create a shore-gen-invertor-off switch using solid state parts

Discussion in 'OnBoard Electronics & Controls' started by sdowney717, Jul 28, 2012.

  1. sdowney717
    Joined: Nov 2010
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    sdowney717 Senior Member

    No never ever have I switched on a full load to the gen.
    Mostly it sense a demand load and starts automagically.
    Like you turn on oven, it starts, turn off oven, it stops.

    If gen is set to the default contacts will be closed for the gen circuit so all is good. The contactors will only switch If I plug in shore grid power, or turn on invertor.

    My big loads could be the cruisair 16k heat pump, the water heater, two electric wall heaters, oven, 3 burner stove top. After that there is a convertor-charger, mid sized upright fridge, various outlets, builtin computer.

    The fridge once it shuts off takes a minute or so to restart, it will click click click click etc... fast, then waits to restart because if you restart right after running, it cant spin the compressor against the high head pressure. I think that is normal? If it is not does it need a super booster?

    My cruiseair offers instant restarts every time. Compressor has a potential relay and start capacitor. Dont think the fridge has that. Is that normal for fridges?
     
  2. jonr
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    jonr Senior Member

    I would do some thinking about inductive loads. When you interrupt the circuit to any inductive load, it becomes a generator that can generate voltages far higher than normal (ie, it creates a surge). You need to dissipate this energy or it will spark across relay contacts.
     
  3. BertKu
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    BertKu Senior Member

    Yes CDK had the best idea.

    Should you ever have a melted together contact and you switch the coil off with your toggle switch, as long you remember just to check, whether there no residual voltage of 110 VAC exist on your lines, to your fridges, charger etc.
    Not necessarely, If the coil voltage is lower, you could use a AC capacitor in series, or if it is a DC coil you use a AC capacitor with a small bridge rectifier. You just have to calculate the resistance of the capacitor. Example 24 Volt AC coil and 240 Ohm (AC Voltage divided by AC current >>>> Not DC resistance ) You need thus 110 - 24 = 86 Volt AC difference to compensate. A normal resistor will get quite hot. 0.1 Ampere x 86 Volt = 8.6 watt, which could be done with a 10 watt (preferable 20 watt power resistor)
    You have measured the current at 24 Volt AC (or it is indicated on the relays) at 240 Ohm , thus you need 86 /24 x 240 Ohm additional resistance. which is 858,34 ohm. rounded off to 858 Ohm.
    XC = 858 = 1/ 2 x pie x f x C = or C = 1 / 2 x 3.14 x 60 x 858 = 3.1 uFarad or rounded off as a 3 uF >> 110 V AC capacitor. Most AC capacitors have a tolerance of up to +20%/ -10% in anyway. It totally depends what the AC resistance is of such a relay.
    You have to ask a local, we are too far away from you.
    Nice open relay, most likely by law, it needs to be covered, if it is not in a place which can be touched by non-experts.
     
  4. BertKu
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    BertKu Senior Member

    Indeed correct. One can easily use a capacitor over the contacts. If you switch DC, one uses a Polyester, paper or policab capacitor. If one switch AC, one uses preferable a paper AC capacitor. Normally 0.1 uF
     
  5. CDK
    Joined: Aug 2007
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    CDK retired engineer

    The sort of relays I had in mind are designed especially for inductive loads. Long contact travel (5 mm or more), tungsten alloy contacts and each pair in its own chamber so the ionized air cannot cause arcing between phases.
    For those who still have "contactofobia" some suppliers offer integrated varistors - General Electric called it G-Mov - as an option.
     
  6. sdowney717
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    sdowney717 Senior Member

    http://my.execpc.com/~endlr/line-filter.html
    Some info here.
    Is it worth doing this? What could happen otherwise?
    "spark quencher"
    http://arduino.cc/forum/index.php?action=printpage;topic=117024.0
    then this here, mentions helps keep the points from wearing out.
    dont they mean parallel across the contacts? So it absorbs the induced energy. Series sounds to me like inline with the circuit, parallel means going across around the points, like a bypass. I assume every point contact should have this and that gets to be a lot, like 16 of these?.

    My current manual switch is 45 years old and works. It has points. It has not worn out. These relays wont be switched very much.
     
  7. sdowney717
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    sdowney717 Senior Member

    http://en.wikipedia.org/wiki/Snubber

    This says they dont work.

    from this
    http://arcsuppressiontechnologies.com/Documents/Lab Note 103 - APR2011 - Snubbers.pdf
    says this
    HAHA fooey

    probably cheaper to just buy new relays after 100,000 cycles! I think I will be long gone way before that.

    http://www.arcsuppressiontechnologies.com/Pages/NOsparcTechnology.aspx
     
  8. CDK
    Joined: Aug 2007
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    CDK retired engineer

    No need to make simple things so complicated!
    Sparking in relays is normal, just like in any other switch. The designer specifies the current and the number of cycles, using a very large safety margin.
    Arcing can damage contacts because the duration is long enough to melt the contact surface. It can be prevented with a snubber network or a varistor. The snubber slows down voltage rise over opening contacts but intensifies the closing spark. A varistor limits the peak voltage over open contacts.

    For your application the above is not important.
     
  9. BertKu
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    BertKu Senior Member

    Probably in your case, no.
    Nothing. If you have purchased a good quantity relay with good quality contacts of palladium or tungsten contacts, over many years it probably will burn the surface a little in your application. In the olden days, with a 4, 6 or 8 cylinder automobile engine, yes in such an application you need it as the contacts are opened and closed many times per second for hours and days and years. One also will use it over the brushes of a motor, as it is also many times per second.
    The question is, are you sitting there on your boat switching whatever appliances 100 times per second on and off?. Probably not.

    Should you ever decide to use varistors, please take the negative tolerance of a varistor into consideration and also your 120 Volt AC will have a peak of 120 x 1.73 = 208 Volt If you varistor has a tolerance of +20%/-10% you need at least a varistor which can handle at least 230 Volt, but this is not good enough as you need to take a safety margin into consideration of 10 % i.e. you must buy a varistor of 260 or 275 Volt DC. The voltage on a varistor is indicated at 1 mA i.e. a 275V DC varistor has a 1mA leakage/suppression current at 1mA , should the voltage be higher, rapidly the internal resistance comes down and it sequels the voltage spikes.

    Before it is misunderstood. Thus if you buy a 300 Volt varistor , that is fine, if you buy a 1000 volt varistor, in that case any electronic device after the varistor, which cannot handle voltage much over the 300 - 400 volt will not be protected. Anything in life you do, has advantages and disadavantages, one has to weigh both up. I have block varistors on my household incoming 230Volt AC for lightning suppression. They are 600 Volt types and can handle a couple of Kilo-Amperes.
     
    Last edited: Aug 9, 2012
  10. jonr
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    jonr Senior Member

    I agree that with the right relay, the contacts will last long enough. Whether your expensive electronics will survive the surges that switching causes is another question.
     
  11. sdowney717
    Joined: Nov 2010
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    sdowney717 Senior Member

    I am thinking of controlling these relays with a single on-off-on switch
    on one way turns on the grid power, off is the default generator, on the other way turns on the inverter. Handy to put all this power into one little switch. Simple.
    Most of the time, only one of the relays will be energized on shore-grid power. then when boat goes out, the relay deenergizes and the default is gen with no relays energized. If invertor is turned on, then other relay is energized. so not a whole lot of relay action will take place.

    I have an LED indicator for the invertor, I need one for shore or possible gen. Or all three?
    I plan to switch shore-grid relay on and off cause I dont want to have to unplug shore power to use the gen at the slip

    As far as expensive AC electronics?

    Ok, what I got is an old convertor-charger, older type fridge, modern microwave, cruisair AC (old not solid state anything), 12 gallon resistance water heater, two bulkhead resistance heaters some lights in the head and anything else that is plugged in. Builtin computer is plugged into a surge strip.

    I do have a GFCI for all the outlets, which is a fancy sophisticated device.

    So items always on will be fridge, charger, microwave display, gfci detector.
    Fridge can never restart quick, the pressures have to equalize.
    I have noticed most fridges run most of the time.
     
  12. sdowney717
    Joined: Nov 2010
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    sdowney717 Senior Member

    Pictures of the box I modified from an old ITE fuse panel made in 1965.

    I cut and shaped and then welded it into a 8.5 by 11 inch shape
    Installed a raised platform for the relays and made a cover with bent edges.
    All the steel came from the fuse panel and still has some left over.

    Looking at it you will hardly know I made this. I kept the nut and bolt stud for a ground connection.

    I will seal the holes in the cover with some PL Poly adhesive and fiberglass cloth. Welding them closed might distort the sheet steel.

    There will be 4 wire sources of power coming in and 2 cable wires going out. The 2 cables will go to the boat breaker panel which is a square D 8 circuit panel. To keep separate the 2 neutrals they will have to be on separate busses. The older panel uses QO breakers and is a QO box and the connection points dont bare down directly on the wires. The ground and neutral connector busses has these flat inserts so the screws dont cut the wires. A nice idea, clip on the screw head, are they still available as a part number?

    The QO panel alternates hot phases on each side when going down the breaker rows, different from panels which one side of the breakers is one phase, and other side is the other phase, if you understand.

    Wire for this is all 8 gauge multistrand romex. I already have all the wires needed. I plan to use 8-3 with ground and 8-2 with ground to go into the box. This way I can use one of the multistrands as the the ground instead of the solid bare single copper wire. All it need is 2 hots, 2 neutral, one ground. I should get some green electrical tape to wrap on the ground wire to show its ground. I think for current carrying use red-white for one side, black-white for other side and the unused black out of the red-white romex will be the new green ground.

    If anyone doubts multistrand romex is durable, the boat gen in 1971 was wired with 8 gauge multistrand and it has never failed. That is over 40 years old. I plan to reuse that long wire to run the line from invertor in the kitchen cabinet to this new box.

    I really like the whole plan. It simplifies the wiring, gets a lot of AC wire and the big switch out of the helm cabinet.

    [​IMG]

    [​IMG]

    [​IMG]

    [​IMG]
     
  13. sdowney717
    Joined: Nov 2010
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    sdowney717 Senior Member

    I installed this about a month ago and it is working very well.
    I have the 2 on-off-on switches with some led controlling everything near the helm.

    To the right is a GE breaker box with 2 double pole 30 amp breakers.
    I bought 2 boxes and fit into a single box the 2 breaker mounts so as to not waste any space. Even heated the cover to bump out the metal needed for the extra breaker and cut the inner panel to fit.

    All wiring is mostly 8 gauge multistrand. I used an 8-2 and an 8-3 bundle to send power to the original square D 8 breaker AC distribution box on the left (not seen here). 8-3 wire with red as ground running to the distribution breaker box way since I had it for no cost and it uses a multistranded ground wire. Inside the square-d box I isolated the neutrals using a large copper electric bolt to join one side together, the other neutral side I just used the existing neutral bar in the box.




    [​IMG]

    Inside view of the relay box. To the back right is a bridge diode mounted on an old CPU heat sink used as a galvanic isolator. It is only rated for 25 amps, so on Ebay I bought one rated for 50 amps to upgrade it. this basically just is inserted into the ground line to stop any DC current flow. If the AC voltage exceeds 1.2v, then it will conduct in reverse bias.

    Above the relay distribution box is another smaller box holding a DPDT breaker. this breaker sends power over to the AC charger. When shore power is connected, the relay coil energizes and automatically turns on the AC battery charger.
    When unplugged from shore power, the relay de-energizes and power is sourced from the generator by another wire running back to the generator control box. this wire is hooked inside the gen control box prior to the auto start sensing of the generator so that the AC charger wont turn on the gen set. Otherwise it would run all the time when you unplug from shore grid power.

    In the hot line inside the big relay box I have installed a 20 amp auto reset circuit breaker. Wire gauge to the AC bat charger is 12 gauge.
    Inside the gen control box, I have installed a 20 amp push pin breaker which is mounted on the front cover. This way the gen and AC charger is breaker protected.

    At the helm one of the DPDT switches for gen is
    on - gen starts and runs
    off - gen is off
    on - gen starts if load is detected

    the other DPDT switch is

    on - grid power
    off - gen power
    on - invertor power

    There are 3 LED lights showing various power combinations.

    green - which shows power is on the AC system
    red - invertor is on
    yellow - generator is on

    Interesting thing is my AC 120v yellow gen led will also light up dimly if I have the gen set to start on load demand.
    I like seeing that. The reason it lights up dimly is LED are DC devices, it has a resistor to limit the current to make it work on 120v AC.
    The gen on load demand start sends a 12vdc signal onto the AC wiring, this is enough to light the LED dimly. So when I set the gen to run, it lights brightly, and when I set the gen to off, it is off, and when I set gen to load demand starting, it lights dimly.

    In a few days, I can post pics of my 3 leds and 2 DPDT switches.
    [​IMG]

    At my marina, the voltage is not great under load it drops. The relays were making a nasty hum or buzz. Turn on the microwave was awful continuous buzzy noise.

    To fix, I bent the spring mount holder arms to lesson the spring pressure on the relay arm, so when activated, the lower coil voltage wont cause a buzz. this has worked out very well and the relay arm still has plenty of pressure on it to open ok.
    The other relay mod is those relay electric lug screws are extremely short. You need longer ones to use with copper lugs. These screws are the same thread as those used for electric outlets. So I changed everyone. Be careful the ends are slightly swedged and you need to file them or they might damage the relay screw holes. Better yet is buy some screws to fit, perhaps SS.

    The relay box handles 3 wires coming in, one from gen, one from invertor, 2 from grid power (twin 30 amp) to switch 3 sources of power.
    And sends out 2 wires runs over to the square-d 8 breaker distribution box.
    I separated the 3 resistance electric heaters into one side, 2 cabin heaters and the water heater are on one 30 amp side.
    Outlets, fridge, marine heat pump, princess stove-oven are on the other 30 amp side.
     
  14. sdowney717
    Joined: Nov 2010
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    Location: Newport News VA

    sdowney717 Senior Member

    Showing the control switches and Led lights.

    [​IMG]

    This shows the leftover holes from where the old manual onan transfer switch was placed. My new control switches are basically in same location. I have already plugged the old holes with new wood. I was wondering if the switches should be labeled and if so not sure how to do it.
    It is fairly simple to comprehend.

    [​IMG]
     

  15. sdowney717
    Joined: Nov 2010
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    Location: Newport News VA

    sdowney717 Senior Member

    I have improved the circuit relay.
    I am now running the AC coil on the shore power relay with DC voltage from a 15 vdc 400 milliamp walwart transformer. It is much better, no buzz ever. Good strong solid click downs, relay arm cant be pushed back to hear that buzz. It only buzzed on heavy loads, but I did not like to hear any buzzing noises.

    There are 2 kinds of walwarts, liner and switcher. I chose linear. Connected to the 120 ohm coil it loads down to 17vdc, The AC coil reaches a max temp of 98*F. I figure if the marina volts drop low, the coil will continue to remain buzz free.

    The switcher walwart itself when I tested, the transformer walwart itself runs a little warmer to the touch versus the linear transformer.

    A switcher is lightweight uses high frequency switching not a big coil of wire and can maintain a steady 15vdc output down to 100 vac, which is good, better than a linear wallwart. Once the relay arm is down with DC volts being steady not alternating current, even a lower voltage wont make it buzz like ac volts can.
    But I want to save it for other uses as it puts out 1 amp.

    Other than occasional slight buzzing, this relay box has been flawless. I did have to replace the 50 amp bridge used as a galvanic isolator. Dont use push on pins, high resistant creates high heat and I burnt it out. So either bolt it together, crimp or solder. Or buy a commercial isolator.
     
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