On Friday 03 October 2014 11:38:26 Billy Huddleston did opine And Gene did reply: > Hey Guys, > > I have a D525MW setup.. using pport and I do use the PC's 12v supply to > switch some relays.. and to handle a charge pump which has a > integrated 5v relay If memory serves me. I'm doing away with the > pport and moving to 5i25 + 7i76 setup.. and was planning on using the > PC's 12v supply again.. but, after reading this.. I'm a tad concerned. > Question.. Does the flyback diode have to be placed at the coils? or > can one be placed at the supply, in front of all the relays? I'm be > using DIN style relays.. or will the 7i76 handle that as the 12v from > the PC will be used as field power ? > > Thanks, Billy
Short answer is no, and so is the long answer. Speaking as the CET I am: Those diodes need to be as close to the coil as physically possible, right across the coil terminals or located on the lines on the pcb going to the terminals. for best response time considerations. Not beyind the coil, but between the coiul and its drive. Generally a 1n914 is sufficient for small coils, maybe a generic 1N4000 family for bigger coils, but if you can find something faster than a 1N4000 series, the rest of the circuit will applaud you. Schotkey would be even better as long as the normally applied coil voltage is within the schotkeys reverse ratings. > > Wow.. I really didn't think about this. > > On 10/03/2014 03:44 AM, Erik Christiansen wrote: > > On 02.10.14 10:04, Dave Cole wrote: > >>>> I used 12V from PC for 7i76 field power (is it wrong?). > >> > >> In general Yes, but I have done it before to power external 12 volt > >> devices. However, you should really use a separate power supply for > >> field power. If you have a switch turning a relay or coil on and > >> off that is connected to the 12 volt supply and you open the > >> switch; The collapsing magnetic field in the relay will spike the > >> power supply as the switch opens. (Think ignition coil.) You can > >> get around that by putting diodes on your relay coils, but miss one > >> diode and you may still take out your PC. > > > > On the (Ford) Falcon, model XD, the prototype LCD clocks were > > destroyed by the back EMF from switching off the relays on the > > ignition switch's "Accessories" line. How much back EMF? A bit over > > minus 1000 volts! As a supplier, we had no way to convince them to > > put flywheel diodes across the relay coils, so had to tweak the > > design of our nominally 12 Vdc electronic clock to handle the 1 kv. > > > > Separate power supplies for electronics and inductive loads is the > > only way I'm prepared to go, after that lesson. > > > > Erik Cheers, Gene Heskett -- "There are four boxes to be used in defense of liberty: soap, ballot, jury, and ammo. Please use in that order." -Ed Howdershelt (Author) Genes Web page <http://geneslinuxbox.net:6309/gene> US V Castleman, SCOTUS, Mar 2014 is grounds for Impeaching SCOTUS ------------------------------------------------------------------------------ Meet PCI DSS 3.0 Compliance Requirements with EventLog Analyzer Achieve PCI DSS 3.0 Compliant Status with Out-of-the-box PCI DSS Reports Are you Audit-Ready for PCI DSS 3.0 Compliance? Download White paper Comply to PCI DSS 3.0 Requirement 10 and 11.5 with EventLog Analyzer http://pubads.g.doubleclick.net/gampad/clk?id=154622311&iu=/4140/ostg.clktrk _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
