12vDC and 120vAC indicator light using same wire?

Discussion in 'General Electronics Chat' started by sdowney717, Mar 31, 2015.

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  1. sdowney717

    Thread Starter Member

    Jul 18, 2012
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    My Onan generator has on demand load auto start feature.
    I managed to configure an LED light to show dimly at 12vdc and brightly at 120vac.
    The gen puts a 12vdc on the AC wires as a sense to determine whether to turn on or not.
    At night you can see the LED, but in the day it is too weak.

    My LED light just sits across the AC wires. I was curious if I can get an arrangement to give a brighter 12vdc, gen in auto start mode without extending extra wires from gen to the panel?
    I could run an extended line from the 12vdc ignition circuit to do that.
     
  2. blocco a spirale

    AAC Fanatic!

    Jun 18, 2008
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    Are you saying that you require a single indicator that provides the same brightness whether fed with 12VDC or 120VAC?
     
  3. Reloadron

    Active Member

    Jan 15, 2015
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    Would this be a Energy Command type controller as used with Gensets found in RV applications and similar? If yes, what controller part number (make and model)? Units like this normally sense the "house battery" voltage and auto start when the battery voltage gets low or on demand for heavy loads like AC or Heating. I have never seen one that actually runs 12 VDC on the actual 120 VAC lines.

    Ron
     
  4. sdowney717

    Thread Starter Member

    Jul 18, 2012
    385
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    Yes a single indicator that shows the same brightness on the same line if it is 12vdc or 120vac.

    It is a genset 6500 watt MCCK marine in my boat, from 1970.
    Called 'Onan Control-O-Matic'
    It uses a circuit board to send a 12vdc signal out on the AC lines so if a load is sensed, it starts the gen. When the load goes away, it shuts it off. It is how Onan made it done. Circuit board had corrosion failure of a resistor and transistor which I replaced about 5 years ago.

    Here it is. I have a better scan somewhere, the control board is to the left of the round relay symbol and to the right of the contactor.
    Also I added the original scan as an attachment which I think is better.
    [​IMG]
     
    Last edited: Apr 1, 2015
  5. Reloadron

    Active Member

    Jan 15, 2015
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    I wish I could better read the schematic. I see where you are talking about. Actually to me T1 which they call a Transformer Current looks to be a center tapped current transformer as drawn. The Center Tap to Ground and the remaining leads to the pair of diodes. T1 senses the current load and the AC out of the current transformer is full wave rectified by the diodes. That is how they sense the AC load and determine when to auto start the genset. One of the resistors in there may be adjustable? That would determine at what load point the generator comes online. Hopefully another forum member will weigh in on this as it is my thinking only and I just can't read the schematic well enough. Old eyes here. :)

    Where in the drawing are you connecting this LED?

    Ron
     
  6. sdowney717

    Thread Starter Member

    Jul 18, 2012
    385
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    I simply connected the diode across the generator AC output.
    If your using Chrome, you can click the attachment to view then zoom by holding the cntrl key and roll the center mouse wheel.
     
  7. DickCappels

    Moderator

    Aug 21, 2008
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    I am closing this thread as it violates the Terms of Service of the All About Circuits forum:


    This is an excerpt of our ToS:Terms of Service
     
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