Three Way Transfer For Power

Maybe this will make it easier to understand what I'm trying to do. I need a switch that will;

Connect a 2500 watt inverter to a single 120 volt electrical panel.
Connect a single 120 volt shore power connection to a single 120 volt panel.
Connect a 3.5 KW generator connection to two 120 volt electrical panels

I have talk to people with similiar challanges, although more often they would describe the challange with a 2kw portable generator instead. I don't know anyone that has done anything about it, other than take the output of the generators to a cord that would plug into one shore power connector or the other.

I think a more elegant solution than the above or transfer switches like you asked about, is available or on the horizon. I hope to evaluate a solution as I describe below. Maybe you want to consider it and write about it here on Panbo.

I think the elegant solution is going to be a move to a single 110 VAC shore power connector, rather than two, and use a combination inverter/charger that will
- scale up/down power allocated to a battery charging function (from shore or generator) in response to AC loads like electric water heaters or HVAC. The ideal system would have seperate inputs for shore power and generator and have user setable maximums (e.g. let your generator have a higher maximum than shore power)
- The inverter function will be able to combine the DC battery and AC generator sources for temporary high loads like an air conditioner starting. In this way a 2kw portable honda generator is all that is needed to run air conditioning on the hook.
- larger boats might choose the above and add a A/C priority switch that will insure competing AC loads, e.g. electric outlets, hot water heater, HVAC are managed automatically switching off those with lower priority when more than one system is in demand.

For an inverter/chargers as I described above look at Victron "Quattro" or Mastervolt "Mass Combi 12V"

In any solution, I would look to take a now unused shore connection and existing charger, and leave that in the boat as a alternative charging option. I might also look to take an existing transfer panel and use it to switch electrical outlets on the boat between an old inverter and the new inverter source, or the extra shore power connector and the new charger/inverter. Then if your at shore and want to use two cables, you could run your outlets on a seperate shore power connection

Thanks Dan, but I'm not ready to reinvent the wheel or throw away a lot of good equipment that works perfectly fine. I am considering two transfer switches. I just found a three position switch. I will use that to connect the shore power, inverter and genset to the main panel. The second switch is 2 positions. I will connect the second shore power and the genset to the air conditioner panel. I can't see how this would be a problem but I'm open to comments. Chuck

Which transfer switches are you considering ?

The 3 way is a Blue Seas 8366. The 2 way is the same type Blue Seas. Chuck

Hi Chuck,

I'm going the other way on Gizmo and that might be useful to you. When I bought her, she had two 30 amp shore power inlets, two AC units, generator and Xantrex Freedom 2.5 kw inverter. I removed generator, one shorepower inlet and one AC unit and now have removed all the associated switching. Some is in Maine and some here on the boat but I'm hoping to sell two Blue Sea 30a shorepower switches, one Paneltronics AC volt/amp panel, and -- most important -- one Blue Sea Generator/Shore/Off rotary switch. The latter controls 4 poles of Shore and Generator and 8 poles output. Note that on Gizmo the inverter was cabled right to the AC panel (one side anyway) and I've kept that arrangement with my new Victron charger/inverter. Works fine. Everything else, including the AC units, switched through the rotary.

Thanks Ben. Ideally I would like to do away with the need for a generator too and add solar panels and a wind generator to supplement the Inverter. But Susan insists on her air conditioning and being in south Florida it is pretty much a must. Time is also not on my side. We have just published our first anchorage book and the second will cover the Bahamas. We will need to leave here December 1 to get over and start research so I don't have the luxury or time for that right now. The generator install will be faster and give us the power on the boat for now. we can make changes later, especially as we spend more time in the north as part of the Great Loop, the next leg of our journey. The generator is scheduled for delivery Friday and the additional parts are all on the way. That gives me a little over a month to get it all installed. Oh boy. Chuck

I didn't mean to suggest that you do what I've done, Chuck. Limited A/C with shore power only is a lot easier decision for a Mainer who only pokes south a little!

But I am wondering why you need to switch the inverter?

Ben, I appreciate any suggestions from you. The inverter is actually used a lot. When we do quick overnight stops we usually use only the inverter to run the TV and small appliances. It's so much quieter than the generator. We also use it when under way and need smaller amounts of AC and the alternator keeps the batteries up. That saves a lot of fuel. I could directly wire the inverter but I much prefer a switch so I can't accidentally forget to shut off the inverter when shore power or the generator is on line. Getting older I find I need to idiot proof everything. Chuck

I can't be trusted with switches like that either, Chuck, but haven't had to worry about them. Both the Xantrex and the Victron sense when there's another source of AC and instantly stop inverting. In fact, with the Victron I can leave my PC on no problem while connecting or disconnecting from shore power. When on the shore wire it's like having a UPS with a 500 amp hour battery! The Freedom 25 might have done the same, but I never tried it. What model inverter are you using?

My inverter is a ProMariner 2000 watt. It's just an inverter, no charger. It needs to be turned on manually and switched to the inverter side of the transfer switch to connect to one of our AC panels. It's a heavy duty piece of equipment and very well built.

Hi Chuck
On our boat which we do a lot of extended cruising on we have the following set up:

1. AC Power sockets throughout boat that supply from shore power or generator via two switches that effectively operate as a two way selector on the main AC panel.

2. Dedicated separate inverter AC power sockets connected to the inverter. Inverter has own AC panel.

3. 12v DC power sockets throughout boat for 12v domestic appliances, including 12v cig sockets (Laptop, iPad, iPhone, hand held VHF and gps chargers, etc)

Having separate inverter supplied AC sockets has worked well for us cruising over the years.

Noel

Capn. Chuck posted:

     I'm ready to install my generator, so now I need
     to find a three way switch that will allow me to
     switch between the generator, shore power, and
     inverter. Here's the rub. The shore power connects
     to two panels via two separate power cords. The
     generator will need to connect to both panels.
     One is dedicated to the Air Conditioner. The
     inverter only connects to one panel. Anyone else
     have this set up and what is your solution? I'm
     thinking I may need two separate transfer switches.

One way to simplify this (at least in terms of day-to-day use) is to have an automatic transfer switch on either the inverter or the generator, or both. For example, in the case of the inverter, the shore-power connection would be led first to the auto-transfer switch, and from there to the AC panel. The switch would sense the load, and then IF there is no shore-power present at that moment, transfer the load to the inverter (which would presumably kick in automagically).

Adding the generator to the mix, I'd guess that you would want it to also be "upstream" of the inverter (but "after" the shore-power input), with it's output split between feeding the inverter's transfer switch, and feeding the Air Conditioner panel directly. At this point, the inverter would only kick in if there was neither shore-power or genset power available; and the inverter would NOT power the Air Conditioner -- but that's probably a given anyway, unless you have a real "King Kong" battery bank.

Assuming that the generator is a single-circuit/single-phase system, having two shore-power inputs obviously complicates this, possibly to the point that a completely automatic setup could not be conveniently (or safely -- there are both load and phase issues to consider) implemented. In that case, a single dual-pole manual transfer switch may be needed to select which shore-power input (and therefore which AC Panel) the geneset intercedes in. In this case, if you were running the Air Conditioner off the genny, all your other AC loads would have to be powered by either shore power or the inverter.

Now, if you were to install a split-phase 120/240-volt generator, things actually get somewhat simpler; each "side" of that split-phase output could power one of the existing AC panels, and at least in theory you could install inverters on each leg to take up the slack when neither shore-power nor generator is available. However, in this scenario you would need to religiously ensure that you are plugging those two shore-power lines ONLY into a proper pair of split-phase outlets, or BAD THINGS [tm] will happen. One way to insure against a plug-in problem is to convert those two independent (and presumably 30A) shore-power connections to a single 50A split-phase connection -- but this inherently limits the number of places you can plug in, which may be an issue depending on where you cruise. So... TANSTAAFL.

Thanks for more good suggestions. Time and tides wait for no man and replacing and rewiring the existing system is just not going to happen in the immediate future. That means working with what's there now and getting it as efficient and safe as possible without pulling it all out and starting over. I have had dedicated outlets on an inverter on our previous boat. While that worked well than, I don't want to have to inverter running full time to provide power to certain outlets. Using the KISS method, a simple way to switch between the three power sources and two AC panels is what I need to accomplish in the next two weeks. I also have ruled out automatic switches. I can easily find an automatic switch that will do everything I need. But anchored off Staniel Cay and having an automatic switch fail is something I don't want in the back of my mind while we are cruising in remote areas. The Next Gen 3.5 is a 120/240 voltage. Chuck

Capn. Chuck posted:

     Thanks for more good suggestions. Time and tides
     wait for no man and replacing and rewiring the
     existing system is just not going to happen in
     the immediate future. That means working with
     what's there now and getting it as efficient and
     safe as possible without pulling it all out and
     starting over.

Understood. But OTOH, you don't want to create potential operational problems if you don't have to. And during the install process is the best time to make those changes which will help insure that the future is as trouble-free as possible.

     I have had dedicated outlets on an inverter on
     our previous boat. While that worked well than,
     I don't want to have to inverter running full
     time to provide power to certain outlets.

I guess this depends in part on what you mean by "running full time". Modern "smart" inverters go into a "standby" mode wherein they draw very little power (perhaps 2-3 watts -- but I don't have a spec sheet handy) from the batteries when there is no AC load on them; so at least under "normal" cruising circumstances, there is really very little down side to leaving them "enabled" all the time. And on those occasions when you are on the hook for an extended period of time and are tightly budgeting every watt, you still have the option of shutting it off entirely at the breaker panel when you know you'll have no need for AC power for several hours (such as at bedtime).

     Using the KISS method, a simple way to switch
     between the three power sources and two AC
     panels is what I need to accomplish in the next
     two weeks.

Your mention that the generator you've chosen is a 120V/240V type actually makes this job MUCH easier, at least presuming a couple of "ground rules"...

First, is it safe to say that you are NOT planning to run the air conditioning off an inverter? To do so is not impossible, but it would require a really serious inverter and an downright HUGE battery bank to make it through even one night in the near-tropics. So as a practical matter... Well, it's not very practical.

Second, did I understand you correctly that ALL of the AC loads, except for the air conditioner, run off a single 120V/30A single-phase breaker panel?

Assuming both of these cases to be true, then the setup becomes pretty straight-forward. I would still recommend converting those two 30A inlets to a single 50A/240V type; but it isn't absolutely necessary as long as you remain vigilant about how and where you connect to shore power.

So... Each of the two AC circuits runs from its respective dockside inlet (preferably through a ground isolator) to one side of a suitably rated dual-pole/dual-throw switch, such as the Blue Seas #8363:

https://bluesea.com/files/images/products/8363.jpg

Both poles of the other "side" of this switch run to the generator output "hot" legs, and the neutrals from both circuits attach (together) to the generator's neutral tap, and from there to the rest of the boat's AC system (alternately, the switch may also switch the neutral legs; but I'm not at all sure this is desirable). One pole of the switch's common lugs feeds the inverter input, and it in turn feeds the main AC panel. When there is AC power present from either shore or the generator, the inverter's internal transfer switch will simply pass that through. The other pole's common lug feeds the air conditioner more-or-less directly (there may also be a simple one-circuit breaker panel intervening here, but for our purposes it is irrelevant).

That is about as simple as I can make it. You won't need to "segregate" your various AC outlets and appliances into "inverter-driven" and "not inverter-driven" groups, which is of course very convenient. You will have ONE switch to throw each time you connect or disconnect from shore power. And of course, you will need to ALWAYS test any pair of dockside power outlets you want to plug into BEFORE actually making the connections, to ensure that together they do indeed form a complete 120V/240V split-phase feed. A 50A/30A Y-cable would surely be a useful thing to keep on board.

     I also have ruled out automatic switches. I
     can easily find an automatic switch that will
     do everything I need. But anchored off Staniel
     Cay and having an automatic switch fail is
     something I don't want in the back of my mind
     while we are cruising in remote areas.

The above scenario assumes that your inverter is equipped with an internal automatic transfer switch, as most of the better modern models do. I really would not worry about that switch; virtually no inverter failure I've ever heard of has been due to that particular part. But if you insist (or if your inverter is not so equipped), you could add a second manual switch to implement the "pass through" function (the Blue Seas #1481 would work, but it would be mislabeled -- perhaps you could convince them to whip up a custom faceplate for you?); it will just be that much more of a PITA to deal with on a daily basis.

     The Next Gen 3.5 is a 120/240 voltage.

I assume you know this; but mostly for the sake of any possible "lurkers" reading this thread: I did indeed check the Owner's Manual for that particular generator; and yes, it is (or at least "can be installed as") a proper 120V/240V split-phase unit, as opposed to a one single-phase output which can be set up as either (or even alternate between) 120V and 240V. That is KEY to making the above work.

Capn. Chuck posted:

     The Next Gen 3.5 is a 120/240 voltage.

One other thing I just thought of...

That particular generator has a rather marginal capacity for what you want to do, at least presuming that your air conditioner is large enough to keep a mid-size cruiser cool where you're planning to go. That "30A" rating applies ONLY if it is running in single-phase mode (see page 23 of the Owner's Manual). For split-phase use such as I described above (see page 24 of the manual), which I think is really the only practical solution for you, each single-phase "leg" of the output is rated at only 15A.

Given this, you might want to seriously consider stepping up to the 5.5kW model, as shown at http://www.nextgenerationpower.com/5kwmarine.html.

FWIW, etc.