House battery seems not to charge.

[Tryweryn]

I have started my moody 30 engine about 20 times so I assume the cranking battery is charging or it would not still be starting. The two house batteries are dead and even after a 1hr pottering out on the engine are still dead. I recently had the boatyard take the engine out and replace it after saildrive work. What I have noticed is, in the engine box by the back of the battery selector knob, the is a black finned object with two thick yellow wires. The wires are not connected! Could anyone please tell me what the object is and should both wires be connected somewhere. I will get a pic and go back to the boat yard but anyone know please?

 

[Richard10002]

Have you got a simple multimeter? If not, get one Even better, get a simple Clamp Ammeter ... About £40 from Maplins UNI-T UT103

Check the battery voltages at rest, then check again when the engine is running.

At rest, if flat, they might be somewhat less than 12V but, when charging, they might start at 12V or so, but should rise gradually to over 14V. You would know something was happening over a period of a couple of hours.

If you get a clamp ammeter, you would see a couple of Amps flowing at rest, (or no amps), when charging this should rise to 20 or 30 Amps, or more, dependent on your alternator. There will be a big difference, and it will be obvious within seconds.

I suppose a simpler test, if they are truly flat, is that nothing would work when they are not charging, whereas most things should work after a short period on charge - even if they are knackered.

 

[Tryweryn]

Thanks Richard I do have a multimeter and I will try that but I agree with u if nothing works it is not charging. Any idea what the black metal finned object is with two thick yellow wires behind the battery bank selector switch?

 

[prv]

Any idea what the black metal finned object is with two thick yellow wires behind the battery bank selector switch?

Almost certainly a diode splitter.

A good first step would be to understand what is wired to where. Ideally draw a diagram. You only need to concentrate on the heavy cables at first.

Pete

 

[Tryweryn]

Thanks prv. Is this what alters which bank is being charged 1 or 2?

 

[mark.adams]

Have a look here, there is a link in this thread that may help re. splitter diodes
http://www.ybw.com/forums/showthread.php?404881-Charging-Alternator-Battery-Question

 

[prv]

Thanks prv. Is this what alters which bank is being charged 1 or 2?

It allows both to be charged at once, without simply wiring them together into one large bank.

Pete

 

[Johntheyachty]

Almost certainly a diode splitter.

A good first step would be to understand what is wired to where. Ideally draw a diagram. You only need to concentrate on the heavy cables at first.

Pete

Agree. I had a similar problem at the start of this season. One half of the diode had died. Changed the diode and all was sweetness and light! Normally for a two battery bank set-up, there will be one wire 'in' from the alternator, and two wires 'out' to the two battery banks.

 

[Tryweryn]

Sorted ...so if it helps future ppl. Firstly both domestic batteries were weak. But also in the past the diode probably failed and was passed. So the mechanic is fitting a new one so that the bats will charge whatever the setting of the battery selector. If the selector is set to 0 it wont now damage the alternator.
Before you had to select 1 or 2 to charge both battery banks. Selecting 1+2 only charged 1 bank.

Many many thanks

 

[ghostlymoron]

You'd be better replacing the diodes with a Volt Sensing Relay as you won't get voltage drop and better charging.

 

[sailorman]

Agree. I had a similar problem at the start of this season. One half of the diode had died. Changed the diode and all was sweetness and light! Normally for a two battery bank set-up, there will be one wire 'in' from the alternator, and two wires 'out' to the two battery banks.

try a VSR ( voltage sensing relay)

 

[ghostlymoron]

Agree. See previous post.

try a VSR ( voltage sensing relay)