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Old 22-09-2010, 16:02   #1
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Wiring Remote Battery Banks

I currently have one bank consisting of two (12v) wet duel-purpose batteries, under the aft bunk. My next big job is to add battery capacity (for refer and solar, ect.). I am thinking of going with six 6v for the house and a back-up (12v) starting batt on an echo charge. I was planing on putting a charger/inverter, echo charger, solar charge controller and starting batt under the bunk. Due to weight (port settee holds tools) and space the best place to locate the four new house batteries is under the starboard settee, unfortunately this splits my batteries apart and away from charging sources.

What suggestion do y'all have on the best way to wire the house bank? The max cable run could be up to 20 feet. Is it possible to wire the six batts so that they share an equal load?

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Old 22-09-2010, 20:48   #2
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You can do the math by choosing the voltage drop characteristics from any wire size chart. Although not an ideal design, for all practical purposes, if you choose the proper sized interconnecting cables, you'll be fine.
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Old 22-09-2010, 20:55   #3
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So size my further batteries properly and don't over size my nearer ones? And the cable resistances will 'equalize' them in a way? Interesting, thanks.
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Old 22-09-2010, 22:02   #4
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I hope the compartment under the bunk is well ventilated!
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Old 22-09-2010, 22:14   #5
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If it were me...I would split the two banks... as House 1 and house 2 with an ACR between them...you can still size the wire and draw from them both at the same time but one will get more draw or charge regardless of how close you come with your math.

Splitting them would give you the added benefit of monitoring them separately through a unit like a Link Pro for any variances due to cable lengths.

I would also start my engine off the house bats...with an echo charger or whatever on the emergency start battery.

In my case I start off the house bats and have a separate dedicated battery for the gen set...If I can get the gen-set going I can charge the house bank at 200 amps if need be.
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Old 22-09-2010, 22:17   #6
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Let's assume that you have a 2000 watt inverter which will draw about 200 amps DC at full load. Then size the wire to each bank to accomodate 200 amps. The minimum size will be #2 but that will cause a voltage drop of about 10% if all of the current is coming from the far battery bank. That might be ok if you rarely or never use the full inverter capacity and with that big voltage drop, if you do use it all maybe half of the current will come from the nearer bank of batteries so it is self compensating.

Purists would say that charging can get screwed up without perfectly symetrical wiring and identical batteries, but I never have bought into that reasoning. I think you will be fine.

Remember to put a 200 amp fuse at both ends of the run to each battery bank.

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Old 23-09-2010, 07:11   #7
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Originally Posted by RQF4 View Post
So size my further batteries properly and don't over size my nearer ones? And the cable resistances will 'equalize' them in a way? Interesting, thanks.
Not quite. The battery size is irrelevant for purpose of this issue in which you specifically asked about the wire runs. It's the size of the wire, not the battery, that is your problem. Forget about the battery capacity for this purpose and consider how the wire size effects voltage - the smaller the wire, the greater the distance effect appears.
You would be best served by reading up on wiring and voltage drop before proceeding.
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Old 23-09-2010, 08:11   #8
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Also have a read of the link I put on post no 3:

Eight Golf Cart Batteries in One Bank ?

However, how big is this boat? your profile says 30 feet and six batteries are a lot of weight. Can I ask why you think you need 6 batteries?

We have 31 feet and in harbour use 30 ah a day in a temperate climate with a fridge. Lots of laptop use might see this go to 40 or even 50 ah, but with two x 110 amp batteries in the house bank and a small AGM engine battery thats fine. Extended crusing might see us fit another 110 to the house bank, but not 6.

Why not 2 or 3 110 ah lead acid for the house bank and a small batery for the engine start. It doesn't need a large battery to start your engine, afterall how big is your car battery?

Save some dollars and a whole load of work.

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Old 23-09-2010, 08:20   #9
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Couple of points to add to other's prior posts:

1) You can equalize loads on all the batts that function in parralel as one bank by connecting all loads to the positive terminal of battery 1 and the negative terminal of battery "n" (n=last in bank).

2) You should evaluate the use of voltage-sensing "battery-combiner" relays as compared with echo-charge, if you haven't already done so. They are more efficient and usually cheaper.

3) I would skip the secondary start battery and use a battery switch to substitute your house bank as a backup to start the engine. That saves weight, space and money.

4) Use a LVD (low-voltage disconnect) if you have constant loads (such as refrigeration or anchor light) and worry about running the house bank flat and possibly causing permanent damage. A LVD set to 11.9 or 12.0 volts will run the refrigerator and keep you from destroying the house bank. (Food in small amounts is cheaper and easier to replace than batteries).

Most 12v refrigerators say they have a built-in LVD but those are all set too low to keep you from running the batteries flat (most are set at 10.5v). If you are using solar (or not) a number of solar charge controllers have an adjustable LVD function built-in. Two I have used are the Morningstar SunSaver mppt and the Xantrex C-12. You could feed the fridge from one of those even if you don't have solar. The C12 is under $100.
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Old 24-09-2010, 01:32   #10
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Quote:
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I hope the compartment under the bunk is well ventilated!
Yes, I'm adding a two pasive 1'x1' vents and a blower.
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Originally Posted by Stillraining View Post
I would also start my engine off the house bats...with an echo charger or whatever on the emergency start battery.
Yes, that's the plan.

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Originally Posted by djmarchand View Post
Purists would say that charging can get screwed up without perfectly symetrical wiring and identical batteries, but I never have bought into that reasoning. I think you will be fine.
I may be overestimating the effects of the unsymmetrical wiring

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You would be best served by reading up on wiring and voltage drop before proceeding.
I believe I have an adequate understanding of these concepts. Perhaps I did not present my question well.

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Originally Posted by Pete7 View Post
Also have a read of the link I put on post no 3:

Eight Golf Cart Batteries in One Bank ?

However, how big is this boat? your profile says 30 feet and six batteries are a lot of weight. Can I ask why you think you need 6 batteries?
Thanks for the link Pete, I read it in the other thread and it partly inspired this thread.

I may well have some calculations off but six 6v @ 225 ah gives me 1350ah with only 40% usable (50%-90%) gives 540ah which will allows us to use 180ah for three days with out recharging. Although as you point out may be overkill. I'm interested in our budget differences though. A refer drawing 5amps and running 50% of the time (12h/day) would draw 60ah alone would it not??

SailFastTri; your first suggestion would be the same as method 2 in the link above right? That would be alright but I'm trying the get a little better equalization such as in method 2 or 3.

I'm most concerned about the difference in draw/charge between my aft two batts and the forward four due to the extra ~20' of cable. Perhaps my question would be better stated as: Using 00 cable, this adds .0032 ohms of resistance to the forward batts over the aft ones. Is this really negligible over the lifetime of the batteries?

I'll try and post a diagram of my intended wiring tomorrow.

Thanks to all for the tips so far.
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Old 24-09-2010, 03:57   #11
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180 amps a day at anchor, are you running a mains electric fire or something

You are planning to spend lots of dollars and have a whole heap of pain installing this lot so that its secure etc. Can I suggest you first fit an amp hour counter for a while to see what you actually use. You may be pleasantly suprised that you don't need a 1350 ah bank on a 30 ft boat, never mind the weight.

Also if you do use 540 ah in 3 days how long will it take to charge the bank back up? hmm best part of a day with the engine running at speed is my guess. Actually I suspect you will use closer to 100 amps a day tops. Our fridge (refer) is quoted at 6ah, but uses about 3 amps each hour during the day, and much less at night, just depends on how many beers you drink.

So before commiting, install an amp hour counter for a while. Then when you know how much you are going to use spec the battery bank size. Finally work out how you are going to replace the amps after a couple of days. We use a solar, so our daily deficit of 30 amps is reduced to 20 amps hence needing to run the genny less and on fewer occasions. Charging batteries whilst at anchor via an engine alternator isn't efficient or good for a diesel. The good news is if you take this slowly you should be able to optimise your requirements to meet your needs in a cost effective manner leaving more dollars for a nice new shinney chart plotter

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Old 24-09-2010, 04:41   #12
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Our 36' boat now has a pair of 8Ds as the house bank with an optima for the start battery on an echo charge. We don't use electric refrigeration and have 110 watts of regulated solar power charging the house bank. Have used this system successfully for years.

We do not especially scrimp of use of electricity have halogen lighting, auto pilot, an extensive instrument package, espar heating and use a laptop etc.

We use the boat mostly in weekends these days and never have a power deficit. The solar amply recharges the system and when we run the engine for the refer and to make hot water, the high output alternator kicks in perhaps 25 amps.

Our "system" is design to give us hot water, cool the frig and top of the batts with about about an hr run time a day and considering we don't deeply discharge the 8Ds with this regimen I can't see why you a yacht of similar size and use would need more than a 500AH house bank and could probably do with less.

Sealed batteries are maintenance free and probably a good idea, although they cost a bit more. Out gasing and battery acid are a problem with wet cells and requires battery boxes - another expense - and complication.

Get some 8D, set them low as possible on the CL of the boat and use a small start batt with a high output alternator, smart charger and a monitor system and your good to go.Save the expensive wire runs putting batts allover the boat. Solar will keep you topped up all year long.
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Old 24-09-2010, 04:47   #13
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Actualy 6 times 225 divided by 2 (ie 12 volt not 6 volt) = 1350/2= 675 amp hrs.

Also as other have said, thats a whole lotta batteries for a 30 footer.

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I may well have some calculations off but six 6v @ 225 ah gives me 1350ah .
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Old 24-09-2010, 05:06   #14
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SailFastTri; your first suggestion would be the same as method 2 in the link above right? That would be alright but I'm trying the get a little better equalization such as in method 2 or 3.

I'm most concerned about the difference in draw/charge between my aft two batts and the forward four due to the extra ~20' of cable. Perhaps my question would be better stated as: Using 00 cable, this adds .0032 ohms of resistance to the forward batts over the aft ones. Is this really negligible over the lifetime of the batteries?

I'll try and post a diagram of my intended wiring tomorrow.

Thanks to all for the tips so far.
Yes it's the same as method 2. Method 3 adds many extra connections and each connection adds a very slight bit of resistance and potential for problems over time. Method 2 is the best, IMHO, and will negate "the difference in draw/charge between my aft two batts and the forward four due to the extra ~20' of cable".
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Old 24-09-2010, 11:36   #15
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Actualy 6 times 225 divided by 2 (ie 12 volt not 6 volt) = 1350/2= 675 amp hrs.

Also as other have said, thats a whole lotta batteries for a 30 footer.
Thanks Joli...That's what I got too but I failed math in school so what do I think I know...

To the OP...FWIW I only have 4 6v Trogn house bats in my 40 footer...But Im very anxious to get out there an see what my Link Pro tell me about them and us as "current users"...

I think the advice you got to install a battery monitor and do some hands on need analysis first is very wise indeed.

Always remember as well that your battery bank is only as good as its weakest link...if one goes bad it will draw down the rest....so the more you have in one un-isolated bank the larger that risk will be.
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