The best practice is to put a diode right at the device that can cause the voltage spike. I usually use socket-ed relays and I put the diode across the coil screw terminals. The same with motor contactors and hydraulic/pneumatic solenoid valve coils that are driven by DC circuits.
You can buy relays that have a built in suppressor diodes but they are cheap and easy to add. The last batch I bought was from Digikey and I think they were $.20 each or less. Dave On 10/3/2014 11:38 AM, Billy Huddleston wrote: > 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 > > 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 >> --- This email is free from viruses and malware because avast! Antivirus protection is active. http://www.avast.com ------------------------------------------------------------------------------ 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 [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
