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Old 10-09-2018, 06:44 PM   #1
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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?
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Old 10-09-2018, 07:50 PM   #2
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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.
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Old 10-10-2018, 12:43 AM   #3
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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.
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Old 10-10-2018, 09:00 AM   #4
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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.
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Old 10-10-2018, 09:33 AM   #5
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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 canít 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.
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Old 10-10-2018, 09:45 AM   #6
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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.
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Old 10-10-2018, 09:59 AM   #7
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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

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Old 10-11-2018, 02:02 AM   #8
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Iím 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.
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Old 10-11-2018, 02:14 AM   #9
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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
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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Old 10-11-2018, 06:15 AM   #10
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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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Old 10-11-2018, 06:57 AM   #11
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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.


Which relay are you using? The alternating relay?

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Old 10-11-2018, 08:34 AM   #12
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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.
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...nvertercharger.

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Old 10-11-2018, 08:54 AM   #13
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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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Old 10-12-2018, 12:18 AM   #14
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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.
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Old 10-13-2018, 11:39 AM   #15
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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.
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.

Inrush current limiters for AC compressors
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