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

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

  1. BertKu
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    BertKu Senior Member

    Indeed that is a very good solution. He just have to work out what the difference in cost will be 3 contactors (heavy industrial relays) with a rotory switch like you have suggested, to give ample time to switch hot lines, or the switch as per thread 4 for $444. In your case, 50 Hz, not a problem of the 2 mS difference between 8 and 10 mS. But your suggestion of a 7 position switch with relays is excellent and would give ample delay times.

    Thanks CDK, now I don't have to fidle with triacs and to write software in 3 weeks time.
     
    Last edited: Jul 30, 2012
  2. Lt. Kludge
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    Lt. Kludge Junior Member

    Technically of Legally?

    Being in the US your local Authority Having Jurisdiction wont be too happy if they find out about it. There are NEC/UL requirements for the separation between the circuits. Hence why the price of the switch is driven up to meet UL construction requirements.
     
  3. CDK
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    CDK retired engineer

    I wouldn't put up a sign explaining the circuit, although they probably don't understand any of it. Where I live we have no such thing as an AHJ and if we had one everybody would ignore it anyhow.

    Btw the high price of these switches is not related to performance. It is boating stuff, so between the maker and the customer is a long chain of people doubling the price. An industrial switch without the words Shore and Gen is a device, available as a kit with a rotary mechanism and any number of switch sections. Made in China, very old fashioned and cheap.
     
  4. Lt. Kludge
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    Lt. Kludge Junior Member

    It depends

    Depends upon Manufacturer. A major supplier in the heavy industrial market is already building a switch with design margin and compliance to standards which are often not mentioned. As causing a production outage at a fortune 50 manufacturer can be far more expensive than the cost of compliance.

    However consumer products are another story and if it's cheaper and not absolutely necessary for all applications, well it may be eliminated. Cost of a product may or may not reflect actual product quality. One engineer will tell you any load transfer switch has to be able to make/break 100% current 70%PF and another may design it to have 0 make/break current.

    In parts of the world there is an assumption in the codes/standards that the unconnected poles of the transfer switch may be un-powered and in the hands of service personnel. Which requires a level of isolation within the transfer switch equivalent to the isolation of Earth from Phase. And as such a single solid state device can't meet that requirement.
     
  5. BertKu
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    BertKu Senior Member

    Very valid point, but in CDK solution are 3 industrial contactors, which has those requirements. He also has proposed a switch which WILL have the time difference between on and off between the contactors.
    a) it takes turning the low voltage switch for the low voltage coil of the contactor approx 100 mS from one position to another. If you are extreme fast.
    b) He suggested to keep 2 free i.e. it takes 300 mSec, but normally in the seconds + the time it takes to pull the contactor in , which is also in excess of 50 mSec. One only need 8 mS . I assume the specification will only state that no feed back to the shore power is allowed from other sources.
    With solid state, I am inclined to agree with you. The max Voltage between the connections is normally max 200 - 800 Volt, while for a contactor probably 2 to 3000 Volt.

    The only advantage solid state has, that one can switch zero switching , i.e. no sparking and a lot of negative arguments are falling then away. Also with a micro one can make provision not to have a dangerous situation, provided the triacs are replaced by Thyristor's of in excess of a thousand volt.
     
    Last edited: Jul 31, 2012
  6. BertKu
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    BertKu Senior Member

    Just to elaborate on the issue of using a mircro. To comply with the regulations, the micro could sense whether there is a voltage on the offshore lines. If not, the micro does not allow or will not switch the contactor to offshore power and thereby avoiding a situation.
     
  7. CDK
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    CDK retired engineer

    SSR manufacturers all use an opto-coupler with at least 4000 V isolation voltage to comply with UL and/or CE. Some of them even exaggerate and use a 6000 V coupler to separate the control input from the power grid.
    Rotary switches are available with make-before-brake and break-before-make contacts; using 2 open contacts between each function allows the use of either type.
     
  8. BertKu
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    BertKu Senior Member

    What Lt. Kludge probably means is the 1st breakdown voltage of the triacs. I still think your proposal is still the best solution (Provided he is able to switch life and neutral simultaneously. Otherwise he must use the 3 contactors) and all what Sdowney has to make sure is that the breakdown voltage of the triacs used in the SSR are > 800 Volt or whatever the Lt Kludge specs state.

    If it comes to the push, Sdowney must just put a 100K resistor, 1 x 1n4007 , zener-diode a cap and a IR photodiode on the 110 V AC side, an IR sensor in line with his Sensor part of the Solid State relay , problem solved. If there is AC, the relay will come in, if there is no AC, the Solid Sate relay refuses to conduct. He is then complying with any spec in the world.
     
  9. Lt. Kludge
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    Lt. Kludge Junior Member

    Would you touch MT2 while MT1 was live?

    In the OP's Virginia. After a major coastal storm there will be several million generators online and thousands of people clearing debris and repairing downed lines. The cleanup and repair crews are not going to be satisfied with just a P-N junction protecting them. That is one reason why the Code requires an approved transfer switch. Would also caution that many Triac junctions will short well before a fuse and particularly a thermal breaker will activate.

    What works because there is an engineer present. Is not the same as what is mass marketed for use by Homer Simpson.
     
  10. BertKu
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    BertKu Senior Member

    I don't think that only an approved transfer switch is allowed. I am convinced that the transfer switch has specifications. As long Sdowney will adhere to those specifications in whatever way, he can use 3 contactors and a rotating switch.

    I don't think you understand Sdowney system. He is not able to feed the offshore power, as only one of the three contactors will be engaged. He cannot feed, like all Simpsons during a storm, the offshore world. You compare him with some idiots who forgot to switch the main switch when they start their generator.

    Sorry, I might agree on the SSR and Triacs. (But only after proof of specifications on the specifications of the transfer switch), but definitely not on good solid industrial 3 x contactors, like CDK first suggested.
     
  11. Lt. Kludge
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    Lt. Kludge Junior Member

    Excuse me didn't mean to imply that only a approved switch could be used nor to imply that Homer Simpson might visit this board.

    Actually I would suggest two contactors. One to connect to either Shore or Onboard and the Other to switch between Inverter and Generator. In-case of contact Weld you will still be interlocked to only one source of supply. But the standard also discusses many other requirements such as Short-Circuit current
    requirements, Overload Endurance, dielectric etc.
     
  12. BertKu
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    BertKu Senior Member

    That does not make sense. It implies that the busbar on which his fridge is connected , can only be attached to the Gen or Inverter, but not to offshore.
    Make a drawing and you will see for yourself. The solution with 3 contactors and a rotating switch to select between the three options, will still be the best and will comply with the regulations, as long he buys contacters for American Industrial use. Or are you telling me that your American Industrial contacters have an dielectric , short circuit and overload problem?
     
  13. sdowney717
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    sdowney717 Senior Member

    It would take 3 contactors of 3 poles to switch 3 separate sources of AC power.

    Though, what if you used 2 contactors and the invertor position of the rotating switch simply turned on the low level 'on-off' toggle switch for the invertor?

    If an invertor is off, and the AC output of the invertor is attached to another AC source that is on, does it destroy the invertor?

    IF the invertor has no problems with that, then you could even use a single 'reversing contactor'. Reversing contactor has the other side mechanically locked out when one side is locked on. A standard contactor that welded its point closed wont open. I dont know how often a contactor will fail in that way.

    Reversing contactor in a power that I would need is very expensive.

    I have a single DPDT relay rated at 30 amps, BUT then your still stuck switching only the hots.

    I suppose I could
    1. keep the current onan manual transfer switching the hots.
    AND
    2. put a DPDT relay on only the white neutral wires.

    OR
    3. just leave everything as it is, it works.

    My invertor output (up to 3000 watt continuous) is only connected to the outlet plugs by way of an 'on-off-on' DPDT 20 amp manual switch
    power output comes from 20 amp branch circuit breaker to DPDT switch
    power output comes from invertor to DPDT switch
    power leaves DPDT switch and goes to a fridge outlet, then a GFCI outlet then on to all the outlet circuits on the boat. So all outlets are GFCI protected except for fridge.
    Fridge I dont trust on the GFCI! nuisance trip and you loose everything.

    There is short circuit protection built into the invertor, I have seen it work. It turns the invertor off.
    The short circuit and overload protection from the breaker panel is a 20 amp breaker for the circuit.
    Output for the invertor has 4 120 volt plugs, it is not hard wired, I have a plug attached to one of the outlets located on the invertor. I suppose you might be able to draw more than 20 amps from the invertor onto the 12 gauge wires. I have 10 gauge wires feeding the switch. I could add a 20 amp breaker on the invertor output. Just have not done that yet.

    Although I wonder the invertor designers must figure people wont be plugging in loads that would exceed 20 amps into a single outlet, so they did not include overload protection, just short circuit protection into the output.
     
  14. CDK
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    CDK retired engineer

    If you make something like this, you don't need any switches. Just a few pilot lights maybe, so you know what is going on.

    Use two serious AC relays from Omron, Siemens, AEG or BB, with 50 Amp contacts and over .2" travel. If shore power is present, the boat is auto-connected, GEN comes second, if both are not available the inverter does the job.

    Lt Kludge happy, everybody happy!
     

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  15. BertKu
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    BertKu Senior Member

    One can see. if we argue enough, somebody puts the ultimate solution as a thread. Excellent CDK, well done. This is what Sdowney should make.
     
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