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 -- The right half of the brain controls the left half of the body. This means that only left handed people are in their right mind. ------------------------------------------------------------------------------ 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
