240v/12v Ideas?

[Kustomcut]

HI all I am looking for some help/guidance.

I have a 25ft springer that currently has electric shorepower hookup (no RCD), and basic 12 volt wiring for lights/horn/water pump etc.

All works fine however I would like to do the following

Add an invertor

Add a second battery on the leisure bank, as I am adding a 12v tv and a few more 12v charging points.

I have seen all the info on "break before make switches" re shore power/invertor.

What I am thinking is as there is very few places where i currently have the boat offereing shore power could I run from output on the invertor to input on the shore power?

This way I can never plug in shore power whilst the invertor is on?

That way could I basically wire as below but just have the invertor output plugging into the whore power input? doing away with second rcd and switch ?

See below

Secondly hull bonding.

Does anyone have a guide as to how to do it basically I undertand the principal but any do's dont's?

Secondly how does the hull bonding work if I am doing as picture but also have 12v on board?

Do I bond the negative of the 12v to the same point?

ANy help much appreciated.

 

 

 

[nicknorman]

I suppose you could just plug the inverter into the shore power socket but it’s not the best idea due to having to somehow get the cable outside the boat only to have it coming back inside via the socket. The cable from the inverter wouldn’t be protected by an RCD against chafing etc and if you think about it, a loose cable poked through a half-shut door or window is probably the most likely thing on a boat to chafe. If you did do as you suggest you’d need to NE bond the inverter output, say in the cable you made up for the purpose, having first checked whether the inverter was already NE bonded and/or whether it could tolerate being NE bonded.

 

Personally I’d go for a proper changeover switch. Doing it “properly” isn’t going to cost much more and it will be much better in the long run, and more convenient. You still just need the one RCD & MCB (or RCBO) - put the changeover switch before them.

 

The diagram looks fine for what it is. The earth bonding should go to a stud welded onto the hull or some other convenient attachment point. The 12v negative should go to a separate hull stud or attachment point nearby. The engine is likely to already be attached to 12v negative and so the best way to avoid any hull currents is to connect the engine block to the hull.

 

 

[Kustomcut]

1 minute ago, nicknorman said:

I suppose you could just plug the inverter into the shore power socket but it’s not the best idea due to having to somehow get the cable outside the boat only to have it coming back inside via the socket. The cable from the inverter wouldn’t be protected by an RCD against chafing etc and if you think about it, a loose cable poked through a half-shut door or window is probably the most likely thing on a boat to chafe. If you did do as you suggest you’d need to NE bond the inverter output, say in the cable you made up for the purpose, having first checked whether the inverter was already NE bonded and/or whether it could tolerate being NE bonded.

 

Personally I’d go for a proper changeover switch. Doing it “properly” isn’t going to cost much more and it will be much better in the long run, and more convenient. You still just need the one RCD & MCB (or RCBO) - put the changeover switch before them.

 

The diagram looks fine for what it is. The earth bonding should go to a stud welded onto the hull or some other convenient attachment point. The 12v negative should go to a separate hull stud or attachment point nearby. The engine is likely to already be attached to 12v negative and so the best way to avoid any hull currents is to connect the engine block to the hull.

 

 

Ok I forgot to mention my engine is an outboard.

So I go for this method instead?

And bond the 12v negative to the hull bonding point? Same point as the 240 earth?

 

 

[nicknorman]

Ok you can do it that way if you wish, seems a bit complicated to me to separate the circuits and it means you need two sets of RCD/MCB but then if you have a battery charger perhaps it’s a good idea to prevent “finger trouble”!

 

Just for comparison we only have one RCBO on our boat, all sources of power (shore, travelpower, inverter) pass through it but then we have a Combi so no chance of running the battery charger from the inverter. We can run the immersion heater from the inverter if we want to - just do that with the engine running to speed up water heating. But there is a risk of turning it on without the engine running and draining the batteries!

 

Bond the 12v to a point near /adjacent to the mains earth bond. It is not good practice to use say the same stud since if the stud corrodes and breaks off you would have the mains earth connected to the 12v negative and not to the hull, which is bad.

[Tony Brooks]

1 hour ago, Kustomcut said:

Ok I forgot to mention my engine is an outboard.

 

 

What is the maximum charging output of the outboard?

 

Have you done a proper power audit to establish your electricity use?

 

When I see inverter & outboard charging I tend to expect a few weeks down the line to see a topic about why have my batteries died.

 

Have you considered the getting the batteries charged aspect of your plans?

[WotEver]

1 minute ago, Tony Brooks said:

 

What is the maximum charging output of the outboard?

 

Have you done a proper power audit to establish your electricity use?

 

When I see inverter & outboard charging I tend to expect a few weeks down the line to see a topic about why have my batteries died.

 

Have you considered the getting the batteries charged aspect of your plans?

You’ve just saved me from having to type all that

[Boater Sam]

Duplicated.

Edited June 14, 2018 by Boater Sam

[Boater Sam]

Having 2 rcds is overkill and unnecessary.  We used to do the job on hire boats simply with 13A sockets.

 

Bring the mains land line in, galvanic isolator, earth to hull, then to a 13A socket inside. Marked " Land Line"

Connect inverter to 12V via a suitable fuse placed so that you can use it as an isolator as well, no separate isolator. Take output of inverter to another 13A socket, marked " Inverter"

 

Take the wiring from the 240V sockets to an rcd/mcb then to a 13A plug which you can plug into either land line socket or the inverter socket.

 

Simple manual change over, no way you can put mains onto the inverter and blow it, and minimal cost

[Kustomcut]

5 minutes ago, WotEver said:

You’ve just saved me from having to type all that

I had on my 20 foot cruiser a 15hp mariner outboard this kept the batteries topped up in addition to that I have a 100 watt solar panel with mppt controller.

I will check paperwork out later for output from outboard.

I also have split relay so starter battery will still be "safe" from discharge and failsafe a 1kw suitcase genny that I can attatch to a battery charger for leisure batts.

All of the feed (solar,outboard charge) would go to starter batt and this would using the vsr relay switch over to leisure/domestic as and when.

If my thought process is right

 

[Tony Brooks]

The only comment I would make is that I would send all charge sources to the domestic bank and use the VSR to charge the engine battery.

[ditchcrawler]

If you use a combi inverter/charger it would automatically change over you could also just plug your genny into the shore socket have 240 volts on the boat and charge the battery

[Kustomcut]

2 minutes ago, ditchcrawler said:

If you use a combi inverter/charger it would automatically change over you could also just plug your genny into the shore socket have 240 volts on the boat and charge the battery

Any models/makes you recommend?

 

[Kustomcut]

Slight update to the above, how does this look?

 

I have a mega inline fuse between the invertor and battery there are also switches hopefully you can understand on the image, then the invertor output is via a 3 pin plug, I can wire opposite end of this into the ac changeover switch yes?

Changeover switch below

http://www.gscontrols.com/ac-panel---2-way-changeover-156-p.asp

 

The 2 ground points will be close but on separate studs (bolts direct to the hull) approx. 3 inches apart?

Do I only need a galvanic isolator when running shore power?

If so could I use one of the inline plug in ones?

 

https://www.ebay.co.uk/itm/Galvanic-Isolator-Boat-Narrowboats-and-Wide-Beams-120Amp-Top-Quality/292271528870?hash=item440cbd9ba6:g:5UYAAOSwv~lau27Z

 

My invertor is not a combi charger/invertor.

Thanks In Advance

 

[nicknorman]

When you say the output of the inverter is via a 3 pin plug, I'm hoping you mean via a 3 pin socket into which you would plug a plug? It would be very dangerous to have the output of an inverter going to a 3 pin plug as the pins of the plug would be exposed and live!

 

You should have a fuse between the batteries and the solar, close to the batteries (this is to protect against some damage / short circuit in the wiring which could dump massive amounts of energy from the battery into the wires). In addition to the one between the batteries and the inverter.

 

Hull bonding arrangement looks OK.

 

Yes you only need a GI when plugged into shore power. You could use an in-line GI but why not do it properly and install in the boat? Not difficult! The GI listed doesn't have any proper spec and presumably isn't ABYC compliant. 120A sounds a lot but a short circuited live to earth can give much higher currents than that which could blow the diodes open circuit before the breaker trips. So the device will work as a galvanic isolator, but it may not work if there is a major short circuit and may fail into a dangerous condition. Your choice. At the very least, be sure to check the GI diodes are still working and not short circuited or open circuited after any and every tripping of an ac breaker. I would use a GI with a meter or LEDs that indicate what is going on. With that inline GI you have no idea if an excessive voltage between mains earth and hull is causing current to flow, or not.

 

 

Edited June 26, 2018 by nicknorman

[Kustomcut]

Nicknorman, Thank you for your prompt reply, I had no internet access until now so excuse my late reply.

Invertor - yes the invertor has a plug socket on it I will be running a plug  from the invertor socket to the ac changeover so no live pins

 

The solar is a 100w with a 10 am MPPT do I therefore use a 10 amp fuse in the live from MPPT solar controller to Battery?

 I will install the GI at a slightly later date ££££ I have in 6 years never moored anywhere with shore power so don't need just yet but as the boat has the shore hookup it will be something I add so it is all proper. And take on noard re a wired GI with indicators, been looking at the Sterling Power ones.

Thank you for you advice much appreciated.

[nicknorman]

30 minutes ago, Kustomcut said:

Nicknorman, Thank you for your prompt reply, I had no internet access until now so excuse my late reply.

Invertor - yes the invertor has a plug socket on it I will be running a plug  from the invertor socket to the ac changeover so no live pins

 

The solar is a 100w with a 10 am MPPT do I therefore use a 10 amp fuse in the live from MPPT solar controller to Battery?

 I will install the GI at a slightly later date ££££ I have in 6 years never moored anywhere with shore power so don't need just yet but as the boat has the shore hookup it will be something I add so it is all proper. And take on noard re a wired GI with indicators, been looking at the Sterling Power ones.

Thank you for you advice much appreciated.

The fuse size relates to the ability of the cable to carry current, rather than the rating of the MPPT - it is to protect the wiring, not the MPPT. With 12v systems normally one selects cable that is much fatter than that required for thermal (overheating) reasons, in order to keep voltage drop to a minimum. Therefore I would expect the cable to be able to safely carry much more than 10A and would select a fuse size according to the cable rating, hopefully quite a bit more than 10A

 

The other thing to consider is that if you have a 10A fuse running at 10A, it can get quite hot at the bit that actually fuses. Over time, the metal can "age" and ultimately fail even though the current is only 10A. Some MPPT controllers will be damaged if the connection to the battery is suddenly lost (due to the fuse blowing) whilst there is a lot of current passing through.

 

So if possible, avoid running a fuse at its rated current for any length of time. Don't forget that the purpose of the fuse is to protect the cable from excessive current coming from the battery - not to protect the cable from excessive current coming from the MPPT since this can't happen. Therefore the fuse should be located as close to the batteries as possible without actually being in the battery box (risk of an ignition source for explosive battery fumes). Then all the cable between the fuse and the MPPT is protected.

Edited June 28, 2018 by nicknorman

[Alan de Enfield]

38 minutes ago, Kustomcut said:

Nicknorman, Thank you for your prompt reply, I had no internet access until now so excuse my late reply.

Invertor - yes the invertor has a plug socket on it I will be running a plug  from the invertor socket to the ac changeover so no live pins

You need to ensure that the plug on the 'fly-lead' (from the AC changeover to the inverter) does not become live when disconnected from the inverter, and you have connected the land-line.

 

It needs to be a failsafe situation for the day when its not you doing the changeover.

[Kustomcut]

32 minutes ago, Alan de Enfield said:

You need to ensure that the plug on the 'fly-lead' (from the AC changeover to the inverter) does not become live when disconnected from the inverter, and you have connected the land-line.

 

It needs to be a failsafe situation for the day when its not you doing the changeover.

Hi Alan, thank you I am using a Break before Make style switch so hopefully all will be ok, BUT I will test with a meter on the plug with shore power in and the plug unplugged to ensure there is never any voltage coming back down the cable.

Panel is here.

http://www.gscontrols.com/ac-panel---2-way-changeover-156-p.asp

 

 

46 minutes ago, nicknorman said:

The fuse size relates to the ability of the cable to carry current, rather than the rating of the MPPT - it is to protect the wiring, not the MPPT. With 12v systems normally one selects cable that is much fatter than that required for thermal (overheating) reasons, in order to keep voltage drop to a minimum. Therefore I would expect the cable to be able to safely carry much more than 10A and would select a fuse size according to the cable rating, hopefully quite a bit more than 10A

 

The other thing to consider is that if you have a 10A fuse running at 10A, it can get quite hot at the bit that actually fuses. Over time, the metal can "age" and ultimately fail even though the current is only 10A. Some MPPT controllers will be damaged if the connection to the battery is suddenly lost (due to the fuse blowing) whilst there is a lot of current passing through.

 

So if possible, avoid running a fuse at its rated current for any length of time. Don't forget that the purpose of the fuse is to protect the cable from excessive current coming from the battery - not to protect the cable from excessive current coming from the MPPT since this can't happen. Therefore the fuse should be located as close to the batteries as possible without actually being in the battery box (risk of an ignition source for explosive battery fumes). Then all the cable between the fuse and the MPPT is protected.

Does the above stand for sealed AGM batteries.

The MPPT controller is currently housed very close to the batteries in the same cabinet, the batteries then are in plastic battery boxes?

 

[George and Dragon]

I'd like to thank the OP for this thread and all those who contributed. I think it's going to be very helpful

[cuthound]

On 28/06/2018 at 13:00, Kustomcut said:

 

Does the above stand for sealed AGM batteries.

The MPPT controller is currently housed very close to the batteries in the same cabinet, the batteries then are in plastic battery boxes?

 

 Yes. Whilst AGM's are sealed, they incorporate a pressure relief valve (PRV). If an AGM battery is overcharged, pressure builds up and then the PRV opens. Not only does this vent the explosive gas hydrogen, but it shortens the life of the battery because this type of battery maintains its electrolyte by recombining the hydrogen and oxygen evolved during charging.