12V DC or 240V AC generator

[anglo_saxon]

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]

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]

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]

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]

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]

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]

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]

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]

Thank you I will take all points mentioned allong to the L.B.Show and discuss them with Panda. Thank you all..

 

[Anonymous]

[ 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]

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]

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]

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]

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]

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]

[ 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]

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]

[ 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]

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]

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?