Uprating 12V service system

[Magic_Sailor]

OK – the Jeannau website is absolutely no use, so here is a question. Posted on SB and PBO – sorry for any inconvenience.

Boat: Jeanneau Fantasia
Engine: Yan 1GM10

I plan to uprate the 12V system by the addition of an extra 75Ah service battery. Currently the system is as follows

Alternator – charge splitter – 1 engine battery (75Ah) – 1 service battery (75Ah).

I do not have a circuit diagram and/or specifications for the alternator or charge splitter. So the question is, am I going to be safe, merely connecting an extra 75Ah battery in parallel with the current service battery? Specific points

1. Can the charge splitter cope.
2. Ought I to lay in extra cable from the charge splitter (companionway) all the way to the service battery (forepeak). Current cable is 4mm squared cross section. I see from the RS catalogue that its rating is 32A, so I suspect its OK.

Thanks in advance

Magic

 

[charles_reed]

I'd suggest a different, less expensive, more efficient and lighter solution.

Fit a smart charger with a 3-way diode.

Make your 2 x 75 ah batteries your domestics, with a 3 position rotary switch connecting them: fit a 30ah cheapy car battery for the engine starting battery.
150ah should be adequate reserve for your boat unless you're running the full panoply of fridge, radar etc.

The 1GM shares its starter with the 2 & 3 GM, it's only 2kW and grossly overspec for that motor, pulling about 1/3 the current of you average car started. In any case adding more ah for your poor little Hitachi 35 amp alternator will just overface it and it'll never be able to charge all your capacity.
The only cable you'll probably need to replace is the one from alternator (B+) to the 3-way diode - I'd put in between 6-8mm2 cable, the problem isn't just the current capacity but the voltage drop. The voltage drop from your diode to service battery will be about 1.2, but the smart charger will just about take care of that.

For prices/advice/supplies phone 01902 380494 and speak to Brian, trevor or John at Adverc.

 

[pvb]

I\'d almost agree, but....

I'd agree with Charles that it makes sense to use your existing 75Ah batteries as domestics and add a smaller starting battery. And a smart regulator will help ensure maximum charging efficiency.

BUT, there's no reason to use a 3-position rotary switch. These things only lead to confusion. The most efficient way to wire the 2 domestic batteries is simply in parallel as 1 bank (with 150Ah capacity). They will last longer and will recharge more easily.

This also means that there's no need to replace your existing 2-way diode splitter (incidentally, diode splitters are sized according to the alternator output; just adding extra batteries doesn't require a beefier splitter).

 

[charles_reed]

Re: I\'d almost agree, but....

I prefer having the 3-way switch purely because I feel a degree of human control always allows for the sheer stupidity of microprocessor programming.
Wouldn't disagree with the point your making - KISS?

 

[pvb]

No microprocessors...

There aren't any microprocessors involved in connecting 2 batteries in parallel! The advantages of having just one large domestic bank of batteries are overwhelming.

The old-fashioned 1-2-Both switch has no place on a boat in the 21st century. A simple on-off switch to disconnect the domestic bank is all that's required.

 

[Robin2]

Re: No microprocessors...

And jump leads so you can start the engine from the domestic batteries if ever it is necessary.

 

[charles_reed]

And

a 35 amp alternator certainly won't fully charge 150ah of battery bank on its standard in-alternator regulator.

So what's the sense of 2 batteries in parallel?

You don't specify why you consider a rotary swith has no place in a modern boat, so perhaps it would be charitable to forego comment until you care to justify your assertion.

 

[pvb]

OK, here goes...

In my first post above, I agreed with you that a smart regulator would maximise charging efficiency. So I haven't suggested using only the existing standard regulator.

A 35A alternator will take a long time to recharge a 150Ah battery bank without a smart regulator, but it will equally take a long time to recharge a 75Ah battery. The current-generating capacity of the alternator isn't all that important in the final phase of charging - it's the voltage which is important (and which is what a smart regulator boosts).

There are many sound reasons for putting the 2 domestic batteries permanently in parallel. Here are a few:-

* For a given usage of electricity, the depth of discharge of the batteries will be less than if just one battery is in circuit. As it's the depth of discharge which ultimately helps to kill off batteries, the 2 batteries will enjoy a longer life if they're used together.

* Whenever the engine is running, both batteries will be charged. This will increase charging efficiency and will help to prevent sulphation.

* 2 batteries in parallel work more efficiently than the same batteries used individually. The Ah rating of batteries is roughly based on a 20-hour constant discharge rate, before the battery drops to 10.5v. So, a 100Ah battery should theoretically be able to deliver 5A for 20 hours. However, if instead you tried to discharge the battery at 10A, it wouldn't last for 10 hours, but maybe only for 8 hours, reducing its theoretical capacity to 80Ah. Similarly, a reduced rate of discharge will slightly increase the theoretical capacity. It follows therefore that if the 2 domestic batteries are in parallel, they will each have their rate of discharge halved (compared to a single battery used independently) and will therefore deliver power more efficiently.


The old 1-2-Both switch really has no place on a boat today. It offers a unique opportunity to introduce confusion and mayhem, especially if fiddled with by well-meaning crew members. Incorrect use of the 1-2-Both switch can stop batteries being charged, and can allow a discharged battery to flatten a charged battery. Many callouts to boats with flat starter batteries are the result of someone using a 1-2-Both switch wrongly.

A far better solution is to have the alternator connected through a diode splitter, with one permanent feed to the starter battery and a second permanent feed to a single bank of domestic batteries. There should be a simple On-Off switch for the starter battery, and a second On-Off switch for the domestic bank. With this setup, there's almost no possibility of anything going wrong, which is why I think it's infinitely preferable.

(Battery combiners can be used instead of diode splitters; they're popular in the USA and are starting to be seen more in the UK).

 

[Strathglass]

Use of 1/2 both switch

I also don't like a 1/2/both switch shared between the engine and domestic batteries. I have had similar problems with people playing with the switches in the past. On my own boat I have fitted a 1/2/both battery but it is only to isolate the two domestic from each other and from the boat, when necessary. There is also a separate switch on the engine battery.

Iain

 

[Roberto]

Re: OK, here goes...

<>A far better solution is to have the alternator connected through a diode splitter, with one permanent feed to the starter battery and a second permanent feed to a single bank of domestic batteries. There should be a simple On-Off switch for the starter battery, and a second On-Off switch for the domestic bank. With this setup, there's almost no possibility of anything going wrong, which is why I think it's infinitely preferable.
<>

With this setup, where would you pick the field/excitation for the alternator?

 

[ccscott49]

Re: OK, here goes...

I have that setup on my boat, with a slioghjt difference as I have two engines, the port engine charges the engine battery bank. the stb, through a smart regulator the domestics. The shore/genny mains charger, has a splitter, with seperate battery voltage sensing, which takes care of all the batteries, the domestics and the engine batts, have seperate switches. I can however in an emergency, through a big solenoid, use my domestics to start my engines, (a button on the dash panel). This sytem works for me and I can't flatten the engine batteries. Apart from trying to start the engines. The genny has it's own batteries (two) with it's own charger and splitter. It has a 1,2 both switch.

 

[ccscott49]

Re: OK, here goes...

Engine start battery, where it is now. Probably wired into the harness for the engine.

 

[Roberto]

Re: OK, here goes...

But supposedly the engine start battery is the one that will be less discharged, so the domestic bank will remain undercharged...?

 

[ccscott49]

Re: OK, here goes...

Two seperate sensing circuits, I thought I'd said that, the splitter is built into the charger. So each bank, gets what it needs.

 

[pvb]

Sensing leads...

If a smart regulator isn't fitted, a battery-sensed alternator will work best with the sensing lead connected to the domestic bank (the domestics are likely to need more charge than the starter battery).

If there's a smart regulator fitted, the sense lead should again go to the domestic bank. Some smart regulators (eg Adverc) incorporate a temperature sensor in the sensing lead, allowing the regulator to modify the charging voltage according to battery temperature.

If there's a concern that either of these scenarios would result in overcharging the starter battery, the easiest solution is to fit a sealed maintenance-free starter battery. These have lead/calcium plate technology, which is quite resistant to over-charging.

 

[saturn]

do not see the need for a battery just for the starter motor.the battery will not last any longer than one in constant use that is looked after.
two batteries in parallel is best in my experience.but do it through a battery selecter switch,then you can run on one when you have a problem with the other.
also most people who sail do not monitor the battery which causes most problems,any battery can fail at any time after you buy it,but usually warns you by the voltage dropping low,i use a digital voltmeter(.1 resolution) and wire both batteries through selector switch 1-off-2 then check/compare volts when on board.

 

[charles_reed]

I tend to agree with you about the futility of reserving one battery entirely for engine-starting.
Seems a lot of waste of space and weight, when a little care and a 3-way switch allows you to use all your batteries or reserve one for emergency use.
Of my 3 batteries all can be connected up to the system and my practice is to reserve 1 for emergency use when the engine is not charging.
When connected up to shore-power or when the engine is running all are on acting as one big bank.
The two batteries of about 200ah give me 5-6 days of electric supply to run fridge, entartainment system etc when at anchor - though that can be extended if we have a brisk wind and lots of sun.

 

[charles_reed]

I tend to agree with you about the futility of reserving one battery entirely for engine-starting.
Seems a waste of a lot of space and weight, when a little care and a 3-way switch allows you to use all your batteries or reserve one for emergency use.
Of my 3 batteries all can be connected up to the system and my practice is to reserve 1 for emergency use when the engine is not charging.
When connected up to shore-power or when the engine is running all are on acting as one big bank.
The two batteries of about 200ah give me 5-6 days of electric supply to run fridge, entartainment system etc when at anchor - though that can be extended if we have a brisk wind and lots of sun.
My last "domestic" (that's the one which is always in service) was changed after 12 years use and that only because 1 cell was not charging at the same rate as the others when cycled through its annual full discharge.

The electrical system on a boat needs, IMHO, to be treated holistically.

Starting with your total mean 24-hour consumption you need to ensure you have between 3 - 5 days of capacity.
You then need to upgrade charging facilities to give you the capability of recharging your full capacity in 120 - 150 minutes.
As a standard in-alternator regulator will never get your battery capacity above 80% of full charge (it's designed to avoid killing batteries by overcharging) one of the first things to do is to fit a smart charger (preferably one with full battery sensing).

I also check batteries individually using a digital universal meter, but have found that lead/calcium batteries, take longer to accept charge and are slower to produce power than standard lead/acid batteries. Best all-round, I've found are proper industrial cells or, failing them, heavy duty auto (diesel truck 9-plate cell).

 

[bedouin]

I suppose it depends on the size of your batteries, and the amount of power it takes to turn over your engine. The risk of using all your batteries for domestic purposes, is that if you get it wrong you end up with flat batteries and no way of starting the engine. Proper management will of course minimse this problem.

The alternative, which I am adopting, is to fit a specialist starting battery. This gives me the same starting current as one of my 110Ah domestics, while weighing only a fifth - so little wasted weight or space. It also has the advantage of being more tolerant to damage/submersion/inversion than the domestics, so can act as an emergency power source.

 

[saturn]

to answer your origional question,no there is nothing wrong with your idea but there are alternatives that all work well,it depends on boat usage etc, but remember that if you do use two batteries in parallel,if one fails it will very rapidly deteriorate the other one, that is why i have a accurate panel mounted voltmeter and selector switch,that also shows you your alternator is ok when you motor.