More on upgrading service system

[Magic_Sailor]

I posted a couple of days ago about upgrading the service system on my boat by the addition of another battery and got some interesting and useful replies (what a creep!) I have some more info which you might (?) find interesting.

The alternator is indeed a Hitachi 35A
The blocking diode is a Lucas 4BD

The blocking diode has 3 terminals - 1 for the alternator, 1 for the service system (B2) and 1 for the engine start system (B1). Now then - interestingly, each of the terminals B1 and B2 have an ADDITIONAL cable. Both of these cables end up in the aft cabin under the bed along with a 3rd cable clearly intended as 0v (originally connected at the -ve terminal of the starter battery for no apparent reason). Now then, without any jokes about power sources for sex aids in the skippers cabin (well if you must); what else could these cables before other than an extra battery? It cannot be merely as a source of power as they are connected to 12V BEFORE the isolator.

NB - I recollect a number of months ago, someone posting that they had found an extra service battery in the aft cabin that they had not realised was there. Could this be the same thing? In which case I've just got to fit a battery box and connect up.

Further, this would make some sense as the other service battery is in the forepeak (remember?) and this additional battery would balance the boat (as pointed out by CCScott I think - 2 batteries in the forepeak would make her by the head a little). So, what are my questions? They are these:

1. Does anybody know where I can get technical info on the Lucas 4BD blocking diode?
2. Can you think of any other reason why these cables go into the aft cabin and stop?
3. Do you have any other postable comments?

Thanks in advance and with bated breath

Magic

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[bedouin]

Perhaps the addtional cables are intended to wire up a battery charger?

I don't think that wires for an additional battery would be connected the way you suggest

 

[Magic_Sailor]

You could be right

But it could be either as the cable size is the same throughout.

Of course a charger would need to be plugged into the mains and there is no facility for this. (There is a ring main but itsnever been conncted and the socket in the cabin is in the wrong place)

Thanks for your thoughts.

Magic

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[HaraldS]

If I read this right, you say that you have a cable from EACH of the two battery terminals, and a ground wire?
What wire size are those?
Here a few possible answers:

1) Sense cables for a solar or wind generator regulator, hence aft cabin.
2) Maybe another isolator before above.
3) Battery monitor like a link 20, (would only require thin cables, but two more for sensing the shunts).
3) Bridging switch for emergency start.

Don't know your blocking diodes. If they are regular blocking diodes, you might want to have a regulator that senses from the battery side. If they have also a ground wire, they could be of the newer MOS-FET types that have almost no voltage drop.
4) Cables for TWO additional batteries.
5) Cables for ONE additional service battery plus a bridging switch for emergency start.





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