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Old 05-28-2018, 08:21 PM   #1
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Thoughts on how AC power comes aboard

Kingfisher is wired differently than previous boats I've had experience with.

When I wired my sailboat years ago, I installed a transfer switch so that AC power could be supplied by the shore connection or the inverter, but not by both.

Kingfisher has no transfer switch. Instead, the shore power goes directly to a small AC panel which feeds the hot water heater and the AC/DC refrigerator. It then feeds to the Xantrex charger/inverter before being distributed to the 110v outlets throughout the vessel.

In other words, all the 110v outlets aboard are actually supplied by the inverter rather than being fed directly by the shore power connection. As a result, we trip the inverter's breakers (2,500 watt rating) in the winter time if we plug in two space heaters.

I would like to be able to have more capacity for dockside power during the winter months, such as an engine room heater plus a cabin heater or two. It doesn't give me confidence knowing that the relatively low-power rated breaker might trip when I'm away from the boat during extremely cold weather.

Thoughts?
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Old 05-28-2018, 08:30 PM   #2
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What is your shore power supply-1 x 30A/125V; 2 x 30A/125V or 1 x 50A/250V?
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Old 05-28-2018, 08:32 PM   #3
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1 x 30A/120v
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Old 05-28-2018, 08:47 PM   #4
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Assuming efficiency is 100% and with a resistive (space heater) load, 30A/125V = 3750W.
If each space heater draws 1200W to 1500W, there will not be much shore power capacity left to run anything else. My first suggestion would be to install another shore power inlet (SmartPlug) and wire it through a separate double pole circuit breaker to feed a sub-panel that feeds the outlets that you use to power the space heaters.

What are the power ratings of the space heaters?
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Old 05-28-2018, 09:03 PM   #5
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You have 30 amps to work with. You are sending 11 amps to the hot water heater, 2 more to the refrigerator and you have an inverter capable of handling 20 amps. If your inverter is throwing a breaker, either it has a faulty breaker or you are drawing too much power. If you are drawing too much power changing thing is only going to result in the shore side breaker popping instead of the inverter.

How much power are you drawing through the inverter before you plug in the heater and how big is the heater?
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Old 05-28-2018, 09:50 PM   #6
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You will have to look up the rating on the transfer switch in the Xantrex. That's the max that it can pass through from shore power. I wouldn't be surprised if it's 30A, in which case it can pass through the full shore power capacity. Next you will need to check wire sizing to confirm it can handle 30A. Then if everything else can handle it, put in a 30A breaker.
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Old 05-29-2018, 02:51 AM   #7
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You have 30 amps to work with. You are sending 11 amps to the hot water heater, 2 more to the refrigerator and you have an inverter capable of handling 20 amps. If your inverter is throwing a breaker, either it has a faulty breaker or you are drawing too much power. If you are drawing too much power changing thing is only going to result in the shore side breaker popping instead of the inverter.

How much power are you drawing through the inverter before you plug in the heater and how big is the heater?
We don't use the hot water heater's electric element at all (only the heat exchanger when running the diesel), so the only power we're using at such times would be the fridge and a few small LED cabin lights. The battery charging system is there, too, of course, but with batteries full at the dock there shouldn't be much current drawn.

The ceramic disc space heater maxes at 1,500 watts, but we rarely run it much above its lowest setting. We have a 1,200 watt oil-filled space heater in the forward cabin but the two can't be run simultaneously. Since the Xantrex handles 20 amps, it seems as if we're giving away almost 10 amps by feeding our 110v system through it.
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Old 05-29-2018, 03:11 AM   #8
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Assuming efficiency is 100% and with a resistive (space heater) load, 30A/125V = 3750W.
If each space heater draws 1200W to 1500W, there will not be much shore power capacity left to run anything else. My first suggestion would be to install another shore power inlet (SmartPlug) and wire it through a separate double pole circuit breaker to feed a sub-panel that feeds the outlets that you use to power the space heaters.

What are the power ratings of the space heaters?
Yeah, I see where I'm running up against that 30 amp ceiling whether or not the Xantrex is feeding the 120v system. It might take both heaters, but not much else. That second feed would solve the problem, wouldn't it?
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Old 05-29-2018, 04:12 AM   #9
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Probably not a viable option for you unless thinking of replacing the Inverter. However, I had a similar situation and went the Victron Multiplus PowerAssist option which I find works very well for me. In my set up (240 / 16 amp shore power) my AC input (via a Shore / Generator selector switch) goes to 2 Victron Multiplus inverter/charges (12/3000/120 configured in parallel).


- If AC in, they will pass-through the 16 amps and "agument" up to an additional 15 amps (drawn from battery bank) depending on load.
- If no AC in then it switches to inverter mode and can then provide (depending on temperaturate derating etc) about 20 amps from the batteries.



The AC out from the inverter is also split into 2 with the second output (AC-2) only being powered if there is AC in (ie not inverter only). We have our hotwater on this circut so this load for that does not come from the batteries.



Took a lot of heavy battery cable (and some battery monitoring stuff etc) but now that it's in I'm very pleased with it. When this stuff works its sort of like magic.
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Old 05-29-2018, 07:07 AM   #10
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As others have noted, it sounds like you are exceeding the limits of 30 amps. But where is the "inverter breaker" that is tripping. Is it on the main AC panel. AFAIK there is no internal AC breaker on a Xantrex inverter/charger. Even though it is rated to supply 2,500 watts AC while inverting, it will pass through the full 30 A available from shore power. There is a thermal overload internal breaker but that only operates on inverter power,



So, the point is, it may simply be a weak panel breaker that is tripping and it will be easy to replace.


The ultimate solution is to install a separate 30A shore power inlet to power a dedicated 120V outlet for one of the heaters.


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Old 05-29-2018, 07:12 AM   #11
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Easiest is run an outlet off the main panel before the inverter for the heater (with 15A breaker)

Better would be to iinstall another 30A cord/inlet just for the heater.....but if you never turn the water heater on, back to paragraph 1.
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Old 05-29-2018, 07:22 AM   #12
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Quote:
Originally Posted by psneeld View Post
Easiest is run an outlet off the main panel before the inverter for the heater (with 15A breaker)

Better would be to iinstall another 30A cord/inlet just for the heater.....but if you never turn the water heater on, back to paragraph 1.
Agree with the above.

On most panels it is easy to bypass the inverter for one circuit or another. Just look at how it was done for the hot water heater. The problem is then doing without that circuit when you are not on shore power.

I solved this issue on Bay Pelican by adding a circuit which fed only two duplex outlets (both added as well). This circuit was powered only by shore power or the generator.
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Old 05-29-2018, 09:03 AM   #13
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First thing is find out what current limit is for the Xantrex when in pass through mode. I doubt it is limited to 2500W or 20A. That would make no sense. Should be 30A. Look up in the manual or on the net.

If pass through is limited to 30A, you may have an undersized breaker somewhere in the path.
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Old 05-29-2018, 02:27 PM   #14
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Quote:
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As others have noted, it sounds like you are exceeding the limits of 30 amps. But where is the "inverter breaker" that is tripping. Is it on the main AC panel. AFAIK there is no internal AC breaker on a Xantrex inverter/charger....
On the Xantrex itself there's a dual-pole breaker that trips. This isn't the same unit, but similar:



Neither the main panel breaker nor the dock breaker have tripped.

Quote:
Originally Posted by psneeld
Easiest is run an outlet off the main panel before the inverter for the heater (with 15A breaker)....
Quote:
Originally Posted by Bay Pelican
...I solved this issue on Bay Pelican by adding a circuit which fed only two duplex outlets (both added as well). This circuit was powered only by shore power or the generator.
Yup, I suspect that this is the easiest/cheapest way to address this. It doesn't solve the absolute limitation of the single 30 amp supply, but it does cut the inverter...the limiting factor in this situation...out of the loop.
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Old 05-29-2018, 03:26 PM   #15
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You can change to 50 amp supply (If available on the dock) then wire in dedicated circuits for the two heaters.

I am not a fan of heating a boat with space heaters, it's the number one cause of boat fires in the PNW.
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Old 05-29-2018, 03:29 PM   #16
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I had my marina add a second 30 amp outlet to the power pedestal. It is on a different leg so I get full 30 out of each (which I never need). My a/c panel on the boat has two rows and main breakers, each coming off a different cord and shore outlet.

I still have to monitor draw when everything is going at once.
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Old 05-29-2018, 07:04 PM   #17
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I support Robert's comments at post #9: a big part of your problem is the crap Xantrex inverter and replacing this with a Victron which has power-sharing and power-boosting abilities may actually end up being the cheapest and easiest fix. It would likely bring you other benefits as well. If you read up on the features of the MultiPlus, you may well be converted (pun intended!)
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Old 05-29-2018, 08:52 PM   #18
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He already has a cheap fix or two or three, a new inverter is far from cheap...especially power assist types and the brands suggested.

If he doesnt need additional power, thats his call.... 30A will run 2 space heaters if all good quality connections and wire us used, much safer if one is on low....

I upgraded to 50A and its far from cheap.

Right now the only problem seems to the limitation of the inverter, though on many inverters, they would pass through 30A like mine does.

No need to complicate or bloat the budget.... there are several cheap, simple fixes.

Not the ones I chose, but I live aboard full time, often in chilly weather...so my budget was geared towards that. Not everyone needs the same.
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Old 05-29-2018, 08:55 PM   #19
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Originally Posted by tiltrider1 View Post
You can change to 50 amp supply (If available on the dock) then wire in dedicated circuits for the two heaters.

I am not a fan of heating a boat with space heaters, it's the number one cause of boat fires in the PNW.
Yeah, I hear you loud and clear. I discovered the Pelonis ceramic disc heater decades ago and have gone with that (or with an oil-filled heater) ever since. No exposed resistance elements, tipover protection, thermostatic control, and the best part is that it operates at a temperature below the combustion point of paper. It will discolor surface finishes if left up against something, but it won't set it afire.
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Old 05-29-2018, 09:03 PM   #20
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He already has a cheap fix, a new inverter is far from cheap...especially power assist types and the brands suggested.

If he doesnt need additional power, thats his call.... 30A will run 2 space heaters if all good quality connections and wire us used, much safer if one is on low....

I upgraded to 50A and its far from cheap.

Right now the only problem seems to the limitation of the inverter, though on many inverters, they would pass through 30A like mine does.

No need to complicate or bloat the budget.... there are several cheap, simple fixes.

Not the ones I chose, but I live aboard full time, often in chilly weather...so my budget was geared towards that. Not everyone needs the same.
Yeah, I have no interest in replacing the inverter at this time. The simple solution noted will address my current need (*groan*) without requiring much investment. The current AC panel even has two extra breakers fed directly by shore power. Heck, I could even install a switch such as below and simply have ALL the boat's outlets fed either by shore power or inverter.

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