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Old 13-07-2012, 11:15   #1
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Adding additonal battery to house bank

We currently have a house bank of three 115 amp hour, wet cell, deep cycle, 12volt batteries -wired to give us a total of 345 amp hours. We also have a separate dedicated start battery. The house bank is on the port side of the engine, and consists of three batteries wired end to end. The start battery is on the starboard side, by itself. We are going cruising in November, and I have considered adding a fourth battery to the house bank. I will be replacing the current three and buying all new ones at one time, so there won't be any problem with mixing old and and new. Unfortunately, there is no room on the port side of the engine to house the extra battery. There is room, however, next to the start battery on the starboard side. To add this additional battery, however, will require me to wire new battery cable to that additional battery. The positive cable connecting this new battery to the last battery in line on the current house bank will be approximately 8 - 9 feet longer to get around the engine and to the battery location, as will the negative cable.

With the above in mind, is there any problem with wiring the batteries this way? Is there any problem with having this length of cabling between battery #4 and the other three batteries? Is there any loss of power, any issue with charging, or anything else I should know that would cause problems in adding this additional battery?

As always, thanks for the help. gchabs.
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Old 13-07-2012, 11:30   #2
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Re: Adding additonal battery to house bank

Having the bank split into different physical locations can cause the odd battery out to have some differences in charge/discharge rate. I'd suggest using over sized wire between the batteries to lower the resistance in the wire runs.

Also see this for wiring:
SmartGauge Electronics - Interconnecting multiple batteries to form one larger bank

As another suggestion, have you considered seeing if 4xGC2 batteries will fit in the same space? I had the same problem and found a battery box made for 4 GC2 batteries that fit in same spot.
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Old 13-07-2012, 11:36   #3
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Re: Adding additonal battery to house bank

except for the few times you have a large load running, like a mircowave, the extra length probably would really not make any difference as for the small current the line loss is going to be minor and the batteries will equalize out

Sure it will in theory have a difference, but as far as a practical thing, I doubt it

have the ground and positive cable go to opposite sides of the combined banks

but as Target says look at upsizing the battery boxes and use larger batteries to start with, I have 2 banks of 6V batteries combined for 460 AH.
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Old 13-07-2012, 12:05   #4
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Re: Adding additonal battery to house bank

I would wire it as a separate house battery bank. This has a lot of practical advantages, even if you keep the batteries paralleled most of the time.
This is particularly advantageous if it evens out the voltage drop in the wiring, which is often the case.
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Old 13-07-2012, 12:18   #5
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Re: Adding additonal battery to house bank

The loss due to length of wire run will cause problems down the road. I know this because I am married to the most anal retentive electrical engineer ever and this was one of his biggest complaints about the preexisting electrical system in the boat. That and shoddy wiring, but I digress...

If you need more amp hours, it makes much more sense as noelex stated to have 2 house banks and it is how our boat is now set up. (after months and months of work), We also have 2 starting batteries just in case one decides not to cooperate. I
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Old 13-07-2012, 12:47   #6
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Re: Adding additonal battery to house bank

One house bank is all you need..
We started with 4 lifeline 4ds.. after burning out the windless due to 40 feet of cable running to the front of the boat and having low voltage under power to the windless, we added 2 more 4ds in the forward compartment.. wired paralell... When we installed the watermaker in the forward head area, we adder 2 more.. and another 2 under the nave station so the SSB has the max voltage.. our batteries are mixed throuout the boat, 10 of them 4d lifelines, and all added at different times..
they are charged in combo solar and wind..
and I was told it wouldnt work.......That was 10 years ago and they are still working fine..
just keep a good eye on how they are charging.. ours are fully charged at 12.8 and 50% at 12.2 ......we've never seen anything below 12.6 on the worst day...
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Old 13-07-2012, 12:52   #7
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Using 4/0 cable with a 100 amp load at 13 volts, a 25-foot (round trip) run results in a voltage drop of only 1 percent. I doubt you ever experience sustained loads or charge currents even 1/2 that high. Tinned copper 4/0 cable is only $6.99 per foot if you shop around and avoid the big stores. Make sure the proper lugs are properly crimped.

But I would agree with whomever suggested the 6-volt route--that's what I did. Or you could look into 2-volt cells, which offer even more flexibility in terms of fitting into boxes.

Personally, I would not go with a second house bank. While two banks offer some added redundancy, which is nice, I think larger single banks offer more efficiency and longer battery life.
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Old 13-07-2012, 13:20   #8
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Re: Adding additonal battery to house bank

I like like having 2 banks! But I always run them as 1 though the selector switch, which is what I normally assume is the story.
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Old 13-07-2012, 14:22   #9
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Re: Adding additonal battery to house bank

On my Beneteau 2001 473 the house bank is split. The OEM version is 2 4Ds in front of the engine and a third 4D behind the water heater about 6 feet away. Virtually if not all 473's came this way from the factory. I have replaced my 4Ds with 6 trojan T105s. Two of the trojans have almost the exact same footprint as a 4D so I put them back in the same places. I charge with a Xantrex 100 amp/2000 watt charger inverter. No problems at all. As has been stated there is some loss but with the right cables it will not be a problem.
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Old 13-07-2012, 23:45   #10
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Re: Adding additonal battery to house bank

We have 5 batteries all in different locations connected with 2/0 cable to a central bus bar. The volt drop to each battery is absolutely minimal.

I would suggest moving all of your batteries out of the engine compartment as batteries do not like getting hot when charging. At 25 degrees C they gas at 14.4 volts, at 45 degrees C they gas at 13.98 volts, so the alternator regulator must have a temperature sensor to reduce the charging voltage. This reduces the charge time considerably.

Do not store sealed batteries in an engine compartment.

To make life easier you might also consider different sized batteries in different locations. This used to be considered bad practice, but Sabre yachts regularly do this with Lifeline AGMs.

Also consider replacing the starter battery with a very much smaller Red Flash or Odyssey AGM battery that can be mounted on its side almost anywhere.
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Old 19-07-2012, 11:35   #11
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Re: Adding additonal battery to house bank

Thanks to everyone for their responses. gchabs
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