Electrical Power Basics

[Joshua]

I am a prospective first time NB purchaser looking for a boat to CC.

 

I am looking for a clear, simple explanation of a typical electrical power system on a NB to give me some idea of what to look for and what I am looking at, when I view boats for sale.

 

Can anyone recomend an earlier thread on this forum that covers this or another web site or good book?

 

And;

Has there been any significant development (say in the last 10 year) to that electrical technology as applied to boats?

I ask the latter to give me some idea of when an unmodified boat may be considered ‘out of date’ as far as electrical systems are concerned.

 

Joshua

[Robin2]

I have a book called "The Canal Boat Manual" which was published by Canal Boat magazine. It seems to be available on Amazon and probably in chandlers. Its chapter on electrics covers the field fairly well, if briefly.

 

Basically a narrowboat should have separate starter and domestic batteries (so that the domestic use can't discharge the starter battery and leave you unable to recharge); the means to charge the batteries - many boats have two alternators with one exclusively for the starter battery. A 3-stage alternator controller is also a good idea as it enables the batteries to be charged more quickly. If you intend to have 240v appliances you will need an inverter to convert the 12v battery power to 240v. And even if you have a very large battery bank it is unlikely to have enough energy to run a washing machine without the engine.

 

The size of batteries that you need will depend on how much electricity you use and how long you are prepared to run your engine to charge the batteries. Electricity generated on a narrowboat will be expensive - perhaps £2.00 per kWh.

 

Some boats have separate petrol or diesel generators and or solar panels. Whether to invest in these is an economic question to be decided after you have a good idea how much it would cost to generate power without them.

 

Batteries themselves can be a considerable expense. Some seem to last much longer than others for no obvious reason. If you don't charge them fully at appropriate intervals or if you over-discharge them they will not last, no matter how much you pay for them. Reckon on replacing them every 2 years until you prove to yourself that they last longer. I would not attach much value to batteries on a second-hand boat unless you were sure they were only a few weeks old as you have no way to know if they were neglected.

[Gibbo]

http://www.smartgauge.co.uk/nb_ac_sys.html

 

http://www.smartgauge.co.uk/evolve.html

[Joshua]

http://www.smartgauge.co.uk/nb_ac_sys.html

 

http://www.smartgauge.co.uk/evolve.html

 

Many thanks for these links.

Does the 2008 conclusion (At the time of writing this split charge system simply cannot be improved upon.) still hold good?

 

As a boy, I practically lived in my fathers garage helping him with his hobby restoring classic cars and bikes but despite this and the fact that my father was a professional mechanical engineer responsible for overseeing the build of the Uk’s first nuclear power stations, I never could grasp electrics ! I’m great with spanners and oily hands but nervous with wire cutters and electrical screw driver.

 

With the help of the almighty ( Wikipedia ) I understand the articles and the simple systems they describe.

 

But what about generators?

How do they dove tail with the boats systems and what are their pros and cons?

 

Also, how do I calculate my likely power demand and then work out what I need to satisfy it?

 

What are the limits, pros and cons of simply adding more and more batteries to the domestic bank?

 

I will be Ccing and hope to expand on a passion for film making.

I don’t think my cameras will be a particular problem (they all use relatively small long life 12v batteries) but my Mac Pro tower computer and wide screen monitor, used for video editing and graphics, I’m guessing will be?

Unless marinas provide a mains power service, on a day to day basis, to passing boats and film makers, I am going to have to generate all my own power.

 

Joshua

 

I have a book called "The Canal Boat Manual" which was published by Canal Boat magazine. It seems.................................

 

Many thanks for this advice, I will look up your book.

 

Joshua

[Heffalump]

I can't help at all with this topic, but I just wanted to say I'm impressed and you seem to be taking this entirely the correct way and asking the right questions.

[blodger]

What are the limits, pros and cons of simply adding more and more batteries to the domestic bank?

 

One problem is finding adequate space to keep adding more & more batts. Your boat will have designed in a battery tray which usually accommodates three 110 ah batts and somewhere else will be the starter battery. Many older boats used to survive on a single domestic with a separate starter battery. It sounds as though you need in looking for a boat to be sure that it can carry a fair few batteries with an alternator/equipment that can maintain them.

 

Batteries are not good at outliving their warranties and are a consumer item with quite an expense. Their capacity starts diminishing from the time they are manufactured. A benefit of having lots of batteries is that you still have a fair bit of amphours even when they have got to half their original capacity.

 

The bottom line is that you have to keep putting back what you take out plus half as much again due to their inefficiency.

 

Adding batts does not work if you do not have a matching ability to keep them charged up.

 

On a positive note,

 

My boat 9 years ago came with 3D & 1S, I replaced the three with four, found that by cutting a hatch in the Engine Room floor I could add a second bank of three. These batts are now 9 & 8 years old respectively and I am in the process of replacing a bank.

 

In the interim, I found I could get three batts on the otherside swim but it involves a bit of moving stuff about, dissembling and, lifting past the calorifier, etc. The batts I have hitherto used there are ones discarded by others that I have 'recovered'.

 

I replaced the 50/55 amp alternator with a 70 and added a second when I installed a washing machine.

 

So anything is possibe.

[Joshua]

What are the limits, pros and cons of simply adding more and more batteries to the domestic bank?

 

One problem is finding adequate space to keep adding more & more batts. Your boat will have designed in a battery tray which usually accommodates three 110 ah batts and somewhere else will be the starter battery. Many older boats used to survive on a single domestic with a separate starter battery. It sounds as though you need in looking for a boat to be sure that it can carry a fair few batteries with an alternator/equipment that can maintain them.

 

Batteries are not good at outliving their warranties and are a consumer item with quite an expense. Their capacity starts diminishing from the time they are manufactured. A benefit of having lots of batteries is that you still have a fair bit of amphours even when they have got to half their original capacity.

 

The bottom line is that you have to keep putting back what you take out plus half as much again due to their inefficiency.

 

Adding batts does not work if you do not have a matching ability to keep them charged up.

 

On a positive note,

 

My boat 9 years ago came with 3D & 1S, I replaced the three with four, found that by cutting a hatch in the Engine Room floor I could add a second bank of three. These batts are now 9 & 8 years old respectively and I am in the process of replacing a bank.

 

In the interim, I found I could get three batts on the otherside swim but it involves a bit of moving stuff about, dissembling and, lifting past the calorifier, etc. The batts I have hitherto used there are ones discarded by others that I have 'recovered'.

 

I replaced the 50/55 amp alternator with a 70 and added a second when I installed a washing machine.

 

So anything is possibe.

 

 

Very helpful, thank you.

 

As far as the number of batteries are concerned and the ability to recharge them, assuming one can find room for them and given that the engine can only run sensibly for so many hours a day, how many batteries can one realistically keep charged if in full time use, day in day out?

I appreciate it will depend on how heavily one draws on them but could you give a ‘more or less’ estimate?

 

As far as adding alternators are concerned, presumably this means the boat engine has to work a bit harder so having a bit more horse power than normal wouldn’t be a bad idea ?

 

And what is the gain of extra alternators, do two charge twice as fast as one ?

 

As to the alternators amp rating what is the normal high end limit and are there any disadvantages other than the initial cost of the unit?

 

I am trying not to carpet bomb you with questions but am struggling to restrain a head full of them!

 

Joshua

[Robin2]

Very helpful, thank you.

 

As far as the number of batteries are concerned and the ability to recharge them, assuming one can find room for them and given that the engine can only run sensibly for so many hours a day, how many batteries can one realistically keep charged if in full time use, day in day out?

I appreciate it will depend on how heavily one draws on them but could you give a ‘more or less’ estimate?

 

Leave the number of batteries to one side until you know your power demand and charging ability. Because they are expensive and unreliable, use as few batteries as possible. If you can find space for them "indoors" where you can easily inspect them, so much the batter.

As far as adding alternators are concerned, presumably this means the boat engine has to work a bit harder so having a bit more horse power than normal wouldn’t be a bad idea ?

 

The alternators only take a trivial amount of power compared to the engine output. 70amps at 12volts = 840watts. 746watts = 1 horse power.

And what is the gain of extra alternators, do two charge twice as fast as one ?

 

Two produce twice as much power as one. Most of the time you will want your engine to run at idle speed to minimize diesel usage. At low speed the alternator will only produce fraction of its rated output. i have two 70amp alternators and between them they produce about 60amps at idle. If I use my washing machine I increase the engine speed to produce more amps so there is no drain on the batteries. One alternator would not be enough for that load.

 

How fast the batteries charge is slightly separate. If you have a 100amp-hour battery discharged to 50% it will take about 50amps (i.e the same amps as the "missing" amp hours). However when it has replaced 5 amp hours (about 6 minutes) it will only take 45 amps etc. Multiply these numbers by 3 for a 300Ah battery etc. In other words with a big battery two alternators are likely to be faster at replacing the first part of the charge, but when the battery gets to be 80% or 90% charged there will be no advantage. I would not buy bigger batteries just to "use up" two alternators.

As to the alternators amp rating what is the normal high end limit and are there any disadvantages other than the initial cost of the unit?

 

Depends on your power needs. I think if you go over 70amps you will need better quality drive belts and pulleys. It is possible to buy special alternators that produce more power at lower engine speed, but they are expensive.

 

I am trying not to carpet bomb you with questions but am struggling to restrain a head full of them!

 

Joshua

[Heffalump]

In a similar vein, what's to stop you putting a smaller pulley on the alternator to increase the drive ratio?

[Robin2]

In a similar vein, what's to stop you putting a smaller pulley on the alternator to increase the drive ratio?

 

The cost. I enquired some months ago.

[Joshua]

....Lots of information.....

 

 

 

Thank you very much Robin2

 

That’s very clear and I have just read the first pinned thread above about paralleling alternators, also read Gibbo’s web site ‘Smart Gauge’, which has answered many questions about the type of equipment needed to keep it all running smoothly (what’s good enough for the MOD is good enough for me).

 

I would still like some guidance on the question of what is a realistic limit to the number of batteries it is practical to work with on a NB.

 

I mean, is it better to reduce the SoC (I’m just showing off my wikipediaknowledge now) on a bank of 8 batteries to 75% than 4 batteries to 50% ?

From what you say, there is a vague idea swimming around in my mind along the lines – more batteries = less discharge = less need for alternator work = less engine work = Quicker recharge = lower running costs

and alternatively – less batteries = greater discharge = greater alternator need = longer recharge = greater running costs ?

 

Also would appreciate some idea how to quantify my needs or at least the right key words to throw at Wikipedia ! ?

 

Joshua

[sociable_hermit]

Don't underestimate the weight of batteries. Adding a new bank could seriously affect the trim of your boat.

[Robin2]

Thank you very much Robin2

 

That’s very clear and I have just read the first pinned thread above about paralleling alternators, also read Gibbo’s web site ‘Smart Gauge’, which has answered many questions about the type of equipment needed to keep it all running smoothly (what’s good enough for the MOD is good enough for me).

 

I would still like some guidance on the question of what is a realistic limit to the number of batteries it is practical to work with on a NB.

 

I mean, is it better to reduce the SoC (I’m just showing off my wikipediaknowledge now) on a bank of 8 batteries to 75% than 4 batteries to 50% ?

From what you say, there is a vague idea swimming around in my mind along the lines – more batteries = less discharge = less need for alternator work = less engine work = Quicker recharge = lower running costs

and alternatively – less batteries = greater discharge = greater alternator need = longer recharge = greater running costs ?

 

Charge times are a complex subject. However much you take out of a battery (no matter what size of battery) you need to put back 20% or 30% extra to make up for battery efficiency.

 

If you can do spreadsheets create one where a 100ah battery starts at (say) 50Ah discharged and then calculate the charge in 6 minute steps. First period current is 50amps for 1/10 hour = 5 amp hours, waste 20% so battery is now discharged by 50 - 4 = 46 ah. For next 6 minutes assume current is 46amps etc. A 200Ah battery discharged to 50% would be discharged by 100Ah and could take 100amps in the first period, etc.

 

Also would appreciate some idea how to quantify my needs or at least the right key words to throw at Wikipedia ! ?

 

If a bulb or appliance uses 100watts it will use 8.33amps at 12 volts (watts = volts * amps). If it is used for 2 hours it will use 16.66 amp hours. This is true whether the watts are for a 230v appliance or a 12 volt one.

 

So for everything you have on board write down its Watts rating, estimate how many hours a day you will use it and work out the amp-hours. Add them all together. Remember that lights are used much more in winter.

 

Fridges are probably the only tricky things because they operate intermittently. It is hard to guess how many hours a day they actually operate. The brochure for the one I have claims that it uses 220 kWh per year. That is an average of 25 watts for the 8760 hour in a year or about 2 amps or 48 amp-hours per day. The real usage is probably higher - guess 55 amp-hours.

 

Don't include appliances like a washing machine if you will only use them when the engine is running.

 

Add a margin of error.

Edited January 17, 2011 by Robin2

[sociable_hermit]

Hear the man! Good advice there.

[blodger]

If you read all of SG site you will be initiated into the Peukert phenomenem and the benefits of operating batts together and how bigger banks are more efficient in the discharge/charge cycle.

 

If I were you I would not decide what to have as an imperative but make sure the flexibility is there to augment from experience should that be the outcome.

 

Charging batts back up to 100% takes a lot of time, as has been posted the short bit at the start might be hastened by a big or two alts but the imprtant tapering off bit is not much affected thereby.

 

It is important to try to use equipment that has low power needs to try to avoid forever running engines or gennies. There is a crossover point where a good genny is more economical than running the boat engine covered by a recent thread.

 

Using solar panels can greatly help in diminishing power consumption/charging batts mainly in the summer.

 

Most of what you are asking has been well covered in the past so some will hold back posting not wanting to repeat themselves.

 

Given what you have said so far I think a minimum would be 4 110ah open lead acid batts and a 70/80 amp alternator and a genny with charger as back up, etc. If you find that's not enough supplement in accord with your experience; that's what we have all done

[blodger]

As far as the number of batteries are concerned and the ability to recharge them, assuming one can find room for them and given that the engine can only run sensibly for so many hours a day, how many batteries can one realistically keep charged if in full time use, day in day out?

I appreciate it will depend on how heavily one draws on them but could you give a ‘more or less’ estimate?

 

As far as adding alternators are concerned, presumably this means the boat engine has to work a bit harder so having a bit more horse power than normal wouldn’t be a bad idea ?

 

And what is the gain of extra alternators, do two charge twice as fast as one ?

 

As to the alternators amp rating what is the normal high end limit and are there any disadvantages other than the initial cost of the unit?

 

I think Robin2 has responded to most of the above.

 

Figures get quoted regarding how much alternator capacity as a ratio to battery capacity. It is more important not to have excessive charging ability than not enough since a small alt will eventually do the job but take a long time.

 

IIRC both the SG site referred to and Tony Banks' excellent site will give the guide ratio.

Of the top of my head, no better not, I'll get shot down in flames

[Joshua]

Lots of stuff

 

Excellent, thank you.

 

Joshua

[Gibbo]

If you can do spreadsheets create one where a 100ah battery starts at (say) 50Ah discharged and then calculate the charge in 6 minute steps. First period current is 50amps for 1/10 hour = 5 amp hours, waste 20% so battery is now discharged by 50 - 4 = 46 ah. For next 6 minutes assume current is 46amps etc. A 200Ah battery discharged to 50% would be discharged by 100Ah and could take 100amps in the first period, etc.

 

Robin that's where you went wrong in your Ruby program

[Joshua]

..........................

 

Most of what you are asking has been well covered in the past so some will hold back posting not wanting to repeat themselves.

 

 

Thank you Blodger, I do appreciate this and do feel guilty trying to take a short cut, but whilst the first pinned thread above with only 4 posts was simple and easy to read, the second with a mighty 638 posts left me gasping for air!

 

I will however try digging into the archives again.

Advice so far very much appreciated and taken on board.

 

As to the Peukert phenomenem I wont be able to sleep now until Ive got to the bottom of it!

 

Joshua

[Joshua]

Peukert phenomenem, good explanation here:

 

http://www.amplepower.com/pwrnews/beer/

 

I was delighted to see that it involves drinking beer, a language even I can understand.

 

Joshua

[Keeping Up]

Again, Joshua, the answer to one of your questions (how much battery capacity should you have) is given on Gibbo's website. He makes the point that if you have too many batteries they will last longer (in years) before they wear out but the initial outlay for all those batteries will not be justified; if you have too few batteries they will cost less initially but they will wear out so quickly that it will cost you more in the long run to keep replacing them. The balance between these two is best achieved by having just enough batteries that your normal discharge pattern will take about 50% of their capacity each time before you recharge them (if I've mis-quoted him I'm sure he'll be along shortly to clarify).

 

So the starting point has to be an estimate of how much power you will be taking.

[Robin2]

Robin that's where you went wrong in your Ruby program

 

As far as I know the spreadsheet method is how you told me batteries work. If not, I am still waiting for you to explain why its wrong, or to tell me what answer my model should give so that I can modify it to make it better.

Peukert phenomenem, good explanation here:

 

http://www.amplepower.com/pwrnews/beer/

 

I was delighted to see that it involves drinking beer, a language even I can understand.

 

Joshua

 

The Peukert effect is a red herring. Its not wrong. It just does not affect things enough to matter economically unless you discharge batteries at a high rate - which most boat users do not.

Edited January 17, 2011 by Robin2

[Joshua]

.........................

 

So the starting point has to be an estimate of how much power you will be taking.

Yes I see that and now feel equiped to begin that process, I never read them but am very organised about keeping equipment technical manuals, just have to retrieve them from one of the packing cases I tossed them into recently!

 

Joshua

 

As far as I know the spreadsheet method is how you told me batteries work. If not, I am still waiting for you to explain why its wrong, or to tell me what answer my model should give so that I can modify it to make it better.

 

 

The Peukert effect is a red herring. Its not wrong. It just does not affect things enough to matter economically unless you discharge batteries at a high rate - which most boat users do not.

 

When I am video editing the lights in my house dim!

 

Joshua

[Robin2]

 

When I am video editing the lights in my house dim!

 

Joshua

 

I assume that is a joke, but if its true it simplifies matters - only do video editing when the engine is running.

 

Alternatively the wiring in your house needs to checked out

[blodger]

KEEPING UP:-

 

The balance between these two is best achieved by having just enough batteries that your normal discharge pattern will take about 50% of their capacity each time before you recharge them (if I've mis-quoted him I'm sure he'll be along shortly to clarify).

 

Of course, the less you discharge them before re-charging and the sooner you recharge the longer the batts will last.

 

IMO 50% discharges mean you only get your 500 cycles if that is what the spec is and the batts will probably need replacing in advance of any warranty period. It's why having more than the minimum batts helps and has Peukert helping.