Battery charging

[tckearney]

Hi guys.   I have recently been looking at why my house batteries charge from the  Mains charger (when on shoreside power) but not the engine batteries.   I have 2000 B42.   The original factory mains charger has at some time been replaced with a modern auto charger and that charges the house batteries fine but not the  engine batteries.   This charger is directly across the house batteries, no diodes, no protection just straight forward connection.   While checking through the circuitry I came across a switch, mounted directly forward of the house batteries and I believe original as the wirers  (about 4mm or 6mm Black)  go into the original loom.  This is under the seating.  Any idea what it is for? It is just single pole on/off.  See attachment  And yes I have noticed one of the wires had fallen off

[elias]

Hi, mine also BV44 the same , motor battery only charged from alternator . I think is ok cause is better to be away from the main batteries that are involved with comfort loads . Also charger like those can’t charge 2 different batteries at the same time ( you might have 2 main batteries but are bridged parallel so they behave like one )

[nightowle]

is it best to leave the switch in the off or on position?

[Salty]

Hi guys.   
.
. While checking through the circuitry I came across a switch, mounted directly forward of the house batteries and I believe original as the wirers  (about 4mm or 6mm Black)  go into the original loom.  This is under the seating.  Any idea what it is for? It is just single pole on/off.  See attachment  And yes I have noticed one of the wires had fallen off

1. I don’t think it is an original switch at all
2. Only you can determine what that switch is for by following the wiring if any is attached to it, to see where the wires go to, if any wires are in fact connected to it.
3. From your photo, clearly the wire with the yellow marker and female spade connector has come off from somewhere, but to the right of the photo is another wire that does not appear to have any connector, and appears not to be connected to anything at that end such that I wonder whether there are any wires connected to that switch.

is it best to leave the switch in the off or on position?

First check whether there are any wires physically connected to the switch, then where they go to and come from. If any wire connection is hanging loose, you have to determine why, because simply re-connecting it might not be the best thing to do. And whether the switch should be on or off depends on what the switch is there for in the first place.

With so little information about an unmarked and possibly disconnected switch, it’s impossible to advise one way or the other about its use or whether it should be on or off.

One thing I would suggest is that if a system onboard becomes redundant, then remove it, but if you are a new owner, then you need to determine what that system was and why it has fallen into disuse before you remove it, and contacting the previous owner to ask about it may be the simple answer.

Probably the best suggestion would be to get a new purpose made and properly designed boat battery charger that will charge both sets of batteries, and have it fitted onboard. Yes, I know they are expensive, but they do the job.

[tckearney]

Thanks Guys,  The wire to the left has fallen off the switch, the other side of the switch has a similar wire but connected.  Both wires go straight into the flexi conduit loom so that is what makes me think it is original.  Also the screw heads that hold the screw are filled and under the grey paint that is applied to the bonded joints during manufacture.  I have tried connecting the loose wire but can't see anything changing regarding charging or electrical activity.  I will progress and find its use one way or another. 

[tckearney]

Oh forgot to mention, thanks Salty but that other wire is in fact the end of a tie wrap . Its just a cheam phone camera !

[tckearney]

Found the switch wiring , It was added after manufacture and is for electric toilet that is no longer fitted.   So back to the charging of the engine batteries.  As I mentioned the shoreside mains charger does charge the house batteries but not the engine & bow thruster batteries.   Is it feasable to add a 100A diode from the positive of the house battery to the positive of the engine battery.  The negative is already common.   I assume this would then allow the shoreside mains  battery charger to charge the engine battery and would also allow the house battery to drive the starter motor, but not allow the engine battery to feed the lighting fridge ect.  Any comments. 

[Lyra]

A diode as you described is not a proper solution.
There are several "non switch" solutions to charge two batteries from one source - B2B charger, VSR or diode splitter just like you have from the alternator.
But then comes the question of why going into this trouble - the starter battery should last a long time on alternator alone, just like in your car (my recent battery lasted 9 years, and probably went dead because of temperature in the Med and not discharge). The thruster battery also works only when the engine is on and for short bursts so should not discharge too much and also last a long time.
You can always (as I do) keep a short jumper cable for cases that one battery needs some help from another.

[Symphony]

As previously suggested if you want the mains charger to charge the other batteries as well you need to replace it with a proper marine charger which will have the facility to charge at least two banks and probably 3. Such chargers will have the ability to set charging regimes for each battery separately so you can charge different types of battery at the same time. As Lyra says this may not be worth it if you use your boat regularly as both the start and thruster battery are almost always fully charged. However if you leave the boat for longer periods when self discharge may be an issue it can be useful. On the other hand a solar panel is probably a better solution, particularly if you are a place with decent winter sun!

[SYJetzt]

i can´t see the need of charging the starter battery (except from alternator!). But if you have the need to charge it from the mains, you also can add an extra charger only for the starting battery instead of changing the housebattery charger to an enhanced one with multiple outputs. It only needs a small charger with little power, because there is usually no current drain from the battery.

[tckearney]

Thanks guys I think I will go for the extra small charger just for engine batteries.  Makes more sense.  I do not use the engine much but am often single handed and like the comfort of a marina, so the Bow thruster gets used a lot.