Battery Isolation Switch Wiring Hookup

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victory

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I have 2 12v batteries connected through an isolation switch which has 4 positions - 1,2,Both & Off.

Using this I was , initially , able to start the engine and run the instruments from either battery by selecting either "1" or "2" and , presumably , although I never tried it , "Both".

Recently , selecting "2" failed to produce any result and I first suspected a failed battery but , after replacing this without any result , I then suspected the Isolation Switch which I have just replaced , also without any change - i.e. selecting one of the batteries produces no current.

I know virtually next to nothing about electrics and , as I bought this boat second hand , I was as careful as possible to re-wire the new isolation switch in the same manner as the old switch although , as the two switches are not identical , even although both have the same selection positions , I'm not certain about the way I have hooked up the new switch internally.

There are 3 connecting studs on this switch - "1" , "2" , and a third the description of which I have forgotten.

Against the positions "1" and "2" there was an instruction which said to ensure these were the same polarity.

This I did by connecting the positives from battery 1 and 2 respectively to stud "1" and "2" on the switch.

I then connected both negative terminals to the third terminal.

On testing this hookup , by selecting either "1" or "Both" - I got the engine to start - these 2 positions also caused the electrics to work.

Selecting "2" produced no result.

Can anyone tell me from this description whether the hook up to this battery isolation switch is correct as described.

As far as I can tell the wire to which both batteries negative terminals are connected goes to the boat "ground" but I am not certain of this.

I'm wondering whether I shoud have connected both battery -ve terminals to the studs "1" and "2" instead of their +ve terminals and then connected both + ve terminals to the third stud on this isolation switch .

Any comments would be appreciated
 
Hi, I would expect to connect the positive leads fron each battery to terminals 1 and 2 and the positive lead from the starter motor to the third terminal. Both battery negatives will be connected together and then to the engine earth teminal. Dont connect positive and negative leads to the same switch, a short circuit could result, with spectacular consequences!

Peter
 
You should have had a big bang when switching to 1 or 2, as you connected battery pos to battery neg.
You are right that battery 1 and 2 positive go to pins 1 and 2. Both battery neg go to a common negative bolt. your positive electrical loads goes to pin three.
Do not go near 230 volt mains, based on the above description of your 12 dc wireing.

Brian
 
Don't use that switch anymore. Th connections you made are definitely and dangerously wrong. Possibly you don't have any current on position 2 because the connection there is melted.

The minus from the batteries should never be connected to the switch but to the engine block.

As halycyon posted the third connection is for the ship's panel. Since you connected the minus from the batteries over there you always put your batteries short what should result in a burnt through switch and even broken batteries and worse...

Connecting those switches is well described in "the 12 volt handbook"

But strange that on position 1 and both everything works.
 
Warning do not connect your negative leads to the switch, unless it is a double pole switch, which I doubt very much..
Only positive cables should be connected to the switch.
I suggest you get an electrician to have a look at it, your boat must at least be worth the price of one hours labour.
 
Persevere but be carefull. Ask lots of questions. I am convinced that you can't run a small boat on a "turn key" principal where you get proffessionals to do everything like you might with a car. It is too expensive/ hard to get good service and eventually you will need to understand your electrics when you get caught out. Boat electrics are unreliable because of the moisture/ corrosion problems.

So read books get a multimeter and fiddle with your electrics. You can't generally go wrong except as suggested fat wires from both positive and negative if connected together in the switch can cause burning meltdown and possibly fire.

The fat wires carrying high current for the starter do not have fuses however most of the lighter wiring for lights etc should be fused which means you burn out a thin piece of wire in a safe environment if you get a short circuit. Rather than melt your wiring in the boat.

Usually the heavy wires use red for positive and these go to the switch while the negative black wires join both neg. terminals together and go permanently to the body of the engine (earth) and a thinner wire goes off to your lights etc. Often to a common negative brass block. (convenient connection).

I would suggest that if you have ruinned your 1,2,both switch that you replace it with 2 individual simple isolation switches, capable of carrying starter current and used individually or in unison.

In simple terms you start on one battery or the other (alternating each start to ensure both batteries can do the job) then switch to both on for charging both batteries once the engine is started. If you have trouble starting on one battery you can try the other or use both at once to help the starting. Hence the backup concept of 2 batteries.
Many people always start and run on both batteries and so if and when one dies they don't know until the other dies also.
good luck..... olewill
 
Most sailboats that I have re-engined have had a birdsnest of wires and multiple single funtion battery switches, I have always tidied up the system as follows and the owners were happy to have a simple foolproof system.
Connect the engine earth and earth from your services together with all of your batteries negatives.
Decide which battery is your start battery and connect to terminal 1 on the switch, the services battery(s) connect to terminal 2. The 3rd pole is usually marked common goes to your starter motor and alternator, you may have a seperate cable from your alternator to the 3rd pole depending on what engine you have.
You also connect your boats services to this 3rd pole. It works thus,
Start the engine and run with it on 'Both', this way all the batteries get to 'work' a little and all will get charged while running the engine. When you stop or sail select position 2, then you can use the service batteries without draining the start battery. You can then in an emergency use power from either bank to power the motor or services.
In position 1 or 2 only that battery will supply power and get charged if the engine is running.
 
scary - you have just described the installation I made in my boat last month perfectly. Only small difference is that I have a big battery to start a big engine and a 'leisure' battery for the ancillaries so tend to start on the start one, then switch to both, then to ancillary when I stop the engine.

I had a 2 switch installation but they were cheap switches and I went through 2 in 3 years - the 12bothoff ones seem to generally be higher rated/more solid than many readily available single ones as well...........

victory - I suspect (given that you are still here to post...and that things run in 1 position, that you aren't actually connecting earths to the common terminal but that they (or one) are power. Definitely worth pulling it all apart and checking which one leads where. Then use a bit of red insulating tape (or a red cable tie, to both ends of any cable you are using on the +ve side and wire up as Spannerman's post. If when you check they are -ves then you are probably lucky that the switch and or batteries have failed........rather than arcing and or worse. By all means involve help but observe and understand.

Good luck
 
I will just add that my own boat had voltmeter in the dash which only showed how much the alternator was giving, so in addition I fitted one in the cabin connected to the 'common' terminal, this showed the voltage of which ever bank I had selected or total if on 'both' so I could see if one particular bank was getting charged or what the remaining voltage was.
And on some of the other installations the owner had an ampmeter which we connected to just the service battery side as thats the load we are most interested in, i.e. how much the fridge or autopilot was using, as its not necessary on the start battery side as the load is only while cranking and of no relevance.
 
As Duncan said, I don't believe you have connected the negs to the common of the switch or it wouldn't work and your boat would be a mess. I suspect you still have the original problem which is posiblya bad neg connection from the second battery. You need to follow the cables carefully and check that the neg's go to the same place but not the switch. Then you need to check the connections at both ends of the neg for the battery that doesn't work. It is posible that you have a duff battery so you do need a DVM. Get them cheap from B & Q.
 
I am currently wiring a change over battery switch too. Brand new made by AAA. I can clearly see the connections for Bat 1 and Bat 2 and there is another connector called "feeder" which I presume is goes to my switch panel. The thing is that I have two smaller connectors that are just marked "Field" and I have no idea what this is? Any ideas? I don't have the instructions for the switch.
 
It's the field connection on the alternator , do you have any electrical experience because I'm not very good at explaining how to do things like this , it's easier just to do it
 
Not really. The thing is that I have the wiring diagram for my Beta diesel and also a wiring diagram for a change-over switch set-up and see no mention of a field connection between the alternator and switch. Is this essential or optional and what is the purpose of the connection?
 
I would like to thank all who have replied with much concern for my safety after my initial post on the above subject which I now realise exhibited dangerous lack of knowledge on such a serious subject!

I would like to reassure all these kind folk that both I and my boat are still unscathed !

I now realise that connecting the negative terminals to the third stud on the Isolation Switch is COMPLETELY THE WRONG THING TO DO AND WAS AN INESCUSABLY ILL-INFORMED ACTION !!

However , that having been said , I have to add - , (in some mitigation for such a rash suggestion of mine), - that , being aware of my almost total lack of knowledge of battery wiring , I was very carefull to copy exactly the wiring hook-up from the old Isolation Switch to the new Switch.

This is what saved me from the dangers of my ignorance of "things electrical" !

On subsequent inspection of the wiring on my boat - (a second hand boat which had contained the old Isolation Switch) - I discovered that the connections which I had assumed were -ve terminals - ( all coloured black incidentally ) - are in fact the connection to the starter motor and the +ve connection to the "services".

Hence no explosions !!

It now seems that the reason for the electrical problem is that I originally mis-identified the failed battery and replaced the wrong one thereby leaving the failed one in situ!!

At least I now know a considerable amount more about battery hookups than I did a few days ago !!

Thanks once again for all the comments - they certainly helped me in this case .
 
Thestandard 1-2 off battery switch is, IMHO , unsafe as turnng it to off when the engine is running will probably blow the alternator diode stack. I try to wire up my boat so its difficult to do serious damage by making tthe sort of mistake that comes from tiredeness, seasickness or just not being very careful when giving instructions to a crew member.
The field connections are intended to interrupt the current through the field windings of the alternator when you switch the batteries off.
I'm afraid I have little idea how to do this.
 
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