* obvious happens other than the device getting hot (100C or so, maybe) and the current drops off to a "safe" level.<br /><br />In some cases - such as where it might be possible that ground currents could flow (say, some mobile installations) then I may even put one in the ground lead. <br /><br />If, for some reason, these don't interest you then I might draw your attention to this GQRP article:<br /><br />http://www.gqrp.com/technical12.htm<br /><br />This describes a FET-based "lossless diode" approach that can work in many situations: It will even work with N-channel FETs if the negative power source is isolated from the load.<br /><br />73<br />KA7OEIhttps://www.blogger.com/profile/01153508130273704727noreply@blogger.comtag:blogger.com,1999:blog-7590176649168185428.post-75209867925016127222016-11-04T11:23:00.871-04:002016-11-04T11:23:00.871-04:00The only possible problem with this method, is tha...The only possible problem with this method, is that some solid state devices can be damaged faster than the fuse can blow. I prefer to just add a large diode in series with the power lead. You loose a little voltage to the unit because of the voltage drop across the diode, but it offers better protection. I usually use a schottky diode because of its lower voltage drop.DuWaynehttps://www.blogger.com/profile/11286645084920270476noreply@blogger.com