Beneteau First 31.7 Battery charging

[hamsap]

Does anyone know what the battery charging system is for a 2002 31.7?

I have Volvo MD 2020 engine and I believe the alternator has a built-in regulator that feeds to both batteries, but the wiring is hard to trace and the Beneteau manual useless. I wish to add a dedicated starting battery then to parrallel up the two current separate batteries as larger capacity domestic bank but need to be sure how they will charge. All help gratefully recieved.

 

[Barry Jones]

No idea about the wiring on that particular boat.

Assume you have a single alternator on the VP - do you have a 1+2+both battery isolator ??

 

[VicS]

If your alternator is fitted with a split charging system you will find two similar heavyish wires running from it. One to each battery.

I believe however that a remote "charging distributor" was used on MD2020 engines. SEE HERE

Id suggest you simply connect the two existing batteries in parallel as a large house bank.and then connect the new one in place of the one transferred to the house bank

You will have to determine which, if either, is the starter battery, remove the connections from that one and connect it in parallel with the other and then connect the new one in its place.


What battery isolation/ selection switching do you have at present?

 

[hamsap]

The First 31.7 has an isolator switch for each battery. The wiring allows either or both to be on at any time and either can start the battery.

At the batteries only one of them has any wiring other than the heavy duty leads. The smaller wiring is on the positive - the system has a negative ground.

Look as I might I cannot see anything resembling a separate regulator in the engine compartment although I guess it could be integrated ith the mains power and charging "Power First " unit.

Irrespective of the switch position both batteries sem to get an equal charge from either the mains or the engine. After a sail yesterday I measured the voltages at the battery as follows:
No engine and no mains power - 12.96V and 12.96V
Under engine (alternator) - 13.73V and 13.73V
With one or other islolator switch off the voltages were similar to when both on.
Under mains only irrespective of which switch was on or if both off the voltages were - 13.41V and 13.41

I have sort of concluded that somehow both batteries are getting a similar charge under mains when I have left the boat with switches off - which is good. And they both somehow get a charge from the alternator when the engine is runing again irrespective of which switch is on ( of course one will be).

Unless any one can advise why this is not a very wise move, I am planning to simply double up the two existing battries a a single bank on one switch and putting a new (Red Flash 1000) starter battry on the other switch, much as you suggest.

 

[Barry Jones]

I'm struggling to visualise your set-up from your description.

You say you have separate battery isolators (one for each current 12V battery) - presumably they are just marked on/off ??

The identical voltages on both banks is very suspicious - I would have expected slightly different voltages on discharge on each battery and its worrying that both banks are seeing the alternator charge voltage of 13.7V when one battery isolator is off (if that is what you are saying).

Probably the mains charger is going directly to the batteries and bypassing the battery isolator switch - not uncommon.

I would be reluctant to do anything until you fully understand your wiring.

Photos would be useful to assist in the detective work.

 

[wiggy]

I have a 31.7 from the same year and added a secon battery to tthe domestic bit of the system. I have always assumed that only the "on" battery would be charged form the alternator and used to supply the 12V system and that both get charged by 240V charger even if swiches ar "off".
I have set up a 31.7 site with a forum, its early days but you could post your question there. Follow the link below for the site

 

[BAtoo]

I have the First 310 - predecessor of the 31.7 - the batteries have individual on-off switches - and a common negative on-off. I did what you propose - doubled up the domestic batteries & installed the RedFlash starter - and had no problems. It seems that the 240V charger does both and the alternator does whichever is on.

(I have since replaced the doubled-up domestic batteries with a single 140AH battery which just fits in the well in front of the engine)

 

[hamsap]

Thanks all. I will investigate a bit more with my trusty multimeter and try to get a clearer understanding of the circuiting over the weekend.

 

[wiggy]

Let us know the results

 

[alan]

31.7 Battery Charging

On the 311 the arrangement was:
Mains charging is fed to both batteries separately and independant from the ON/OFF switches.

The ON/OFF switch #1 is for the engine start battery

The ON/OFF switch #2 is for the house batteries

There was no earth ON/OFF switch (Black)

There is a parelleling wire from the "output" side of switch #1 to the "output" side of switch #2 on the switches.

So, when both switches are closed the charging from the alternator goes to both; when switch #1 is closed then the battery #1 is fed to the starter, when the engine starts, the output from the alternator goes to the battery #1; if you then close switch #2 the output form the alternator goes to both batteries.

The normal mode of operation is:

Close switch #1, start engine; close switch #2 thus charging both batteries; turn engine off and then open switch #1 thus sailing on battery #2 for instruments e.t.c.; when you want to re-start the engine close switch #1 and open switch #2 then start engine; close switch #2 and charge both batteries. In emergency (i.e. battery one flat) you can start the engine with both switch #1 and #2 closed.

I suspect the 31.7 will have the same/similar set up ..... but check!!

Alan.