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Electrics - Inverter vs Transformers


Alethea Price

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Hi there new to the community so I hope it's alright to create a new thread.

The narrowboat I'm currently looking to purchase is set up with an alternator, 3 new 12v batteries, no inverter, mains cabling throughout. There is also a generator on board. I'm sorry I can't provide specifics at this point, but even general advice much appreciated.

If I continue with the purchase, I'm intending on putting on 4 Renogy 100 Watts 12v Monocrystalline Solar panels and doing my best to use the engine for power as minimally as possible (going into winter I realise that the solar is not going to give much power).

The current owner will also be putting on a new 12v Fridge if I go ahead with the purchase.

The appliances I intend on running would be a toaster, iron, TV, record player, iMac (I already own this and not looking to replace it), Laptop charger, Mobile charger. I'll be replacing all the current lighting with LED. There is currently a Washing Machine on board but the owner says its best to remove it as its on the mains (makes sense, although I would consider keeping it if anyone could provide a realistic solution).

Stove and oven will be gas, have yet to decide on a water heating system. The current gas boiler is defunct. Currently considering a new gas boiler or a back boiler for the burner (no burner currently on board looking to purchase) to fuel hot water (taps, shower) and heating (there are radiators throughout but I'm not sure if they would be necessary once I purchase the burner - she's 63'.

To be clear I will not be mooring up and 'plugging in', so everything needs to be off grid power.

My knowledge is limited so being completely open, I apologise if my questions appear naive any support appreciated:

  1. Is it better to consider investing in a good inverter, or should I look at transformers on an appliance by appliance basis?
  2. If primary usage was 12v, would installing an inverter affect functionality or can you run both 230v and 12v with an inverter?
  3. I'm not particularly keen to keep the generator but would anyone advise that I do and why?
  4. Instead of an inverter or transformers would anyone's opinion be that I simply run the engine (with alternator) when using non-12v appliances, and why? I want to reduce emissions and costs from over using the engine unnecessarily wherever possible.
  5. Will the current 'all mains' wiring cause any problems with purchasing 12v appliances e.g. the fridge.
  6. If I wanted to consider keeping the washing machine what would you recommend having in place?

Thank you for your advice.

Edited by Alethea Price
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To start the ball rolling -

A transformer is a completely different animal from an inverter.

To help you better can you describe what transformer is already on the boat - is it something to do with the generator?

While on that subject do you have any details of the generator - it's voltage, output power, what fuel does it use (petrol (UGH!) or diesel. Is it built into the boat?

 If going off grid, I'd be tempted to dump the toaster, instead use the grill in the cooker - I assume it has one. All the other equipment will then run on a small(er) inverter.

'We' need a lot more information - the title of your thread has not encouraged others to jump in - as yet

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Transformers require an AC (mains0 input and give AC out. Inverters take a DC, typically 12 or 24 volts from the batteries and gives an mains type AC output. 12v DC equipment will not normally work on 12V AC and if you tried you may ruin them. 240V AC equipment will not run on 12V DC and the same applies.

12V DC and "mains" AC wiring should be totally separate so there will be no problems running both a the same time be t from a shoreline or inverter apart from battery bank capacity to supply mains via an inverter.

3 x 12V batteries, assuming about 110 Ah each, is not that large when you start talking about inverters. Once you have reliable "mains" on board 24/7 new mains appliances tend to get brought aboard.

1, Tell us how you intend to use your boat (livaboad or holidays).

2. Give us the results of your power audit and charming calcs (Examples on tb-training.co.uk and other online resources.

3. Ignore solar foe the winter moths, say October to April.

4. From what you say and reading many similar posts in the past I would suggest that you need to reconsider your electrical needs, especially powered via and inverter and expect to need a generator plus, potentially more batteries. The problem is likely to resolve down to your being able to charge them enough.

 

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6 minutes ago, OldGoat said:

To start the ball rolling -

A transformer is a completely different animal from an inverter.

To help you better can you describe what transformer is already on the boat - is it something to do with the generator?

While on that subject do you have any details of the generator - it's voltage, output power, what fuel does it use (petrol (UGH!) or diesel. Is it built into the boat?

 If going off grid, I'd be tempted to dump the toaster, instead use the grill in the cooker - I assume it has one. All the other equipment will then run on a small(er) inverter.

'We' need a lot more information - the title of your thread has not encouraged others to jump in - as yet

Thanks for the input to clarify there is no transformer currently on the boat. From my inexperienced research i was looking into how to have my iMac and chargers on the boat and I read a number of feeds suggesting that you can purchase a small transformer for such appliances which goes between the electrics and the plug cable for that appliance in order to convert from 12v to 230v. If however I have misunderstood a general description of a transformer would be much appreciated.

As for the generator - I am still awaiting details from the Seller. When I asked on the day he couldn't provide me with much of the specs for anything, so I'm waiting on that hence the vague description. However I can tell you it's a portable diesel.

Dumping the toaster is no problem and totally logical thanks.

Once I have more info I'll tried to inform you all better. I was hoping it might be possible so get some general info on best electric outfits (as a general rule) but completely understand the need for specifics. Will update when I can but any advice in the mean time is helpful thanks!

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12 minutes ago, Tony Brooks said:

Transformers require an AC (mains0 input and give AC out. Inverters take a DC, typically 12 or 24 volts from the batteries and gives an mains type AC output. 12v DC equipment will not normally work on 12V AC and if you tried you may ruin them. 240V AC equipment will not run on 12V DC and the same applies.

12V DC and "mains" AC wiring should be totally separate so there will be no problems running both a the same time be t from a shoreline or inverter apart from battery bank capacity to supply mains via an inverter.

3 x 12V batteries, assuming about 110 Ah each, is not that large when you start talking about inverters. Once you have reliable "mains" on board 24/7 new mains appliances tend to get brought aboard.

1, Tell us how you intend to use your boat (livaboad or holidays).

2. Give us the results of your power audit and charming calcs (Examples on tb-training.co.uk and other online resources.

3. Ignore solar foe the winter moths, say October to April.

4. From what you say and reading many similar posts in the past I would suggest that you need to reconsider your electrical needs, especially powered via and inverter and expect to need a generator plus, potentially more batteries. The problem is likely to resolve down to your being able to charge them enough.

 

Thanks for the input a helpful start.

 

In response:

I don't know the size of the batteries yet I've requested full specs of everything from the seller but still waiting on that.

1. I would be living on the boat.

2. Unfortunately without the current spec and due to the fact much of the appliances will be new and not yet bought I can't provide a power audit yet but will do as soon as I have that information.

3. Solar - I agree. I realise solar will have limited if any value in winter, I'm just looking to gain a better understand of my options as this point.

4. Buying more batteries is not an issue and the generator is onboard although I was hoping to accomodate so as not to need it. Do most live aboard keep a generator?

 

Thanks again for all the advice.

17 minutes ago, mross said:

Is the generator built in or portable?

To get 230v from batteries you need an inverter.  Transformers can only convert one AC Voltage to another AC Voltage.

Much appreciated thank you.

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If the generator is built in, rather than portable, I don't understand why you would hope to accommodate so as not to need it? Many would consider a built in generator a big asset for off grid living, the cost of supplying and fitting from new runs into several thousands of pounds.

you will always have to charge your batteries via engine, generator, or solar. For several months of the year, solar is out, so many use a portable generator or engine, or both. Even in summer, you may need something in addition to solar.

Keep the generator - a no brainier!

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58 minutes ago, OldGoat said:

 If going off grid, I'd be tempted to dump the toaster.....................

And the iron!

Echoing what others have said 3 times standard domestic battery is not a lot for live aboard use, but it's not so much ultimately about total capacity, as your ability to recharge the back.

Even a modern 12 volt fridge can account for up to about 50% of all battery usage on some boats, so needs to be factored in very much to your power audit.  Make sure they are supplying a compressor type, not a 2 or 3 way absorption one that can also run on gas, (desperately inefficient on 12 or 240 volts), or something based on piezo technology, (also a battery killer).

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8 minutes ago, Richard10002 said:

If the generator is built in, rather than portable, I don't understand why you would hope to accommodate so as not to need it? Many would consider a built in generator a big asset for off grid living, the cost of supplying and fitting from new runs into several thousands of pounds.

you will always have to charge your batteries via engine, generator, or solar. For several months of the year, solar is out, so many use a portable generator or engine, or both. Even in summer, you may need something in addition to solar.

Keep the generator - a no brainier!

Hi Richard thanks for the input and for your view to opt to keep the generator, much appreciated

My reasoning for wanting to avoid the generator is:

  1. It is portable not inbuilt
  2. It is noisy
  3. I've been advised to use it sparingly to avoid drawing attention and creating a security risk from those who might want to nab it
  4. I want to be as low in emissions as possible.
  5. With the engine on, would I still need a generator?

With that in mind would your opinion still be to keep the generator?

Regarding power requirements I realise that solar is out of the question for the winter months, so I am fully prepared that I would need additional options however as the Engine is already set up with an alternator would it then be necessary to have the generator as well? Also regarding emissions - if you had an opinion regarding which is more efficient - using the engine or the portable generator that would be greatly appreciated.

At the moment I'm afraid I don't have the specs for the generator (waiting on the seller) but general opinion would be great. Thanks.

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1 minute ago, alan_fincher said:

And the iron!

Echoing what others have said 3 times standard domestic battery is not a lot for live aboard use, but it's not so much ultimately about total capacity, as your ability to recharge the back.

Even a modern 12 volt fridge can account for up to about 50% of all battery usage on some boats, so needs to be factored in very much to your power audit.  Make sure they are supplying a compressor type, not a 2 or 3 way absorption one that can also run on gas, (desperately inefficient on 12 or 240 volts), or something based on piezo technology, (also a battery killer).

Thanks Alan. From the discussion so far is looks like my questions have been a bit too pre-emptive. I was hoping to be able to discuss general rules of opinion, but it looks like it doesn't quite work that way. Sadly without the info from the seller I'm yet to be able to do a power audit, but once I have that it looks like I'll have a better idea for my consumption and needs.

 

Thanks for the advice. Am already looking at compressor type fridge but good to also understand the reasoning.

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2 hours ago, Alethea Price said:

Thanks for the input to clarify there is no transformer currently on the boat. From my inexperienced research i was looking into how to have my iMac and chargers on the boat and I read a number of feeds suggesting that you can purchase a small transformer for such appliances which goes between the electrics and the plug cable for that appliance in order to convert from 12v to 230v. If however I have misunderstood a general description of a transformer would be much appreciated.

For laptop / TV/ DAB Radio (that I always forget to turn off properly so it eats batteries) I have a small RING 120W cigar lighter inverter (it is quite old...) that is not terribly inefficient.  It will run both TV & laptop charging (not happy to power both switched on, but my laptop draws 90 watts-ish if being used for graphics intensive applications) through an extension lead quite happily.

We have a small inverter for the twin tub but no other mains appliances on board otherwise.

I don't know if the little RING inverter is what you were thinking of, but I would happily give it a 'thumbs uo' for convenience.

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2 hours ago, Alethea Price said:

Hi Richard thanks for the input and for your view to opt to keep the generator, much appreciated

My reasoning for wanting to avoid the generator is:

  1. It is portable not inbuilt
  2. It is noisy
  3. I've been advised to use it sparingly to avoid drawing attention and creating a security risk from those who might want to nab it
  4. I want to be as low in emissions as possible.
  5. With the engine on, would I still need a generator?

With that in mind would your opinion still be to keep the generator?

Regarding power requirements I realise that solar is out of the question for the winter months, so I am fully prepared that I would need additional options however as the Engine is already set up with an alternator would it then be necessary to have the generator as well? Also regarding emissions - if you had an opinion regarding which is more efficient - using the engine or the portable generator that would be greatly appreciated.

At the moment I'm afraid I don't have the specs for the generator (waiting on the seller) but general opinion would be great. Thanks.

4. Whist its an laudable aim it is probably not practical although frugal living (electricity wise) on a oat and no car will very much reduce your emissions. Many boasters also burn a lot of wood on their stoves so less CO in the long term when compared with solid fuel.

5. You need to grasp that however large the output of a generator or alternator is it will take many, many hours to full recharge your batteries. Exactly how man depends on a lot of things but in all probability well over 4 and 12 hours or more is not uncommon. CaRT rules say that you should not run your engine while tied up between 8pm and 8am if other dwellings or boats are close by. If you are working it follows that it will probably be impossible to fully recharge your batteries in the winter. Even f you are not working it can be a challenge. Many boaters try t charge to about 80% during the week and fully recharge at weekend. This is OKish but WILL lead to a reduction in battery capacity and life. It is not pleasant sitting close to an engine running for 12 hours at a stretch or even a non-cocooned generator such as you often see fitted to the stern of livaboard boats.

When ever you discharge a boat battery the slightest bit the chemicals inside it start to change. The more you discharge it the greater the amount that changes. When you recharge it almost all the chemicals charge back to what they were before discharge. However the longer you let it stand in a discharged state the more difficult it becomes to charge the chemicals back so less get reconverted during charging. This cause a  loss of battery capacity  and is called sulphation.

Just to add complications batteries have a finite number of charge discharge cycles that could be as low as 150 to 250 cycles. The more you pay the greater number of cycles you tend to get.  The deeper you discharge the batteries the more of the cycles you use up. This is why we say only discharge to 50% so you in effect get about double the cycles.  An ill informed livaboard boater can easily ruin their batteries in a very few weeks.

A modern 12V electric compressor fridge will demand about 40 Amp Hours per day, less in winter but potentially more in summer. When new the batteries you are likely to be supplied with will hold about 330 Ah assuming its three domestic batteries and not two domestics and one engine battery. If that is the case the batteries will hold about 220 Ah. I repeat WHEN NEW!!! Using the 50% thing this means you will have 165 Ah or 110 Ah of usable electricity stored. The fridge will take 40Ah leaving 125 or 70Ah for everything else. With fully LED lighting and not much else apart from water pump etc. this is doable but start adding mains equipment via an inverter and things very soon get tight, as they inevitably will do as the batteries age and suffer sulphation.

Storing the required electricity is not the problem as long as you are willing to and can add extra batteries but recharging them really is.

On a brighter note as long as you only use higher powered mains devices when you have the engine running fast enough for the alternator to provide the electricity required it will not be discharging the batteries but it will be reducing their rate of charge.

 

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1 hour ago, Ratkatcher said:

For laptop / TV/ DAB Radio (that I always forget to turn off properly so it eats batteries) I have a small RING 120W cigar lighter inverter (it is quite old...) that is not terribly inefficient.  It will run both TV & laptop charging (not happy to power both switched on, but my laptop draws 90 watts-ish if being used for graphics intensive applications) through an extension lead quite happily.

We have a small inverter for the twin tub but no other mains appliances on board otherwise.

I don't know if the little RING inverter is what you were thinking of, but I would happily give it a 'thumbs uo' for convenience.

As a warning. Ring tend to be a budget  automotive brand and the inverter above is very likely to be what is known as a modified sine wave inverter rather than pure sine wave. Modified sine wave inverters can produce strange buzzes on audio equipment and artifacts on audiovisual equipment. They are known to destroy electric tooth brushes and hair curlery type things. It also seem that certain computer power supplies run hot and use more electricity than they would with a pure sine wave (PSW) inverter.

For running laptop computers a 12V car power supply is probably the best option but some computer makers fix things so their computers will not run on generic 12V power supplies. Some Apple, Dell & HP come to mind.

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13 minutes ago, Tony Brooks said:

For running laptop computers a 12V car power supply is probably the best option but some computer makers fix things so their computers will not run on generic 12V power supplies. Some Apple, Dell & HP come to mind.

True - I have an HP (had a Dell until recently) that refuses to charge on a generic 12v adaptor, the Dell had the same attitude - unable to comment on Apple.  Both the HP and Dell are able to 'detect' the power supply attached and complain bitterly if they don't 'see' the genuine article.

True comment on the RING - budget item, although I am not certain if it is MSW (suspect it is) but runs my equipment without any ill effect, this may just be good luck though!

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Revisiting the thread starter, I notice you said that the engine had an alternator. It is usual for boats (nay, essential for any real use of electricity) to have at least two. One (small) to charge the starter battery and a second much larger one to charge the batteries. Your boat has a diesel generator and I'm wondering whether it was because it was impractical / expensive to fit a second alternator.

You 'need' at least an 100 amp alternator - preferably more - to charge a reasonable battery bank.

So could you clarify what the engine is (make and model), how many alternators there are and what make / model they are.

Therein will lie the reason for the diesel genny.

while being a Misery, please don't treat the general water heating as an afterthought. Putting a stove in could require quite a lot of modification to the hull for a chimney and some convolutions in pipework if it's going  to heat your domestic hot water as well.

Sorry!

 

  

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2 hours ago, Ratkatcher said:

For laptop / TV/ DAB Radio (that I always forget to turn off properly so it eats batteries) I have a small RING 120W cigar lighter inverter (it is quite old...) that is not terribly inefficient.  It will run both TV & laptop charging (not happy to power both switched on, but my laptop draws 90 watts-ish if being used for graphics intensive applications) through an extension lead quite happily.

We have a small inverter for the twin tub but no other mains appliances on board otherwise.

I don't know if the little RING inverter is what you were thinking of, but I would happily give it a 'thumbs uo' for convenience.

A great starting point. Will explore more thank you.

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1 hour ago, Tony Brooks said:

4. Whist its an laudable aim it is probably not practical although frugal living (electricity wise) on a oat and no car will very much reduce your emissions. Many boasters also burn a lot of wood on their stoves so less CO in the long term when compared with solid fuel.

5. You need to grasp that however large the output of a generator or alternator is it will take many, many hours to full recharge your batteries. Exactly how man depends on a lot of things but in all probability well over 4 and 12 hours or more is not uncommon. CaRT rules say that you should not run your engine while tied up between 8pm and 8am if other dwellings or boats are close by. If you are working it follows that it will probably be impossible to fully recharge your batteries in the winter. Even f you are not working it can be a challenge. Many boaters try t charge to about 80% during the week and fully recharge at weekend. This is OKish but WILL lead to a reduction in battery capacity and life. It is not pleasant sitting close to an engine running for 12 hours at a stretch or even a non-cocooned generator such as you often see fitted to the stern of livaboard boats.

When ever you discharge a boat battery the slightest bit the chemicals inside it start to change. The more you discharge it the greater the amount that changes. When you recharge it almost all the chemicals charge back to what they were before discharge. However the longer you let it stand in a discharged state the more difficult it becomes to charge the chemicals back so less get reconverted during charging. This cause a  loss of battery capacity  and is called sulphation.

Just to add complications batteries have a finite number of charge discharge cycles that could be as low as 150 to 250 cycles. The more you pay the greater number of cycles you tend to get.  The deeper you discharge the batteries the more of the cycles you use up. This is why we say only discharge to 50% so you in effect get about double the cycles.  An ill informed livaboard boater can easily ruin their batteries in a very few weeks.

A modern 12V electric compressor fridge will demand about 40 Amp Hours per day, less in winter but potentially more in summer. When new the batteries you are likely to be supplied with will hold about 330 Ah assuming its three domestic batteries and not two domestics and one engine battery. If that is the case the batteries will hold about 220 Ah. I repeat WHEN NEW!!! Using the 50% thing this means you will have 165 Ah or 110 Ah of usable electricity stored. The fridge will take 40Ah leaving 125 or 70Ah for everything else. With fully LED lighting and not much else apart from water pump etc. this is doable but start adding mains equipment via an inverter and things very soon get tight, as they inevitably will do as the batteries age and suffer sulphation.

Storing the required electricity is not the problem as long as you are willing to and can add extra batteries but recharging them really is.

On a brighter note as long as you only use higher powered mains devices when you have the engine running fast enough for the alternator to provide the electricity required it will not be discharging the batteries but it will be reducing their rate of charge.

 

Thanks again this is really helpful and reflects much of what I've been reading. As you say I'm not concerned about storing more batteries my queries today have been regarding the purchase of an inverter and keeping the generator.

In general principal all have agreed to the need for an inverter - my next plan will be to determine on what scale I need one, and it would seem the best option to keep the generator. I have done some rough estimates for power usage and I believe the required charge would be approx. 4 hours. Beyond the LED lighting I don't use a huge amount of electric. I imagine however the rule for not using the engine between 8pm and 8am would also apply to using a generator which then raises a problem of how I would do this during the week without damaging the batteries.

I'm sure solutions exist however as so many people do live on the water ways. I will continue my research and thanks so much for the in-depth assistance (and pointers re PSW, MSW)

16 minutes ago, OldGoat said:

Revisiting the thread starter, I notice you said that the engine had an alternator. It is usual for boats (nay, essential for any real use of electricity) to have at least two. One (small) to charge the starter battery and a second much larger one to charge the batteries. Your boat has a diesel generator and I'm wondering whether it was because it was impractical / expensive to fit a second alternator.

You 'need' at least an 100 amp alternator - preferably more - to charge a reasonable battery bank.

So could you clarify what the engine is (make and model), how many alternators there are and what make / model they are.

Therein will lie the reason for the diesel genny.

while being a Misery, please don't treat the general water heating as an afterthought. Putting a stove in could require quite a lot of modification to the hull for a chimney and some convolutions in pipework if it's going  to heat your domestic hot water as well.

Sorry!

 

  

No need for sorry's, the more information the better. I don't plan on doing this half heartedly so your advice is greatly appreciated. I am and will be putting great thought and research into everything including the water heating system, there will be no afterthoughts.

Regarding the alternator - thank you for the advice I am still waiting on the specs for the engine and alternator(s) from the seller, but as soon as I have them I will update the thread.

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1 minute ago, Alethea Price said:

I believe the required charge would be approx. 4 hours.

It would be a VERY shallow discharge that could be recharged in as little as 4 hours. Perhaps your usage would be that light but not if you're powering mains stuff from an inverter.

3 minutes ago, Alethea Price said:

I imagine however the rule for not using the engine between 8pm and 8am would also apply to using a generator which then raises a problem of how I would do this during the week without damaging the batteries.

Yes, it is a problem for all off-gridders who are away from the boat during the day. @Mike the Boilerman can tell you all about it. 

5 minutes ago, Alethea Price said:

so many people do live on the water ways.

If they're off grid and away from the boat during the day they struggle to keep their batteries charged and probably replace them yearly. 

6 minutes ago, Alethea Price said:

it would seem the best option to keep the generator.

Don't forget that you'll also need a decent mains charger to go with it. 

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If charging time is an intractable problem, it might be worth considering going to 24V -

  • double up the batteries
  • 24v inverters can be more reliable and cheaper watt for watt - sometime available at very attractive prices (Sterling has an eBay site and 24v stuff goes for peanuts)
  • 24v alternators are more often designed for continuous use (not so relevant here)

May be a step too far perhaps...

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32 minutes ago, WotEver said:

It would be a VERY shallow discharge that could be recharged in as little as 4 hours. Perhaps your usage would be that light but not if you're powering mains stuff from an inverter.

Yes, it is a problem for all off-gridders who are away from the boat during the day. @Mike the Boilerman can tell you all about it. 

If they're off grid and away from the boat during the day they struggle to keep their batteries charged and probably replace them yearly. 

Don't forget that you'll also need a decent mains charger to go with it. 

Hi thanks for the comments yes the 4 hours does not yet calculate for an inverter as I have yet to have chosen the best one for my means in order to calculate in. The 4 hours was an approx prior to inverter. Have also requested details from the seller regarding mains charger already. Many thanks.

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9 minutes ago, OldGoat said:

If charging time is an intractable problem, it might be worth considering going to 24V -

It ain't going to shorten the charging time though. The same amount of energy has to be replaced. 

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10 minutes ago, OldGoat said:

If charging time is an intractable problem, it might be worth considering going to 24V -

  • double up the batteries
  • 24v inverters can be more reliable and cheaper watt for watt - sometime available at very attractive prices (Sterling has an eBay site and 24v stuff goes for peanuts)
  • 24v alternators are more often designed for continuous use (not so relevant here)

May be a step too far perhaps...

I haven't explored that avenue yet so I will certainly consider the option thank you.

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Hi Alethea.

Great to see you asking the right questions and listening to the answers! Lots of newcomers on here do neither!

i would suggest a "back to first principles" approach. By which I mean that whatever electrical energy you want to consume, has to be created in the first place. That is the difficult bit. Whether you consume that energy at 12v DC or 230v AC (or both) is a less important issue.

I think we are struggling in the dark until we know the engine type and alternator type / output, the generator type/ output too. That realistically determines whether it is worth having an inverter and being able to use appliances that take a lot of power.

Once you have created the energy you probably want to store it - in batteries obviously - and you want to have sufficient capacity that you can go for a day or preferably two, without having to charge the batteries.

But batteries are not a terribly easy way to store energy ( nothing is!) and so for any high power appliances it is generally considered best to generate the power at the time it is being used - ie run the engine or generator whilst you are using a high power appliance, presuming that said alternator or generator can produce sufficient power.

It sounds like the boat has mains wiring for shore power so it shouldn't be too hard to add an inverter - just remember that inverters are typically capable of proving a lot of power, and that is a lot of current at 12v.

Just on your environmental point, although running the boat's engine is easiest, typically you will have a large engine designed to propel the boat, and the load presented by the alternator is very small compared to that required to propel the boat. So if you run the engine whilst tied up just to charge the batteries, it is fairly inefficient because quite a bit of fuel is used to just keep the big engine spinning. A smaller generator, working harder, is more efficient but of course less convenient. Frame generators are cheapest but tend to be the noisiest and IMO are pretty antisocial as a result. There is no easy answer!

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I want to emphases Wotever's post about charging taking longer that four hours. taking a "typical" boat 2 to 4 hours may get you to 80% fully charged but the other 20% takes an extraordinarily long time.  If you do not fully recharge you will sooner or latter destroy your battery.

Now a word about charging. The mistake most newcomers make is to assume the rated output of a battery charger or alternator will be supplied all the time it is running. Nothing could be further from the truth. You will get the rated output for a comparatively short time, probably less than an hour) while the batteries demand more electricity than the alternator/charger can supply but very soon that alters.

As the batteries charge up they demand less current so the alternator produces less. Apart from that first short period its the batteries that control the charge NOT the alternator or charger.  The amount they take gradually reduces over the next hours until the charging current reduces until it reaches 3 to 6 amps for the 330 Ah battery set or 2 to 4 amps for the 220 Ah battery set. The last few hours will be at a very low charging currant (amps).

Taking a typical system (if there is such a thing) you can probably assume that a charger or alternator will produce an average charge of about half its rated output over 2 to four hours. From then on the average will get lower and lower. This is why it takes so long to fully charge batteries.

The alternator on a single alternator engine is likely to have a maximum output of 70 amps but 40 to 50 are probably just as common. I can get away with a single 70 amp alternator on a all but totally 12V holiday boat. I would not like to try it as a livaboard unless I was cruising for at least six hours a day.

 

Now about running the generator. Yes the 8 till 8 rule applies but a proper cocooned generator will be in a sound proofed box so anyone close by will not know its running. You can also get away with running engines and generators when mooring way out in the sticks with no boats or houses anywhere close but remember sound travels a long way over water at night.

 

PS - if you do not want to buy new batteries every few months some form of battery monitoring will be required so you do not over discharge them and also avoid wasting fuel by running the alternator/generator for longer than needed. We can advise but there are entrenched views on here. The simplest is an ammeter and voltmeter but that requires some diligent study and experience from you.

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