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The Norfolk Broads Forum / Broads Boat Owners Q & A / Additional battery wiring
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Posted By Discussion Topic: Additional battery wiring

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Uncle_Nobby
Apr-28-2012 @ 2:02 PM                           Permalink
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Hello, looking for advice please... My boat has a 2 litre BMC engine, which charges a 110a starter battery and a 110a domestic battery.  When hooked up to 240v (most of the time), there is a Victron Centaur 20amp charger on board which charges both batteries.  

I need more juice when moored overnight as there are quite a lot of electrics on board, so I need to wire in another 110a domestic battery.  The Victron charger has a third output, so I can connect to that quite easily.

What about the engine charging/supply?  I need to keep it at 12 volts, and not suddenly whack it up to 24 volts and melt everything, so can anyone tell me how to wire it up please?  I can't remember the difference between 'in series' and 'in parallel' (school long time ago!)  

I also need to remove this second domestic battery for the electric outboard on the tender from time to time so need to connect up with quick release terminals.  

Please help, many thanks


Robin

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Apr-28-2012 @ 2:57 PM                           Permalink
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Hi Robin,

The hi-tech electricians will come on with minute detail but yes in principle you can tag another battery to your domestic bank to give you more/longer battery availability.  They need to be in Parallel (positive to positive, negative to negative).

The alternator on you engine will work harder for longer to replace the discharge, a bigger output might help.  Our boat has 2x 110amphour domestic batteries and 1x 110amphour engine battery all supported by a 40 amp alternator.  We were brought up in the days of minimal battery power and always switch light off hence we are not normally big battery users.

You will need to have the battery properly secured and vented to maintain your BSS compliance.  There are issues around an old battery and a new battery 'equalizing' it may be better to have 2 domestics of the same age.  There are safety issues around sparks and hydrogen from charging batteries when connecting and disconnecting.

Mal
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Uncle_Nobby
Apr-28-2012 @ 4:04 PM                           Permalink
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Thanks Mal

As the battery compartment is already vented, I think all I need to do is put another battery box next to the existing one, screw it to the floor and make sure I put the lid on with a strap.

Good call about old and new.  I can put the two existing batteries together and put a new one on the starter side therefore.  

As I need to put them in parallel (thank you!), I am not sure whether I will need to connect the 240v charger to the extra battery, or whether the charge will come through the 'original' battery.  

One of the reasons I need the extra battery is the D2 heater conks out after five minutes, and I suspect it's due to the battery voltage as it works fine when hooked up to shore power.  Seeing as this year looks like the heater will be needed until September, I do need to get it sorted.

Thanks again


Robin

Grendel
Apr-28-2012 @ 4:37 PM                           Permalink
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As mentioned above, parallel connection, positive to positive, negative to negative. if you want to have a quick disconnection, make sure the connectors can carry the maximum current. that is if connectors are allowed, might be worth checking what is acceptable to pass the safety certs. as mentioned the charger should cope, but will take longer to get a full charge.
Grendel


we do the impossible every day, miracles take a little longer

Uncle_Nobby
Apr-28-2012 @ 4:49 PM                           Permalink
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Great, thanks Grendel.  So no charger connection to the extra battery?

Thanks


Robin

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Apr-28-2012 @ 5:17 PM                           Permalink
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The single charger connection should be fine.  Add the other if you feel like it. Grebe has a single shore charger connection to the domestic bank via the isolator switch.  She has no charger connection to the engine battery - that tops up very quickly after start up.

Those D2 heaters require over ten amps for quite a long time when they start up.  It sounds like your domestic battery has a weak cell that fails under high load.  Does one cell need a lot of topping up?

Edited to add: A battery charger can make a battery with a failed/failing cell worse by 'boiling' electrolyte.

Mal
16E

I am always amazed at the theraputic properties of chocolate digestives.


This message was edited by 16E on Apr-28-12 @ 5:21 PM

psychicsurveyor
Apr-28-2012 @ 6:19 PM                           Permalink
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Might be worth checking if you should swap the batteries around as you are suggesting, engine start and domestic batteries operate and charge/discharge in a different manner, I am sure we have a battery expert on the forum. My supplier told me it was a bad idea to use domestic for starting, but then he was selling me a battery but i do trust him.


Mark

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Some days all I need is to have a
beer and be afloat.

BOATERS
Apr-28-2012 @ 10:34 PM                           Permalink
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I think you will find quick release clamps run foul of the BSS and have to be solid clamps .Hope this helps  Smile

Roy and Diane

Hope to see you on the river,

Stranger
Apr-29-2012 @ 4:34 AM                           Permalink
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Hiyas yes great keep the two 110a batterys together of the same age but i would be tempted to not use a leisure battery for starting purposes as they are designed to discharge over a longer period of time and not sudden bursts of 200 to 300 amps when starting i would sugest a 644 or 645 battery for the start circuit the numbers being different for polarity

have a nice day all the best Dave

Uncle_Nobby
Apr-29-2012 @ 2:17 PM                           Permalink
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Thank you all for your brilliant help and advice.  Swapping batteries, putting in new box, making cables and attaching terminal clamps this afternoon.

Thanks again


Robin

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