From My Design to My Installation: New AC Power System

[Whimsical]

Originally Posted by bobfnbw

If you mean 200 AMP alternators, look at the electodyne. They have the best high output alternators out there. 160, 300 and 360 amps at 12 volts. takes a lot of hp to drive them.

No i meant 220V alternators. I was responding to s/v Jedi's idea of using high voltage alternators and a victron charger/inverter to replace a generator. I presume it would just run in invert mode and not use the transfer function at all. I don't know how the Victron would respond to a quite variable input voltage and freq. Need to do some more reading and see if it is as programable as the quatro.

Mike

[s/v Jedi]

Originally Posted by Whimsical

Just looking at this thread and it certainly gives me ideas. Had a look at the Victron site and the multiplus doesn't have parallel operation untill they get up to the 12/3000/120 unit so tying 2 together is out for the small units. Bugger, hope they are not too expensive.

Just need to find some suitable 200V alternators, any ideas Nick

Mike

Did I write the text of that quote? I hope not because I am not a fan of engine-mounted AC generators. You will never match rpm's with the needed AC frequency range while under way.

What I would propose is rectifying to DC and see what charger(s) take what input DC voltage range. I am sure it is not too difficult to find a rectifier that can handle wide frequency. I believe that some Victron chargers take 400V DC input.

In the end, for myself, I wouldn't use the main engine for AC generation except for back up. And I like it the way we have it: two additional 210A 12V alternators that can output 400A at 12V to the house battery bank. Instead of charging the batteries, you can also switch on the inverter(s) for AC. This is not too bad efficiency-wise as the alternator output will flow into the inverter(s) directly, skipping the charge/discharge cycle of the batteries.

cheers,
Nick.

[Zednotzee]

Originally Posted by s/v Jedi

Did I write the text of that quote? I hope not because I am not a fan of engine-mounted AC generators. You will never match rpm's with the needed AC frequency range while under way.

It's true, frequency is determined by engine RPM (& hence, generator RPM) alone.

It could be done though, either by running a hydraulic drive unit, or a variable pitch prop. I don't think a sane person would change their propulsion just to have steady AC underway though!

[s/v Jedi]

Originally Posted by Ultimarv

Two schmatic links for above post:
ATS diagram: http://i63.photobucket.com/albums/h122/UltimaRV/ATS.jpg
Power distribution diagram: http://i63.photobucket.com/albums/h1...aAnnotated.jpg

Hi,

an isolation transformer also makes sense on a motor home or even a regular home. In fact, it is often used by electric engineers while repairing equipment that uses AC power. The reason is personal safety. Most boat owners only look at galvanic corrosion because they don't know much about the subject.

So, I would keep the IT. If you like, you can put my design in your motor home too because it'll work just as well as on a boat.

The Victron IT has 2 primary windings and 2 secondary windings. But you should never connect 1 primary winding to outlet A and the other winding to outlet B. In the EU, you will always get 220-250V AC with 3 conductors: hot, neutral and ground. This means that you jumper the IT primary windings in series. The 3.6 kW IT can handle 16A that way, which will be the value of the breaker on the outlet. On th secondary side of the IT you can now select either the same voltage as you get from shore (both windings in series) or you can half that value (110-125V) by connecting the windings in parallel. If you go for half the value, you get double the current: 32A. So there's no worry about just getting 16A from shore, you get the usual 30A anyway.

But all this is just one voltage present between two conductors. If you need an L1+L2 setup, you still need the Auto Transformer (AT). In that case you jumper the IT for 240V output and feed that to the AT.

cheers,
Nick.

[Whimsical]

Originally Posted by s/v Jedi

What I would propose is rectifying to DC and see what charger(s) take what input DC voltage range. I am sure it is not too difficult to find a rectifier that can handle wide frequency. I believe that some Victron chargers take 400V DC input.

Nick.

I had understood your comment to mean that the Victron would just operate in invert mode and become in essence a seperate charger and inverter that could be paralleled to double the ouputs of both. All the chargers are switch mode devices and must rectify the input to feed the battery charger. Have to ask Victron if they are happy with a large input variation.
As the smaller ones can't be paralleled it is a moot point anyway. I only want about 3Kw to drive an AC watermaker. Probably cheaper to use seperate devices, just need to find a couple of chargers that can be paralleled.

The big idea for me is that with the higher voltage from the alternator i can move the chargers closer to the batts which are very remote to the batts. With 2 motors being wide apart and house batts forward it gets messy trying to avoid lots of heavy cabling

Mike

[s/v Jedi]

Mike,

You miss one crucial point: for an engine mounted AC generator, varying the engine-rpm's leads to a change in the AC frequency, not voltage. So if you rectify that to DC, you would end up with a stable DC voltage within a considerable range of engine rpm.

What size electric motor do you have on your watermaker? We have a 1.5 hp version and I found that I can't start it (surge) with a 2500W Trace inverter. I could start it with a 3000W Victron but only just. I recently re-jumpered the motor to 240V and now it easily starts from the Victron. So, it is better to use 240V for that instead of 120V. I think every motor in that size can be jumpered for either 120/208/240V service.

cheers,
Nick.

[Ultimarv]

Nick, thanks for the guidance and the quick side-step to assist us. You have made a tidy job of your onboard electrics.

I think exactly your schema of placing a Victron Isolation Transformer (in our case 32A) feeding a Victron Autotransformer 32A 240VAC, while stepping down and feeding two separate legs 120VAC sharing a common neutral is the way to go.

This is a more expensive solution to the norm, but the IT offers onboard safety, a small boost in low voltage situations, while the AT offers shorepower to our systems exactly the way it would appear in a standard USA 50-amp 4-wire set-up (except for the resulting 50Hz).

Even though we normally see mostly 16-amp 240VAC coming from shore pedestals, we want to be prepared in the event we manage to gain a 32-amp 240VAC circuit somewhere on our travels - especially if we decide to sit in a "marina" for longer periods.

Thanks, and happy sailing from our 45' Asphalt Cruiser!

[Whimsical]

Originally Posted by s/v Jedi

Mike,

You miss one crucial point: for an engine mounted AC generator, varying the engine-rpm's leads to a change in the AC frequency, not voltage. So if you rectify that to DC, you would end up with a stable DC voltage within a considerable range of engine rpm.

What size electric motor do you have on your watermaker? We have a 1.5 hp version and I found that I can't start it (surge) with a 2500W Trace inverter. I could start it with a 3000W Victron but only just. I recently re-jumpered the motor to 240V and now it easily starts from the Victron. So, it is better to use 240V for that instead of 120V. I think every motor in that size can be jumpered for either 120/208/240V service.

cheers,
Nick.

Yes my point exactly and i think we are talking about the same thing. I would expect all alternators to be DC and even if they are not all the modern chargers are switchmode devices so they rectify the AC and hence don't particularly care about frequency. I would most likely put in an external bridge as well if it not in the alternator. An alternator will be stable voltage as long as the RPM is suficient to supply the demanded output. Trying to draw too much at low rpm's will result in a low voltage. Not to sure how stable the output voltage is when a load is suddenly disconnected without a battery to absorb the surge, this is what worries me about a small input voltage range. The Iota chargers handle low voltage but obviously with reduced output but they don't have a very large input range and thier 240V models only go to 55 amp. Need to research some more brands.
All the AC equipment will be 240V as Australia is a 240 volt country. I don't have the watermaker yet. Good to hear the 3kW Victron handles 1.5 HP. I was thinking of an engine driven pump but this method gives me a lot more flexability. I will put the watermaker together myself with an adjustable pressure regulator so the pressure can be bought up to operating after the motor is running. That would give a nice soft start for the AC motor.
240 V makes life easy as all i need then is an isolation tranny with a split primary to step up to 240 if needed.

Mike

[pbiJim]

Originally Posted by s/v Jedi

- 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 AC service, making the whole boat installation much safer.

Wow,
I just got done reading this whole thread for the first time. There is a great deal of wonderful information here. It was very informative for me. I thank you for taking the time to post all of this. I also compliment you on a very nice installation of a very useful system. I am left with one nagging question though & it pertains to the paragraph above.

You seem to be completely isolating the boat ground from the shore ground. I would think that this would create a shock hazard for a person with one foot on the dock & one foot on the boat. Is this not the case?

Thanks,
Jim

[s/v Jedi]

Originally Posted by pbiJim

Wow,
I just got done reading this whole thread for the first time. There is a great deal of wonderful information here. It was very informative for me. I thank you for taking the time to post all of this. I also compliment you on a very nice installation of a very useful system. I am left with one nagging question though & it pertains to the paragraph above.

You seem to be completely isolating the boat ground from the shore ground. I would think that this would create a shock hazard for a person with one foot on the dock & one foot on the boat. Is this not the case?

Thanks,
Jim

Not the case. Ground does not shock you, we walk/sit/sleep/swim on/in it all the time. You only receive a shock when your body completes an electric circuit.

Also, note that I do not polarize the output from the isolation transformer; I keep it floating.

[pbiJim]

Originally Posted by s/v Jedi

Not the case. Ground does not shock you, we walk/sit/sleep/swim on/in it all the time. You only receive a shock when your body completes an electric circuit.

Also, note that I do not polarize the output from the isolation transformer; I keep it floating.

Yes, the floating ground is exactly the part that concerns me. If the ground potential at the dock is different from the ground potential at the boat & someone touches both "grounds" at the same time, do they not then complete the circuit between the two nodes at different electrical potentials? In other words the person becomes the load that connects the two different "relative ground" voltages. no? Is there something that prevents the two separate floating grounds from reaching different potentials?

[goboatingnow]

Originally Posted by pbiJim

Yes, the floating ground is exactly the part that concerns me. If the ground potential at the dock is different from the ground potential at the boat & someone touches both "grounds" at the same time, do they not then complete the circuit between the two nodes at different electrical potentials? In other words the person becomes the load that connects the two different "relative ground" voltages. no? Is there something that prevents the two separate floating grounds from reaching different potentials?

Ah ha we return to my favourite subject , " do isolating transformers add any safety benefit over just suppressing galvanic currents , if yiu follow ABYC strictly, they do not . Diagrams to follow later today

Dave

[Dockhead]

Hi Nick:

Nice system, thoughtfully designed and executed, as always from you. You've always been an inspiration to many of us, including me.

The only thing I don't like about your system is the degree of complication. As the years go by, as I am bit in the backside again and again by the tendency of systems to fail in the harsh marine environment, and see more and more see the value of avoiding any unnecessary complication on board.

So I would have tried my best, in your case, I think, to avoid having different AC voltages on board. Obviously 230v/50cycles is superior, and if you are really wandering the world where you will encounter all kinds of power, I would just go with that. If you are planning to stay in those parts of the Americas which have 120v/60cycles, then the technical inferiority of that system would be outweighed, in my opinion, by the hassle of constantly dealing with shore power which is different from my AC equipment. Maybe in your case you have no choice, because of the requirements of your air conditioning equipment.

In any case, as you obviously know, it's not impossible to deal with out-of-cycle shore power -- you just charge your batts with shore power and invert power you need for on-board equipment. Anyway, inverted power is cleaner (if you have good equipment) than unknown shore power -- inverted power is kind of like watermaker water.

Having only one flavor of on-board power means you have to source all of your AC gear in one region -- could be a bit of a hassle, but worth it to avoid all this complication, in my opinion.

Having 230v/50 cycle power also means you don't need any special power to drive heavy equipment like air conditioning, which doesn't like 120v very much, as you know.

By the same token, 24v is massively superior to 12v -- you would not be struggling with huge, fat cables and worrying about distance to your batts if you had 24v. And you would not need a separate flavor of DC power for your thruster and windlass.

One thing for others to note (I'm sure you're aware of this, Nick) -- Victron rate their inverters by VA -- n.b., not watts! -- and at a lower temperature than what you typically see in your engine rooms. If you have the misfortune of being 12v rather than 24v, then you are also likely to see a voltage drop between batts and inverter, which will further reduce realistic output. At a realistic operating temperature, and taking account of power factor, a 3000VA inverter (which is also what I have) is already starting to get stressed above 2kW. So for anyone who decides to run everything on inverted power, you need to be sure to size your inverter generously. If you are accustomed to 16 amp/230v or 30 amp/120v shore power, then a 3000VA inverter will not nearly do -- think more like 5000VA. The good thing is you can buy a bigger Victron unit and derate the charger -- easily done with dip switches. Or you can run two or three identical units in parallel (given their proneness to failure, having a couple running in parallel is probably a good idea -- provides useful redundancy). I suppose Mastervolt and other reputable types also provide this option.


By the way, why did you replace your Northern Lights generator? I thought those things live forever -- longer than we do.

[Dockhead]

Originally Posted by Whimsical

I had understood your comment to mean that the Victron would just operate in invert mode and become in essence a seperate charger and inverter that could be paralleled to double the ouputs of both. All the chargers are switch mode devices and must rectify the input to feed the battery charger. Have to ask Victron if they are happy with a large input variation.
As the smaller ones can't be paralleled it is a moot point anyway. I only want about 3Kw to drive an AC watermaker. Probably cheaper to use seperate devices, just need to find a couple of chargers that can be paralleled.

The big idea for me is that with the higher voltage from the alternator i can move the chargers closer to the batts which are very remote to the batts. With 2 motors being wide apart and house batts forward it gets messy trying to avoid lots of heavy cabling

Mike

The Victron charger/inverters are not switch mode devices. They have regular (massively heavy, unfortunately) transformers.

But rectifying AC to DC is not done by this part of the device anyway -- that's done by rectifiers.

[s/v Jedi]

The Caribbean is mostly 60Hz territory, as was our boat from launch. Everything we buy is 60Hz and most is 120V. This is just how it is on this side of the Ocean

The Autotransformer which takes care of creating the 120V service is very reliable; I expect no trouble with it.

The Northern Lights did not really need replacement. But it was within a year of more serious maintenance and the economic downturn provide opportunity to buy a new one at a very high discount. The old one became a big supply of spare parts as I almost kept all except the block and generator end.