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anglo_saxon
30-12-04, 16:55
Whilst looking at new Island Packet i noticed that they installed 12v DC (Fischer Panda) generators. We asked FP. at the boat show which would be better suited for our boat and they sugested to go the same route stating the unit was lighter, performed better, more economical, charged the batteries better and was cheaper.
Dose anyone have any views on this, maybe somene who has used both types.

Talbot
30-12-04, 17:30
Dont have knowledge of these specific generators. Dont like having 240v onboard when at sea- dont even have an inverter, just shore power connection.

salt water and 240v AC are not a good mixture.

ashley
30-12-04, 23:50
DC charging is more efficient if you have large batteries and/or are using an inverter. It really depends on your application.

Using a DC generator to charge batteries means you'll be getting the best efficiency from your fuel. This is assuming you are anchored or sailing and might otherwise use an AC genny or engine to charge house batteries.

If you are considering air conditioning at any point you'd be best with AC generators as you'd have the thing running most of the day.

ashley

Anonymous
30-12-04, 23:53
Are they suggesting using a 12V diesel generator and a large static inverter to provide 230V ac, or simply to produce 12V to charge the batteries? If so, have you allowed for the cost of the inverter and checked that the proposed inverter is suitable to power all the 230V equipment you wish to run (i.e. is it sine wave, can it handle transients, etc.?). If it is only to charge the batteries, what is their proposed generator size and what is the proposed battery bank size in Ampere hours? If you would like to post the details here then I and others will be able to give a better-informed opinion.

Ships_Cat
31-12-04, 00:12
For your proposed 43 foot boat I would personally probably go for the 12 v DC generator. The only downside is that one cannot run big electrical loads such as electric heating or AirCon. But again, my personal view is that if you want heating away from the marina then running a generator all day and night on a 43 foot boat is much inferior to a fuelled heater. I personally would not want to live with an AirCon system on a 43 foot sail boat under any circumstances.

As others have said, I assume that you would have an invertor anyway for 230 v - but if not, on a smaller boat it is not convinient to have the 230 v supply totally dependant on a 230 v generator eg "Dear, would you start the generator so that I can use the cake mixer (grind some coffee, or whatever)?" - on larger boats the 230 v demand is such that the generator can efficiently run most of the day (and night).

John

Anonymous
31-12-04, 07:36
Aside from aircon and heating, a generator allows you to heat the hot water and cook. Our hot water tank takes around 3A (@230V) and we like to cook with the Foreman grill, electric steamer, microwave, toaster and electric kettle where possible as it is better for many things, less expensive (with red diesel) and you don't need to store or lug around so much gas. So leaving aside aircon and heating, we can run the generator for 60 minutes or so which gives a good charge into the batteries, heats the water, makes the water, and cooks the dinner. That's a sensible load over a sensible time for a decent 230V generator.

anglo_saxon
31-12-04, 12:19
Battery size is 560 Ah for domestic and 62 Ah for engine.
Generator is Panda AGT-DC PMS 4000-12V.
We are not having air con. but debating on microwave as we never used the one on our old boat but we did not live aboard on that one. Most of equipment uses 12V inc extra Freezer.
Batteries are supposed to last longer as they are seldom discharged by more than 60% keeping them in the best state.

Ships_Cat
31-12-04, 13:01
Assuming your freezer is of the holding plate type the 4 kilowatt generator would obviously comfortably meet both the combined peak charge rate of your batteries while pulling the freezer down, with some capacity to spare for other normal demands on the boat while charging.

Most of my experience is with AC generators on larger vessels (25 kW up) but the DC ones have become very attractive for smaller vessels that are DC oriented. They now seem to be a commonly recommended choice and the cabling/switching is also easier, albeit it larger.

As Lemain says (and as I did), if your AC demands are large then an AC generator becomes more attractive but, in my view, one still needs an invertor on a smaller vessel if the normal demand does not justify running the generator all the time or one does not want to go without AC for low loads if the generator is not running.

If your AC demands are within the capabilities of a manageable invertor (size and cost) then a DC generator, in my opinion, becomes the most attractive. I think, in the Panda range, you get a small weight saving if you choose DC out of the smallest AC or DC generator.

In the end, the decision is partly personal.

John

anglo_saxon
31-12-04, 14:26
Thank you I will take all points mentioned allong to the L.B.Show and discuss them with Panda. Thank you all..

Anonymous
01-01-05, 17:34
[ QUOTE ]
Battery size is 560 Ah for domestic and 62 Ah for engine.
Generator is Panda AGT-DC PMS 4000-12V.
We are not having air con. but debating on microwave as we never used the one on our old boat but we did not live aboard on that one. Most of equipment uses 12V inc extra Freezer.
Batteries are supposed to last longer as they are seldom discharged by more than 60% keeping them in the best state.

[/ QUOTE ]A 4kW 12V generator is going to provide, at 13.8V, 290A. That is far more than a 560Ah battery bank can handle. You should not normally charge at much more than the C/10 rate, i.e. 56A. You can charge at higher levels for a very short while at the start of charging but it will fall back very quickly. Indeed, you should find that if you buy this generator the current will quickly fall back to below 50A. Plus whatever load is being taken from the 12 supply, of course, but unless you have a large inverter driving a large 230V load, what is all that surplus generating capacity for? It sounds to me that what you need is a 700W generator, not a 4kW.

Ships_Cat
01-01-05, 22:33
You are incorrect in your assumptions Lemain.

The 4kW Panda DC generators are rated around 195 A CONTINUOUS (ie below 4 kW, but with peaks above 4 kW though). {Edit: I have now checked - one model is stated as being 195 A and the other is 220A). That is derated further for higher ambient air temperatures and cooling water temperatures.

For deep cycle batteries highest charge rate during the bulk charge will be around 20 -35% capacity depending on batteries, say 150 A. If one has a holding plate type freezer its highest draw is likely to be 35 - 45 A (obviously depending on size, cooling water temperature/flow, and 1/2 hp drives are typical) settling lower as the cycle progresses.

Add those up and allowing that the above are highest continuous draw and both will fall off as the charge/freeze down cycle proceeds I think you will see that the size of the generator is correct assuming a holding plate freezer (and with plenty of headroom if not). If there are other DC loads during those highest draws, then that will subtract from the battery charge rate.

{I would be interested (genuinely) to know where one can get the 700 W diesel generator you suggest?}.

John

trouville
01-01-05, 22:37
I think a small inexpensive 1kw 4stroke generator, i dont use mine more than a couple of times a year,My solar panels keep the batteries charged and in topform.

For 240v i use a 300watt inverter ive just bought a new 300/600w one from a german company-- hear: http://www.fraron.de/ unfortunatly like other companies that use private post/packet service the postal charges are redicules but the company gets 30% plus back--their inverters are good and a good price.

Anonymous
01-01-05, 23:33
I deliberately didn't say {diesel} generator. It doesn't sound to me as though he will be best served by installing any 4hp generator, mains or dc - it will take up a lot of space in the engine room making it harder to service and he doesn't sound like someone who is very energy-hungry; he's not even sure about wanting a microwave. Much as I hate petrol on board, I think he should seriously consider that - maybe the almost silent and very light Honda 1000W that seems very popular. Wind and solar could also be useful adjuncts. He'd probably be perfectly happy with a generator smaller than 1000W. He'll save quite a tidy sum if he doesn't have a fitted generator, aside from the weight and space issues.

Sooner or later someone - Honda? - is bound to produce a more appropriate small diesel for yachts around the 1000W to 1750W range which would be far more suitable for many people than running a 4kW/6kW on a 42/43' yacht where space is at a premium.

Anyway, now he's got some ideas and numbers to play around with and he can plug in other numbers after talking to FP and the other equipment suppliers. Hopefully the different viewpoints will help him to decide on the best compromise for him - and let's be honest, there is always a compromise between space, cost, weight and performance - even if money is no object, space and weight is!

Anonymous
01-01-05, 23:45
I've forgotten the size of your boat and you don't mention it in you bio. The choice depends on your energy budget. We are unashamedly energy-hungry and have a 6kVA generator - we have 2 air con units, large batteries, water maker, electric grill, toaster, steamer, kettle, laptop, enjoy lots of hot water, etc. That means we have to generate a lot when we are not on shore power which is a pain both in term of noise and cost, but it is our choice and it is not for everyone. I very nearly went down the low-energy route - it was a toss-up between the two approaches and we preferred the high-energy approach by a head and shoulders, not a full length!

However, since we are planning to spend a lot of time in busy anchorages I am arranging to have generous solar and wind power to reduce our generator running time to a neighbourly level.

Ships_Cat
02-01-05, 01:01
I hope no one would consider putting a portable petrol generator on a nice HR43. Apart from the issues of floating neutrals, one forumite, at least, lost his brand new boat last year through refueling a portable generator on board.

John

Anonymous
02-01-05, 10:32
[ QUOTE ]
I hope no one would consider putting a portable petrol generator on a nice HR43. Apart from the issues of floating neutrals, one forumite, at least, lost his brand new boat last year through refueling a portable generator on board.

[/ QUOTE ]What electrical problems do you see with a portable generator feeding L and N direct to the L and N shore power connection of the boat? Electrically, such a generator looks idential to the secondary of an isolating transformer - probably the best and safest way to connect any boat to shore power.

As for the fire risk of petrol, I totally agree and I hate petrol on board. Then again, portable generators are used (with care) on a high proportion of serious cruising yachts - particularly those doing trans Atlantic crossings. I would have gone down that path had I not decided to go for aircon, etc.

Ships_Cat
02-01-05, 12:27
There was quite a comprehensive thread on floating neutrals some time ago (maybe 12 months ago now). The main electrical issues that concern me are the possible consequences of the live neutral (isolation issues with switching and neutral to earth shorts, etc), the evidence I have seen from tests that RCD's may not work reliably in floating neutral systems, plus (rightly or wrongly) they are banned for safety reasons from many work sites.

The floating neutral is not the same as one finds when an isolating transformer is installed on a boat. When an isolating tranformer is installed on a boat the "neutral" on the boat side should not be left floating (although it sometimes is) like it is in the on shore use of an isolating transformer for powering a power tool or whatever. The recommended practice is to ground the on board side neutral to give a three wire grounded neutral system on board (which is required in any event for the boat's own AC generation (eg from generator or invertor).

The shore side earth when on shore power connects only to the transformer's primary side shield - this also means that as the boat's AC earth is isolated from the shore power one, the boat side neutral to earth connection does not have to be switched open circuit when on shore power as is the case if an isolating transformer is not used.

In the end, I have not fussed too much about exploring the floating neutral matters myself because the fuel (especially while refuelling) and carbon monoxide dangers put the small petrol powered generator's use completely out of my consideration too, apart for perhaps occasional powering of maintenance tools if at a dock or permanent mooring and no other supply.

Regards

John

Anonymous
02-01-05, 15:42
[ QUOTE ]
There was quite a comprehensive thread on floating neutrals some time ago........

[/ QUOTE ]Whatever one's views on where to connect the neutral (or 0V connection on a dc generator) this is irrelevant to the question of installed generator vs portable generator. You are free to connect the chassis, or either pole, of a portable generator to whatever you (or the authorities) require.

[ QUOTE ]
In the end, I have not fussed too much about exploring the floating neutral matters myself because the fuel (especially while refuelling) and carbon monoxide dangers put the small petrol powered generator's use completely out of my consideration too, apart for perhaps occasional powering of maintenance tools if at a dock or permanent mooring and no other supply

[/ QUOTE ]Fair enough - there is a risk and that cannot be denied. Whether the risk/benefit ratio is acceptable is a matter of personal judgement. In the hands of a careful, prudent, knowledgeable skipper the risks are very low indeed - on a par with carrying a petrol outboard.

Regards, David

castlevar
02-01-05, 16:52
Hi I have a 43 ft boat Yes it is a motor boat 6 knots heavy diplacment when i built the boat I decided not to install gas.
The main reason for this was not so much safety but the difficulty of buying gas in different countrys with different tanks regulators etc.
So we have an all electric boat cooker kettle microwave washing m/c etc, the battery bank is 500ah @ 24v 6 kva genny 220volt solar panels 160watt.
We run the genny when we anchor to cook the evening meal for 1 hour charge the batteries at the same time with chargers totaling 100 amps.
So far it has been very sucessfull but this year we did suffer a bit with the heat a were running a lot of fans of the inverter a 2.5 kw victron the batteries started to suffer so we increased the charger from 50 a to 100 amps this has cured the problem.
However we have now fitted aircon as we hope to get to greece next year but we will probably only use it in marinas at anchor it is usually cool .
But if I had to do it again I would probably fit a dc generator about 200 amps double the battery bank and fit 2 invertors about 4 kw total.
Geoff /forums/images/graemlins/smile.gif

ean_p
02-01-05, 18:16
Is this grounding of the neutral(ex isolation transformer) big boat practice? Why would you benefit from such a grounding on a small pleasure craft?

Anonymous
02-01-05, 20:21
[ QUOTE ]
... the battery bank is 500ah @ 24v

[/ QUOTE ]Which is, of course, twice the energy capacity of a 12V 500Ah battery bank - i.e. the equivalent of a 12V 1000Ah battery bank[ QUOTE ]
6 kva genny 220volt

[/ QUOTE ]That sounds reasonable for the sort of loads you have[ QUOTE ]
We run the genny when we anchor to cook the evening meal for 1 hour charge the batteries at the same time with chargers totaling 100 amps.

[/ QUOTE ]So you are only replacing around 90Ah per day from the genny - the rest must be coming from solar and running the main engines when you move?[ QUOTE ]
... we increased the charger from 50 a to 100 amps this has cured the problem.

[/ QUOTE ]Do you have the means to monitor the net current flow into the batteries? If so, how long does it take, when the batteries are really low, for the current to fall from around 100A to the C/10 rate - i.e. 50A? I'm just about to order my new batteries - Varta flooded lead acid, 3 x 180Ahr 12V, stated to be Deep Cycle. The old batteries are Sonnenschein gels, around 3 years old and completely shot - I think the previous owner had the battery charger set incorrectly and the gels just couldn't take the continual overcharging. From your experience what do you think of my choice of flooded lead acids?[ QUOTE ]
But if I had to do it again I would probably fit a dc generator about 200 amps double the battery bank and fit 2 invertors about 4 kw total.

[/ QUOTE ]Can you talk me through your reasons - I don't mean to appear to be critical, just interested in hearing what you feel would be better by having a dc genny rather than ac

David

Ships_Cat
02-01-05, 21:34
Is this grounding of the neutral(ex isolation transformer) big boat practice?

No, it is every boat practice, although I have seen amateur wired boats that are not - usually when the boat changes hands and the new owner discovers the hash up and gets the boat rewired.

Your boat's AC system is supposed to be a 3 wire system like a house - not treated as if it is just some super sized electrical appliance that you can walk around inside of. I know some amateurs do not even bother with an AC earth on board running just a 2 wire system even without a transformer /forums/images/graemlins/crazy.gif.

John

Ships_Cat
02-01-05, 21:47
Whatever one's views on where to connect the neutral (or 0V connection on a dc generator) this is irrelevant to the question of installed generator vs portable generator.

Unless I misunderstand the point you are making, it is not irrelevant if the portable generator is plugged into the boat's shorepower connection as is the common practice. All (except in some special circumstances that do not worry most of us, such as, I am told, on some naval vessels) installed marine AC generators are not floating neutral - they are conventional 3 wire. Many (most? all?) small portable generators are floating neutral and they remain such no matter if you ground them or not.

I do not know if they are still there, but Honda did have their small generator manuals on their internet site. It is clear when one looks at the cct diagrams in those.

John

Anonymous
02-01-05, 22:31
[ QUOTE ]
All (except in some special circumstances that do not worry most of us, such as, I am told, on some naval vessels) installed marine AC generators are not floating neutral - they are conventional 3 wire.

[/ QUOTE ]On yachts, the neutral is usually a single point, often for convenience but not of necessity, on the engine chassis. The idea is that any unbalanced currents all flow to one point and do not flow through the structure of the vessel or via skin fittings and seawater to other underwater parts of the vessel because this could cause galvanic action and result in corrosion or de-zincification of bronze parts. This single neutral point is also often connected by a single wire to a designated earthing plate in contact with the sea - this can be the keel or a special sintered plate (sintered plates give a greater effective surface area). This arrangement is most commonly used where powerful radio transmitters will be used - e.g. SSB. I assume at this stage that this is, in your terms, a 'conventional' system? Now, if you connect a generator via the shore power socket, the wire designated 'Neutral' will go to this single point designated as Ship's neutral. It will most usually also be grounded to earth, as mentioned.

So I am completely lost when you say......

[ QUOTE ]
Many (most? all?) small portable generators are floating neutral and they remain such no matter if you ground them or not.

[/ QUOTE ]'Floating' by definition means not referenced to any other fixed level so a generator output cannot be 'floating' if you ground one of the poles, connect it to Ship's neutral or connect it to any fixed point of reference. This is true by definition of the term 'floating'. It is true that a portable generator sitting on a deck and connected to nothing else has a 'floating' output but the moment you connect either pole of the output to something that has a fixed potential (e.g. Ship's neutral or earth) then it ceases to be 'floating'.

David

Ships_Cat
02-01-05, 23:02
If the boat is correctly wired then when you switch to the shore power inlet connection the grounding of the neutral on board the boat should be broken automatically. This is usually done by the boat/shore power selection switch isolating the generator and/or invertor from the shore supply, and consequently the bonding of the neutral to earth which is permanently made at the invertor/generator, or is automatically broken on some inverters eg the Freedom ones.

The above may not apply, of course, if the boat has no on board AC supply (ie no invertor or generator, so only ever gets AC from shore), but in that case the neutral on board should not be grounded, the neutral grounding on shore has to be relied on.

So if you plug a portable generator into the shore power inlet connection the neutral will not be grounded.

I would be most surprised if you found a professionally built boat that was not so wired. Calder's book has quite a good bit on this and the safety issues as does the ABYC standard (which I think I have seen on the internet somewhere and a google may turn that up).

John

Anonymous
03-01-05, 00:26
[ QUOTE ]
If the boat is correctly wired then when you switch to the shore power inlet connection the grounding of the neutral on board the boat should be broken automatically.

[/ QUOTE ]Well naturally you would expect to connect the generator correctly - be it bolted down in the engine room or left running on deck - that isn't a valid reason for not having a portable petrol generator. The only reasons that I can see for not using a petrol generator on board - and which you have already mentioned - are the use of petrol, CO fumes and the danger of a heavy portable item flying around if not properly stowed. I don't really like the idea myself but I do consider it to be a perfectly valid and acceptably safe solution if done correctly and the only practicable solution for a good proportion of cruising yachts where there are cost and space constraints or where the power demand doesn't justify a fixed diesel. The other benefit for many people is that when they are not cruising they can use the portable for other things when not actually aboard.

Ships_Cat
03-01-05, 00:36
Well naturally you would expect to connect the generator correctly

Think you are stretching our imaginations a bit there Lemain /forums/images/graemlins/smile.gif.

That can only be done if a special permanent inlet connection is made for a portable, floating neutral generator and which is in turn isolated from the distribution when shore power is connected. How many do you think have gone to the trouble of doing that or would want to do so? If connected to the boat's AC distribution system 99.999% would be plugged into the shore connection as is.

John

castlevar
03-01-05, 10:39
Hi David
I dont have any serious monitering just use a volt meter on the battery bank I have a good controller on the solar panels with a display for amps and volts I find that with experence of the system I am able to judge the contents of the battery bank.
I stick to this ritual of 1 hour per day when at anchor we usually anchor for 7 to 14 days at a time.
The reason for me stating that I would prefer dc charger is that my generator does not generate a true sine wave this causes problems with some equipment also the bulk of the generator work is battery charging.I would recomend Fitting trojan batterys 6 volt units as fitted to golf carts.
Geoff /forums/images/graemlins/cool.gif

Anonymous
03-01-05, 10:47
[ QUOTE ]
If connected to the boat's AC distribution system 99.999% would be plugged into the shore connection as is.

[/ QUOTE ]John, as I see it, that isn't the issue here. We were talking about the suitability of the generator, not how it is connected. There are many other bits of boat apparatus with, frankly, far greater safety risks if not used correctly. I'm sure we could both think of plenty of examples and maybe that would make an interesting thread of its own!

As an aside, I don't think that 99.999% is anything like the real number who would connect a generator without thinking or asking. You only have to listen to these forums to see that a large number of non-electrical yachtsmen do come here and ask questions, and for every one of them there are probably another 10 lurkers who are taking in the information. Most yachtsmen are very careful and thoughtful though there is undoubtedly a cavalier minority - but in a sport with inherent risks, like yachting, it's self-regulating /forums/images/graemlins/smile.gif As we say in the flying world..."There are old pilots and there are bold pilots but there are very few old, bold pilots".

Regards, David

Anonymous
03-01-05, 11:14
[ QUOTE ]
I dont have any serious monitering just use a volt meter on the battery bank I have a good controller on the solar panels with a display for amps and volts I find that with experence of the system I am able to judge the contents of the battery bank.I stick to this ritual of 1 hour per day when at anchor we usually anchor for 7 to 14 days at a time.

[/ QUOTE ]Hi Geoff, with a 100A charger, assuming 90% efficiency of charging, you are putting in around 90Ah per day from the generator. You have 160W solar power, and if you are in the Med you might get around 40Ah per day (since you are a 24V boat) when the weather is good, giving 130Ah total input per day. For comparison, for those of us who think in terms of 12V systems, that is the equivalent of 260Ah per day for a 12V system. I am a little surprised if the charger will give a continuous 100A for the whole hour - I would have thought it would have settled back to around 50 to 60A after a while but if you are using Trojans, maybe the charging characteristic is sharper than some other lead acid batteries. What I am saying is that a 100A charger will not provide 100A all the way to full charge and then drop off, like filling a petrol tank. The output current all depends on the battery voltage and measured temperature (presumably you do have a temperature sensor on the batteries going to the charger?)
[ QUOTE ]
The reason for me stating that I would prefer dc charger is that my generator does not generate a true sine wave this causes problems with some equipment

[/ QUOTE ]I am surprised - I don't have any problems with my FP 6kVA - what equipment is causing problems?[ QUOTE ]
also the bulk of the generator work is battery charging

[/ QUOTE ]I though that you were an all-electric boat, no gas, so all your cooking and hot water is electric? If so, I imagine that if you checked where each kWh from the generator was used you'd find that most went on cooking and water heating.A small electric ring is about 1kW, a large one 1.8kW and an oven is around 2kW, I think. The water heater is probably around 750W to 1000W. Most microwaves draw around 1000W from the mains.[ QUOTE ]
I would recomend Fitting trojan batterys 6 volt units as fitted to golf carts.

[/ QUOTE ]I agree, I'd love the flooded Trojans but I have a serious size problem. To modify my battery storage area to take the right number would be a major project and involve moving the watermaker, and other equipment. It's a shame because the reputation of Trojans is first rate. Regards, David

anglo_saxon
03-01-05, 11:27
I have just printed all your points out and will discuss all with F.Panda at Excel. Thankyou once again.

Anonymous
03-01-05, 13:17
You're very welcome. I'd be very interested to hear what you decide, and your reasons. It isn't a straightforward decision because so much depends on your lifestyle and how much you wish to invest in your boat (bearing in mind that it will hardly affect the resale value at all, whichever way you go).

castlevar
03-01-05, 14:35
Hi David
our cooking when we are on the boat in the med is totally different from what we eat when we are at home we eat salad with grilled fish micro wave fish 100 watts imersion 30 min 250 watt our genny is a hfl no frills 6kva reg hz with speed so when it comes offload hz rises this can give problems to printer w/m and micro.
Now I have eliminated most of the problems fitting chokes etc.
but for our type of boating the dc option would be the best.
Geoff

Anonymous
03-01-05, 17:20
Geoff, I'm surprised you've had trouble with the HFL but it depends on your computer system. All small ac generators have a delay in speed control on change of power since the throttle is mechanical. For close frequency control the only sensible alternative is to use dc and a static inverter, which is what you are proposing but not many things are very frequency-intolerant over the short term (1 second or so). I only use a laptop and laptop printer, which I power from a small square wave inverter when not on shore power - no problems except lots of RFI which wipes out HF weather fax, etc. so I run on the internal battery at that time then recharge later. There are other solutions, but that works so I'm happy but might buy a cheap dedicated dc dc converter (which I'll suppress if needed) for the laptop. Note: I don't use the laptop for real-time nav, only passage planning, etc. Even XP freezes too often for me to want to rely on it for proper nav though maybe that's because I have a lot of other stuff on my laptop from home movies to my accounts! Regards, David

Ships_Cat
04-01-05, 09:52
<<<If connected to the boat's AC distribution system 99.999% would be plugged into the shore connection as is.


--------------------------------------------------------------------------------

John, as I see it, that isn't the issue here.>>>

Not sure what the issue is with you now as it seems to be a changing feast. You made it the issue by suggesting that by plugging a portable generator into the shore inlet all would be fine as it would look like the secondary of an isolating transformer (as you now know, it will not look like that at all) /forums/images/graemlins/crazy.gif.

Responding to you just raises another nit picking silly suggestion or technically incorrect belief, so doing so is just a waste of time.

Anyway, the thread has moved a long way from the original poster's question and it would seem clear that the advice he received outside of the forum is correct.

John

Alastairdent
04-01-05, 12:28
There is another option - adding an alternator to the inboard diesel engine. A clutch can be added - so that the 2nd alternator isn't always on. Combine it with a charging management system, and it will do the job perfectly well.

This could be far, far cheaper than installing another engine!

Anonymous
04-01-05, 17:12
[ QUOTE ]
Not sure what the issue is with you now as it seems to be a changing feast. You made it the issue by suggesting that by plugging a portable generator into the shore inlet all would be fine as it would look like the secondary of an isolating transformer (as you now know, it will not look like that at all)

[/ QUOTE ]Rubbish, as any first year engineering student would tell you. The output from a portable generator is from a coil that is not referenced to earth, or any other potential. Electrically, this makes it identical to the secondary of an isolating transformer. I cannot believe that any person qualified in electrical engineering would say otherwise...from your past postings I had assumed that you have had a formal training in electricity, but presumably not.

David

Ships_Cat
04-01-05, 22:08
See what I mean Lemain? It is a waste of time persevering with you.

You said Electrically, such a generator looks idential to the secondary of an isolating transformer - probably the best and safest way to connect any boat to shore power. That is what I answered.

You will see from my response to your claim, that when a boat is connected to a shore supply by an isolating transformer it in no way looks identical to a floating neutral generator.

It seems that you do not understand my description as to how isolating transformers are used in a boat's shore power installation. In which case I suggest that you do some research (and I actually gave a couple of references) before pulling the posts apart of someone who does know what they are talking about.

John

Anonymous
04-01-05, 22:55
[ QUOTE ]
It seems that you do not understand my description as to how isolating transformers are used in a boat's shore power installation.

[/ QUOTE ]This has nothing to do with how one should or should not wire it up. I am saying that the output from a portable generator is electrically IDENTICAL to an isolating transformer and that it is perfectly suitable for connection to a boat's electrical system provided that it is connected correctly.

More to the point of all this, you were arguing that 99.9999% of people would wire portable generators incorrectly because there would be a problem with 'floating neutrals', so they shouldn't be used. But that is incorrect, as I am trying to explain to you. There is no electrical problem in using a portable generator as long as it is wired in correctly. I have never tried to tell anyone how to wire it correctly - you have - and I don't take issue with any of that, it sounded correct.

By all means warn people to wire them correctly, take advice, or get an electrician to wire it and by all means warn people that petrol on boats can be dangerous, but PLEASE don't tell everyone that portable generators cannot be used for technical reasons such as 'floating neutrals' because that is simply untrue.

David

ean_p
05-01-05, 00:02
But what are the benifits of grounding the neutral on a generator supply and /or an isolating secondary ?

Ships_Cat
05-01-05, 03:43
For the same safety reasons as applies to the 3 wire polarised system in your house's AC supply (assuming you are in the UK or similar) where AC sources have their neutral bonded to ground (as at the house switchboard) so that the house wiring's earth conductor then provides a return path in the case of fault on an appliance or cabling.

For on a boat most (all?) codes require, to achieve the same thing, that all AC sources have their neutral grounded at the source. So, for example, an installed generator, which is an AC source in the same way as a house's switchboard is an AC source, has its neutral bonded to earth at the generator and same for an invertor.

If the boat has an isolating transformer then the shore neutral (and its earthing) is, of course, isolated from the boat side of the transformer so it cannot be "seen" from the boat's point of view, so the transformer is regarded as an AC source in the same way as an invertor or generator is and the neutral on the output side earthed to again give a 3 wire polarized system on board.

For a portable generator with floating neutral the effect is similar to not correctly bonding to earth an on board transformer's neutral. However, as explained before, if it is plugged into the boat's shorepower connection, as they usually are, then the whole of the boat's AC distribution will be floating neutral (as for other safety reasons the neutral on the boat is lifted from the boat's earth when the AC supply is switched to the shore power connection).

Now one could possibly provide a special switched connection for a portable generator seperate from the shore power one such that the generator's neutral is earthed but I suspect no one does or is likely to do that. Furthermore, while the generators have fault protection built in, I suspect that this will in most (all?) cases enable preventing generation if the neutral is earthed and the generator chassis is also earthed, as it should be, or leaks to earth if it is not (I have not and never will have a need to see if this is so).

From time to time I hear some say that if there is an isolating transformer (or small floating neutral generator) you don't need to earth the neutral on the output side, just as when they are used on land. However, in the land case they are thinking of only a single appliance being normally connected to an isolating transformer, so no other AC distribution/appliances are able to be implicated in a fault situation to cause a shock hazard.

Obviously, people get away with ignoring all of these things, just as in a house incorrect wiring may last the life of the house without the circumstances arising where an accident occurs.

Hope that is clear.

John

Anonymous
05-01-05, 07:18
[ QUOTE ]
For the same safety reasons as applies to the 3 wire polarised system in your house's AC supply (assuming you are in the UK or similar) where AC sources have their neutral bonded to ground (as at the house switchboard) so that the house wiring's earth conductor then provides a return path in the case of fault on an appliance or cabling.

[/ QUOTE ]You are dreadfully out of date - at least in the UK. Since the mid 1970s houses have been wired with Protected Multiple Earthing (PME) where the neutral is NOT bonded to local ground and can rise many volts - even to phase volts - with respect to local earth. This is why bonding of all metal pipes, etc., in modern homes is so vital. It is perfectly valid technically for a boat to be wired in the same way. I am not familiar with all the boat standards and had assumed that you are current on them but if you didn't know about PME I question that. Exactly which regulations or standards have you been quoting in this thread?

David

Ships_Cat
05-01-05, 11:18
Oh my goodness Lemain here you are at it again off down another tack that does not show anything. I live many thousands of miles away from the UK so cannot profess to be exactly correct as to the specific point at which the earth and neutral is bonded there for the electrical distribution to houses. But in effect what I say is still correct, the neutral and earth are bonded.

You are very strangely picky, I suspect trying to prove some sort of superiority of marine knowledge by confounding with irrelevant tangents.

In what I said the neutral is bonded outside of the installation at the point of service which in many places is actually at the switchboard. That is also essentially so with PME albeit the neutral to earth bond is down the wires a bit from the installation rather that at the switchboard.

It is still as I describe so one can only imagine that you are making an attempt to unravel what I say by irrelevant comment.

If anyone has any questions they wish to ask specifically of me, would you please just send me a PM and I would be happy to try and answer if I am able. I think it is clear that it is pointless me trying to make any comment or provide any responses on here as it only leads to time wasting for all.

So have your last say Lemain, I am sure it will be pathetically picky and confounding - however, I will not be reading it. Seems though that you ran out of criticisms of the generator and marine bit - it took some time.

Many thanks to everyone else.

John

Anonymous
05-01-05, 15:54
It is sad that you have sunk to personal attacks - indeed almost from the outset. Having sent you two polite PMs and received rude replies I really give up all hope of having any reasonable discussion with you.

Clearly you don't understand basic electricity - it seems inconceivable to me that you actually hold any sort of formal electrical qualification. Do you?

Ships_Cat
05-01-05, 21:34
The answer to your question is "Yes" at university level.

I can add that I am in New Zealand and work in the marine industry, among other things, managing the design and construction of high quality boats (built in various countries) for clients as far away as the East Coast of USA. They seem to say that I know what I am talking about (but I am too modest to claim that they are correct /forums/images/graemlins/blush.gif) and I suspect that they also know what they are talking about.

John