Electrics puzzle

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cliffb

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I'm confused. The boat is a 2002 Beneteau 36CC. Whilst delving about in the engine room in a quest to see how to fit a second domestic battery I found something ODD, (or so it seemed to me). FYI, there's three battery main switches. One Neutral (black), one Engine Start (Red) and one Service (Red). The odd thing is that there's a great big electrical strap between the the two red switches. Which accounts for the reason why, on the occassion of forgetting to turn on the 'Engine' start switch, I have started the engine; presumably from the service battery.
Now, to me, this seems nonsense. What's the point of having two batteries, and two switches if they're strapped together. It is clearly a Beneteau factory fitted item and there must be a reason for it... I suppose. I'm tempted to take the strap off, but my concern is that the engine alternator may not charge one or other of the batteries (not knowing how this charging circuit is typically set-up).
So....
The question for the panel is....would you take off the strap? If so, is it likely to effect the battery charging circuit?
And whilst asking questions...
If I put in a second service battery, does this have any bearing on the shore-power charger and its ability to charge two batteries instead of one...or more accurately, three batteries instead of two?
As always, any advice/help much appreciated.
 
A) This seems to be a typical Beneteau set up: the logic (? /forums/images/graemlins/confused.gif) behind this is that if You are a good boy, you'll remember NOT to start the engine with the service battery or vice-versa; if You remove the "electrical bridge" the 2 batteries will be completely separated.
B) I have the same problem on my 393, where I installed a 3rd battery; at the link below You can see a diagram I sketched of the existing situation and how I THINK it could be enhanced.

http://album.foto.alice.it/cravenna/972652

C) Regardless of the "bridge" or "bridges", the fact is that under engine and with services on (i.e.:fridge, navigation, VHF) any charge splitter would not know how to optimize the charge on the individual batteries (which I assume being of different capacities, made, model and state of charge) AS ALL POSITIVES FROM THE BATTERY BANKS do connect together in one spot, with charge current/s adding and mixing up; even mooring at the quay and with a sophisticated battery charger with 3 separate exits (one for avery battery) the situation looks confusing.
D) Some manufacturers of chargers / splitters, whom I consulted and who were kind enough to spend some of their precious time trying to explain things to me, suggested You just connect the batteries in parallel and forget about it OR use a rotary (1, 2, Both, None) switch to put one service battery into use.
E) Some 4 monts ago I mailed the diagram and the question to PBO The experts answer You, but to no avail.
F) I too would welcome any suggestion on how to be sure that, whichever the charging device in charge (oops!) (splitter, mains charger, solar panel regulator...), this could charge at the best any and every single battery.

OR AM I MISSING SOMETHING? /forums/images/graemlins/confused.gif
 
Does seem very odd. If as you seem to indicate the two batteries are connected on their positive terminals this effectively means turning either switch on would do exactly the same thing. Are these simple on off switches though or two way distribution rotary switches? If they are simply on off switches one switch is redundant. Is there a seperate distribution switch to change over batteries though? If there isn't you would not be able to use the service battery to start the engine in an emergency.
There might be a clue in that you have earth switching too by the sound of it. This is unusual, but an excellent safeguard if true. It would be unusual to see a production boat wired this way I believe. Are both batteries connected to the same black terminal or only one? I suspect this is a previous owners mod rather than makers original.
Your second question if I understand you correctly is that if you connect two service batteries in an identical manner to common terminals it effectively makes one battery bank and merely increases amp hour capacity. Your charger will still work the same but obviously take longer to bring the increased capacity up to full charge. I would be interested to hear comments from others with similar boats. Doesn't sound right to me!
 
[ QUOTE ]
There might be a clue in that you have earth switching too by the sound of it. This is unusual, but an excellent safeguard if true. It would be unusual to see a production boat wired this way I believe. Are both batteries connected to the same black terminal or only one? I suspect this is a previous owners mod rather than makers original.


[/ QUOTE ]

In all 393 I examined, there ALWAYS is the NEGATIVE on/off switch AND the positive switches
 
I could only view your diagram 1 but if this is Benny logic I don't understand it. As I said before having negative isolation is great. tiying all the battery positive switches together seems crazy. With a 3 battery set up like you show my preference would be not to have diodes but to take the strap off the engine battery switch (no1) and introduce a two way rotary switch between no 1 and the still connected 2 and 3 with the common pole going direct to the engine starter. Then with the switch in pos 1 you have battery I dedicated to starting and if it fails you can use the service bank in emergency. You will need to make sure you have a seperate charging cable to each battery bank though with either a diode bridge or some such to split the charge between batteries and stop back drain. I don't think you want a diode in the main feed for the starter motor as shown though as it will never stand the current!
Edit..... Looking at your diagram again there is a charge splitter there already. Just ensure the cable to that remains on the no1 battery switch and all should be well.
Take strap off and fit rotary switch.
 
I have my service and engine start batteries shorted at all times for reasons given on the other generator thread running now. If if was my boat, I'd leave it shorted all the while I am watching it carefully, and remove the link if unsure of whether I would remember to keep an eye on the battery state (or on leaving my wife alone on board).
 
It sounds the same as our old setup where two switch terminals were connected together so you could switch on either/both batteries independantly - it does the same as the 1-both-2 combi switches. The black one sounds like it is (as said above) a negative switch.
We removed the strap that connected the engine and domestic circuits - but had to add a split diode to charge the two battery banks.
 
[ QUOTE ]
I could only view your diagram 1 but if this is Benny logic I don't understand it. As I said before having negative isolation is great. tiying all the battery positive switches together seems crazy. [ QUOTE ]

This, again, is the std set-up and I agree it is at least questionable.
[ QUOTE ]
With a 3 battery set up like you show my preference would be not to have diodes but to take the strap off the engine battery switch (no1) and introduce a two way rotary switch between no 1 and the still connected 2 and 3 with the common pole going direct to the engine starter. Then with the switch in pos 1 you have battery I dedicated to starting and if it fails you can use the service bank in emergency. You will need to make sure you have a seperate charging cable to each battery bank though with either a diode bridge or some such to split the charge between batteries and stop back drain. [ QUOTE ]

Yes, the charging devices have separate charging cables; I'm looking to avoid to remember which was the battery last used or charged.
[ QUOTE ]
I don't think you want a diode in the main feed for the starter motor as shown though as it will never stand the current!

[/ QUOTE ]
But as the current flowing from (e.g.) the generator through the diode splitter is in the order of 40 amps and the diodes stand it, I wonder if there are not available diodes of greater capacity.
 
Are the engine and domestic batteries the same size and type? It could be that you're supposed to remove the bridging connection if you're mixing deep cycle and cranking batteries. If both batteries have cranking capability then in theory you have greater charge capacity keeping them in parallel due to the Peukert stuff. Until they're both flat.
 
The cable to the starter motor needs to be as direct from the battery as possible. Any switches need to be very high amp. Certainly not through a diode. You are confusing charging the battery with using it to crank the engine. Even if you could find a device to do what you suggest ( and I don't think you would very easily) it's failure would mean you can't start your engine in an emergency. Bad Idea. All you need is one rotary switch. I humbly suggest don't make life complicated by re-inventing the wheel.
 
This is pretty normal for Beneteau and I had the same arrangement on my 311; on my current boat (343) there is an SCR and so no wire connecting the engine and service batteries.
Having this wire is just the same as the "old" rotary,1/2/both/off, switch. I used to use just battery one for the engine start, then when the engine is running switch in battery2 for charging both; then when engine off, switch off battery one and leave battery two in circuit for services[note that it is the output side of the switches that are wired together]. The third switch (negative) is for "safety"; a way of disconnecting all power should there be a short somewhere that is not protected by the positive switches. I think the Beneteau arrangement is a good one .... you just have to remember to do the battery management yourself; I never had a problem with it.

I later actually rewired mine to have diode splitters, and used this wire connecting the two batteries together to connect in a third positive switch for emergency paralleling use. That is: I could leave both switches on for batteries 1 and 2 without fear of discharging the engine battery (diode splitter) and did not have to remember to switch off battery one when under sail, but in the event of a completely discharged engine battery could use the third positive switch to parallel battery1 and 2.

I also fitted a second service battery and the 8 amp (I think) charger was up to supplying three 70Ah batteries; or at least I never had any problems, but also had an Adverc and a 56W solar panel.

I think the arrangement that you have is a good one and is pretty fool proof as long as you remember to do the switching.

Alan.
 
With respect I don't think it is the same as a rotary switch at all. with a rotary switch in position 1 which connects the cranking battery to the starter motor there is absolutely no danger of flattening it by leaving the lights on or fridge running inadvertently, which is the whole point of the exercise. With this arrangement unless you deliberately switch the cranking battery off when not using it you can flatten the whole system below the level that the cranking battery can operate effectively at very easily. It is in effect like running a rotary switch on "both" all the time. all for the sake of buying a £30 switch.....
 
Also, with respect, it is not like running on "both" all the time; you use batt 1 for starting the engine, both when charging, and batt 2 when engine is off. Of course, as I said, you have to do the management yourself much as you have to do with the rotary switch. But (IMHO) it is a very simple system with little to go wrong, and "rotary switches" can/do fail with time. But I take your point: "unless you deliberately switch the cranking battery off" : and in fact this is what I was trying to say, by one having to do the battery management oneself.
Typically:
start engine with batt1
motor out of the harbour with both batts connected
get the sails up, and switch off motor and batt1 (should be charged up by then)leave batt 2 connected.

Alan.
 
Ciao Gianenrico,
No, you only need a switch for each battery bank. Even if you have four service batteries (in parallel) you still only need one switch; just treat a bank as if it was a single battery. (Except of course the capacity of your alternator/charger ........ but that is another story!!!).

Alan.
 
Well we agree then, but all that is required, as I said before to make the system automatic without the need to keep remembering to turn it off is a £30 switch, and if you forget to turn the battery off it is exactly the same as having a rotary switch on both with the danger of flattening your cranking battery. It also means that if you forget to turn it on and try to start the battery it will use the domestic service battery bank to start it which is where the original post started. Not good! All for the sake of saving £30......
 
Ruffles. Yes. The batteries are of different sizes and possibly/probably types (but I couldn't swear to this as I haven't looked). So your point is well taken. But all of this talk of Split Diodes etc is getting into areas I'm not comfortable with and so, working on the principle of 'if it ain't broke, don't fix, I'm not going there.

Alan. Thanks for your input on this. I hear what you're saying. I have to admit, I haven't investigated which side of the switches the strap is, and now, in thinking about it some more, I guess this is quite pertinent. The next time I'm on the boat I'll have a deeper investigation of this and get back to you if I may.

With regards to my wanting to put a second service battery in circuit and concerns over the alternator and shore power charger, I had intended merely to take a cable from the pos and neg of the existing battery to the relative posts on the additional one. Do we think this will be OK? Or is there something else I should be wary of?
Thanks as always.
 
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