Not familiar with term "flywheel diode", tell me more. :) Since the issue seems to be with decaying voltage wanting to be quicker, then the zener diodes or MOV's might help. Since this is AC current, I'm assuming MOV's might help, and am I correct in assuming that adding a MOV at the coil might be a fix. Tried a V150LA10A MOV across the coil terminals without the capacitor, no good. Don't kow how to use zeners with AC current. Richard Prosser wrote: > Just a quick comment that may be relevent. > The relay will NOT take the same amount of time to connect and disconnect. > In order to connect the current in the coil has to increase to a level > sufficient to generate enough magnetic flux to start the armature > moving. To disconnect, the > coil current has to decay to a low level. Normally, the hold current > is a lot less that the pull-in current so there is considerable > hysteresis involved. If a flywheel diode is used the current can take > a noticable time to decay before the actual disconnection occurs. This > can be sped up using zener diodes (or MOVs etc.) in place of the > flywheel diode if required but the switching device must be OK with > the higher voltage generated. > > > RP > > On 12/04/07, Carl Denk wrote: > >> I'm not an electrical engineer :( , the formal training in that area >> was 1 semester in 1963, and haven't calculated any of that. There was >> question in my mind if the relay would actually switch over quick >> enough, that the latency of the power supply and PLC would cover the >> time. Since I had the necessary hardware laying around, I tried it, and >> it worked on the bread board. Went through 2 versions of the PCB where >> other things changed (AC voltage and frequency measurement to the PLC is >> on the same board). It was just recently I stumbled on the issue, after >> a year of operation, it has switched over OK many times with utility >> power, and then with generator power it fails in the direction of the >> spring moving the contacts every time. In the direction that the coil >> moves the contacts, it's OK either power source. >> >> By asking when does it actually switch over, I assume you are talking >> the brief time from when the 120 volt is down to the contacts moving. >> All I can say is the 120 volt wire to both the relay coil and the 12 >> VDC power supply are the same length from the plug strip within say 6". >> The power supply is a International Power model IHC12-34 with over >> voltage protection. >> >> I looked at the AVR butterfly info. With the 2 sources and diodes is >> what I have for the 2 batteries. I don't know the function of R400, >> maybe to charge maintain the battery. Unfortunately the 12 volt that is >> my preferred source is less voltage than the batteries, and the diodes >> won't work. The capacitor across the contact points seems to be working, >> but it has been pointed out, this could be hard on the contacts, but the >> usage is going to be very few cycles, could be less than 6 in a year. >> >> Thanks again. :) >> >> >> >> John Chung wrote: >> >>> Carl, >>> >>> I have read your circuit diagram. I have some >>> questions. Have you calculated the time constant for >>> the relay? The amount of charge and discharge for the >>> resistance and the inductance of the relay? From what >>> I see the relay switches the power between them which >>> is fine but the problem is that when does it actually >>> switch over? >>> >>> Regards, >>> John >>> >>> >>> >>> >>> --- Carl Denk wrote: >>> >>> >>> >>>> The PLC also closes the ground side to the 12 volt >>>> relay coils which are >>>> fed from the PLC 12 volt supply, and has 8 ADC >>>> converters. And yes the >>>> PLC can operate easily up up to 24 volts. Here's a >>>> link to the PLC >>>> http://www.tri-plc.com/t100md888.htm. The outputs on >>>> the PLC are >>>> ULN2803A and TPIC6A595NE. The PLC does have a 5 >>>> VDC Vref for the ADC >>>> that I use most of the time, would have to look and >>>> see if somewhere I >>>> use the 12 volt. >>>> >>>> Would be nice to have an electronic switch that >>>> works off the output of >>>> the AC optoisolator, defaults to the AC, except when >>>> AC is down, but >>>> that's beyond me. Wouldn't bother me to use one or 2 >>>> of those OPTO 22 >>>> type I/O modules. Have used the IAC-15. >>>> >>>> Dwayne Reid wrote: >>>> >>>> >>>>> Hi there, Carl. >>>>> >>>>> I know that all the 12V stuff is fixed. But >>>>> >>>>> >>>> doesn't the PLC operate >>>> >>>> >>>>> up to 24Vdc input? Remember, the only thing the >>>>> >>>>> >>>> output from the 3 >>>> >>>> >>>>> diodes feeds is the PLC supply rail. >>>>> >>>>> Also keep in mind that the supply that feeds the >>>>> >>>>> >>>> PLC doesn't have to >>>> >>>> >>>>> be regulated. It simply needs to be higher than >>>>> >>>>> >>>> the float voltage on >>>> >>>> >>>>> the batteries - that ensures that the charge is >>>>> >>>>> >>>> not being removed >>>> >>>> >>>>> from the batteries while AC power is available. >>>>> >>>>> I guess that I may not be seeing the whole >>>>> >>>>> >>>> picture. >>>> >>>> >>>>> dwayne >>>>> >>>>> At 05:43 PM 4/10/2007, 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. >>>>>> >>>>>> >>>>>> >>>>> >>>> -- >>>> http://www.piclist.com PIC/SX FAQ & list archive >>>> View/change your membership options at >>>> http://mailman.mit.edu/mailman/listinfo/piclist >>>> >>>> >>>> >>> >>> >>> ____________________________________________________________________________________ >>> Food fight? Enjoy some healthy debate >>> in the Yahoo! Answers Food & Drink Q&A. >>> http://answers.yahoo.com/dir/?link=list&sid=396545367 >>> >>> >> -- >> http://www.piclist.com PIC/SX FAQ & list archive >> View/change your membership options at >> http://mailman.mit.edu/mailman/listinfo/piclist >> >> -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist