Retro fitting a battery charger......

[Alphekka]

Hi

 

We have recently aquired our boat. All the DC electrical systems are 24V.

 

There are 3 battery banks charged through a 3 output splitting diode:

200Ah Domestic.

100Ah Engine.

???Ah Bow Thruster.

 

There is a 240V AC shoreline circuit already fitted.

 

I have been given a 24V battery charger with a single 24V DC output which I would like to fit as we are mainly going to be in moored with the availability of a shore hook up.

What is the best way to connect it?

 

I have included a rough/basic wiring diagram of what I think is there at the moment (I have not included the fuses but they are all there!) and where I think the charger should go.

 

 

Hopefully I am not a million miles away??

 

P.S. I have no idea how to put pictures on yet...hopefully this is visible somehow??

[by'eck]

Your suggested wiring of the charger through the diode splitter will work providing it can take the max current the charger outputs. However since diode splitters loose you at least half and maybe a whole volt or more this will reflect as lower charge voltage to all the batteries when using mains charger or engine alternator. The subject is discussed at greater length here.

 

One answer with the alternator is to use an external regulator that senses the domestic battery bank voltage so can compensate for the diode voltage drop. Even this is not perfect though since the starter and bow thruster batteries may get too higher charge voltage.

 

A mains charger with external sensing may provide a similar answer but its unlikely yours has this option.

 

The third more radical answer which would benefit both charger and alternator, is to bin the diode splitter and use heavy current relays (contactors) to join the individual battery banks together whilst being charged. A degree of automation is required here since you may otherwise forget to disconnect them later.

 

This could be achieved with voltage sensitive relays, a Smartbank or a Sterling three way intelligent zero-volt drop splitter. FWIW I use the latter.

[trackman]

The usual route with a charger is to get one with enough separate outputs for the number of battery banks you have. Given that the charger you have doesn't have that facility, I reckon you have two choices, as already described by bye'ek.

First you could keep the existing diode splitter and use it to split the charger output as well as the alternator's. As already said, this wastes some charging power.

The second, and significantly more efficient way would be to switch to a relay based splitter as bye'ek recommends. We have a Smartbank Advanced system that charges two banks efficiently from one alternator. I'm not sure it can deal with three banks though, so the Sterling device may be better in your case.

This does all beg the question whether the free charger is worth the cost and trouble of fitting all this new kit. A new charger with three outputs would allow you to leave the existing alternator charging system alone. That would still leave the inefficiencies of the diode splitter in the alternator system of course, but the charger wouldn't be affected by that issue.

You'd need to investigate the relative costs of a new charger and a Sterling unit, including any fitting costs, before deciding which option to take.

[Alphekka]

Thanks guys

 

This is purely an interim solution to take advantage of a shore hook up.

Long term I am looking at rewiring so I know what goes where.

This will include a review of the current components. The batteries are about 6 years old for example !

 

In the short term I need to move her closer to home to be able to do a full audit.2 hour drives mean we are spending euphoric weekends away on our "new" boat with little working.

 

Thanks by'eck for confirming my understanding of the diode splitter.

thanks trackman for agreeing with by'eck. That makes 3 heads better than 1.

 

New info

 

I believe the alternator is 30A and my "free" charger is 23A 3 stage job.

 

Looking at the sterling "no volt splitter" at £160 could be a long term solution?

 

Cheers

[GUMPY]

Much cheaper to join the banks using these

http://www.iem-services.co.uk/showdetails.asp?id=1171

And junk the diode splitter

Then batteries will charge no matter what source you are using.

[by'eck]

New info

 

I believe the alternator is 30A and my "free" charger is 23A 3 stage job.

 

Looking at the sterling "no volt splitter" at £160 could be a long term solution?

 

Cheers

 

The Sterling zero-volt drop splitters come in many variants, 12 or 24 volt, two or three output, one or two alternators and varying max current handling. Make sure you buy one that's well over-rated current wise to allow for future improvements in your charging systems.

 

If you later buy a more powerful mains charger, Sterling among others, offer three (isolated) output ones which could be wired directly to each battery set.

[sassan]

Noone's mentioned the simplest solution, which is to connect the charger directly to the domestic battery bank! How much do your starter and bow-thruster batteries need charging when you aren't using them? Probably not for a good long time!

[dor]

Noone's mentioned the simplest solution, which is to connect the charger directly to the domestic battery bank! How much do your starter and bow-thruster batteries need charging when you aren't using them? Probably not for a good long time!

My thoughts exactly!

 

It used the charger in the short term and gives the OP time to research the best options for his particular system.

 

 

 

I believe the alternator is 30A and my "free" charger is 23A 3 stage job.

 

30A alternator? Are you sure? This is quite small, even at 24V.

[Tony Brooks]

My thoughts exactly!

 

It used the charger in the short term and gives the OP time to research the best options for his particular system.

 

 

 

 

30A alternator? Are you sure? This is quite small, even at 24V.

 

 

1. Absolutely agree.

 

2. That = 60 amps at 12V, many older boast had 50 amp 12V alternators, its only the floating cottage brigade that thinks that is small.

[Alphekka]

Hi

 

If I connect directly to the bank will the charger need isolating when not charging?

i.e. will it draw anything from the batteries when not charging?

 

And tony thanks for the alternator info. I was starting to feel a bit inadequate

 

Cheers

[bottle]

No and no

 

Size does not matter, it is the way you use that is.