Master switch issue?

[Ian_Rob]

The last few times I have been to my boat, I have noticed on arriving that the panel voltmeter needle is indicating a voltage - this despite the fact that the master switches haven't yet been turned on. As soon as they are, the needle drops to zero and the meter appears/ed to function properly thereafter.

However, when I left the boat yesterday morning , shortly after turning all the master switches off, an 'under voltage' light appeared on the electric panel and a buzzer started. Curiously, whilst the alarm light related to the domestic batteries, I could only turn it off and silence the alarm by disconnecting the engine battery.

What is going on here? Is it time to replace the master switches?

There is a 'link all' master switch but this was turned off.


PS The boat isn't connected to shore power.
PPS I brought both domestic batteries home and find that they have a charge of 12.79 and 12.89 volts respectively.

 

[VicS]

You don't say what voltage the voltmeter indicated when you arrived, presumably not the full 12+ volts?

You don't say how you normally get a reading. By operating a normally off switch to read one battery or the other?

You don't say how the link all switch works. By linking the batteries upstream of the isolators or by linking the circuits down stream of the isolators?

Anything switched on?

Relevant facts but I'll still be puzzled knowing the answers.

Dampness in a switch ........ but ????????. Cant think of one single thing that might explain.

More testing checking needed.

 

[Ian_Rob]

Not sure I can fill in many of the blanks without further checking. I didn't record the voltage on arrival but the panel meter reading was 'normal' (allowing for the fact that I hadn't used the boat for 5 weeks) and the engine started immediately.

The voltmeter is connected to a normally off rocker switch. Pressing one way gives a reading for the domestic batteries and the other way for the engine battery.

I would need to check whether the link all switch is up or downstream of the isolators.

Nothing was switched on when the light/alarm fault appeared.

The batteries had been on shore power overnight - though I did drain down the water system after the shore power had been disconnected just before leaving, using the pump.

 

[salar]

A long shot but it could relate to the way bilge pump switches are wired, especially pumps with integral sensors. Bilge pumps are wired directly to the battery and to a manual switch. When the pump is on, both are live. If there was a short at the pump end then the wire to the pump manual switch will be live, by-passing the battery master. If there was a further short or dampness it could mean the live circuit has power that way. I found that route when setting up a bilge monitoring system.