If someone could come up with a replacement for the relay, that would be great. Need to actually switch between the 2 batteries OR'ed together and the 12 VDC power supply. Thinking FET's or something, but, although LOGIC, TTL, some OP-AMP design and Ohm's law is my level, my expertice is more toward structural concrete. ~) Carl Denk wrote: > I wish I could do that, but The battery voltages are fixed at what they > are, and the maximum voltages of the other parts is fixed too. Looks > like the next higher voltage supply is 15 volts, that's a little higher > than I would like to operate, plus the batteries float at 13.8 volts. > That relay is quite beefy, with 10 amp contacts, and if the move maybe a > dozen times a year, that would be a lot, plus it could be put on > maintenance schedule to replace every few years. The whole system is > based on the Kohler engine electrical which is 12 volts (nominal), then > all the sensors (pressure, voltages, temperatures) are selected and > calibrated based on the 12 volts. > > What about adding a diode across the contacts with the capacitor ? > > Dwayne Reid wrote: > >> I think that I'm still gonna beat the same drum. >> >> Eliminate the relay that switches the PLC power line. Use a diode >> array of 3 diodes so that whichever voltage is highest feeds the PLC >> power input. >> >> Ensure that the AC power supply is higher than the float voltage >> present on the batteries when fully charged. No relay needed. >> >> Then try it and see how you make out. >> >> dwayne >> >> PS: the only problem with adding that large capacitor after the relay >> contacts is inrush current eventually damaging the relay >> contacts. But I still don't see the need for the relay and think >> that eliminating it will get rid of your problem. >> >> dwayne >> >> At 01:06 PM 4/10/2007, Carl Denk wrote: >> >> >> >>> Powered from the non-generator engine battery, all OK. If it's powered >>> >>> >> >from the engine's battery, upon starter energizing, voltage is pulled >> >> >>> down to 9 volts, and PLC resets, had that issue some time ago, and added >>> a second battery (from a homebuilt airplane we had dismantled) with the >>> diodes to select the higher voltage one as described earlier. No >>> problems when powered off either battery, except when starting. Issue >>> only when switching from the switching power supply to battery, when the >>> relay coil is deenrgized and spring pulls contacts open. No problem when >>> coil is energized and contacts are switching. >>> >>> >> >> -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist