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Thursday, December 13, 2012

Shore Power Conversion

Boats all have the ability to be plugged into shore power to run everything when at dock.  For boats that only travel in one part of the world, their shore power is set up for that particular region.  In North America, that would be 120/240V 60hz.  In Europe, 230V 50hz is the norm.  Other parts of the world follow one of these two standards, or variations on each.  The challenge for a boat that will travel all over the world is that it needs to be able to run on all the different forms of shore power, or at least some reasonable subset of them.  The question is, how?

If you really want to go all-out, there are companies that make universal shore power converters.  They take in whatever you give them, and put out exactly what you want.  But they come at a high price in $$, space consumption, heat dissipation, and complexity.  If for no other reason, the cost eliminates them as a possibility for me.

The other approach is to use boost/reduce transformers to match up the voltage.  This is a much more cost-effective approach, but it only matches voltage, not frequency.  60hz power will remain 60hz, as 50hz will remain 50hz.  As a result it's a partial solution, but for me, it will have to be close enough.  After all, firing up the generator is always an option to get exactly the power we want.  At a minimum, I want to be able to leave the boat in a foreign marina on shore power for extended time while we are away.  To do that, the bare minimum is to be able to run the HVAC so the boat doesn't become a Petri dish, keep batteries charged up, and run whatever alarm and monitoring equipment is on the boat.  Anything beyond that is icing on the cake.

Given all this, here's what I think we need to be able to handle for shore power, and what it needs to be converted into on board.

  • 120/240V 60hz shore -> 120/240V 60hz ship
This one is easy since it's the power that the boat is designed to use.
  • 120/208V 60hz shore -> 120/240V 60hz ship
This one is a bit trickier, and represents a 15% voltage boost.  For a variety of reason that I'll skip over, some marinas only have 120/208 shore voltage.  Given the way the N60 is wired, this turns into 104/208V on board.  Many appliances will work fine on this, but the lower voltage means that those appliances will draw more current than normal, and that means more internal heating, and possibly shorter life.  A 15% boost fixes this.

The cases above can be handled with a boost transformer.  Several different companies make them, and the transformer used on the N60 can be adapted to do this as well.  We have elected to make this feature part of our build so we can run on 208V shore power without stressing any of our electrical appliances.

50hz operation is a lot trickier.  Not only is there a voltage difference to deal with, but some 60hz devices can handle 50hz, where others can't.  This means that when plugged into 50hz power, we will only be able to run selective devices, and the list is short.
  • Hot water heater
  • Battery charger
  • HVAC
That's it.  All other 240V appliances like the washer, dryer, watermaker, and oven can't be used unless we run the generator.  120V appliances are fine because they all run off the inverter which will continue to operate at 60hz.  They key is to be sure the battery charger can keep up supplying all the DC power needed to run the inverter.  As a side note, the charger-feeding-inverter combination is a mini version of the bigger universal power converters that I talked about earlier on.

The above appliances will run at 50hz, but there is some fine print involved, including one little tid bit that was completely new to me.  The first bit of fine print is on the HVAC components.  They warn that when run on 50hz, their output is reduced by 17%.  OK, that's not a bad price to pay, and something I can live with.  But there is another more subtle part to the fine print.  It says they can be run at 200V 50hz.  Not 230V, not 240V, but 200V.  What's with that?  I started hunting around and found this article which explains it in more depth http://www.usmotors.com/TechDocs/ProFacts/Voltage-Frequency-Variation.aspx.  The key is that if you reduce the frequency, you need to correspondingly lower the voltage or you risk overheating and burning out the motor.  Running the HVAC directly off 230V 50hz would appear to be really bad for the compressors and fans.

The solution to this obscure problem is to apply a voltage REDUCTION when operating at 50hz, intentionally bringing the voltage down to 200V - at least for the HVAC.  That will make it happy, and be operating it completely within manufacturers specs.

Although the HVAC wants to see 200V 50hz, the water heater and battery charger will actually be happier with the native 230V 50hz power, so ideally it would be nice to have both.

After a bunch of back and forth with PAE, their transformer manufacturer, and the HVAC manufacturer, we now have both a Boost and Reduce setting on our shore power transformer, and we have added a second transformer on the dedicated HVAC shore power connection so we can independently Boost/Reduce that power source too.  Operationally, here's how it works:

Rotary Switch 1 selects which ship's shore power inlet to use:
  1. Off
  2. 240V FWD
  3. 240V AFT
  4. 120V FWD
Rotary Switch 2 selects the Ships power:
  1. Off
  2. 20KW Generator
  3. Shore (Normal)
  4. Shore (Boost)
  5. Shore (Reduce)
Rotary Switch 3 selects the HVAC power:
  1. Off
  2. Ship's Power
  3. HVAC Shore (Normal)
  4. HVAC Shore (Boost)
  5. HVAC Shore (Reduce)
This lets us run off any combination of shore connections with Normal/Boost/Reduce, including different settings for the Ships power and HVAC if desired.  It's not prefect, but is a very affordable approach that gives us a lot of flexibility and I think will allow for use of most shore power sources around the world.

4 comments:

Anonymous said...

You said
"If you really want to go all-out, there are companies that make universal shore power converters. They take in whatever you give them, and put out exactly what you want. But they come at a high price in $$, space consumption, heat dissipation, and complexity. If for no other reason, the cost eliminates them as a possibility for me."

Can you give me an idea of how much we're talking here? 10% of the cost of the boat? 3 x the cost of the system you chose?

You chose the hydraulic thrusters at " 2 - 3 x the cost " of the electrical versions.

Not trying to criticize your choice in any way, just curious. I just found your blog, really enjoy reading so far. I love seeing what goes into the choice of a new boat, and the level of transparency you've brought to the process. Thanks so much :)

Tanglewood II said...

Hello and welcome. I did not price out an Atlas system because I was told they were on the order of $100k. In contrast, the extra transformer and selector switches for converting my AC voltages is costing about $3500, so that's about a 30x cost difference. With the lower cost system I can still leave the boat unattended at a dock with the HVAC operational, and when on board, I only need to run the generator to operate the over or the dryer. And all of my 120V power works fine. For me, that's an acceptable compromise for for the savings. Plus, there is a lot that can go wrong with an electronic power conversion system, and if it breaks you are stuck running the generator all the time while waiting for parts. In contrast, there isn't much to go wrong with a transformer, and even if it were to fail, I could wire up a bypass and keep going.

Yes, I did pay up for the hydraulic thrusters, and perhaps it's irrational. But I see a few key differences. First, good thrusters can be the difference between staying out of trouble and trashing the boat. That matters a lot. Second, the thrusters are something that get benefit and satisfaction from every time I dock the boat. The shore power compromise - which is simply that I need to turn on the generator - only occurs when in a 50hz power region, and only when we need to do laundry or use the big over. One thing to keep in mind which I don't think I mentioned earlier is that in addition to the full size electric over, we also will have a microwave/convection oven that runs on 120V. So even on 50hz shore power we can still use the convection over without running the generator.

Anonymous said...

That's some serious coin to lay out, no doubt. I totally think you made the right choice, on both counts (not that my opinion matters for much :P). Ninety thousand + just so you can leave the generator off while in port, while using the dryer or oven. Doesn't even seem like much of a decision to me. Especially if you put a good bbq somewhere ;)

The thrusters, I think that's a safety issue. When you need them, you need them to work. That's money well spent.

Did you ever think about increasing the generator capacity given the loss in rating due to the hydraulics? Or is that not something easily (or economically) done?

Just want to say thanks again for being so forthcoming and putting this out there, not only helps me feel engaged in the reading but seeing the process and your decisions fuels my own imagination :)

Tanglewood II said...

I'm actually more worried about under-loading the generator than over-loading it. If we are running the Stabilization at Rest feature, all the air conditioning, and drying clothes, we will be right at the edge by my rough calculations. Worst case I'll need to dial back the AC in some unused part of the boat until the clothes are dried. The bottom line is that I think a little load management will take care of it.

The bigger problem that I anticipate is under-loading of the generator. If we are on a multi day passage and want to run the oven, dry clothes, or make water, but are not using the AC, we will have a light load on the generator. Just the other day it occurred to me that by switching the stabilizer load from the main engine to the generator, I can load up the generator under such a circumstance. I'm checking with ABT to see if this is possible. I know the hydraulic pump on the generator can be engaged/disengaged, so that part isn't a problem. The pump on the main engine is direct coupled and runs anytime the engine is running. To unload it, the hydraulics would need to be able to divert the pump output back to the supply tank so it's just pumping oil in a free loop. It does this when the stabilizers are deactivated, but I'm not sure if it can be done at anytime, and selectively for the main pump.