So, it's time for a real and decent AC power system aboard Jedi. Our isolation transformer didn't isolate, the Freedom 30 inverter/charger is ancient technology and blew some diodes and I never liked it anyway, and we want 240V in addition to 120V. See s/v Jedi: Jedi AC power system (English)
for the old system.
I decided to post my progress in a separate thread here. This first post has the system diagram and explanations about equipment
selection. I attached the diagram to this post, click on the thumbnail for a bigger picture.
Every cruiser has a different view of comfort aboard. Some feel that it is good to go with the absolute minimum because that costs less and equipment
that is not installed can't break. If you are like that, you will feel an urge to post about all this being foolish. That's cool, but remember that we are a couple of "kids" born in the 60's and raised in a big City with all luxuries and don't want to find out how bad we can make it while still surviving and loving the cruising life.... we want computers
, DVD's, hot showers, clean clothes, A/C and loud rock music! ;-)
Due to circumstances, we have been in a marina for a year now.... after living 6 years at anchor
or sailing. It's a very different experience. Yes, we like it at anchor
better, but we are heading to places where we will have to moor more and anchor less.... we think.
When we are at anchor for some time, I always hang a "grouper zinc" overboard
which saves the other (more expensive) zincs somewhat. I did the same in this marina and to my horror I find myself on the 2nd one after a year... the first one completely eaten away. I even get bad dreams about it.
Some time ago, there was another thread on this forum about the Victron 3600W isolation transformer. I was impressed by it (my background is in electrical
and electronic engineering). My current
transformer is a joke compared to it. So I had a good look at other Victron equipment and what users think of it and it's availability and decided to go ahead and order it.
About the diagram. For the past months this lived in my head
but I just finished putting it in TurboCAD. In the rest of this post, I will explain the components from the diagram;
Crucial for spoiled cruisers like us. We had a Northen Lights 6 kW and just replaced it with a brand new one, same model. Most 60 Hz gensets have two windings, both 120V. You can connect them in parallel for 120V output, or in series for 240V or 120/240V output. We connected ours in series and only take L1 and L2 (the two "hot" wires with 240V between them) out of it, leaving the neutral for what it is. The metal parts
of the genset are connected to the boat-ground but there is no connection between ground and any windings. The output is a floating 240V.
- Isolation transformer.
These are basically transformers with a center tap on both primary (input) and secondary (output) windings. You can step up to double the input voltage, step down to half the input voltage or keep the output voltage the same as the input. The special feature is that the protective ground (green wire) from shore stops inside this unit, ie. there is no connection between shore ground and boat
ground, so no galvanic corrosion
. Even better: there is no galvanic connection between the shore AC service
and the boat
, making the whole boat installation
We keep the output of the transformer at 240V floating. This means that both output wires are hot (no connection of one of them to ground). We prefer to take 240V from shore so that we have less loss in the cable and less trouble with melting contacts in the plugs etc.
Our setup is not a standard configuration. Most inverter/chargers would need internal modification which is not easy and voids warranty. Lucky for us, the Victron MultiPlus and Quattro units allow you to change the configuration with internal small (DIP) switches or even with a connected PC. The big difference with standard configuration is 1) 240V output, 2) 60Hz output and 3) no neutral (inputs and output are all floating). Compare this to our old Freedom unit: 120V output only but 60Hz and output neutral is grounded with an internal relay when inverter
is switched on.
We have an EU version of the Quattro model. It's standard features are: 230V, 50Hz, 3000W, 12V DC, 120A battery charger
, 50A AC input and a 2nd 30A AC input. You can change the inverter
to 240V and 60Hz output.
This is almost the best part of it. An auto transformer has only one winding with center tap (or two equal windings in series). It is much like the windings in the genset. You connect the 240V floating AC to the winding and the center tap becomes the neutral. You create your own neutral. So after this, you have two hot wires with 240V between them (the auto-transformer only uses them, doesn't "change them") and a neutral that gives 120V between itself and any one of the hot wires. This connects to a standard 120/240V switchpanel, spreading/balancing the 120V consumers over both hot wires. I know this sounds like you can do without this transformer, so now the good stuff about it: the auto transformer (called AT from here on) takes care of any in-balance between the two hot wires, to a maximum of 32A. I will explain this with an example:
Let's say we connect our genset to supply the 120/240V directly. This means we pull two hots out of it (L1 and L2) and a neutral. Each hot can carry a maximum of 25A. If you would draw 20A out of each hot, you can't switch on another 120V 10A load because that would overload the genset winding (30A instead of max. 25A). But at the same time, you have 5A left in the other winding... you just can't use it.
Now the same scenario with the AT. You don't use the neutral from the genset, only the two hot wires. This means the genset is always balanced perfectly. There is no problem loading one hot wire with 20A and the other with 30A behind the AT. The genset only sees a 240V 25A draw and the inbalance is only 10A which is far below the AT maximum of 32A. You can take it much further: draw 40A from L1 and only 10A from L2. For the genset, this is still 25A at 240V and the in-balance is now 30A, still below the 32A max. of the AT.
The AT makes sure you can use all available power without worrying about balancing the two hot wires in a 120/240V setup.
There are many other ways to put an AT to use, like step up from 120V to 240V (connect input-hot to center tap, neutral top one side of the winding and get 240V between both sides of the winding).
The Victron AT has an relay that can connect the center tap to ground. The control signal comes from the inverter/charger; only connecting it to ground when the inverter switches on. In our setup, this isn't needed because everything in front of the AT is floating. Instead, we connect a jumper wire between the center tap of the AT and the boat ground, ie: it is always grounded.
- The 1500W inverter and the 50A charger.
These are just there as a second system, backup or whatever you want to call it. Maybe we will use the inverter for light loads at night when I determine that is has less overhead (less draw from batteries) later. The charger is one of those "world" models so you can connect it to AC anywhere in the world, regardless of voltage and frequency. Nice for backup or when leaving the boat for a couple of weeks.
- The main panel service select breakers.
Here I get a little tricky. Almost every AC panel have these: two double pole breakers with some slider that forces you to switch off one before you can switch on the other. They are intended for shore/generator or generator/inverter selection. I select between the main system and the small inverter. But now the tricky part: the main system is 120/240V and the small inverter is 120V only. The double-pole breaker for the main system has L1 on one pole and L2 on the other, at 25A breaker value. We don't put neutral on there for several reasons (need 3-pole breaker, neutral=jumpered hard to ground etc.). The second breaker, for the small inverter has a trick: one pole switches L; neutral isn't connected here either and the second pole inter-connects the two 120V bus bars of the panel (L1 and L2). This means that the output of the small inverter is available at all 120V breakers. You normally need two inverters for that, or an extra AT.
- The 12V wiring.
Normally, the inverter (or inverter/charger but it is about the inverter part here) must be very close to the batteries
. However, as you can see in the diagram (blue line), the inverter/charger is in the engine
room and the batteries
are in the main cabin
. There is 30' of wire distance between them (30' positive and 30' negative). This means that the voltage drop becomes significant and full inverter output is not available. So, keep it as close to your batteries
We can get away with this for several reasons: we have 12V bus bars in the engine
room in addition to the main ones in the cabin
. The distance between them is 20', so 2/3 of the total length. The cables
between these bus bars are two 4/0 for positive and two 4/0 for negative. A brute force solution with a lot of weight and cost. It also means that the voltage drop at 400A is 0.39V. A single
2/0 cable as often used would create a drop of 1.232V and would be overloaded at 400A.
The reason for these massive cables
is the big alternators on the main engine for charging
the house batteries (max. 440A output).
But there's more: who needs 3000W of inverter power? not us, normally. We select an inverter/charger first for charger output and this brings us to biggish units. The only use for 3000W inverter would be to power the water
maker when the genset doesn't work
, so in a fall-back scenario. Our batteries wouldn't handle that for long so we would run the main engine and it's 12V alternators provide the juice. And these alternators are connected to the same bus bars in the engine room, making the path to the inverter/charger very short again. (when two power sources are connected parallel, like alternators and batteries in this example, the source with the highest output voltage "wins" and supplies all the power). As long as the alternators output more than the inverter needs, no power from the batteries is used... instead, when the alternators generate more than the demand from the inverter, the rest is used for charging
I know that there are more cruisers that select a high power inverter for this reason so keep this in mind. When your inverter is close to the batteries it is always better, because you can still use the output from the alternators as long as their voltage after the drop in the cabling is still more than the battery
voltage (is easy, no brute force methods needed).
So, that's part one of it. My next update will be the wiring
diagram, which I am working on now. I hope to show photo's with amps flowing soon ;-)