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Old 21-07-2013, 16:32   #31
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Re: Moving towards an AC boat

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Sure. But only if from now on we call our DC alternators also AC generator instead
See, now we've broken down into semantics
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Old 21-07-2013, 17:35   #32
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See, now we've broken down into semantics
It is. When people talk about a DC generator, they mostly mean a diesel engine coupled to a DC alternator. But the alternator isn't DC without it's diodes to rectify it's AC into DC.

The honda generator is a small gas engine coupled to a DC alternator, using diodes to create DC.
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Old 21-07-2013, 21:44   #33
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Re: Moving towards an AC boat

If we are going to talk about correct terminology, I think that technically, if it produces DC directly, (like on a 1958 pan head), it's a generator & if it produces AC, it's technically an alternator, even if the AC is then rectified to become DC, like on a modern automotive charging system. I think that the portable 120vac "generators" are actually alternators, because they produce AC, but because everybody has called them generators for so long, the technically incorrect name has now stuck. I believe that an actual generator is pretty much a DC brush motor that is being driven by a mechanical force & therefore produces DC power. At least, that is what I think is technically correct. I may be wrong & I'm too lazy to research it right now. Besides, I'd rather talk about how we can figure out better ways to get useful power back into the boat batteries. Regardless if you want to go AC or DC, I think that we still need to keep the battery bank as the main primary source while on the water.

What I would really want is a small portable stand-alone 12vdc generator that runs off of gas, diesel or propane. Little portable 12vdc generators do exist, but they are not real common. My cousin had one about 15 years ago that he used for jump starting dump trucks in the winter, but he was the only guy I knew that had one. I did a little googling & I found a place in China that will sell a 4-stroke, 60-amp unit with a 1 gallon gas tank for less than $200, but shipping from China for 1 piece is more than the base price of the unit. Most of the Chinese generator manufactures that I found had minimum purchase quantities of at least 10-30 pieces. I also found a lot of homemade units on you tube, but I did not find a lot of commercially made 12vdc units, aside from that one Chinese source. The larger (1200w-4400w) 120vac generators, that also have a 12vdc output, generally do not have more than 10amps available at the 12vdc outlet & the cheap versions of those things are noisy, like 65db @ more than a boat length. I don't see those as a good option for charging your batteries, unless you use the 120vac to run a battery charger.

I also looked up charging capacity of outboards that one would likely find on a sailboat or a sailboat's dingy. Honda comes in about the best on a 9.9hp with 12 amps available. Yamaha comes in best on a 4hp with 6 amps available, but keeps that same 6 amps all the way up to their 9.9. Merc had one of the smallest outboards with charging capability, but that little one only had about 2 amps available for charging.

I found some little windmills for a few hundred bucks that were good for 600W which means about 50 amps. I think that this might need an external controller though.

Solar in any useful wattage ain't cheap, at least not the stuff that I found.

What to do...what to do...what to do?
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Old 21-07-2013, 21:57   #34
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Re: Moving towards an AC boat

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Let us not forget that DC is a lot less likely to grab hold of you and cause the 120vac shuffle. One frayed/rubbed through wire and not only do you have a chance to blow a fuse but when you reach into that compartment running your new antenna wire and touch it by mistake you get to have a good check of your cardiac health.
I may be making a grand assumption here, but I would expect that any boat wired for 120vac (or higher) would be wired through a 5ma GFCI breaker to prevent that unpleasant shuffle. Is that not generally the case?
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Old 21-07-2013, 22:10   #35
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Re: Moving towards an AC boat

Most applications nowadays don't care much about AC or DC. Light doesn't care. Electronics rectify AC to DC. Electric motor controllers nowadays rectify AC to DC and then back to AC again. The exception are applications where a fixed RPM is not a problem like washing machines, which are run directly off three phase AC where I live.

The advantage of AC is easier to generate, and to transport.
the advantage of DC is that it is easier to store.

On land the advantages of AC outweighs the disadvantages (although DC is making a comeback, thanks to residential solar). On a boat however the fact that you can store DC outweights its disadvantages.
In fact, I see an evolution towards more DC, not less, with AC gensets being replaced with DC ones.
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Old 21-07-2013, 22:18   #36
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Re: Moving towards an AC boat

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Originally Posted by pbiJim View Post
I may be making a grand assumption here, but I would expect that any boat wired for 120vac (or higher) would be wired through a 5ma GFCI breaker to prevent that unpleasant shuffle. Is that not generally the case?
Generally, no that is not the case. For convenience outlets the circuit from the GFCI outlet to the device plugged in is GFCI protected. But internal boat wiring is not generally fitted with GFCI protection. I personally have never seen a yacht with the entire AC power system protected by GFCI although some may have it. To make it work an ELCB or other similar device must be installed at the prime source of AC power (e.g. generator and/or inverter).
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Old 21-07-2013, 23:06   #37
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Re: Moving towards an AC boat

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As regard safety and unwanted circulating currents we solved that problem years ago shore side.
As you say, safety problems with AC were solved shore side.

On the water not so much. In the US 2 or more swimmers a year die from electrocution swimming in marinas. Really this is an understatement because some deaths by drowning miss the underlying cause of incapacitation due to the electrical currents leading to drowning. Any fault in the system that goes into the bonding system will put stray AC in the water be if from a boat or dock wiring.
http://www.harborbayyachtclub.org/Im...hockHazard.pdf

OK that's marina life, with an inverter the return path is to the batteries and is unlikely to go thru the water around the boat. Boats are still moist environments with vastly increased likelihood of corrosion of electrical parts. Given that people on board are much more likely to be wet when operating electrical equipment the likelihood of shook goes up. While the US voltage standard of 120v is less likely to kill you than 240v in Europe or Oceania it is still possible.

When the next boat comes around, soon I hope, there will be an inverter aboard, but uses will be intentionally limited for safety as well as efficiency reasons.
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Old 22-07-2013, 01:50   #38
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Re: Moving towards an AC boat

To pbiJim your detail is not nauseating to me, tell me can you get a 3ph variable frequency drive static inverter powered from 12V DC and to what size. Did you mention that the motor and the inverter have to be matched. (Of course the voltage would have to drop as freq goes down) Tell me thou with suitable switching and similar motors and you only use one at a time, could you, have one static inverter supplying two motors but not at same time.
To answer somebodies question about AC machine being efficient on board ship, the machines are efficient but saving power is rarely considered, on one vessel I was on, just running Hospital services only, HVAC, lighting, Domestic I calculated that each man on board was using 33KW each.
Another about safety that all electrical machines are tested for earth leakage as a routine anything below 1 Mohm would be unacceptable. Any earth faults are treated with priority. All cabling is protected by steel braid, its a much higher standard electric motors are water proof but not submersible, shore side I've seen submersible pumps. I believe this level of protection is transferable to small boat.

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Old 22-07-2013, 01:55   #39
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Re: Moving towards an AC boat

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I may be making a grand assumption here, but I would expect that any boat wired for 120vac (or higher) would be wired through a 5ma GFCI breaker to prevent that unpleasant shuffle. Is that not generally the case?
I have never seen a gfi breaker on a boat. common to see a few gfi plugs on the boat (bathroom) but even then most plugs on a boat usally aren't. and anything not a plug wouldn't be. (water heater, charger etc)
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Old 22-07-2013, 02:21   #40
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I have never seen a gfi breaker on a boat. common to see a few gfi plugs on the boat (bathroom) but even then most plugs on a boat usally aren't. and anything not a plug wouldn't be. (water heater, charger etc)
You never saw these: (upper right corner)?
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Old 22-07-2013, 04:46   #41
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Re: Moving towards an AC boat

Having built a modern boat around 12v DC, that is electrically self sufficient with only solar panel input and battery storage, no battery charger, inverter or generator, I can't think of a compelling reason for AC at all. I'll keep the safety and simplicity of DC thanks.
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Old 22-07-2013, 07:51   #42
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Re: Moving towards an AC boat

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I have never seen a gfi breaker on a boat. common to see a few gfi plugs on the boat (bathroom) but even then most plugs on a boat usally aren't. and anything not a plug wouldn't be. (water heater, charger etc)
If it is just on the plug itself, like some air conditioners these days, then just that one device is protected. If you get a GFCI receptacle, then anything plugged into it is protected. A GFCI receptacle is just as good as a GFCI breaker. Most of the GFCI receptacle have a primary side & a secondary side. If you wire other devices (lamps, other receptacles, refrigerator, etc.) off of the secondary, then those devices get the same GFCI protection. Since the GFCI receptacles can ge had for less than $20, this is a good cheap retrofit.

There are 2 levels of GFCI protection available in the US that I am aware of. 10ma trip point is for protecting equipment. The more stringent 5ma trip point is for protecting people. Anything that you find at Home Depot, Lowes, or Ace Hardware is going to be 5ma class.
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Old 22-07-2013, 08:26   #43
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Re: Moving towards an AC boat

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To pbiJim your detail is not nauseating to me, tell me can you get a 3ph variable frequency drive static inverter powered from 12V DC and to what size. Did you mention that the motor and the inverter have to be matched. (Of course the voltage would have to drop as freq goes down) Tell me thou with suitable switching and similar motors and you only use one at a time, could you, have one static inverter supplying two motors but not at same time.
Static inverters & variable frequency inverters are different.

Static inverters only produce a single 3 phase voltage at a single frequency & only work with a specified range of HP. I think that you may be able to directly switch a load onto the secondary of a static inverter while it is running, but I need to look that up before I swear to it. Static inverters are small, cheap & weigh very little. They are pretty simple to wire. If you find a static inverter that is rated for 3/4hp-1.5hp, you can run a pair of 3/4hp motors or a single 3/4hp motor because either load falls within the specified range. You can not run a single motor or multiple motors that total to fall outside that range. There is also a device called a Ronk box, or roto-phase, or rotary phase converter that does the same functional job in a different way. The static phase inverter is basically an electronic device that creates a synthetic third leg. A Ronk box is more like a combination motor & generator (aka M-G set) that is all wound on a single armature inside a single case. They are big & heavy, but they don't care how much load they carry, as long as it's below the maximum. In fact, they actually run smoother if they are already under load when you switch on a second load. You can be running a 1/4 hp load & then switch on another 7.5hp with no problems if you are running a 10hp Ronk. The electronic static inverters are much more power efficient though, especially when switched on at no load.

Variable Frequency Drive Inverters are a slightly different animal. These are the ones that let you control motor speed, generally from about 10% to 300% of the motor's nameplate RPM. These drives are larger & more expensive than static inverters. You have a lot of room to oversize them. A 10hp VFD will generally be happy to run a 2hp load, a pair or 3hp motors, or a combination of a 1hp motor, 2hp motor & 5hp motor. They usually like to be over-sized a little bit for reliability. They are programmable & can be controlled internally, or via a host of external controls including switches, potentiometers & in some cases, fiber optics or distributed I/O busses like CAN buss, Device net, or Profibuss. In many cases, you can not direcely switch a load onto a VFD that is already running or you will blow up the output thyristors. The exception to this is if you get one that is rated to "catch a running load", which many are not. With the VFD inverter, you can program different acceleration & deceleration curves. You can run forward & backwards. You can electronically brake the motor in a few different ways. Some require 3-phase primary power. Some can also run off of single phase. A few can take 120vac primary power & put out 220vac 3-phase. Many can be wired for common buss DC power, where high voltage DC is used as primary power or where the internal DC buss of several drives is wired together. This is useful in applications such as multiple elevator banks where one elevator slowing down is creating power that is then absorbed & used by another elevator that happens to be accelerating at the same time. This can save a lot of energy. The basic way that most VFDs work is that they take in AC, rectify it to DC, stick it into a big capacitor bank for storage, & then use IGBTs controlled by a firing circuit to produce a pulse width modulated output that approximates a 3-phase sign-wave, for use as AC power. The actual output signal has voltage peaks that are well above the apparent output voltage. The high carrier frequency of the output can sometimes beat on older motors that are in poor condition. Motors with winding insulation that is in poor condition can also suffer from corona effect when run off a VFD. Most any modern motor that I have tried has run quite happily off of a VFD. I never buy the official "drive rated" motors that cost twice the normal going rate. I have seen "regular" motors used in installations in several million+ dollar industrial machines that have been in the field for more than 10 years. The VFD rated motors are just not needed, except for a few special cases.

At this time, I am not aware of any VFD, that can be directly run from 12vdc primary power, being available on the open market. If there were sufficient demand, they certainly could be designed & built. The necessary parent technologies & components do exist. At this time, if you already had 120vac present, you could buy equipment off the shelf to run 3-phase motors up to maybe 2hp or so. If you had 220vac single phase primary power available, you could go much larger.

This is the Cliff's Notes version of it all. I can easily blather on for pages on this subject.
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Old 22-07-2013, 11:22   #44
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Re: Moving towards an AC boat

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OK that's marina life, with an inverter the return path is to the batteries and is unlikely to go thru the water around the boat.
most invertors are isolated, so teh batteryis not in the return path

pbiJim

I agree variable frequency AC drives are a beautiful thing , I designed several in my earlier days ( 10% circuitry to do teh job, 90% protection circuitry to keep the MOSFETS alive!).

But none of this supports AC on board. Low voltage DC is simple, 12V and 24VDC are standards in industrial control and many devices are made to suit.

That aint going to change.
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Old 22-07-2013, 11:24   #45
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Re: Moving towards an AC boat

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we'll see 24vdc boats before we see 120vac boats. I don't know why everything is still being made in 12v.
quite a few boats in the early 70s and 80s in the Uk were 24V, mine is. but th tendency to standardise on 12V caused most to revert to 12v. cant see 24V coming back any day soon.

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