Duel battery wiring

[John little]

Hi Folks,

 

I have almost completed refurbishing a 27 foot Madeira canal cruiser.  My final task is to completed the duel battery system but I don't know what the  mechanism is that is currently installed.  As she is ~1975 build its a very old system.  Any help would be much appreciated.

John   

[Tracy D'arth]

It looks like a 2 diode splitter. Each battery is connected to the generator (dynamo or alternator) via a semiconductor diode which prevents one battery taking power from the other but enables both to be charged at the same time.

Drawback is that a diode will loose approximately 0.6v.

[Tony Brooks]

1 hour ago, John little said:

Hi Folks,

 

I have almost completed refurbishing a 27 foot Madeira canal cruiser.  My final task is to completed the duel battery system but I don't know what the  mechanism is that is currently installed.  As she is ~1975 build its a very old system.  Any help would be much appreciated.

John   

 

 

It is a very crude split charge diode system, very old hat and almost designed to ensure the batteries undercharge.

 

My advice is a bit of a rewire, ditch that and fit a Voltage Sensitive Relay

 

Rewire thus.

 

Main alternator output to DOMESTIC battery positive.

Ensure engine and domestic battery negatives are linked - they should be.

A heavy charging cable thus: Dom bat pos >> VSR >> eng bat pos

Then connect the VSR small negative wire to any suitable negative.

 

 

Note: The alternator connection is to strictly comply with the BSS, many boats get away with it on the other side of the master switch (which has advantages). If you have solar of a shoreline charger do not use the alternative connections.

Edited July 15, 2023 by Tony Brooks

[John little]

Thanks so much. The posts have really cleared things up for me. Tony do they fail? 

[Tony Brooks]

26 minutes ago, John little said:

Thanks so much. The posts have really cleared things up for me. Tony do they fail? 

 

Every thing fails eventually. I would not buy a no-name Far Easter product, even though they may or may not be identical to one marketed by a UK company such as Cargo or one of the main stream marine suppliers.

 

You need to allow a decent overhead between their rated current and the alternator maximum output. In your case, I expect your alternator will be rated at about 50 amps, so a 140 amp VSR should be fine. Under certain circumstances, the VSR may have to pass the full alternator output plus a bit more so the bigger the safety margin the more reliable it will be. I had a Cargo 140 amp VSR running well for five years or so before I sold my boat.

[John little]

Thanks again Tony. I will go looking for a unit now. IOU

[John little]

Sorry Tony, one more question.

From my photo, as yet I haven't checked with the multimeter. The center lead I've traced to ignition and left/right lead is to each battery. Is that right? 

[Tony Brooks]

8 hours ago, John little said:

Sorry Tony, one more question.

From my photo, as yet I haven't checked with the multimeter. The center lead I've traced to ignition and left/right lead is to each battery. Is that right? 

 

Now you raise it, that photo looks very odd. It looks as if at least the red leads from what looks like the diode on the left is connected to the hull, and I am not sure about the one on the right. That is not normal. The metal case seems to be mounted on insulation blocks, as I would expect if it were a conventional split charge diode. 

 

Here is a typical diagram:

 

 

Your alternator probably does not need the sensing wire.

 

I think that it would be best if you traced all the wires connected to it and sent a diagram.

 

 

 

 

 

[John little]

Good morning Tomy,  I won't get to the boat until tomorrow.

But I can tell you that the center red lead goes to the ignition. The one on the right goes to the starter battery. This battery has an isolator to stop it draining. I am assuming the left lead goes to the lesure battery which has constant feed to the system. I found this out when I replaced the lesure battery with a new one. Diagram to follow. 

[Tony Brooks]

12 minutes ago, John little said:

Good morning Tomy,  I won't get to the boat until tomorrow.

But I can tell you that the center red lead goes to the ignition. The one on the right goes to the starter battery. This battery has an isolator to stop it draining. I am assuming the left lead goes to the lesure battery which has constant feed to the system. I found this out when I replaced the lesure battery with a new one. Diagram to follow. 

 

The centre red lead normally comes from the alternator main output positive terminal (B+). I don't see how it would work if connected to the ignition switch UNLESS this is an active zero volt drop "diode", but if it were there would still be a heavy lead fed from B+ on the alternator.

 

Do not assume, the left-hand lead looks as if it is connected to a meal bracket.

 

It sounds as if you may have a missing master switch for the domestic system.

 

I await the diagram.