12V DC or 240V AC generator

[Anonymous]

[ 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]

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]

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]

[ 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]

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]

[ 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]

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]

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]

[ 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]

[ 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]

I have just printed all your points out and will discuss all with F.Panda at Excel. Thankyou once again.

 

[Anonymous]

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]

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]

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]

<<<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]

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]

[ 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]

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]

[ 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]

But what are the benifits of grounding the neutral on a generator supply and /or an isolating secondary ?