Fitting an inverter into an existing AC system

[Jimlad]

Hi Folks

My existing shore power set up takes the feed into an RCD protected distibution box and then feeds individual MCB's to sockets, fridge, calorifier, battery charger and galley sockets. All works well.

I now want to install a combi inverter/charger.
I believe I will need to fit an RCD into the feed from the inverter. I will of course disconnect the existing charger feed as this will be redundant and I will need to ensure that the calorifier can never be run from the inverter power.

Someone told me that I will need some 'load-shedding' arrangement within the distribution box, but I'm not sure what is meant by that.

Any other issues that I need to know?
Some pointers from someone who has been down this route on how I should do the job would be much appreciated.

[a64pilot]

OK, I'll admit I don't know what an RCD is.
Way I wired my inverter / charger is disconnected the wire from the Master AC circuit breaker and connected it to the inverter, then wire goes back to the Master AC circuit breaker. It's designed of course for all the AC power to pass through it.
I do have to be smart enough to not run the AC's, Water heater, and other battery charger off of the inverter of course, it's not fool proof.
But I left my other battery charger in place as when I run the generator it does supply enough power to run both and running both of course gets me through bulk phase of charging faster. I have an AGM bank, so it can take anything I can throw at it.

[a64pilot]

Load shedding is a term to mean for example if shore power is lost, automatically the power to your Air Conditioner is cut off.
Common on aircraft for example that if the alternator goes off line, all non critical electrical loads are automatically "load shed"

Maybe it's an American term?


Link to my inverter, it discusses installation wiring

http://www.magnum-dimensions.com/sit...-MS-Manual.pdf

[exMaggieDrum]

My current boat has all shorepower AC go to the inverter and then the inverter AC output goes to the AC distribution panel. This means that the inverter has to work for any AC on the boat. It is easy to install this way, provided the inverter is a marine type with an AC transfer switch that will make a ground to neutral connection when off of shorepower and break that connection when shorepower is sent to the inverter. This is a US type setup and I don't really know if it is required for European or other boats. There have been numerous posts about this.

Another way is to wire shorepower to the inverter and then have the inverter output to a "split" AC panel, i.e. so you can isolate heavy AC uses (water heaters, air conditioners, heaters, etc.) to only have AC when shorepower is available (or from an AC genset). If this is done the AC neutrals have to be split and isolated for the shorepower only circuits and the inverter only circuits. Same downside if the inverter dies - you will not have AC to the inverter loads and will have to route around it if necessary on a temporary basis. But you avoid ever having the situation of overusing your batteries for high usage loads. I've attached a sample diagram of this design.

Another way is to wire in a rotary selector switch so you can bypass the inverter, or leave it in the circuit. If the inverter goes down or has to be removed I can easily bypass it. This is more complicated but is what I am doing on my boat right now. As a tech, I had to wire around many inverters when they had to be removed for service or were left in place but were not working. The AC rotary switch has to have the correct switching configuration - there are a great many so you have to really know what you are doing to do this. You can also put in a temporary terminal strip to take the AC input leads from shorepower that goes to the inverter and attach them to the AC output leads that go from the inverter to the AC panel, on a temporary basis.

Another, less common design (which my boat came with) is to have separate AC panels and separate shorepower inlets to split the AC heavy loads from the AC light loads. There is a 1-2-both AC rotary switch to allow either shorepower to power either or both panels. This is somewhat unusual in my experience.

[witzgall]

Residual Current Device. You can think of it as Ground fault protection for the whole boat, not just GFCI protection at outlets.

This can save a swimmer's life if there is AC current that would otherwise enter the water from a boat. Children swimming are killed every year by this issue and an RCD goes a long way to reducing these deaths.

Chris

Originally Posted by a64pilot

OK, I'll admit I don't know what an RCD is.

[witzgall]

Some inverter chargers, like Victron's Multiplus units 3000w and their quattro line, have two outputs, one will be powered by the inverter, and one will not.

I would look for a unit that has the features you want: output, reputation, features, and then read the installation manual for THAT UNIT. It should tell you how it should be installed.

Chris

[Jimlad]

Hi Pilot, Drum and Witz

Thanks for the input - well done W for knowing what an RCD is!
I guess its a peculiarly British term.

I personally dislike electricity as I can't see it!

Nevertheless our boat refit has to be done on a strict budget so I try to avoid
hiring in expertise. Hence my use of this forum.

Keep ideas/views/opinions coming forumites! Wiring diagrams welcome!

Oh yes one last thing, our refit is an F&C 44 ketch - who's heard of that marque?

[a64pilot]

Of course read the Manual for the unit you buy.
Just know there is no reason to make it complicated and expensive, adding second panels etc. just have to have enough smarts to know you can't charge your bank from the other charger, running it off the bank. No perpetual motion machines unfortunately.


Sent from my iPad Pro using Cruisers Sailing Forum

[rwidman]

It's far from as simple as some folk have made it. If you arrange the inverter to power the boat's AC electrical panel, it, and the battery bank will have to have the capacity to power the entire boat's electrical load which will probably include air-conditioning and a water heater. As a practical matter, that's impossible. And as someone mentioned, you would be trying to charge the batteries that you are drawing power from. Not a good idea.

For practical purposes, you will be limited to small plug in appliances so the simplest thing to do is just to power the 120 volt receptacles. You will need to install a switch to disconnect the cable (both conductors) from the electrical panel and instead, connect it to the output of the inverter. Don't forget overcurrent protection unless it's built into the output of the inverter.

Some inverters have a built in transfer switch to do this.

Disclaimer: This is not step by step instructions. If you don't understand what I posted, hire a pro. Electricity and water are not a good mix.

[a64pilot]

Or you can just be smart enough to not try to run the AC, water heater, and any other high amp loads.
Just like you do if you plug in a Honda suitcase gen for example


Sent from my iPad Pro using Cruisers Sailing Forum

[carstenb]

One issue that had us scratching was that all shore power went through the inverter. We installed a 1200W inverter - result? we could only draw 1200W shore power or else the inverter crashed.

hmmmm - we had to install an automatic switch so whenever the shore power was plugged it, it circumvented the inverter

another thing to be aware of is some inverter have a high power usage even when they are "turned off" drawing up to 1AH

[Dockhead]

Originally Posted by carstenb

One issue that had us scratching was that all shore power went through the inverter. We installed a 1200W inverter - result? we could only draw 1200W shore power or else the inverter crashed.

hmmmm - we had to install an automatic switch so whenever the shore power was plugged it, it circumvented the inverter

another thing to be aware of is some inverter have a high power usage even when they are "turned off" drawing up to 1AH

Modern Inverter/Chargers run all shore power through the inverter.

What the OP needs to keep in mind is that many inverter/chargers separate the ground into boat ground and shore ground. So I think you actually need two different RCD devices, because the one on the shore power side will not work after the inverter.

Be sure and wire in a bypass switch so you can bypass the charger/inverter in case of failure -- don't ask me how I know this is needed.

You must really use a professional electrician or EE to at least design the system -- this is a life safety critical system.

[captjcook]

I agree with Dockhead on the bypass switch and don't ask me why either...I have a 8 gang 110 ac panel, I "broke" split the buss bar feeding the hi-power stuff directly including a breaker to the inverter charger (no back feed) and just the two outlet breakers from the inverter. Having lost three Heart/Zantrex units to lightning spikes??? I am going to use separate units...not a combi, I can live without inverter...but when it takes out charger as well it is...well you got it...good luck with your refit! Cheers!

[Dockhead]

Originally Posted by rwidman

It's far from as simple as some folk have made it. If you arrange the inverter to power the boat's AC electrical panel, it, and the battery bank will have to have the capacity to power the entire boat's electrical load which will probably include air-conditioning and a water heater. As a practical matter, that's impossible. And as someone mentioned, you would be trying to charge the batteries that you are drawing power from. Not a good idea.

For practical purposes, you will be limited to small plug in appliances so the simplest thing to do is just to power the 120 volt receptacles. You will need to install a switch to disconnect the cable (both conductors) from the electrical panel and instead, connect it to the output of the inverter. Don't forget overcurrent protection unless it's built into the output of the inverter.

Some inverters have a built in transfer switch to do this.

Disclaimer: This is not step by step instructions. If you don't understand what I posted, hire a pro. Electricity and water are not a good mix.

Well, it actually IS so simple, if you use a normal charger/inverter.

You run all the shore power through the C/I.

The C/I will power the whole AC system from the inverter, if shore/generator power is not present. One cool thing about this is that it acts as a UPS, and keeps everything working in case someone kicks your shore power plug out, for example. Obviously you have to be careful that this doesn't happen without your knowing about it, and you kill your batteries.

Any loads you want to never run from the inverter, you hook up to the special load-shedding circuit of the inverter. People often connect their calorifier immersion heaters up to this. But I don't -- I sometimes run the immersion heater off the inverter.

For this to work well, you need appropriately sized:

1. inverter
2. battery bank
3. alternator

If any of these is too small, then the system won't work as well.

On my boat, the inverter is 3 kW (for a few second at a time, 6kW), and the alternator will produce about 2.5kW. So I can happily run washing machine, dryer, microwave, electric kettle, or calorifier off this system PROVIDED it's not all at once -- obviously you have to manage the loads so that you don't have too many things running at once, but this is obvious and is the case even with normal shore power.

With the main engine running, it's almost like having shore power (3kW vs 3.6kW), which saves a lot of generator hours. And the batteries will power the system for a while without any power being produced at all. This gives you seamless, continuous AC power in all circumstances, at dock, at anchor, under sail, under motor.

For example, if I'm running a load of laundry at the dock, when I switch off shore power, the inverter takes over using battery power. I then start my engine, and the alternator powers the system through the inverter. Maybe I'll sail for a while -- batteries take over. Drop anchor, and start my generator, and finish drying the load. All without ever switching off or interrupting the washing machine.

As A64 said, you have to be aware of what loads are being run at the same time, and manage them, but that is always the case anyway and on every boat. It's actually easier to manage loads with the charger/inverter, because:

1. The C/I will sound an alarm in case you overload it.
2. You can set the C/I to limit power taken from shore power or generator, which will prevent overloading those systems, which is extremely handy. The C/I will supplement shore or generator power with inverted battery power to supplement that, so on my boat, for example, I can run loads of up to 3.6kW (shore power system capacity) plus 3kW (inverter capacity) - 6.6kW for as long as the batteries hold out, which is extremely handing for short-term loads (using the kettle for a couple of minutes when the system is already at capacity) or surge loads (electric motor start-up loads), which would otherwise blow your shore power breaker, or overload your generator.

[Dockhead]

Originally Posted by a64pilot

Or you can just be smart enough to not try to run the AC, water heater, and any other high amp loads.
Just like you do if you plug in a Honda suitcase gen for example


Sent from my iPad Pro using Cruisers Sailing Forum

!