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Old 25-06-2005, 18:51   #1
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Auto-transfer switch

Here is a link showing automatic transfer switches (by Todd Engineering) several of which I have installed:
http://www.cmsquick.com/prod_17_REL_TOD.html

The smalles load rated one is the LPT30 rated for 30A shore power.

Pay attention to what Gord wrote above: it uses a DPDT (NOT DPST as I mistakenly wrote earlier, sorry!) switch.

Of particular note, as Gord says, is the concept of neutral-to-ground shorting. ABYC (derived from the NEC's years of credibility) "requires" that a power source connect the neutral to ground ONLY AT the source. When using shore power somewhere on the shore that connection is already made and, therefore you need to make sure that an additonal connection between neutral and green-wire-ground on board is not made.

Integrated inverter/chargers DO automatically make that connection when operating in the inverter mode to adhere to that requirement. This can be a problem if you do not use a grounding isolator on your boat when using both the inverter to drive its dedicated loads AND shore power connected to your vessel's electrical system. Verify whether or not your inverter makes a ground to neutral connection by checking for continuity without power applied (in the case of the integrated inverter/charger it must be actively inverting to verify continuity).

The safety idea is that should your load develop a short between hot ground that a fuse or breaker on the inverter output will open circuit the source (ineverter). If there is no neutral-to-ground at the inverter then in that fault case you have a potential safety problem. Do not attempt to use a GFCI to get around this issue because your inverter will not like the GFCI in its output circuit. The GFCI will not function properly.

"Inverter-only loads" are loads that you are willing to drain your batteries in order to use them. This usually excludes outlets which someone might happen to plug space heaters into, for example. That doesn't mean that when shore power is available you want to drain the batteries to drive those loads. One exception to this is when you use shore power to power space heaters and you are "maxed-out" on your 30A shore power breaker AND you want to use the microwave oven. In that case you defeat the automatic transfer switch (modification required using a low-current SPST) or keep the manual transfer switch in the inverter position, remembering what is happening to your batteries because you ALSO have to shut off your battery charger otherwise it will attempt to provide the inverter power from shore power and the breaker will still blow.

Hope that this is not too detailed or confusing.
Check me out here Gord, did I mistate or mistake anything?

Regards,
Rick
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Old 26-06-2005, 02:11   #2
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i've never dealt with automatic transfer switches.what are their main function. i know the principal on what they do but what is their main application. if its for shore power and generator switching while your at the panel turning on your gen set why not just manually switch from shore to gen while your there.
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Old 26-06-2005, 12:50   #3
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Auto-transfer switches ensure that only one input power source is connected to the loads (AC Panel) at any time, but that one is always connected.
They are often used with Inverters, which do not have their own internal transfer relays, to select between Shore Power and Inverter or Generator power. The time delay allows the Generator to come up to speed before switching.
The LPT-30 (etc), that Rick linked, acts like an “Automatic” Two Pole 30 Amp (30A DPDT) AC switch (tho’ it’s actually an interlocked pair of contactors), that automatically connects Shore Power (when available) to your to AC Breaker Panel.
When you unplug from Shore Power, it automatically connects your Inverter output to power your Panel. You don’t have to “manually” switch anything.
The Shore Contactor is Normally Closed, and the Inverter/Gen Contactor is Normally Open. When the Shore coil loses Voltage, it opens and rhe Inverter closes (I think).
I wouldn’t normally recommend Auto Transfer Switches for boats. I don’t think that the seamless transfer of source power is necessary, in most cruising applications.
I suppose I'm just a twentieth century guy, in a twenty-first century world - I'd stick to the KISS principle and switch manually.
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Old 26-06-2005, 20:51   #4
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How and automatic transfer switch can benefit you.

Although your electrical system may be set up for cruising and hanging on the hook if it is also designed to be automatic you will benefit from the simplicity of not having to think about it....it just works for you when you need it.

Many modern laptops, compact stereos, LCD TVs microwave ovens and clocks have internal power supplies which "carry-over" operation during an automatic switchover between shore power and inverter operation. Many times I have been at the dock watching some DVD or listening to music when shore power was interrupted (for whatever reason). With the "autoinvert" function on the inverter/charger enabled a seamless transfer occurs with no interruption of my enjoyment.

If I am leaving the boat I disable the autoinvert function so that should shorepower be interrupted no battery drain occurs when I'm not there. I found a Casio alarm clock which has an LED backlight running onlywhen shorepower is available, otherwise it is out and can run on its own AA batteries for long times. Most batery backup clicks have horrible run times on their internal batteries, if you've discovered.

Do not confuse automatic with unreliable. Do not confuse what appears to be complex with bad mean-time-before-failure. Integrated circuits have very complex internal designs yet are orders of magnitude more reliable than simpler discrete components....that is what put man on the moon!

People decry their lack of ability to do their own repairs on modern automobiles yet do not take notice that, in general, they don't need repair as compared to the early ones which you could work on (other than changing oil and plugs).

Wouldn't you rather have your boat's electrical system function without anyone having to think about it? Wouldn't it be nice to be able to turn your boat over to someone without having to give them a long list of directions of how to switch this or that in case this or that happens should you have to leave and not worry?

Several of us in the industry have worked for years to make this a reality and know how to do it yet are frustrated with the fact that the marine market (below the superyacht level) is not as lucrative to develop as other markets (like the RV market which is a HUNDRED times more lucrative. The automotive market it a thousand more times more lucrative than that, just to put the economics in perspective).

At least on my own boat the electrical system is automatic enough so that I tell my wife: "You can connect or disconnect the shore power without being concerned with throwing any breakers or switches anywhere." "You can start the engine at anytime with or without shorepower attached without first checking any switches". If there is not shore power you can use all of your hairdryer and stereo and microwave." "If you see that LED turn yellow start and run the engine untill it turns green then turn off the engine". That is as complicated as it gets. Not totally automatic yet quite so. How simple is that? (what a diatribe!)

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Rick
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Old 27-06-2005, 00:10   #5
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i've hooked up at least 50 inverters in my time but they have always been automatic transfers, i see where the automatic switching device would be handy.
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Old 27-06-2005, 00:26   #6
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Well guys, you make authoritative & plausible arguments for “automation”. Like I said elsewhere, I’m just a 20Th century guy, but I can learn from credible debate ... automatic transfer it is.
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Old 24-03-2016, 12:10   #7
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Re: Auto-transfer switch

Found an old thread that is right on topic for me, so a little nudge. I have two generators which I want to feed into a the generator input of a Victron Quattro. The generators and Quattro will live in the engine room.

Current there is a manual transfer switch to select either generator in the pilot house. So to wire this up using the existing manual transfer switch it will take three more runs of 6GA cable to return the power to the engine room and then return both the always on inverter output and the pass through inverter output back to the pilot house and the distribution panel. Both the expense and time of running another 100 feet of 4 conductor 6Ga wire doesn't appeal to me and also the extra loses seems inelegant.

So I am considering just using an Auto Transfer Switch to switch between generators depending on which one is running. I am not keen on too much complexity since we like to be far from civilization on the hook. Could easily put together a manual transfer switch in the Engine Room that could bypass the auto switch if it failed. What have you seen in reliability in these?

Thanks everyone
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Old 24-03-2016, 12:14   #8
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Re: Auto-transfer switch

I've never seen one fail, but all relays will eventually fail.
Just mount it so you can get to it and in the event of failure you can wire direct by putting the generator wires on the same terminals as the output wire.
Just don't then hook up to shore power as it would then put power to your generator and I'm unsure what would happen then? Likely nothing as long as you didn't start it?
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Old 24-03-2016, 12:33   #9
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Re: Auto-transfer switch

Thanks a64pilot

It's true they all will fail sometime. I was looking at their web site and need to call to find out about the delay that is available to allow the generator to get up to speed before switching over.


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Old 24-03-2016, 12:58   #10
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Re: Auto-transfer switch

Automatic transfer switches like the one described here use spring loaded contactors to maintain connection to shore power. If the generator is turned on, the coil is then energized and the contactors snap over to the generator input. There is some small delay when it switches over and it depends on the TV or whatever power supply whether this delay will reset or turn off the device.

Keep in mind that every time the spring loade contactor moves, it produces a spark, the size of which is determined by the load on it at the time. Keep that in mind when deciding where to mount the ATS, somewhere where there are no flammable gases to ignite.

The auto transfer switch function in most inverter - chargers are solid state, and much, much faster at switching over from shore/gen power to inverter power, so one will more than likely not experience a reset or shutdown of a TV or satellite receiver.

I've installed quite a few inverter - chargers in RVs and love them because they combine 3 devices in one (inverter, ATS and charger) and a lot of RVs come with 12v converters that power the lights, etc but don't charge the batteries. Installing an 1800w inverter with a 40 amp charger drastically reduces generator run time by charging the batteries much faster and saves the installer and owner needless hassle by integrating all 3 devices.

I've installed a couple of inverter - chargers on boats, but never a separate ATS.
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Old 24-03-2016, 13:10   #11
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Re: Auto-transfer switch

This is the one I used, $85
Furrion 30 Amp Automatic Transfer Switch
Transfer is so fast when I'm on shorepower and crank the generator, nothing flickers, when I turn the generator off, my Magnum picks up the load so fast, nothing flickers.
There is a 30 sec time delay to allow generator to stabilize and if you want to, the delay can be set to zero.

On edit, its a 60 sec delay, not 30
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Old 24-03-2016, 20:20   #12
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Re: Auto-transfer switch

wether you have an ATS or manual switch, all other wiring on the boat is the same. I'm not sure what this post is trying to do....
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