Battery No 1 or batter No2!

TwinRudders

TwinRudders

Well-Known Member
Joined
15 Nov 2004
Messages
207
Location
Poole & Bath
Visit site
Hi,

I have a 2 battery system controlled by a rotary 1-Both-2 switch.

Now...I need to replace the domestic battery (No1) but am unsure which one it is....yes it sounds simple but...

So I turn the switch to NO1 and disconnect one battery - and nothing happens power, stays on in the boat. So I leave that battery disconnected and disconnect the other battery -ve terminal as well, power still stays on.

With Switch turned to No2 - I can take the power off the boat by disconnecting one battery - how come with the switch on No1 I can take one battery totally out and the -ve terminal off the other battery and power still stays on...

Now can someone explain that to me please. Apologies if it's obvious.

Jonny
 
Are you quite certain there are only two batteries? Some boats have two domestic batteries, and an engine start battery hidden in a different compartment. If there are only two batteries you cannot have a circuit if both have had the cables disconnected from either their positive or their negative terminals.
 
Do you have a VSR or a DIODE in the system?

Are you disconnecting at the battery terminal or at the switch? If disconecting at the switch then you have a diode or VSR somewhere. If disconnecting at the actuall battery terminals then you have a 'third' battery (or battery charger/shorepower) connected.
 
So the power remains on if you disconnect both batteries in "1" position, and "2" position switches in one of the other batteries?
Where are you measuring the voltage? It should be actually at the 1-both-2 switch output, if you are just seeing if the lights stay on (a) there's another battery, or large capacitance in there or (b) the lights are not connected through the 1-both-2 switch, but direct to one of the batteries.
Well that's my guess.
 
Do you have a shore power battery charger wired in? If so they allow a small voltage to pass between the batteries, so disconnect either one and you will still have a reading on your battery meter regardless of switch postion, it should however not be the full 12/13 volts, and I was assured by Sterling this is normal and will not drain the starting battery.
 
Well I was staring at it frowning for a while...and decided to come and get some advice in case I was missing the point.

Yes i do have shore power - but it wasn't plugged in.
I was removing the actual terminals off the battery - and the leads from the charger are attached to these so they were being disconnected too. i.e nothing was attached to the battery terminal I was disconnecting.

There's no third battery as I have been through this boat inside and out for three years...but I will look again! One of the reasons being that I was looking for somewhere to put a third battery for a while so have looked around extensively.

I just can't see how with just a +ve lead attached to one battery and nothing else how the cabin lights and switchboard would remain on...

Thanks for your ideas.

Jonny
 
Solar panel or wind generator?

For sure, there must be another power source feeding in upstream of the battery contacts UNLESS there is some other connection around the batteries or switches that you are not telling us about.

As for other batteries, are you sure there isn't a windlass or bow thruster battery, or a back up battery for VHF / GPS / Radio memory?
 
I would always disconnect the positive from each battery on mine as the negative is common. Not sure if I fully understand whether you have done this. Need to read it again.

Also, how are you testing to see if power is still on - is it something like a power hungry interior light, or something that just might have an internal battery (or feeding from similar).

Certainly a bit of a puzzle. Can never guarantee that you don't get feed from a failed rotary switch, but doesn't sound like the case here.
 
I am doing the same thing
[ QUOTE ]
I was looking for somewhere to put a third battery

[/ QUOTE ]
I have just had the same conundrum, disconnect battery 1 and on the position no1 on the switch I still had power at the main fuse board did it vice versa and still the same, I was not connected up to shore power. Take off one of the +ve leads and the common earth connecting the batteries to the battery charger, I am assuming you have fixed stepped charger that is wired up pemanantly, reconnect one battery, with the charger now effectively disconected you hopefully will only have power through the BOTH, or 1 of the switch positions.
 
I have a sterling 20 amp stepped charger I phoned sterling power up yesterday asking them if it was right that the 3 +ve terminals should allow a voltage to pass between them. The teccy assured me this was right as the charger needed to monitor both batteries, and the drain was so minimal it would take months flatten the starter battery.
 
So.

You were disconnecting the batteries, and leaving the terminals connected together through the charger control wiring.

Power from one battery was passing through this wiring to the battery terminals for the other battery.

The fault in the logic here is that the switch panel gets it's power from the battery terminals. Whilst disconnected from the battery (1 say), can still draw ower from the other battery via the charger links.
 
You must log in or register to reply here.

Share this page

Top