zener diode with mcck onan control-o-matic genset?

Discussion in 'OnBoard Electronics & Controls' started by sdowney717, Nov 22, 2011.

  1. sdowney717
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    sdowney717 Senior Member

    the generator sends a 12 volt DC power threw the ac power lines. When something turns on perhaps 50 watts, it automatically starts the generator.

    that is just fine for most electrical devices.
    But what about the charger-converter that runs off ac power to charge the batteries?

    Currently I have run a wire that connects to the generator before this special circuit, and powers up the converter-charger. So that charger cant turn on the generator as it would run all the time.
    I have a SPDT relay in there also. The relay lets shore power to the unit when ever shore power has power, otherwise it falls back to the generator wire. That relay switches hot and neutral simulataneously.
    BUT, of course that means the converter cant be part of the AC load center. Which means for now, the line has no over current protection. I could I supose add some, which would cost me about $5 from drillspot.com for a couple 20 amp breakers

    What I was wondering was, what about a zener diode with a 50 volt breakdown conduction voltage?
    So, if ac power was on the line, the zener diode would conduct and allow the device to function, but if 12 volt DC was present, it would be blocked, and keep the generator from sensing the load and starting.

    The charger is a 30 amp charger. What watt zener and does anyone have a source or another idea? Seems like the zener diode is a simple solution to me, if it would work.
     
  2. sdowney717
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    sdowney717 Senior Member

    or what about using a capacitor to block DC and pass AC?
    If so, what size and type?
     
  3. garyohv
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    garyohv Junior Member

    1. The 110vac generator does (should) not send 12 vdc to the ac lines.
    2. The Charger does (should) not make a demand to the auto-start controller. That is activated by low battery voltage.
    3. The relay is a DPST. the 110vac come from an inverter first and generator second...when bat. voltage low.

    If your generator autostarts, the load is not coming from your bc/converter.
     
  4. sdowney717
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    sdowney717 Senior Member

    I dont think you understand this onan "control-o-matic."

    It sends out a sense voltage of 12 volts DC onto the AC circuit. when it detects a demand, like you turn on a switch and it exceeds a certain thresh hold it tells the generator to auto start.
    When you turn off the device, the generator will auto stop.

    It wont start automatically if I flip on a spiral flourescent bulb.
    It will start if I turn on a power tool, a 60 watt bulb, a TV, a fridge, stove, etc...

    The setting is hard wired into the circuit with a large ceramic resistor. If you change the resistor value, that will adjust at which load sense point the generator will auto start.

    Anyway, the converter battery charger does have fuses internally if it shorted.

    It works well, but in concept, a fridge needs to run a lot. The battery charger would run all the time so it has to be separated from the control-0-matic or the generator would always run.
    A zener diode might block the DC and keep the convertor from always starting the generator.
    The convertor is an older model Crown Raritan model R and has no special capabilities other than general charging which it has done since 1970.

    Since my first post, I have installed a 3000watt 6000 watt surge 12 volt DC to 120 volt AC Inverter. I have it setup with a 20 amp double pole single throw switch and use that to transfer the source from inverter to electrical breaker panel. It allow me to run the fridge and any item plugged into an outlet off the inverter when underway and mostly just use the generator for when the main engines are off.

    This invertor knows if something is shorted and will shut itself down, like it has a builtin solid state breaker. Which is nice cause I dont have any other circuit protection on the 12 gauge lines hooked up to it thru that transfer switch. A 10 gauge wire feeds the transfer switch and 12 gauge out to the GFCI outlet and then onto all the other outlets. I might someday add a push button breaker into the invertor output when I get the time to think about it some more.
     
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  5. BertKu
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    BertKu Senior Member

    I would , if I understood your problem correctly, have a sensor which senses the voltage level of the batteries. If the battery voltage would drop below a pre-set level, I would have a sleeping small 8 pin Microchip micro (with ADC input, analogue to digital converter, cost about 1,5 dollar) which then starts the 3000 watt converter with 2 or 1 MOSFET (Cost about 2 - 3 dollars each).
    A zenerdiode I think will not work nor a varistor which could be also used. I agree that a converter should only be consuming energy, when the batteries need to be charged and switched off when the batteries are 99% full. Have I understood your problem correctly, or should I be writing " battery charger instead of inverter" which charges the batteries and should be only come on when batteries needed to be charged.

    Bert
     
    Last edited: May 17, 2012
  6. sdowney717
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    sdowney717 Senior Member

    My invertor here is a plain jane invertor, not an invertor- charger combination.

    charger is a crown rariton marine charger. The only auto sense it does is detect if the engine alternators are running which then shuts it down. It supposedly detects each alternator, at least it has these 2 blue wires hooked up to the terminals which are hooked into the ignition switch-coil circuit of the engine. So I guess if spark coil gets power, it turns off its output. Reading the documentation, it advertises a automatic starting load burst, so dont know how that jives with the turn off when ignition is on idea.

    Right now my charger, when it's on switch is flipped on, is on all the time and would therefore always be running the onan control-o-matic generator. And that would be undesirable.

    So what I did was connect the onan generator output before the automatic part to a DPDT relay to isolate the control-o-matic from always starting up when the convertor flipped to on.

    The DPDT relay takes 2 sources of power, one source is defaulted to shore power. Plug in shore power and the relay activates and sends shore power to charger.
    The other source is generator. When you unplug shore power, the DPDT relay de-energizes and then the charger is connected to the generator as source power.

    So if you could simply block DC on the AC sense line to the charger and only pass AC, I could get rid of the relay and extra wiring.

    your idea of a sense circuit to detect battery voltage is interesting. I wonder though how that would jive with the concept of a trickle charge which this unit sort of does. When engines are off and boat is at the dock, various items will need power like dc lights, fans, etc... which the Raritan convertor charger supplies. So the convertor-charger has a dual purpose, power DC loads at the dock and keep batteries charged.
    The meter on the convertor charger goes up to 30 amps but it is steady rated at 20 amps. It is a pretty rugged unit, heavy with a larger transformer and several circuit boards. It has an adjustable voltage output that is set with a variable tubular resister locked with a metal
    clamp. It will charge up to 3 battery banks.

    Years ago I had a shorted battery which caused it to get pretty hot and it still works fine today. I talked to VIC at Raritan about this and he said it was built off a design in popular science from the 1960's. It was designed to be long lasting. The only thing it does not do which would be nice is 3 stage charging.
     
  7. BertKu
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    BertKu Senior Member

    Wel, I don't know what the maximum impedance (AC resistance) is allowed, but you could use 2 electrolytic capacitors in oposite direction and connect it in series. None of the two capacitors will blow up, if you use 1 electrolytic capacitor, you will blow it up. The two in oposite direction connected capacitors will block your DC, but allow the AC to pass. I assume you need something at 60 Herz. i.e. the impedance is then 1 divided by 2 x pie x f capacitance in Farad.

    By the way what is the AC voltage potential between the 2. >>> 120 Volt? then you need 180 Volt DC capacitors. The reason why I say two capacitors in series, you are then able to go for cheaper capacitors than AC capacitors, instead of a motor condensor (capacitor) 10uF/150 VAC or 30 uF/150 AC

    Example you can buy 2 x 4700 uF /180 Volt DC The AC resistance at 60 Hz = 1 x 1.000.000 divided by 2 x 3.141 x 60 x 4700 = 0.56 Ohm (remember you have microF and not Farad.

    If you use 30 uF electric motor capacitor it is = 1 x 1.000.000 / 2 x 3.141 x 60 x 30 = 88,4 Ohm

    Try first with an old motor capacitor, then you know whether you need a higher value or not
    Bert
     
  8. sdowney717
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    sdowney717 Senior Member

    yes it is standard US voltage so 120 volt AC single phase 60 hz.

    Interesting idea to use capacitors like this. I might have some around here to try.
    I might have start-run or run capacitors from fan motors off furnaces and also might have some from old microwave ovens.
    What about those? I dont know if they have a polarity marking.

    high voltage 4700uf caps are pricey!
    http://www.ebay.com/itm/4pcs-KENDEI...ltDomain_0&hash=item2a0ee3f202#ht_4972wt_1228
     
  9. BertKu
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    BertKu Senior Member

    No I need to know the voltage potential difference between the 2 connections. It maybe even a few volt DC. In that case you could use very inexpensive capacitors. Measure it with a multimeter on DC and also on the AC position. That will tell you what you have to use.

    No, not interesting, fact of life. Any loudspeaker has capacitors to block the output DC stage from saturating the loudspeaker. Your problem is the same principle. You just need to calculate or to speculate what the resistance and voltage has to be.
    Some types you mentioned maybe paper capacitors and that is fine. Any capacitor, other than electrolytic capacitors can be single, but electrolytic caps must be 2 opposite, except if it is indicated as an AC capacitor.
    Come on, you are rich. You have a big boat with lots of pleasure. All joke's aside. You need to find out what the voltage potential is under all conditions. i.e. switching other appliances on and off etc. I bet you that you probably could get away with a one dollar capacitor.
    Bert
     
  10. sdowney717
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    sdowney717 Senior Member

    I am pretty sure it uses 12 volts DC to sense in the control-o-matic function. I will measure and post back.
     
  11. BertKu
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    BertKu Senior Member

    O.K. if it puts 12 Volt DC onto the line, you still need to know whether the AC component is 120 VAC. Also whether the return line is at the same time ground/mass/earth. Then it wan't help you, because the DC will come via the earth en short circuit/bypass your capacitors.
    Bert

    P.S. you can always paralleling your capacitors you found from old equipment and double or triple up. i.e. a 30 uF 150 V AC capacitor, you add 2 or 3 or 4 or whatever and bundle them parallel. In this way you reduce the AC resistance by 2, 3 or 4 or whatever factor.
    But if you use elco's (electrolytic caps) you need to place over each capacitor connected in oposition direction one. i.e. you need 2,4,6,8,etc. Not 1,2,3 capacitors parallel.
    bert
     
    Last edited: May 17, 2012
  12. BertKu
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    BertKu Senior Member

    Hi Sdowney717,

    How far are you? I am flying to Europe on Friday and want be able to reply. By the way, those 4700 uF capacitors, the price was for 4 pieces, that is not too bad. But I agree, it is better to find cheaper capacitors. I don't mind making something with an 8 pin Microchip, to sense the low window of the battery voltage and have a 30 A/120 V AC contact 12 Volt relay to pull in or with another means. I haven't the time at present to shop around for a solution, only maybe in 5 weeks time. I have made something for another forum member and will have a cup coffee in Europe with him. If he likes what I have made for him, I can always give it a try for you also. I don't charge him nor you.
    Bert
     
  13. sdowney717
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    sdowney717 Senior Member

    Hi, thanks for responding.
    I found out by asking on the onan forum at smokestak that blocking the DC sense current will keep it from starting, but not auto stopping.

    When it senses that no AC current is being desired, it automatically shuts off.
    Their is a reversing contactor inside the control box which toggles the DC sense voltage off and on opposite of the AC voltage being generated by the genset.
    So that is NC and goes open when contactor is energized.
    Generated AC power is NO and goes closed when contactor is energized.

    Seeing this info, I dont know how you could do this as the device will be powered and desire AC current.
     
  14. BertKu
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    BertKu Senior Member

    It is a pity that I don't have a circuit diagram of your complete system. I am a great believer that for every problem there is a simple or cost effective solution. While I am flying, I will have 11 hours to figure out, how your system realy look like. I still need to grasp the way they have made it and is linked to each other.
    I will take a print out of all your threads with me.
    Bert
     

  15. sdowney717
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    sdowney717 Senior Member

    Some time ago I posted the genrator manual to docstoc.
    Page 42-43 has a schematic of the whole system.
    That is zoomable to get better detail.
    http://www.docstoc.com/docs/34443851/Onan-Operators-Manual-and-Parts-Catalog?

    A1 is the small circuit for control-o-matic starting sense.
    S1 on-off-on toggle switch turns it gen on and off etc....
    Where it detects the load loss and shuts down I dont know.
    [​IMG]

    https://lh6.googleusercontent.com/-TIcA8T_MtvY/T47HFUiGD5I/AAAAAAAABNA/i6WjqWTJwjw/s800/diagram.png
     
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