Mains wiring & inverter

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Elemental

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I'm just investigating at the moment, so I'm not about to blow myself and the boat up imminently...

My boat is wired for shore power. However, as I spend as little as time as possible in marina's I'd like to have an inverter on-board. Can I safely distribute the resultant AC around the boat by making a lead, with a plug at each end, and connecting the output of the inverter to one of my 13A sockets... It seems like a dodgy thing to do - and I know that simultaneous connection of shore power would create a spectacular lightshow but on the face of it I can't see what the problem might be. Would the RCD consumer unit that protects shore power be happy?

Perhaps a better question is "Can someone point me to a good source of digestible, practical information on this topic?"

Cheers

Mark
 
Re: Mains wiring & inverter

I suspect a safer way would be to put a plug for your shore power socket on your lead and connect it that way - then you can't connect both at once (which would not be good)
 
Damn ! Beaten to it !

Rather than plugging in to "one of" your 13A sockets why not plug in to wherever your shore power line normally plugs in to ? You would have to ensure that any mains battery charger was disconnected otherwise flat battery syndrome would rapidly ensue.

You don't mention how big an inverter ?
 
Does your shorepower distribution unit on board also power a 3-stage or similar internal battery charger? If so then I guess that the charging element in that would have to be switched off at the time.
I am imagining the boat batteries powering the invertor which is now supplying power through the shorepower connection, to the shorepower distribution unit on board that has a built in battery charger that is now trying to charge the depleting batteries.

PS - plug to plug not too safe. If you connect the powered end first you would have live pins (not holes) at the other end. Similar reason to why the shorepower leads have different end connectors and can therefore only fit one way round to the shore supply.
 
Not a big inverter, just enough to run ipods, hair straighteners ( :-0 ) that sort of thing.

I was thinking of 150W or so.

I hadn't thought about the mains battery charger. Won't that preclude using the shore lead?
 
Re: Mains wiring & inverter

I recently bought a little inverter from Maplins for £15, up to 150 watts, bought it mostly for the laptop , even this will flatten batteries if you are not careful so I don't think you would be able to do much with your planned system anyway.
Plug to plug is pretty lethal as others have said, don't do it. Keep it simple or get a generator if you have space for it. Oil lamps, led bulbs, small inverter.
 
Re: Mains wiring & inverter

Mark_H...

I think that cormorant is saying this too but your idea would leave you holding a live unguarded plug live with 240 V on the pin(s) if you happened to turn the inverter on first.

W.
 
Re: Mains wiring & inverter

I'll agree with Wilson, BG & CSail ....

Our inverter just plugs into the same place as the shorepower - so you can't have both on at the same time. We do have to ensure the 500w immersion heater is off though. If your battery charger has a switch to turn on/off whilst on shorepower then just flick it to off, plug in the inverter and away you go...

You should _NEVER_ have a 240v plug that could be live whilst not plugged in - you may be fine with it, but if someone else picks it up to be helpful you could easily kill them with it....
 
Re: Mains wiring & inverter

I think that with a small inverter you shouylkd stick with plugging the appliance into the inverter or if that is not in a convenient place a dedicated socket in the right place. You could never get the females to understand that the inverter is not as powerful as the mains. They would just plug everything into the usual mains socket. olewill
 
Re: Mains wiring & inverter

I agree with William_H, keep the inverter for the small stuff, completely seperate, just plug it into a cigar lighter socket and have a small extension lead to run from it.
By the way, 150 watts is not a very big inverter, I would have thought 300 would be a better bet.
 
Re: Mains wiring & inverter

Regarding the plug <-> plug lead; I know it's a bad idea, which is why I referred to it as dodgy in my original post.

I do like William_H's point that it's probably better to have a seperately identified mains source as people will probably start plugging higher power stuff in.

I was thinking that 150W should be enough for the sort of stuff I do want people to be able to run. 300W would require 25+ Amps, effectively killing 100AH battery in well under 4 hours. I have 2x120 AH domestic batteries and presuming a max of 50% discharge that would flatten the pair in the same timeframe.
 
Re: Mains wiring &amp; inverter

You'll find that some appliances take a high start-up current, but then run at a much lower current. Some inverters will shut down if overloaded, and this may happen with the start-up current. Remember, a 300W inverter running on a 150W load will draw only about the same (or little more) than a 150W inverter on the same load.
 
Re: Mains wiring &amp; inverter

The idea of 300w, was "in case" you needed more umph to start some things which will run on 150w but not start at 150w. But you go ahead with whatever size you feel comfortable with.
 
Re: Mains wiring &amp; inverter

Good point about the startup current. I'm probably just concerning myself about nbothing really as there's probably not much that will actually be plugged in at all.

Thanks very much for all the smart advice.
 
The problem with having the inverter and the shore power going at the same time is two-fold. Firstly you're putting a voltage across the output of the inverter - it almost certainly won't like this though some do have backfeed protection. Secondly you're dealing with AC so you need something clever too get the two supplies synchronised (think what happens when waves bounce off a quay or sea wall; sometimes they're amplified and sometimes they cancel). Again you can get get synchronising inverters but they tend to be very expensive.

There's no problem with having the shore-power charging the battery-charger which is running the inverter of course. As you said you'd need at least 30 Amp charger to get anything into your batteries if you had a 300W inverter.

Have a wander in to Waterstone's or Border's - there's usually a couple of books that will cover this sort of thing in the boaty bit. You can decide for yourself whether it's worth buying one of them once you've had a browse.

How about this? Shore power comes in and goes to the battery-charger. It also goes to a 13 Amp socket somewhere dry inside the boat. Beside that 13 Amp socket is another 13 Amp socket which is the output from the inverter. Take the feed to the boats ring main and put a 13 Amp plug on it on a lead that's just long enough to reach either of the two sockets. When you want to run off shore-power plug into to the shore-power socket; when you want to run off the inverter, plug the boat feed into the inverter output socket.

Please say "that would work fine Geoff" as I helped wire a boat up like this late last year - with appropriate C/Bs, RCD's , etc. of course and it seems to be going okay at the moment
 
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