AC power

I recall reading here somewhere about some kind of electronic load balancing thing I can install but can't find the thread. I want to wire my boat so that when the water heater comes on, power to another circuit is cut to avoid overloading the circuit. Basically I want to automate the 30 amp dance; what is this thing called?

Load shedding is one term. I may have participated on that thread you mentioned. As I recall, no good solutions were found. These things tend to have very specialized, often industrial, applications. And big price tags.

So I do the 30A dance.

One huge help has been a selector switch so I can choose to power my water heater from either of the two 30A legs I have coming into my panel. If I'm not using heat or air conditioning, I can power it from that side. If I am, I'll switch it to the other side.

It also has an "off" selection, so I can flip it off long enough to run the range or whatever, then flip it back on when done.

You can use relays. I used a relay to turn the hot water heater on when ever I was plugged into shore power. You can set it up to turn off one circuit when it senses power on the other circuit.

I recently had a generator installed at my house. They installed a device that staggers the start of my air conditioners so they don’t overload the genny. You might want to look at the home generator market.

At the dock I use my phase matching inverter to cover any slight loads in excess of my shore power limit as the inverter makes up the difference. You can’t do this with the more common inverter that switches away from the shore power in this scenario as it would take the whole load and rapidly deplete your battery reserves. The inverter buffers the load peaks and the batteries are always fully charged by nightfall.

Since setting up this way infers that all my loads can be powered from the inverter, not just a set few, it opens up a potential problem space when your shore power is unexpectedly disconnected and your inverter is running the whole show. To solve that problem I have all but a few electrical outlets on a relay that opens whenever there is a loss of shorepower. Thus automatic load shedding. There is no complicated logic deciding between two high demand loads, all high demand loads drop when not on shore power. Peak load buffering is the main idea to get around choosing between high loads.

Works freakishly well, but requires an inverter with a decent capacity, decent battery banks and generally a condition where you really only need another 5 to 10 amps of shore power capacity. Otherwise, you really need to just bite the bullet and find a way to increase the shore power sizing.

I used to do the dance when running two electric heaters and the water heater for example, or running the trash compactor. They rarely all came on at the same time, but when they did, POP. Now, everything just works. YMMV, it really comes down to how close to the margins you are. With 50 feet and a single 30 amp to plug into, the answer for me was always.

OK, so load shedding was the term I was trying to recall and it seems I can use relays to rig it up; just what I was looking for. I'd also wondered if my inverter could help supply additional amps short term when on shore power during a spike, good to know with the right wiring that's possible; I'll have to get my head around how my inverter setup works.

Ghost your setup sounds just right, what's your inverter capacity and house battery sizing? Still getting my head around everything, but I have a 15amp inverter, 20amp battery charger, and 4x215 amp hour 6v golf cart batteries which I believe is a total capacity of 430amp hours at 12v. And yea I'll be on 30amp shore power 99% of time.

Phase synchronizing inverters aren't common. The quality guys like MasterVolt, maybe Victron and others make them, but not Xantrex.

As described above a phase synchronizing inverter can help ride through short term, medium amperage loads and let a 5KW genset do the work of a 7.5KW one and keep it more loaded.

A relay to only power selected breakers would be necessary, but would require splitting the AC buss into low power, inverter only supplied loads and the others. But this is how a good inverter installation should work in any case.


But more money and work than I would want to fool with. Keep doing the load shedding dance for me

David

I’m using a 3k Victron Phoenix, which has an integrated 120amp charger. Batteries are I think 1200ah lifelines AGMs. I just had to replace the original Victron, the new one now has the load shedding relay built in, which would have saved a lot of effort originally. Obvious downside is it all works as a system, so not a single component upgrade, but was upgrading start to finish at the time anyway. Also, when the inverter internal transfer switch failed recently, I realized just how much of a single failure point it was. Interesting tidbit, even though the internal transfer switch failed, the inverter kept on working. But I could not charge and could not use shore power, just watch my expensive battery bank slowly drain. Future project will include an ability to bypass the inverter for plane Jane shore power.

Victron has come down in cost quite a bit over the years and while still expensive, much more competitive now.

djmarchand said:

Phase synchronizing inverters aren't common. The quality guys like MasterVolt, maybe Victron and others make them, but not Xantrex.

As described above a phase synchronizing inverter can help ride through short term, medium amperage loads and let a 5KW genset do the work of a 7.5KW one and keep it more loaded.

A relay to only power selected breakers would be necessary, but would require splitting the AC buss into low power, inverter only supplied loads and the others. But this is how a good inverter installation should work in any case.


But more money and work than I would want to fool with. Keep doing the load shedding dance for me

David

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How would you prevent a grid tie inverter from sending out power to everyone on the dock? When the AC power dips or would want to brownout, the grid tie inverter would desire to prop up the grid, which could be other people running their heavy loads at the marina. Your boat batteries would be supporting their power use.

I want to wire my boat so that when the water heater comes on, power to another circuit is cut to avoid overloading the circuit. Basically I want to automate the 30 amp dance; what is this thing called?

Automatic Load Shedding can be done with a simple about $60 relay from Graingers.

Load control is wired to open a NC (normally closed , passing current) relay with a thin wire from the higher priority load, as it turns on. .

They can be daisy chained so the air cond can turn off the fridge and water heater.

The fridge would be the control for the HW heater as the heater can sit for hours with no power .

With a switch to enable/disable the sensing relay living well on a 15A house circuit in a 30A boat is no big deal.

FF said:

I want to wire my boat so that when the water heater comes on, power to another circuit is cut to avoid overloading the circuit. Basically I want to automate the 30 amp dance; what is this thing called?

Automatic Load Shedding can be done with a simple about $60 relay from Graingers.

Load control is wired to open a NC (normally closed , passing current) relay with a thin wire from the higher priority load, as it turns on. .

They can be daisy chained so the air cond can turn off the fridge and water heater.

The fridge would be the control for the HW heater as the heater can sit for hours with no power .

With a switch to enable/disable the sensing relay living well on a 15A house circuit in a 30A boat is no big deal.

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Which relay are you using? The alternating relay?

John

sdowney717 said:

How would you prevent a grid tie inverter from sending out power to everyone on the dock? When the AC power dips or would want to brownout, the grid tie inverter would desire to prop up the grid, which could be other people running their heavy loads at the marina. Your boat batteries would be supporting their power use.

Click to expand...

Well even though they do synchronize phasing with the grid (or more typically, the genset) power, these marine inverters are not "grid tie". They have circuitry to only produce enough power to make up for what the generator (typically) cannot cover, so they never send battery sourced power to the grid.

Check out the product description for MasterVolt Mass Combi or Victron PowerAssist inverters. This Soundings article describes the Mastervolt inverter- https://www.soundingsonline.com/news/its-not-just-an-invertercharger.

David

My problem with relays is my load shedding priorities change, literally with the weather.

Some days, air conditioning is #1. When I need to cook a meal on it, the range becomes #1. If it's a hot shower I'm interested in... Well, you get the picture.

Then there are variable loads. The battery charger is one example. At first, when they're accepting a bulk charge, the batteries can be the highest priority. As the charger ramps down, other things can be powered up without shutting off the charger.

The range has three burners. If I'm only using one, I can power up something else.

The battery charger often IS one of the biggest loads if you have a decent sized bank. This is one of the use cases arguing in favor of an integrated inverter/charger constantly monitoring shore power automatically. In that case, the charger is aware of the amount of shore power current remaining after your other electrical loads and will tailor itself to what is available. That in and of itself is a big part of the battle and why I accepted the additional risk of an integrated charger.

CaptTom said:

My problem with relays is my load shedding priorities change, literally with the weather.

Some days, air conditioning is #1. When I need to cook a meal on it, the range becomes #1. If it's a hot shower I'm interested in... Well, you get the picture.

Then there are variable loads. The battery charger is one example. At first, when they're accepting a bulk charge, the batteries can be the highest priority. As the charger ramps down, other things can be powered up without shutting off the charger.

The range has three burners. If I'm only using one, I can power up something else.

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If it is a starting current problem, when running too many other loads, then how about using an Inrush current limiter?

So far, I really have no use for an inrush current limiter as my 6500 watt generator can handle starting and running all loads simultaneously as can the shore power.
A startup current for a motor can be significantly higher than a running load.
My shore power voltage at my slip under heavy loads close to 30 amps does drop too low,IMO, it can get to low 100's. I suppose I should hook up the other shore cable then. Right now I don't run heavy loads hardly at all. I have a 30 amp DPDT switch to join all my loads to run off the single shore cable.

http://www.trawlerforum.com/forums/s4/inrush-current-limiters-ac-compressors-39637.html

gnaritas said:

I recall reading here somewhere about some kind of electronic load balancing thing I can install but can't find the thread. I want to wire my boat so that when the water heater comes on, power to another circuit is cut to avoid overloading the circuit. Basically I want to automate the 30 amp dance; what is this thing called?

Click to expand...

We also have the Problem of loads switching on automatically like heaters, chargers and also the water heater. In my opinion ist not a good solution to start automating as things get too compley for our kind of boats and automation also fails from time to time and gives you additional problems.
The water heater is the easyest to solve. The water heater generally has a big volume that is a buffer so the water heater generally can take ist time to heat up. I have had a Special heater made that has two heating elements. The one that comes in automatically just has 600 Watts and does not cause an overload Problem. If heat is needed quickly, I can manually switch on an additional 1500 Watts and of course have to monitor the total load.

A custom water heater sounds pricey, and as you say, the heater if left on will have hot water most of the time, so to me that's the simplest thing to load shed when more power is needed elsewhere. I'll never notice if when I turn on the coffee pot or the heater that the power is automatically cut to the water heater for a while until those loads reduce.

I'm a computer programmer, automating things is what I do, it's my nature, I despise doing things I can make a machine do automatically for me. I've found exactly the device I was looking for that will do exactly what I want here: https://www.defender.com/product.jsp?id=1452310

sdowney717 said:

How would you prevent a grid tie inverter from sending out power to everyone on the dock? When the AC power dips or would want to brownout, the grid tie inverter would desire to prop up the grid, which could be other people running their heavy loads at the marina. Your boat batteries would be supporting their power use.

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The Victron units do NOT feed the grid, UNLESS you have specifically programmed them to do so

The Victron units have 2 outputs, when you have shore power, BOTH outputs are provided with shore power ( and additional power of the battery in case you need more than your 30 amps).
When there is NO shore power, only the A circuit gets power ( from the batteries). with the built in SOC settings you can turn on/off a built-in relay to send power to the heater based on how full your batteries are, like you can power your heater when the batteries are full, but once they reach 75 % SOC you stop feeding the heater

Yes, it's called an easy-start and made and sold by Micro-Air. I'm putting one on my RV A/C so I can start and run it with a Honda 2Kw generator.

An update, I ended up going with this much cheaper solution[1] that did exactly what I want. Whenever the water heater comes on, it cuts power to the circuit the heaters are on allowing me to keep my two big draw items on all the time and not worry about them being on at the same time and blowing the breaker. Works beautifully and installed easily-as long as you understand AC power.

[1] https://www.amazon.com/gp/product/B00NUKJKLW/ref=oh_aui_detailpage_o03_s00?ie=UTF8&psc=1

I looked into this device as a possible solution for load shedding.

https://www.boats.com/on-the-water/paneltronics-ac-load-shedding-smarter-power/

In my case it was unnecessary for me to auto shed any loads so I never bought one.

Check out Paneltronix

I looked into this extensively since buying my trawler last summer. A previous owner installed a commercial "vessel automation system" (VAS) that among other things did automatic load sharing with a bunch of current sensors and dozen+ relays, a set of four microprocessor controllers from https://www.reliablecontrols.com/ with wireless web access and completely programmable operation.

The VAS also provided heat pump/HVAC temperature control, vessel security alarms, remote telemetry monitoring, and managed engine and diesel boiler operation plus hydronic pump and valve controls, and more. All this on a 40' Taiwan trawler with a single Lehman and two cabins. It was a very complicated science experiment, wasn't working at all when I purchased the boat last summer, was impossible for me to troubleshoot, and so I've removed it. The VAS was not a product meant for boats, rather for industrial plant and building systems automation (a previous owner was an installer). Very cool stuff and nice in concept. Too complex for real life. Parts available if anyone wants them...

• FWIW, generator load shedding modules from companies like Generac don't work by current sensing - rather they sense the changes in AC voltage frequency when the GenSet is overloaded and they shed circuits based on that. Thus won't work on your shore power or inverter.

• There are some RV load shedding packages that do what you want based on current sensing on the AC supply input, and one fairly attractive version is available in a marine package described here... https://www.defender.com/product.jsp?path=-1|328|2290000|2290002&id=1452310 and here https://www.paneltronics.com/ip.asp?op=load_shedding_system

• An alternative, to automated systems that use current sensing, is to configure simple relays (contactors) setup to disable the water heater when the HVAC compressor relay is energized. But I would be cautious on that front since it may not do what you want it's simple but could result in less than optimal results. Sure, you could get fancy with this approach using delay relays, or latching relays that have a settable delay between activation and release.

I'm simplifying everything on my boat to get rid of this automation crazy-town stuff and will only consider the Paneltronics product above if I get tired of manually managing overloads and tripped breakers. Simple is usually better. A side benefit is that I have removed a lot of wire, sensors, relays, controllers, etc. and had an opportunity to update and verify every circuit on the boat.

My final conclusion on MY boat is that whatever does automatic stuff on my boat needs a BYPASS switch and an OFF switch and can be explained to a six-year-old.

P.S., I'm involved in my work with mega-scale networks used by some of the worlds largest web-scale data centers – which are very highly, highly automated. But, I would recommend the same approach that they use. Whenever possible keep it simple. Automation should not make troubleshooting more difficult or create new failure domains.

Yea but that paneltronics load shedder is 6 times the cost of the simple relay based shedder I just posted, and the simple one works perfectly and does exactly what I needed; shuts down the heater when the water heater comes on. No fancy electronics or monitoring devices, just a relay in box designed to only let one circuit function at a time, cheaply.

The Paneltronics does fill a niche that can’t be accomplished by relays but if you don’t have that need it’s best to keep it simple.

Yea I know, I posted the link to the Paneltronics one earlier in the thread months ago; I just couldn't bring myself to spend that much money to solve such a simple problem.

I know there were solutions to this already proposed, but I've done this on two boats with the inverter configuration several people have mentioned. One was a MasterVolt MassCombi 2500W, the second my last boat with a Victron MultiPlus 3000W. Both have one AC input, which was direct from the dock (of course with appropriate breakers, etc.) and two AC outputs.

One of the AC outputs would only work when plugged into the dock, the other would work in both situations, as long as the inverter was on.

I specifically purchased these inverters for this feature, and it would allow me one "choke point" to control who uses that 30 amps. And if I needed more than 30 for some reason, I could also siphon power off the batteries if I was at the dock and plugged in, assuming that it could be charged up rapidly at some point. It did provide great visibility, but it was costly. Thankfully neither boat had an inverter already on board, so it made it less sticker shock.

I have a single 30A 120V AC shore input on my current boat, and have had to go back to the dance. The worst part of the dance is not remembering to turn the hot water heater on before you go to bed so that you wake up to a lukewarm or cold shower. I really, really hate that.

I will likely be replacing my current inverter with a similar one to the above, or even considering moving up to a 50AMP service (120 or 240 not sure yet). Those are 2020 projects as 2019 is already booked, bought and paid for

If you change to 50a. Go all the way to 50a 120/240v. 50a 120v plugs are phasing out for the 50a 120/240. I have no doubt that once you have 240v availableyou will come up with some clever ways to put it to work.

tiltrider1 said:

If you change to 50a. Go all the way to 50a 120/240v. 50a 120v plugs are phasing out for the 50a 120/240. I have no doubt that once you have 240v availableyou will come up with some clever ways to put it to work.

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That is definitely the current thought. However, switching to 240 is a bigger project than I want to take on this winter. All of the choices and things you have to do when going that route require some longer term thought.

My biggest issue is in the winter with heaters being on along with everything else. In the summer, I doubt this will be much of an issue. One of the proposals someone made was having just the heaters on a separate 120V 30A circuit, but I would prefer to not go that route if I can help it.

ghost said:

I’m using a 3k Victron Phoenix, which has an integrated 120amp charger. Batteries are I think 1200ah lifelines AGMs. I just had to replace the original Victron, the new one now has the load shedding relay built in, which would have saved a lot of effort originally. Obvious downside is it all works as a system, so not a single component upgrade, but was upgrading start to finish at the time anyway. Also, when the inverter internal transfer switch failed recently, I realized just how much of a single failure point it was. Interesting tidbit, even though the internal transfer switch failed, the inverter kept on working. But I could not charge and could not use shore power, just watch my expensive battery bank slowly drain. Future project will include an ability to bypass the inverter for plane Jane shore power.

Victron has come down in cost quite a bit over the years and while still expensive, much more competitive now.

Click to expand...

Ghost,
Your Lifeline house batteries are not 1200 ah, the biggest they make is 400 ah, deep cycle. You might be thinking starting battery.

Yes, a back up charging system is a great idea. Let me know what you do, I've got the same limitation, except I can charge using the engine, or a portable charger which would be a PITA.

> The worst part of the dance is not remembering to turn the hot water heater on before you go to bed so that you wake up to a lukewarm or cold shower. I really, really hate that.

I feel your pain and know exactly what you mean, thankfully that's no longer a problem.

My next problem is being able to actually use 30 amps, the PO wired the boat in such a way through the inverter that my breakers blow at 20 amps. I'm living on 20 amps.