the perennial battery charging problem

[wotayottie]

On my mooring I use about 70aH per 24 hours, mainly on the fridge but with some for lighting. I suspect that my figure is reasonably typical for the majority who do not want to do the hair shirt camping on the water bit. Civilised sailing if you like with ice for the G&T.

Problem is how to keep up with it and do away with the hour or more per day of engine running.

According to the PBO test only the biggest of the windmills will generate that sort of output in typical UK breezes, and that ignores the losses in charging ( to get 70 aH in you need to generate more than 70aH) and the issue that we moor or anchor in sheltered spots where the wind is hopefully less than average. And then these windmills are noisy, have 4 foot diameter fans on them and are as ugly as h*ll.

But a 100 watt solar panel can only be expected to deliver 30aH during the 24 hours of a normal UK summer day so that means I would need something like 230 watts of panels to match the windmill which we already know isnt sufficient. At 100watts per square meter ( Solara smk220 type) that is 2.3 square meters of panel at a cost of about £1900. And where do I have that amount of spare space?

So has anyone found a solution to this conundrum other than running the engine or festooning the boat with ugly tube structures on the stern? Honest answers please and I am not interested in reducing consumption and standard of living on board.

 

[cimo]

have you consider reducing your consum.......oh sorry.

have you considered going nuclear?

Honestly though, I think you know the answer already.

Setting a budget and living within it can in fact increase one's standard of living imho.

 

[TopDonkey]

you could keep your solar panel you currently have, and run a genny for an hour a day to top up the batteries, you should be able to get 50ah into your battery bank in an hour if its fairly low

 

[pvb]

So has anyone found a solution to this conundrum other than running the engine or festooning the boat with ugly tube structures on the stern? Honest answers please and I am not interested in reducing consumption and standard of living on board.

It's an interesting problem. My solution was to increase the size of the alternator (to 90A, the biggest I could properly run on a single V-belt), then increase the size of the domestic battery bank to 660Ah (about the most I could easily fit in). The result is fairly good. The big battery bank gives a good reserve of power, say 250Ah. Because it's a big bank, it will accept a big charge current, so when I do run the engine I get a decent charging efficiency. No solar, no wind, no generator. Can't stay out at anchor for ever, but never worry about having to turn lights off, etc.

 

[wotayottie]

You're deceiving yourself about the battery bank size pvb. Sure you will have an initially large safety margin but the rate of charge that a battery can accept is a function of its state of discharge, so 600aH discharged to 500 ( ie batteries at about 12.55v) will accept less charge than 200 discharged to 100 ( ie batteries at about 12.1v) . And in any case you still have to match whats taken out with what goes in.

The size of the alternator isnt as obvious as you might think either. It only affects the rate of charging until the voltage at the batteries gets up to 14.4 or whatever the regulator is set at. Thereafter, charging current is dictated by a variety of factors but mainly by the voltage and not by the alternator size. A digi regulator is more use than a big alternator.

Done quite a bit of investigating on this and was surprised by how fast the charging current fell away and how little of the alternators maximum capability was supplied as a result. Within an hour, with a 200aH domestic bank, the charging current was down to 10A !

But thats all about engine charging efficiency and I'm looking for a way not to use the engine at all.

 

[pvb]

You're deceiving yourself about the battery bank size pvb. Sure you will have an initially large safety margin but the rate of charge that a battery can accept is a function of its state of discharge, so 600aH discharged to 500 ( ie batteries at about 12.55v) will accept less charge than 200 discharged to 100 ( ie batteries at about 12.1v) . And in any case you still have to match whats taken out with what goes in.

The size of the alternator isnt as obvious as you might think either. It only affects the rate of charging until the voltage at the batteries gets up to 14.4 or whatever the regulator is set at. Thereafter, charging current is dictated by a variety of factors but mainly by the voltage and not by the alternator size. A digi regulator is more use than a big alternator.

Done quite a bit of investigating on this and was surprised by how fast the charging current fell away and how little of the alternators maximum capability was supplied as a result. Within an hour, with a 200aH domestic bank, the charging current was down to 10A !

But thats all about engine charging efficiency and I'm looking for a way not to use the engine at all.

Not deceiving myself at all. I should have said that the alternator also has an Adverc booster, so charging is generally at 14.4-14.8v. A big bank, even when only partly discharged, will accept a bigger charge current. So, in terms of actual Ah replaced (and ultimately that's all we're interested in), it's more efficient. Smaller banks don't work as efficiently - as you said yourself "Within an hour, with a 200aH domestic bank, the charging current was down to 10A!"

 

[photodog]

http://www.fuelcellsystems.co.uk/shop/SFC-EFOY-Comfort-80-Fuel-Cell.html


At £2300 it's twice the price of a air ex... But add in solar some solar panels to the equation and it starts to make sense.... The 80 will give you loads more power than you need, you will get 5.5kw worth of methanol for about 60 quid...

Sorry that methanol price is way out.... You can get 25l for 35 quid... So that's circa 35kw .... So about 40p per day to get your power needs unless someone is better at the Maths..





Quiet, unobtrusive...

The way to go.

 

[Rigger Mortice]

Improve the insulation round the fridge.
Improve the efficiency of the fridge by improving airflow or give thought to water cooling instead.

 

[wotayottie]

now that really does look interesting photodog. if they get the price down as most new tech eventually does, I will have one of those. Beats the normal diesel genny doesnt it.

 

[noelex]

70 Ahrs is not a big demand but it requires:

200w of solar in UK summer, or 800w in winter, or
1.5-3 good wind generators and a very large battery bank to cover the days with no wind, or
1.5 -2 hours engine run time and a largish battery bank, or
1-1.5 hours of generator run time with a large battery charger and largish battery bank.

Or a combination/mix of the above options.

You need to decide the best option, for your situation, to replace the power, but it has to be one of the above, or a mix of the above, giving equivalent power, if you want to live without a shore connection.

A suitable solution might be 200w solar plus a wind generator, with a medium sized battery bank. The shortfall would be made up with engine running, which on many days would be zero. In the worst conditions less than 1hr engine run time Per day would be needed.

 

[photodog]

now that really does look interesting photodog. if they get the price down as most new tech eventually does, I will have one of those. Beats the normal diesel genny doesnt it.

I think with that sort of pricing it's got potential... But of course with that unit you don't get 240volt, and if you want more than 90amps or so you are going to have to spend more...

If the price was circa 1500 It would be a no brainer.... With normal leisure yacht use the methanol price will not be a issue... But for a liveabord having to keep a second fuel type might be a problem..

 

[pvb]

now that really does look interesting photodog. if they get the price down as most new tech eventually does, I will have one of those. Beats the normal diesel genny doesnt it.

Does it? 80Ah a day, but that's if it's on for 24 hours a day. Now I'm sure they're better than they used to be, but the stack life in fuel cells used to be about 1500 hours. So, after only 2 months of your 80Ah a day use, you'd need to buy a new fuel stack, costing what? £1000? £1500? Who knows? They look good on paper, but you need to dig deeper.

 

[Blueboatman]

Rigger Mortise+1
Spend the money on reducing the fridge consumption ( or insulate and buy block ice or £1 supermarket bags of ice every couple of days)
Handful of LED reading lights and a candle and or oil lamp for ambience, sorted, surely?

70a/h per 24h in British summer light/temp just sounds plain excessive ( IME)

Three real examples. (not nec hairshirt)

Boat one, 18w solar panel, one x 75a/h battery, 4amp outboard, useless wee wind charger-shan't embarass the manuf. Lived on board for years but happy without fridge. Usual a/p, nav lights, radios etc

Boat two, same 18w panel, two x 75a/h batteries, 8amp outboard, Aerogen wind, no fridge, massively insulated ice box, lots of electrics and stuff. Lived on board etc

Boat 3, same 18w panel ( now lives in a cupboard as back up, one (shade tolerant) 75w solar panel, two x 110a/h batteries, smart alternator, Rutland 913 wind, a 12v WATER COOLED fridge, lots of lights NOT LED, Led nav lights,anchor, lots of usual elec and electronic, big a/p....You know what Im going to write next don't you?....It is a balanced system. Live aboard a lot of the year, never engine charge deliberately at anchor nor regularly, no complaints from nice happy visitors, comfortable as an 'ouse

Its the fridge and you know it, er, probably..sorry that sounds rude but is not meant as such..

 

[Chalker]

You can buy 3 80W solar solid, aluminium framed panels on EBay for £300 plus a regulator. Other sizes available. I used these for 18 months whilst living aboard, no problems and no sign of poor construction or lifetime.
Compared to the Solara price you can replace them a few times and till save money.
The Solaras MAY be a little more efficient, but nowhere near that ratio.

 

[CAPTAIN FANTASTIC]

I have 5 x 110 amp batteries charged by a Rutland 913, never short of power; the good thing about the wind genies is that they will charge non stop day and night. If necessary, any top up comes from either engine run or petrol geny.

 

[photodog]

The efoy cells are dmfc ... Lifespan for pem types in fixed installations can be in excess of 20,000 hours... Iirc in experimental dmfc cells they were getting circa 3000 hours from the stack... I would think that will have improved a bit so I don't think 4000 hours in a portable device would be unreasonable...

We use 40 amps per day and would expect to motor for an hour a day on a average cruise just mooring etc... Never mind the every fourth day in the marina overnight... So we would need maybe 180 amps a week x 4 weeks a year so be generous and say 800 amps or 240 hours of run time.. So a stack could last 10-15 years....

Still needs to be a a bit cheaper I think.... But for our sort of use it looks not far off.. Though it gives off co2 so needs to be properly vented..

 

[Mistroma]

I did think about an EFOY unit but decided against it because:

1) Amount of methanol for 6 months cruise was quite large (& expensive if using supply ex. mfrs.)
2) Difficulty in getting methanol when needed
3) Price of fuel cell
4) Worries about longevity

Max. output falls with time but data not available from mfrs. I think I found some literature that indicated 80% of initial output after 18 months was a reasonable expectation. Can't find it just now.

I finally went with:
1) Reduce usage a bit (LEDs & move to sl. warmer climate so no heating needed)
2) Fit some solar (65W)
3) Fit Wind gen (Rutlan 913)
4) Better batteries (golf cart type) well better than original leisure ones
5) Backup Honda petrol gen. (Hardly ever used now)

I have a larger alternator but bought it as a spare. Previous posts have mentioned that a big alternator doesn't solve all problems.

Having thought about it, EFOY would work as replacement for Honda gen. as other steps taken mean it isn't used often. So it would work in that role instead of as a main power source. However, fuel availability still puts me off that idea.

 

[Richard10002]

I use about 70Ah per day on board. I have a Honda Eu20i and a sterling inverter/ charger which charges at a max of 70A. My battery bank is 330Ah.

If I let my batteries fall to about 50% SoC, I find that in the first hour of running the genny, I get almost a full 70Ah at bulk charging. Then, as the voltage reaches the limit, (I use 15.1V), the Amps fall over time, and I generally get about 40Ah in the second hour. Which probably replaces my daily usage, perhaps plus a bit.

I also have a 100W solar panel, but this provides between 0A and 3A, and the idea behind this is that it should top up the batteries if I spend 3 or 4 days away from the boat.

I am therefore resigned to running my genny for an hour or two a day, and accept that my batteries will generally be between 50% and 75% SoC, which may mean they don't last as long as if I kept them between 80% and 100% SoC, but I save money on petrol by using the genny and charger fairly efficiently.

I guess if I ran the batteries between say, 40% and 60% SoC, I might get 70A for 90 minutes, to 2 hours, thus getting my fill sooner - but at the expense of battery life.

As stated above, you need a fairly big solar capacity, and/or wind, to be self sufficient in energy on a boat.

 

[Blueboatman]

Whilst fuelcell technology is coming along nicely, I will be delighted to be buying affordable-safe- smart battery technology in the future that lets anyone use the 'other' 80% charge in there.

The typical one or two hours of engine running can then really be put to use but far less frequently -or people will go a whole 2-and-a-bit-days weekend before returning to shorepower

 

[James_Calvert]

Is KISS still best?

When we bought our Sadler 32, we queried why the specification no longer included a refrigerated icebox. IIRC, Martin Sadler explained they'd been dropped from the options because they were nothing but trouble.

So we took delivery without one.

It almost seems that not much has changed in the new millenium...

And you can still buy a lot of ice for the cost of a marine refrigerator, large battery bank,wind generator, smart charger, generator set, shore power set up etc.

You can even earmark some cubes for your g and t if you really have to.

But, to be fair, I guess that I'm probably nearly as obsessive about securing new ice supplies wherever we go as others are about recharging their amp hours.

But the penalties of failure for me are no more than soft butter, not so cool beer, and Fray Bentos.

Happy to be persuaded otherwise, but for us, the ice hunt still seems a lot less hassle.