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Having been reading up in Books & Mags. about safety & stuff before we pluck up the courage to bung our boat in for the 1st. time, I've bought another Battery to match the one in the boat. They are 85ah. "Squadron" Marine & Leisure Batteries. (Lead/acid, sealed for life). Now, as recommended in the books ('cos I'm completely green with electrics & boats & stuff!!) I want to connect both Batteries. I have bought a 2 way switch to enable use of either or both Batteries, (or none!) but need to know how to connect the 2 Batteries together. I've bought a couple of books about boat electrics but they both seem to assume some degree of prior knowledge! A book I have about household electrics is brilliant, it actually shows pictures of switches, sockets, etc. and exactly where to poke yer' wires & things! Can anyone advise please?
Also, (encroaching upon your good nature even more) I am confused about the right sort of Battery charger to use for these Batteries. In the books it goes on about normal Car chargers not being refined enough for Marine Batteries, and you should only use specialised chargers (3-stage,4-stage, & heaven knows what other technical stuff they're goin' on about) which seem to cost from around £130 upwards. Any comments please?

Thanks! VL1500
:cool:
 

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I presume you have got a 1,2, both, off switch. To wire it in you connect the negatives of the battery together and to the negative on the boat. On the back of the switch there will be 3 terminals. Probably marked 1, 2, common. The boat's +v'e supply comes off the common terminal, positive on battery 1 to terminal 1 and so on.

Caution....do not alter the switch position when the engine is running. Some switches of this type dissconnect the batteries momentarily when the switch is moved and this will damage the alternator on the engine as the power is is producing has no where to go.

For this reason I am not a fan of these switches allthough there are some that maintain the battery connection as they are changed, the chance are that unless you specify this type when you buy you will get the disconnect type supplied as they are much cheaper to produce. If you just want the security of a second battery in case the first goes flat why not carry a pair of jump leads.

The type of charger you want is sold at places like Partco Motor Factors, for sealed batteries, buy one from a marine place you will pay twice as much. In normal batteries you belt a charge in and if the battery gasses a bit it is vented to atmosphere. In a sealed batery this is not an option so the battery has to be charged slowly to avoid gassing.
 

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Hi Folks,

I post this as an electrical engineer.

First and foremost, working with electricity in a boat or car with batteries is more dangerous than working with electricity at home. Not from electrical shocks but from the chance of a fire.

I would advise anybody contemplating an electrical job on a boat to have a good think first. If you have to consult a book for advice i.e. "What do I do next or how do I wire this up?" then I would suggest that you leave it to a quallified marine or auto electrician.

Cheers

Drew
 

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Hi VL,
I agree with Drew if your not realy sure and confident contact a qualified electrician, even if its only for advice on the installation. It also goes without saying all Chris has said is all Spot on.
That said with the right guidance and taking time to do it properly and safely, Im sure you can handle it. I have installed 2 x 110 amp Hr batteries on my boat. I used a Bep Marine 716 Switch gang complete with a Voltage sensitive relay. To be honest the swiches and relay cost just under £100, but they seem to be the business, I have put a diagram of how I have wired things up, but you may require something a bit different and I'm sure it could be taylored to suit.
Cheers Steve
 

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Hi Fishy Finger,

Great diagram. What size of cable would you recommend. Hope you see what I mean.

Cheers

Drew
 

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There is also an opinion that you should have battery fuses next to the battery to save any danger of shorts in the heavy cabling that goes from battery to switch, to engine and to distribution panel
 

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Hi Drew,
With you 100% Mate. Fuses fitted at the batteries is a good point , I must admit I do not have them fitted at the moment, Chris.
I work on the powerlines so Safety allways comes first so I'll be looking into fitting them. Another trip to Maplins then.
As regards to the cable sizing, all the main load wiring between the batteries, engine and battery switches is in 25mm Cu, then I have 2 seperate 6mm Cu feeds going to the switch panel and bilgepump circuits. These are additional to the boats original wiring which is in 4mm Cu. I have all the cables from the feeds terminate behind the steering consul in the cabin into soundsystem gold terminal blocks. The circuits are then individually fused at the correct rating for the equipment connected. As you know cable sizing depends alot on the length run and also how much heat can be dissipated away, thats where the Books and charts come in.;)

Steve
 

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Hi Fishy Finger,

Please don't think that I am criticising you, I'm not.

When it comes to vehicle wiring whither car or boats, if you have to ask questions, or, if you are unsure, then DONT TOUCH.

I have seen more fires started from batteries than anything else. Hence the reason that I would never assist in a thread regarding an electrical problem.

Cheers

Drew
 

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Discussion Starter #10
Hi ChrisP!

Thanks for the info., the instructions you supplied are just what I needed. Why can't books put things like that? Yes, the switch is as you describe, and it does warn in the books about switching when the engine is running! The bit about using jump-leads makes a whole lot of sense, (I'm kicking me all round the room at the moment for not thinking of something so obvious!) but being I've already bought the switch I might as well complete the job.

Fishy!

Much appreciate the diagram, it certainly simplifies things when you have a plan to follow. The cable sizes to use are also handy (essential?).

Drew!

Understand fully your concern, and appreciate the warnings! Don't worry, there is no-way I would attempt any electrical work unless I was sure of what I was doing. When I moved here to West Wales 15yrs. ago I new nothing about house wiring, and the old cottage we bought had no electricity! By doing as I am now, and asking questions and advice from folks that do have the knowledge, I gleaned enough info. to completely wire the cottage, including consumer unit, RCD's, MCB's etc. This then had to be all checked and passed by the Electricity Board before they would lay on power. Everything was A1. As you can tell from my posts I am very green with boats and boat gear, but not thick. (Honest!!).
Your advice to use a Marine Electrician is sound. Unfortunately because of the costs involved in doing this, it is not something we can afford to do. (Go on, say it, can you afford not to?) I appreciate that boat electrics is a whole new ball-game, with wet environment and added risks, but if I limit my involvement to just connect the 2 Batteries & the switch, I'm sure with all the info. provided by ChrisP and Fishy it should be pretty safe.

Thanks again folks, you're worth your weight in gold!
 
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