Portable Genny - Worth bothering with?

[Richard10002]

I've got an SIP Medusa Compact 950 2 stroke portable generator which I tink has only been used once by previous owner to test it works.

Anyway, I've dug it out, (no mean feat in itself!), and have a few queries before filling it up and getting it going:

1) It says it needs earthing by attaching a metal pole and sticking it in the ground - fair enough, but how on a boat? I had hoped it would be earthed by the boats' system when I connect it to the mains AC input, which is the plan... any thoughts?

2) I want to use it mainly instead of the main engine to charge the batteries... the plan is to connect it to feed the 240V AC supply, then charge the batteries from there, and maybe use the laptop and whatever. However, it says it the output current at 230V is only 2.8A... how would this get converted back to DC to charge the batteries, i.e. would it rise when the voltage becomes DC, if you know what I mean.

I think I use about 60A per day, so not much use if it only charges at 2 or 3 Ah.

You might ask why I dont just connect it to the batteries to charge them - I dont have a normal battery charger, and there would be cables all over the place - feeding the AC then taking stuff from there seems a neat solution.

3) It says it's noise level is 86LWA - presumably that's not
quiet.

The rated Output is 0.75Kw.

Many Thanks

Richard

 

[captainslarty]

Hi Richard.
How do you intend to charge the batteries with it if you dont have a charger, or do you mean a built in charger ?
the output at 230 v may well be 2.8 amps or so, this is apx
650 watts, which is probably the rated constant output. If you were to hook up a charger, then (not counting inefficiencies)
You would have roughly 43 amps available to charge with providing your charger is capable of that.
Hope that helps.

 

[Anonymous]

Richard, if it is a really nasty genny the waveform might not be tolerated by your charger but hopefully not. If you find that the load on connecting is too high, then make a point of starting the boat engine first, then the genny, and after the initial charge surge has passed, after ten minutes, or whatever, turn off the main engine.

 

[Anonymous]

Sorry, I missed out a chunk...yes, of course you have to put the earth stake in - that's what it says in the manual so that's what you gotta do /forums/images/graemlins/wink.gif

Connect the output of it just as if it was the dockside supply - you have got an RCD breaker so you shouldn't have a problem.

I'm sure I know what you mean by ordinary battery chargers - you meant that you have the one that works when you plug into a marina but not the sort that you use to charge a car battery at home? The one fitted into the boat is fine.

 

[captainslarty]

Re: earth stake

I think you will find it referred to GROUND STEAK...
No good throwing good meat overboard...
/forums/images/graemlins/laugh.gif

 

[Richard10002]

[ QUOTE ]
Sorry, I missed out a chunk...yes, of course you have to put the earth stake in - that's what it says in the manual so that's what you gotta do /forums/images/graemlins/wink.gif

Connect the output of it just as if it was the dockside supply - you have got an RCD breaker so you shouldn't have a problem.

I'm sure I know what you mean by ordinary battery chargers - you meant that you have the one that works when you plug into a marina but not the sort that you use to charge a car battery at home? The one fitted into the boat is fine.

[/ QUOTE ]

Thanks for that David,

Just so I get this right - I obviously cant put a stake in the earth but, by just connecting to the boats' input as if we were in a marina, the RCD breaker will provide the protection - i.e. a virtual stake.

(I ask, because I could connect a wire and throw it over the side, thus using the sea as earth... or I could connect it to the engine block, which is what I think is used as earth on the boat, (I'm guessing the engine block then has a connection to the sea, perhaps via the anode))

looks like it could be a goer tomorrow - we'll see whether it starts, how much noise it makes, how much charge it provides, and how much fuel it uses.

many Thanks

Richard

BTW - on the subject of things starting - the outboard continues to work with the choke fully out. It will now run at very low revs, (and I think the clutch disengages), although if we turn the handle to its' lowest setting, the engine cuts out. Havent found anywhere with a Honda Service facility yet, so will wait for Malta. Out of about 60 nights, we have only spent 18 in marinas, so your help has saved us a fortune!

 

[Richard10002]

[ QUOTE ]
Hi Richard.
How do you intend to charge the batteries with it if you dont have a charger, or do you mean a built in charger ?

[/ QUOTE ]

Yes.. the charger is built in and works either off the engine alternator, or of the marina 240v supply, (or off the inverter 240v supply if I forget to switch the battery charger off!!! Only done it once!!!).

I've seen the charger charging at about 35A when the engine is running, so I guess it can handle 43A less inefficiencies.

Thanks for the help.

Richard

 

[Anonymous]

Richard,

The whole business of earthing is quite a complicated subject and has consequences not only on safety, but also corrosion and electrical noise that can cause problems with radio and nav gear. However, I know a bit about your setup from previous threads and I think you will be best advised this season to just plug in the genny L, N & E point to point as commonsense would suggest. Then, if your system is 'earthed' to seawater or not, nothing will change. We are possibly not necessarily protecting you against leakage from the alternator to the RCD breaker and that is a weakness although if your existing wiring is earthed to the sea then you will get a high degree of safety due to that. Ideally the generator chassis should be earthed as this would blow a fuse (or trip a breaker) in case of serious leakage and in any case the earth would protect people. OTOH in my experience you will float up and down electrically as well as literally, on the boat. Years ago we didn't have an isolating transformer or an earth on my dad's boat which resulted in the whole boat being live /forums/images/graemlins/shocked.gif unknown to us. It came to light when I had a pee /forums/images/graemlins/shocked.gif /forums/images/graemlins/shocked.gif and it was a shocking experience.

It's not right to joke about a serious subject like this /forums/images/graemlins/smile.gif but seriously provided you don't make a habit of resting against the generator housing you won't get a shock. When, and only when, you have proved that you want to make that genny part of your kit, then let's talk again about how to arrange it in a more sanitary manner. Among other things you need a four positiong switch - off- shore - inverter - genny and then you won't be using the inverter to run your battery charger! When you come to wire all that, you will need to draw up a proper wiring schematic and that's when you will trace out the wiring and decide what should be done.

 

[Richard10002]

Thanks again David.

The earth point on the generator has a green/yellow wire which looks like it goes to the AC output socket, so I am guessing that this will connect the chassis to the RCD, once it's plugged in.

As you say, nothing will change on the boat and I dont intend to be touching the generator to any degree once it's started, so I'll have a go with care tomorrow.

Richard

 

[Anonymous]

[ QUOTE ]
The earth point on the generator has a green/yellow wire which looks like it goes to the AC output socket, so I am guessing that this will connect the chassis to the RCD, once it's plugged in.

[/ QUOTE ]
It isn't quite like that, really, but as long as all you are doing is to use the generator with its output socket in the same way as you'd use a marina mains connection then you will be OK unless there is a gross problem on the generator. That can happen in marine environments. You will be protected from problems downstream of the RCD (i.e. everything plugged or permanently connected into the ship's mains supply). Nothing upstream (i.e. on the shore side of the shore power socket) will be protected and it isn't very easy to provide decent protection other than by using an earth stake, or a good earth to the sea. Turn the genny off when fiddling with it or filling it (not a bad idea, anyway /forums/images/graemlins/wink.gif)

 

[jimbaerselman]

[ QUOTE ]
Yes.. the charger is built in and works either off the engine alternator, or of the marina 240v supply, (or off the inverter 240v supply if I forget to switch the battery charger off!!! Only done it once!!!).

[/ QUOTE ] Forgive me, but that sounds most unusual. It suggests that your engine alternator outputs 230v, which is fed into your charger . . .

Much more common is a 12.6v to 14.4v output from the alternator, controlled by an internal voltage regulator, or sometimes by an external smart regulator (Adverc or Sterling or whatever) which feeds the batteries, usually via splitters (diodes).

The mains charger would then be a separate animal, fed with 230v either from your mains, or from your portable genny, (never from both!), which feeds your batteries with separate, diode isolated lines, at 14.4v (or less as they charge up).

But maybe you have a really fancy system beyond my ken . . .

Whether any system works well with a portable genny will depend on how intelligent the mains battery charger is. Usually they're designed without speed of charge in mind - so many just shove out a paltry 13.5v for a very long time. Fine in a marina, a pain for genny charging. A good genny charging unit will output 14.4v, giving a much quicker charging rate.

Sorry, more to say, but SWMBA calling . . . will follow up later if nec.

 

[Richard10002]

Jim,

Sorry for the confusion - I dont actually know how the alternator is connected to charge the batteries - it will be whatever is normal - i.e. there may be 2 chargers.

When charging, if the batteries are down to say -50Ah, it starts pumping in around 20/30Ah, and this gradually reduces as the batteries fill up, to as little as 1Ah or so when they are nearly full, say -15Ah.

So I'm guessing it's "Smart".

 

[jimbaerselman]

OK. Alternator will output nominal 12v ie, about 13.6v once the battery is reasonably charged using its own internal voltage regulator.

A 'smart' voltage regulator (Adverc type) can be fitted which will take over voltage control from the alternator internal regulator. This will sense the voltage at the battery (rather than at the alternator) and will be able to input 14.4v at the battery end of the wiring, dropping to 13.6 when the battery is charged (I'm over simplifying a bit). This will much more rapidly and effectively re-charge your battery when the engine is running. You can tell if you've got a smart voltage regulator by checking your battery voltages while charging. With a smart charger they'll cycle up and down by 0.3v to 0.9v every few minutes.

If you're using 60AH a day and not mainly connected to the mains overnight, having a smart charger is probably the first and most cost effective way of improving your battery state and life. Cost around £150 or so. See Adverc for details. There are other makes.

With respect to mains chargers, they also come in two flavours, not dissimilar in some ways to the voltage regulators above. The first type senses the voltage while charging and modifies its output (up to 14.4v) to give a quick charge, then down to 13.2v to 13.6v 'trickle' once the batteries are charged. The second type assumes that 13.xv is fine since you'll be plugged in for several hours and who cares about rapid charging.

As you can guess, rapid charging (ie, a short running time on your portable generator) will not result from the second type. However, the quick chargers can have a snag - by calling up 14.4v when the battery is down, they may consume more amps than you genny can handle (20a max with your 750kw job). In which case they'll trip the genny. No problem - it just means that you should run your main engine for ten minutes or so to charge the batteries a bit first, then try the genny. Either way, it's unlikely you'll be able to charge at better than 10a to 15a, so that still leaves quite a lot of genny time to catch up 60AH!

Earthing - you're quite right - earth to the water if you want your 240v RCB to be effective, and if you want your neutral not to be part live. As pointed out already, this is belt and braces safety.

Summary - check for a smart voltage regulator. If you haven't got one, consider this as your first step to reducing main engine running time to charge and improving battery life. If you've already got one, a portable genny with a suitable mains charger will reduce the amount of main engine running time you need to keep the batteries up.

Sorry if I've repeated stuff here. Had to rush away . . .

 

[andygreen84]

My boats alternator wasnt charging my batteries effectively, i had a firm from Beaumaris install a digital alternator regulator ( Sterling ) and now all is well. You can ask questions on their website and they e-mail back, marinelectricalpower.com i think

 

[rogerthebodger]

Lemain and I have been discussing this on another thread.

Pls ensure the neutral and the earth of the generator are connected together and if your existion installation has an effective connection to earth (the sea) use it otherwise if not cirtain hang a wire over the side which has been striped of insulation below the water for as much as practrical connected to earth and neutral of the generator

 

[Anonymous]

[ QUOTE ]
Lemain and I have been discussing this on another thread.

[/ QUOTE ]Hey! We have been disagreeing. If folks want to follow your suggestion that's fine but let them do their own research first. There are potential problems with what you are recommending.

 

[rogerthebodger]

OK we have been disagreeing.

I have no problem with anyone doing their own research and looking at all points of view.

So to that end pls let the fora into what you consider to be the potential problems with my recomendiations

 

[Anonymous]

You mean problems with connecting N to E where E is seawater earth? I have explained some of the problems (though not exhaustively) over on the winches thread. Anyone who does this needs to fully understand the consequences, and have some means of disconnecting it when appropriate.

I don't connect the earth of my ship's mains system to anything. It is floating insofar as that is possible on a boat. Pair of sidecutters. Snip.

But not everyone agrees with me, and there are arguments against, so I don't want (in this forum, at least) to be giving people 'advice' on this particular point. If folks don't understand these things then they should do some study or pay for professional advice rather than rely on comments from posters on fora, however well-qualified or intentioned those posters might be.

 

[jimbaerselman]

Interesting difference of opinion. I must go and review my AC theory.

Greek houses in the countryside are generally supplied with 240v over a single wire to their meter and 60a circuit breaker. Neutral is several interconnected stakes in the ground, which feed both an earth line and a neutral line. The resulting three line cable goes to the house and RCB . . .

My boat main is driven through an isolating transformer, with the earth line connected to a skin fitting. One or other of the isolating tranformer outlets is connected to earth, and the other labelled 'live'. Whether this is good practice or not I don't know, but it was done by professional electricians who worked on marine installations.

I can see though, that if an isolating transformer is not used, or if the earth is also (or separately) connected to the shore earth line, there's a risk of stray voltages around - perhaps a shocking experience for someone having a swim.

So, back to the manuals to see if I can understand this better . . .

 

[captainslarty]

reference the earthing situation on marine installation, I think theis is a VERY important subject, and as such, deserves it´s own thread. I have therefore started one in the main area entitled ´grounding methods of marine installations - Discussion

Joe