> 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 <
TakeThisOuTcdenkEraseME
spam_OUTalltel.net> 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 <
RemoveMEcdenkTakeThisOuTalltel.net> 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.
>>>>>>
>>>>>>
>>>>>>
>>>>>
>>>> --
