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Old 19 February 2008, 17:29   #1
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Charge splitting/isolators

My old boat had one oversize battery through a Hella Isolator which was fine, the new console is huge and I am thinking of installing two batteries of the proper smaller size but linked for redundancy.
I want to run switched to one battery and have the second battery charged through a blocking diode so it is always charged and available. I would prefer one with the necessary diodes built in if possible and with the capability of switching to battery two or both as the needs may be. All the boat is to be run off the one battery with the second only for backup.
I don't really want to go for switching to keep batteries charged so Is there an isolator out there, preferably a good one from Blue Sea or Hella, that will do what I want?
Or is there a better way of doing this?
The c/b switch panel mentioned in the archives, all OK after some use? I am going down the same route and would appreciate reliability info before spalshing out the large amounts of cash from anybody using them?
Cheers
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Old 19 February 2008, 18:23   #2
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"BEP" VSR Voltage Sensitive Relay has provided the best solution for me. Not cheap, circa 50.
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Old 20 February 2008, 00:43   #3
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Further to my first reply I have looked on the BEP website (www.bep.co.nz) and they have at least 2 combined switch/vsr units, one of which would probably suit your needs. Either 714-100A or CC-801 are the simpler solutions, there is lots of other information under "Battery Management".
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Old 20 February 2008, 02:17   #4
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Your average twin battery isolator would suit your needs wouldnt it? Most can switch between batt 1 - batt 2 - both - off. Switch to both while underway to keep both charged and switch to either batt 1 or batt 2 if you are stopping for any length of time to keep one battery spare for engine starting etc.

Saves paying money for sensitive electronic charging gear which probably wont handle the rib environment.
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Old 20 February 2008, 02:18   #5
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Merlin are very helpful, just give them a call for some good advice.

Their product web site is Power Store.

Tim
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Old 20 February 2008, 02:25   #6
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Hi

I use the Blue sea kit very nice

http://bluesea.com/category/1/productline/overview/329
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Old 20 February 2008, 07:44   #7
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Quote:
Originally Posted by martini View Post
Your average twin battery isolator would suit your needs wouldnt it? Most can switch between batt 1 - batt 2 - both - off. Switch to both while underway to keep both charged and switch to either batt 1 or batt 2 if you are stopping for any length of time to keep one battery spare for engine starting etc.

Saves paying money for sensitive electronic charging gear which probably wont handle the rib environment.
Agreed
Keep it simple in 'our environment'.

I use 2 similar sized batteries, and a switch as above.
I use Batt 1 on the outward trip, and Batt 2 on the return.

Nasher.
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Old 20 February 2008, 08:12   #8
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A cheap and cheerful way to do what you're trying to do would be an "OFF-1-BOTH-2" switch

Make sure you get a 'Make before break' connection

OK so you're running your engine, switch to BOTH. That way both batteries will charge
Say, when you anchor up and have the stereo/vhf/whatever running, switch to battery 2
Then when you want to start your engine, switch to 1 and your engine will start
Then switch back to BOTH

You can install a diode to stop reverse charging, but since you're only going to have 1 battery running at a time, and when both are connected they're going to be charging, whats the point? My boat has a split-charge-diode in place but I could live without it - it was there when I bought the boat (I only ever really use 1 battery at one time)

Obviously I leave it at BOTH if im only going to be anchored up for a short while - I guess this is where the diode comes into play

-EDIT- I see that my above post has already been mentioned, d'oh
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Old 20 February 2008, 08:29   #9
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Answered my own question when i looked properly Duh
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Old 20 February 2008, 10:16   #10
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Avoid blocking diodes at all costs as they will prevent the 2nd battery from getting fully charged. Average voltage drop over a diode is .7V which varies with current and temp.

Batts need to be charged to 14.4V to prevent sulphanation (usually in 3 steps - bulk, absorption then float). 2nd batt will never reach this with a diode.

I have always used switches in multi-batt installations and they have worked really well. It also allows you to easily compensate if the engine start battery dies for example - the only thing this setup does need is for you to remember to switch the switch at appropriate times!

Failing that, VSR's are great and relays are not that sensitive - fine for boats.

Ideal soln would be a proper intelligent split circuit charger but they are expensive!

You could always have a batt switch plus a VSR :-)
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