Making an automatic transfer switch

Discussion in 'Electrical Forum discussion & Blog' started by alternety, Sep 24, 2008.

  1. alternety

    alternety Like an engineer

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    Washington
    In my ongoing project (called a house) I want to add a backup generator. I prewired for this. One subpanel has all the backed up circuits. I am going to used an inverter based Honda generator. It is not designed to be used as an automatic backup generator.

    I have available a controller that understands the Honda and sees internal faults (e.g., oil pressure) and does the proper starting and stopping protocols. The problem is a transfer switch. I find only two types. Manual and automatic. The only automatic units I have found want to be the processor that runs the generator. But they don not know the internal details of the chosen generator.

    So, what I need is an automatic transfer switch that will take commangd from the generator controller. The controller will sense power loss, wait to be sure it is not just a short term transient problem, start the generator, and when it is up to speed, transfer the suppanel. On grid restore it must transfer power back to the grid and cool down the generator.

    OK. Got that. I need a transfer device. My thinking is a 3PDY contactor. A contactor is designed to minimize arcing and handle a bunch of current. I have spent a bunch google hours trying to find a device. There are more annoying terms used for these contractors than I am familiar with. The sites that sell them also tend to assume that if you don't know the manufacturer and part number; you really don't need to buy one from them. My guess is that what I am looking for is a reversing contactor (to get the 3PDT) but I am not sure. The current rating must be for the types of loads expected in a residential subpanel. Not resistive. To minimize cost I have been trying to find a surplus contactor.

    Can anyone give me a hand in identifying what device(s) I should be looking for. Manufacturer and part number would be most appreciated. A surplus source. even more. I need 240VAC, 60 or 100A. There seems to be a real price premium to get 100A.

    An additional question; what are the regulatory constraints of doing this?
  2. jwelectric

    jwelectric Electrical Contractor/Instructor

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    It is called third party testing.
    UL is one of the best know third party testers.
    What you are proposing is nothing short of suicide
  3. Speedy Petey

    Speedy Petey Licensed Electrical Contractor

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    Location:
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    I have two comments. Please don't be offended as this is simply my own opinion.

    1) I think you are crazy for trying to "build" you own automatic transfer switch.
    You say you found something that knows or senses what is going on inside the generator? I highly doubt that.
    Transfer switches are made to work with specific standby generators. The switch is the brains and the generator is the brawn. They work together and only together.

    2) I see you said inverter type. I was under the impression that the largest unit was 3000 watts. I just checked it out and they do make a 5k and 6k unit.
    This makes a difference. I was going to say 3k is not nearly enough IMO to run a transfer panel.
  4. alternety

    alternety Like an engineer

    Messages:
    671
    Location:
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    JWelectric. - A double pole relay is what is inside an automatic transfer switch. It is unable to be in two positions at once. I did see one unit that used two relays. It was capable of making a mistake. If what you said had any credence it would be murder, not suicide.

    Speedy Petey - 1) Generally. But I would not have said what I did unless it was true. Why would I lie? And no; I do not simply not understand.

    2)Yes.

    Anyone want to actually help?
  5. jimbo

    jimbo Plumber

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    Location:
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    In their own gentle way, I belive the folks are trying to tell you not to do this....in other words a "home made" device is probably a code violation, in that it is not listed by UL for the use. I am sure you are well aware that the sensitivity on the transfer switch issue is related to the safety of linemen and the public. I believe people have been killed by home generators backfeeding a "dead" main. You don't really want to be involved in that.

    By the way, a UL listing for your "invention"......I think runs about $25,000.
  6. Speedy Petey

    Speedy Petey Licensed Electrical Contractor

    Messages:
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    Location:
    NY State, USA
    I'd be very curious to see this controller then. I have never seen nor heard of a generic controller available to the general public.
    Or maybe you have an inside track......?
  7. alternety

    alternety Like an engineer

    Messages:
    671
    Location:
    Washington
    It is not generic. www.atkinsonelectronics.com

    Actually it probably is pretty generic. All you have to do is map the engine signals for oil temp, etc. to the inputs and deal with their start circuit. But they have already done the generator of interest to me.
    Last edited: Sep 24, 2008
  8. Bill Arden

    Bill Arden Computer Programmer

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    584
    Location:
    MN, USA
    There is one way to do what you want within code...
    1. Install a large outlet.
    2. Install a generator panel that lets you switch circuits over to a generator plug. This type of panel has wires that go from each panel breaker and wires that connect to each load that used to go to the breaker.

    The switch is then not part of the house wiring and thus not subject to UL requirements when used by the house owner in his/her own house .

    I used this method to feed UPS power to a light circuit.

    -
    I'm not sure what controller you are talking about.
    Personally, I like the Atmel AVR and ARM processors. ;)
    The coldfire based NetBurner boards are nice too.

    -
    A simpler option is to use a standard automatic panel and trick it into waiting for the generator to be ready and to switch on when you want it to.
  9. alternety

    alternety Like an engineer

    Messages:
    671
    Location:
    Washington
    Bill, yes you see the issues. The manual switch is however not automatic; which I need to keep food frozen if I am not home.

    Yes the control of an ATS would do it. But it would significantly increase the cost. That is why I did not mention that in this thread. It is a last resort in terms of cost. I would need to know a bit about how any specific ATS works to try to fool it. Some of the generator vendors are real difficult about explaining how their stuff works. There are some generic ATS's out there. It would probably work to intercept their start signal and start the generator with the other controller. UL is a significant advantage of this approach.
  10. Bill Arden

    Bill Arden Computer Programmer

    Messages:
    584
    Location:
    MN, USA
    Yes, but what I'm saying is that the manual generator panel would be permanently in "generator" mode and you would provide power either from the inverter or the big outlet.

    It's also interesting to note that you might be better off buying a UPS since they already have a "transfer switch" and an inverter that can run off battery's.
  11. alternety

    alternety Like an engineer

    Messages:
    671
    Location:
    Washington
    I am not sure you understand "inverter" in this context. The inverter I am talking about is internal to the generator. The generator behaves just like any normal generator in terms of output. The merit is very clean power and a variable speed engine tied to actual power consumption. Forget that inverter.

    There are no batteries with an associated inverter.

    Here is what I would really really like. A set of grid attached inverters (say OutBack) with internal transfer switches which produce the generator start signal this controller prefers. One side of the ATS to grid and the other to the inverter. With a battery bank this gives me millisecond transfer (effectively a part house UPS). With this scenario I would have to rectify the generator output in a battery charger (which also needs to be smart). If I void the warranty big time, I might be able to get some sort of DC from the generator. I would need another transfer switch if I wanted to do anything else. Now this inverter/battery configuration would be slick. But very very expensive. Have you priced big deep discharge batteries lately. One online store mentioned they had gone up 300% in, I think, 5 years. And still going. They are also sort of a pain in the butt. Assuming flooded cell (which still seems the best $/AH deal) you need an enclosure, venting for H2 and acid fumes. They have to be watered and the charge/discharge closely controlled. A modern charge controller handles the charge part. The inverter does discharge (probably).

    Even slicker is to add some renewable energy source. I have no hydro potential. I have insufficient wind resources. I have real questionable solar prospects. I live near Seattle. We don't actually get sunlight. The state flower is a moss covered mushroom. And, hills and trees significantly shorten my sun day on the rare occasions there is some. Some compensation could be had by using a very big solar array. Can you say $$$?

    So, with everything considered, I am trying to grid connect with a generator backup not designed to do this.. And we are back to the beginning of the thread. The generator is expensive (about $3500) but is quiet and has the best operation fuel consumption of any standby generator I have found. This is important for operational cost, but more importantly, in case of a long term power outage. A bit low on capacity, but my numbers say it will be OK. Some loads may have to be managed, but they are not connected at this time. There are going to be a couple of 5 HP motors eventually, but I can do without them in an emergency. For long outages the battery bank would be useful in that the inverter could handle the house and when the batteries got to 20% (or max of 50%) discharge, the generator would kick in at max capacity, charge the batteries, and go back to sleep. This may or may not minimize fuel consumption. But it should run the generator for less hours. The losses due to conversion in the charger, conversion in the inverter and cycle losses in the chemical processes in the batteries may cancel the fuel savings of full capacity operation for a shorter time. Depth of discharge is a MAJOR determinate in battery life. You really don't want to go below 50% and less is much better.

    Another issue I have not mentioned with many, if not most, ATS boxes is the inclusion of distribution panels and breakers. This is already in place. All that it does is add cost. And it may prevent a single 240V circuit from using the full capacity of the ATS.

    I have thought this out and analyzed a whole bunch of stuff. My question is about a relay. Period. Access to the relay can be creative.
    Last edited: Sep 24, 2008
  12. jimbo

    jimbo Plumber

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    8,997
    Location:
    San Diego
    "" The generator is expensive (about $3500) ""

    You mentioned a relay rating of 240 volts/100 amps. That's 24KW. You think $3500 is expensive for a 20+ KW generator??

    Most of us here live in the real world, not the back-woods survivalist world. You are welcome to your project, but notice that we just can't offer much in the way of the type of help you need. It's not in our genes!
  13. Bill Arden

    Bill Arden Computer Programmer

    Messages:
    584
    Location:
    MN, USA
    I have priced deep cycle battery's and had an opportunity to buy a 10Kw UPS and some clear tank battery's, but the power utility would not let me use the off-peek meter to power the unit. The unit would have been able to handle the 4 hours per day that the off-peek meter turns off, but apparently regulations have not caught up.

    I still think your best bet is to separate the house wiring from the project.

    Here is what I would suggest.
    1. Separate non backed up loads from backed up ones to reduce the amps needed. A separate Sub-Panel would work good for this. The high amp loads would be in the main panel. (Electric stove, Electric Hot water heater, welder)

    2. Add a generator breaker bracket to the sub-panel to "side power" the panel. This switch would be manually set to generator when you aren't working on it.

    3. Add a 50 amp 4 wire outlet

    At this point your automatic transfer switch would plug into the 50 amp outlet and would provide power to the side breaker of the sub-panel.

    This allows you to manually switch the sub-panel back to the main for maintenance, or upgrades, or if you sell the property.

    I could take photos of my setup if you are interested.

    PS: I also wired my generator to apply the same 120 volts to both phases so that all 240 volt loads don't draw any current.
    Last edited: Sep 25, 2008
  14. Bill Arden

    Bill Arden Computer Programmer

    Messages:
    584
    Location:
    MN, USA
    I can't think of any reliable survivalist power sources in Seattle.
    1. cloud Solar is too expensive.
    2. Wind is an option, but not very continuous.
    3. I'm not sure about ground source heat power since your outdoor temperatures don't change as much as they do here in MN.

    4. I don't see any high temp geothermal sources near you.
    5. It does not sound like you are in a area where you can access the ocean for tidal or a thermal difference power.

    That just leaves bio-fuels, wood, natural-gas, and oil for Seattle.
  15. alternety

    alternety Like an engineer

    Messages:
    671
    Location:
    Washington
    The generator is 5KW. The sub-panel is wired for 100A from the main panel. It would be easier to leave that alone. But I may reduce the breaker there. The loads on the sub-panel should be fine at 30A. The sub-panel is specifically configured to be only the backup loads.

    My original intent was to get a generator in the 15KW range, but that seems unnecessary. There is also a very large jump in price between 60A and 100A breakers/ATS. I will run wire for 60A to the outside to allow for any future upgrade.
  16. Bill Arden

    Bill Arden Computer Programmer

    Messages:
    584
    Location:
    MN, USA
    It looks like all you need is a manual transfer switch bracket for that sub panel and to add a 50 amp breaker from the main panel

    It's ok to power the sub panel using a 50 amp outlet, 60 amp wire and a 50 amp side breaker. The key here is that the outlet has a 50 amp breaker and that all the house wiring is UL certified.

    On the other hand, any transfer switch that is installed between the sub panels "main breaker" and the main panel has to be UL certified and rated for 100 amps.

    That is why I'm saying it would be cheaper and easier to route the power to a smaller transfer switch threw a smaller breaker and then run the power back in the side of the sub panel.

    Note: The small bracket on the sub-panel prevents the main breaker from being turned on while the side breaker is on.

    Edit: The other advantage of this side-breaker plan is that you don't have to pull an electrical permit every time you change something since you can use 50 amp outlets to divide the "house wiring" from the transfer switch and generator.

    Note: You will have to run a separate hard-wired ground wire between everything, but that does not require changing the house wiring.

    Here is an image of a metal bracket Interlock for a sub-panel.
    http://www.interlockkit.com/images/MEPanel033a.jpg
    Last edited: Sep 25, 2008
  17. maintenanceguy

    maintenanceguy In the Trades

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    Location:
    Pennsylvania
    If you install a UL listed generator with it's UL listed ATS according to all the rules and codes and something goes wrong and it kills somebody, you don't go to jail.

    If you self-engineer the most brilliant system ever seen by man without following all the rules and codes and without UL listing and it kills someone, you go to jail.

    For the same amount of work and less liability, you could invent a freezer that will stay cold for longer in a power outage. I see CO2 tank with a solenoid valve that opens to trickle liquid CO2 into a dry ice generator when the power drops.
  18. alternety

    alternety Like an engineer

    Messages:
    671
    Location:
    Washington
    Do you perhaps have a link to the UL procedure for testing ATSs? Or the stamped metal plates that prevent you from manually turning the breakers to the wrong position before the other has been changed (kind of like a DPDT relay)?
  19. jwelectric

    jwelectric Electrical Contractor/Instructor

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    Location:
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    This is contained in the UL Standards and one must buy a copy of the Standard in question. Access is not available without cost. See UL Standard 1008 for transfer switches.
  20. jimbo

    jimbo Plumber

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    8,997
    Location:
    San Diego
    First step in the procedure: take the item to be tested to a UL Certified Testing Facility. second step...pay the fee....Approx. $25,000
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