Advice requested on Battery Bank size & charging for our new boat.

Re: Advice requested on Battery Bank size & charging for our new boat.

Agree with all that, we have no solar, no wind genny, 2hrs a day keeps the fridge cool + hot water and the other electrics going at anchor. 300ah batteries.
 
Thats right, but most people fit the ams to get the domestic batteries up to a fully charged state as normally they never actually reach this state. The Engine start batteries do get fully charged as they are connected directly to the Alternator. The domestic batteries were fed via a diode which produced a voltage drop of around 1 volt. Fitting a voltage sensing relay which only closes when the Engine start battery is around full charge avoids the need for diodes etc and therefore the domestic battery reaches a fully charged state.
 
Re: Advice requested on Battery Bank size & charging for our new b

" horrible noisy Aerogen"

I think you will find its an ampair you are talking about all the aerogens are quite unless a bearing is going, and I have only come across 1 amoung hundreds
 
OP plans to fit a multistage charger. This would sense domestic voltage direct, so bypasses problems of voltage drop through diodes. However, this does introduce the possibility of overcharging the starter battery.

Voltage sensing solenoids in conjunction with multivoltage regulators requires careful thought and design if you want to avoid interaction between the two - setting off a buzzzzzz as they each switch each the other in and out.

An earlier point on 100a alternators; the battery bank will only accept a charge rate (amps) related to 1. It's state of charge and 2. The bank capacity.

A small bank (don't know how small) will be incapable of using the output from 100a alternator, even when 50% discharged.

I'm sure someone will pop up here and give us a suggested relationship between bank size and alterntor capacity!
 
There are quite a lot of variables involved in this one, but assuming you do not allow your batteries to drop below 50% charged, the actual alternator output ideal for lead acid batteries would be 25% of the total capacity of the domestic batteries. Any more than this would be pointless and a waste of money. A smaller alternator would simply take longer to recharge.

This would be the output produced at normal engine speed and will vary depending on the pulley ratio.

The engine battery does not come into this calculation as it shouldn't take more than a few minutes to charge it fully.
 
If you CAN fit a big alternator, even better, and yes 25% is the norm in relation to max efficiency of charging (Engine run time).. the normal guide is that on a single v belt 130A is about the limit. the Balmar alts for example, can chuck out there full hot rating at low comparative revs to an automotive type.
The bigger alt maximises the efficiency of the engine run time (if needed at all)

Based on a 130, the bank could be up to 520 ah and still get the best bang for yer buck, having a smaller bank wont be an issue as the alt will adjust, larger bank (800+ in my case) means more charging time.. at least fitting the big alt, space, money, engine size considered) is a great starting point for building up bank capacity later.
on a 130 alt, a good all round compromise is 4 trojan t105´s giving apx 450ah in a fairly small package size.

The less you have to use the main donkey the better afaiac...
 
[ QUOTE ]
.... the actual alternator output ideal for lead acid batteries would be 25% of the total capacity of the domestic batteries.

[/ QUOTE ]That's a pretty bold statement and doesn't leave a lot of room for different lifestyles. You haven't taken into account the fact that the alternator is powering the load as well as charging the batteries, for a start. While 25% of total domestic capacity might be fine in some cases it most certainly is not even a 'rule of thumb'. It could be way out.

For example, suppose the alternator supplies, say, 60A and the standing load is, say 25A, then the net charge is only 35A. There are other issues but I think that the point is clear? This is not a formula you can use safely and it will become progressively inappropriate as people add more electrical things to their inventories, which we do, every year.
 
Fair point David.. I will slightly rearrange that to read...

"the actual alternator output ideal for lead acid batteries would be 25% of the total capacity of the domestic batteries AND expected load at charging time"

the 25% IS a good general rule based on charge acceptence of LA batteries in general. Yes, it is wise to add in the load if high at the time of charging.

The limiting factor for many is the alternator size on a single pulley, AND the load on the engine if a very small one pot for example. On my OM636 there is caution advised in the service manual re applying too much torque load to the fron pulley of the engine, even with a dual belt or toothed belt I wold not like to add more load onto the crank front than the 130 and the water pumps(s).

Joe
 
[ QUOTE ]
"the actual alternator output ideal for lead acid batteries would be 25% of the total capacity of the domestic batteries AND expected load at charging time"

the 25% IS a good general rule based on charge acceptence of LA batteries in general. Yes, it is wise to add in the load if high at the time of charging.

[/ QUOTE ]Sorry to be absolutely pedantic about this, but you are giving a mathematical expression albeit in words. You meant "25% for the total capacity.... PLUS expected load...." Otherwise this might conceivably be construed as 'either or' because it is too loose. Essential pedantry aside, are we really happy with the proposed 25% rule? Take a domestic bank of 1000 Ah - this would 'need' 250A (plus the load) from the 'rule'. Quite aside from the multiple belt issue, I am not convinced that a yacht auxiliary engine is the best way to generate such power. If you have a 1000 Ah bank then maybe you should have a dedicated generator? Anyway, 250A sounds silly, so I think that the proposed '25% rule' is inappropriate for general use. For many yachts it will be about right but it is not suitable for use as a design aid.
 
re 25%, it is simply the normal "rule" for inputting the max safe input into a given LA bank.
I agree fully that a genny is the way to go for larger demands.
I dont think it is either bold or inaccurate David. ie, thats the normal max safe input in relation to capacity for the "normal LA Battery"
Also, I didnt propose the 25% rule, it is based on Calder et al. Stirling agrees too. So as a norm, I think it is sound.
For a boat with very large (relative) power demands, yes a genny is good. there is also some merit in the deisel powered dc genys as (once) produced by Balmar using Kuboto diesels to a very large alternator. Using the yacht auxilliary engine is definitely NOT my preferred choice of charging under any circumstances, only as a last resort.

Joe.
 
Yes you are certainly right about other loads coming into the equation, which is why I started my post by saying there are a lot of variables which come into play, however unless they are continuous heavy loads, which I would have thought unlikely, they would just make the recharging process take longer.

You could be using a big invertor to power electric cooking for instance, or a washing machine and if you do want to go down that route you would almost certainly have a much more comprehensive electrical setup than a 12V alternator to keep the batteries charged.

Then I guess the only ways to keep up with the load would have to be with a generator, or at the least something like the Electrolux 3.5kva 240v alternator, but with that you would be running the main engine a lot at anchor.
 
Re: Advice requested on Battery Bank size & charging for our new boat.

This thread is terribly interesting.... no, really, it is!
And I'd like to apply it to my own situation. But I haven't a clue what my alternator outputs. If any of you experienced types know, then please do let me know. I've a bog standard Volvo 2030 28hp job with a factory fitted alternator.
Also.... whilst on this subject.
My mains charger is a Dolphin 12v 20a switch mode job. I've a 130ah LA battery on it at the moment but I'd like to add another of the same size. Is this going to be OK? and if so... what's the max amount of amperage (batterywise) that I could load onto it should I want to increase the house bank further at some stage.
Thanks in advance
 
[ QUOTE ]
Yes you are certainly right about other loads coming into the equation, which is why I started my post by saying there are a lot of variables which come into play, however unless they are continuous heavy loads, which I would have thought unlikely, they would just make the recharging process take longer.

[/ QUOTE ]Yes, that's right, but when you say "just....take longer" there could be a huge difference. Obviously I don't know what sort of cruising turns you on but we used to anchor up the Helford or at Fowey from April and up until November so the heating was used quite a bit. Cabin lights, telly, laptop, fridge....can add up to 20A or more. I suggest that you really want an alternator big enough to put a good charge into the battery in the time it takes the engine to heat enough water for the washing up and a shower each. Of course, if you buy a petrol generator big enough to heat the water as well, you are laughing especially if the generator is a nice quiet Honda which you can usually leave running without upsetting too many people (though not always...it would not be welcomed in a quite stretch of water like the Helford).
 
Re: Advice requested on Battery Bank size & charging for our new b

Hi cliffb,

According to the workshop manual which you can download here:
http://www.bluemoment.com/downloads.html
The alternator you have has a maximum output of 60a which sounds a bit small for the extra battery, but probably not worth changing it for that.

Lemain, I think if I was going to spend the winter using all those I would want to be in a marina with shore power. Otherwise you would be running a lot of hours on low load, which would be a bit hard on your engine. Cylinder glazing?

I guess you would really need a decent diesel generator for that.

It is 38 years since we spent a wlole winter on a yacht with no electricity connection in Malta. We did have a small Honda for keeping the batteries up, but I fitted whale footpumps by the basins and our heat and light were both provided by a Tilley lamp.

The best £5 we spent though was on a secondhand Electrolux kerosene fridge which could make ice in the hottest weather. The Maltese countryside was getting electrified and they had a wharehouse full of trade-ins, where you could choose your own.

We had a 70ft narrowboat built to live on with a Lister JP3 Diesel which only ran at about 300 rpm and had twin 70a alternators with a 400 amphr domestic battery setup. That would charge at 100 amps but not for long and soon dropped to about 50. That boat had the TV, electric fridge etc as you describe together with a 1200watt combi unit which charged at 50 amps from the mains.
 
Re: Advice requested on Battery Bank size & charging for our new b

James, interesting post and I agree with all that. Might we have met in San Antonio harbour this summer?

We have much more kit than I was outlining to the OP and we have never done a winter off-grid (nu-speak for having no electricity). I wonder if we would? There would have to be compensations as I rely on PC connection to gain my income and we do like comfort. If the financial markets continue to move in their present direction we'll all be off-grid before long!

I was trying to guess what use the OP might make of his new yacht in northern European waters. I imagined that he might do several nights up to a couple of weeks off-grid and then be looking at a dedicated generator? Those little Honda generators are brilliant and have revolutionised comfort afloat for many. For a whole winter I think you'd want to have an installed diesel generator but even that takes managing.

Some friends of mine who have a very large yacht (a small ship, actually) tend to make their own electricity as the marina's price for such a large vessel is horrendous - they charge here by the size of the yacht, not the amount you use which is actually quite fair value for us but terrible for just a couple living on a ship. They have two generators and an unbelievable battery bank. Even then, they pay for an electric lead for the day, every so often, for washing days, I think!
 
Re: Advice requested on Battery Bank size & charging for our new b

Ibiza? No we haven't been there since the 70s when we based the boat in my avatar in the harbour opposite Ibiza town for two years.

We have a mooring booked at Sant Carles for next year, so hope to get over there again. We have been rather disappointed with cruising in the med recently. The thing we used to like was being on the public quays with a lot of other cruisers coming and going, we got to meet a lot of people doing that, but now we just get put in a marina berth among a lot of empty boats which isn't the same. Most of the boats look like ours too which is rather boring.

So I am not really sure about going back to Espalmador for instance, it is all probably much too crowded.

All the best,
 
Re: Advice requested on Battery Bank size & charging for our new b

Another James. My own Med experience goes back to 1972 so I know what you mean about change. But provided you accept that some things are no more, there is still good in the cruising ground. Folks are just as nice. Marinas are a pain and they have taken over a high proportion of the anchorages but there are always places if you ask the old hands as you move about. The real Med issue - poor wind and sea for sailing - is unchanged and you just learn to live with it or go elsewhere. It suits us and Spain is comparatively cheap without being too third-worldy.
 
Re: Advice requested on Battery Bank size & charging for our new b

[ QUOTE ]
It suits us and Spain is comparatively cheap without being too third-worldy.

[/ QUOTE ] Lemain, just as a matter of interest, have you done Greece recently? If so, does that come into your 'third-worldy' category?

I'm asking to get another perspective . . .
 
You must log in or register to reply here.

Share this page

Top