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Old 29 March 2010, 23:26   #1
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Battery Setup Question

I currently have 2 batteries, 1 connected to each engine and then the electrics connected to just one of the batteries. I recently drained one, figuriung out how to use the toys onboard. The other engine started fine, but took a good 10min to get enough power into the drained battery to start the 2nd engine and i had to attach jump leads whilst at sea.

I have been told to hard wire the -ve's together and then wire the +ve's via an isolator switch. Is this a good option? Or can i connect both engines to one battery and the electronics to the other and then join then the same way. Would the engine battery get over charged being connected to both engines?

Also, can any suggest anywhere that sells decents battery cables? As i need to get longer to move the batteries under the console, hence the decision on which way to connect them up after the move.
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Old 30 March 2010, 03:02   #2
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What you have described is normal - there are standard switch arrangements that would do what you want off the shelf - For example BEP do this and can also take care of charging the opposite battery as well.
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Old 30 March 2010, 05:32   #3
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As above - being able to "bridge" batteries is (should be) part of any twin isolator switch setup. From memory the Halmatics at work have three switches - one for each side and one for bridging the two banks, so when they have one bank of batteries flat (from leaving the bloody engine room lights on again, just to pick a purely random example...) you can start the good engine, bridge, start the flat side, and then have both alternators pumping charge into the flat bank for a while to bring it up, then open the connection and go back to normal.

The only other thing worth mentioning is that in the interests of battery life, it is worth charging any lead-acid batteries properly with a charger on shore power, as an alternator never really brings them right up to full charge if they have been flat.
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Old 30 March 2010, 06:54   #4
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Ed if you do a search under battery you will find a thread started 15th march by paul E that covers the bases.

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Old 30 March 2010, 08:17   #5
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Also, can any suggest anywhere that sells decents battery cables?
Dale Sailing, or you could try a welding equipment supplier.
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Old 30 March 2010, 08:17   #6
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The only other thing worth mentioning is that in the interests of battery life, it is worth charging any lead-acid batteries properly with a charger on shore power, as an alternator never really brings them right up to full charge if they have been flat.
And also as alternators are designed to top up a battery rather than charge it from flat not all types have any form of current regulation.
I found this out recently the hard way after bump starting the landrover when the lights had been left on, The hitachi alternator overheated when charging the flat battery and blew a diode, which in turn took out the regulator, which stopped regulation, the stator then melted, 100 for a
new one, could have been saved if I had charged the battery instead.
interestingly the old lucas ACR alternators don't suffer this problem as the iron core saturates limiting the current to a value the rest of the alternator can cope with.
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Old 30 March 2010, 20:24   #7
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That's what happens if you use a nasty foreign Hitachi alternator

I've never seen the problem on quite a lot of Land Rovers with flat batteries over the years but most/all would have been Lucas/Magneti Marelli alts.
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Old 31 March 2010, 07:21   #8
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how's anything going to overheat down there? too flippin cold init?
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Old 31 March 2010, 07:34   #9
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how's anything going to overheat down there? too flippin cold init?
Listen DP never mind the FI's you should be up here, what a lovely spell of spring weather!!

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Old 31 March 2010, 11:54   #10
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Its not too bad here today, 9.9c and sunny at the moment. did snow yesterday though, briefly still i keep telling myself its uphill from here on
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