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Old 10-09-2010, 18:24   #16
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Well it's complicated because I will soon be adding a wind generator and solar panels. I'm also going to add some refrigeration which will be a power drain as well. At some point in the near future a auto pilot, so it all adds up hence my desire to have a slightly larger bank. Of course, the debate rages on whether this should be one large bank, or several smaller ones that I switch between.

Thanks,

Thomas
Thomas, There is a difference between debate and advise from those that don't yet have all of the information. Bill's advise on one large battery bank is the best and the most efficient for a cruising boat. Based on what it sounds like you plan for the future, you certainly will want the most efficient system you can get and starting out right from the beginning is very helpful, not to mention cost savings. Chuck
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Old 10-09-2010, 19:23   #17
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I think in some ways this is kinda like which is better, a mono hull or a multi. Of course we all know mono's are better, but there are still uninformed folks out there who simply can't accept our brilliance! ;-) Isn't that a shame? LOL

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Thomas
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Old 10-09-2010, 20:10   #18
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Is it too late to rturn these batteries and come home with 2 single 4D batteries. A hell of a lot less crimping, and cabling. Not too large a bank that your alternater can't handle the load. Way way way fewer cables to move and lids to lift to check the water levels every few weeks. (less chance of acid burns!) And with a wind and solar gagets you'll hovering somewhere in the 75% (just a SWAG but that's where I've ended up) and won't need such a large bank in the first place.
Sorry I am off topic, it was what to do with the eight batteries not what I would do with them.

Kris

8 6volt batteris at about 60 lbs each is 480 lbs, hopefully sitting somewhere central and low in the boat.
Did I mention that 2 4D batteries will be heck of a lot easier to secure.
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Old 10-09-2010, 20:29   #19
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Well yeah a lot less, but a lot less ah too! I'm buying them for the ah not the weight. That said, they are fairly low (below the water line) but not at the lowest point of the bilge.

Thomas
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Old 10-09-2010, 20:44   #20
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Thomas,
I guess I asumed that you were aware of the bennefits of the single house bank by your stated plan. I was concerned about what seemed to be your plan of hooking two parallelled six volt chains together in series to make 12 rather than paralleling 4 12 volt chains made from 2 six volt batteries in series. Something to look at is the lead in and out of the series and the charging flow and possibly connecting all of the pos and neg terminals together on the series batteries, the pos to neg batch only if that makes sense. Yes more darn wires and connections, but trying to equalize the charging and discharging of the induvidual batteries is the goal for making those little cheap suckers last as long as you can. (I'm with you here!) Check out Nigel Calder's Mechanical and Electrical Manual. No, buy it! It should be on the shelf. Chapter 1 I think...
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Old 10-09-2010, 20:48   #21
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I did the mod you are proposing to my Ponderosa a couple of seasons ago. I used the Smartgage interconnect #4 that Pete posted. The one problem I didn't see coming was that I didn't replace the internally regulated (Delco style) alternator. The poor thing just poured out all the amps that it could back into the big bank till it had a meltdown. Replaced it with a Balmar externally regulated alternator and a 612 "smart" regulator and all has been fine since. About 70 nights on the hook over two summers. The Costco GC-2's made it 16 months without needing an equalization. Two one hour equalization shots brought them to an even SG. Still balanced after a month.
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Old 10-09-2010, 22:37   #22
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Thomas, this warrants a read about wiring up multiple batteries.

SmartGauge Electronics - Interconnecting multiple batteries to form one larger bank

Pete

Great link. That is really surprising.
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Old 11-09-2010, 05:38   #23
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It is an excellent article, and points up the importance of wiring multiple batteries correctly.

One thing I've found from my own battery research and testing is that with respect to the interconnecting cables, SIZE MATTERS!

I found this when testing battery resistances using a Micronics electronic tester. The size of interconnecting cables makes a HUGE difference.

The author of the referenced article noted this difference, and stated that 35mm cable is found in "good" installations. From my own testing, I'd say that 35mm (AWG2) is TOO SMALL. I now use not less than 1/0 cable for all interconnections of batteries which are co-located, and larger cable in installations where the batteries in a single bank must be separated.

Bill
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Old 11-09-2010, 15:52   #24
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Great link. That is really surprising.
Thanks, sadly I wired up my bank before reading it so now have a another job to do this winter, to do it properly. Thankfully we only have two house batteries so only one lead to move.

Bill, 35mm sq is quite big, what size are you recommending instead?

Pete
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Old 11-09-2010, 16:43   #25
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12 6v AGM's

works great
I liked your graphic.

I noticed you charged the bank from opposite ends of the bank but feed the house from the same end. Was there a reason?
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Old 11-09-2010, 17:40   #26
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I may have gone overboard, but I used 4/0 interconnects on the installation I described above. The feed lines to my Magnum 2800W inverter are 4/0. Didn't want to create any more resistance than necessary.
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Old 12-09-2010, 20:38   #27
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I noticed you charged the bank from opposite ends of the bank but feed the house from the same end. Was there a reason?


I don't think there was a particular reason, just the location of the alternator on the stbd side feeding the batteries on the stbd side first.

So geography of the bank.
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Old 12-09-2010, 22:04   #28
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12 6v AGM's

works great
You might think about feeding the positive buss from the other end of the battery bank (where your alternator is connected). This would make each battery set the same cable distance from the load.

All interconnect cables should be the same length and the buss' should connect to opposite ends of the bank. Since all cables have voltage drop, the goal is to make each battery the same cable distance from the load and charger.

Example: In your picture, if your cables are 2/0 and each jumper cable is 18" long, your top left battery set is .024 volts away at 25amp from the house buss compared to the lower left battery set. The far away battery set will have different usage characteristics over time.
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Old 29-09-2010, 06:42   #29
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Single bank hard to charge?

Isn't it very difficult to truly fully charge a single bank if you constantly have a draw on the batteries? You are changing the voltage and current profiles of the bank, therefor 'misleading' the charger.

With 2 banks your allowing your charger unfettered access to the bank it's charging. Doesn't this guarantee a much more complete charge?

Don't laugh I'm new to this, but why do the banks need to be the same size?

How are you charging your batteries? If your running your engine or using shore power to charge,, why not go with:
660Ah bank - House bank
220Ah bank - Reserve power, for when charging.

Or you could figure out how long it takes you to charge your full 880Ah bank from 50% discharge, and have a secondary bank, say ~100Ah or so that will go to 50% discharge during the time it takes to charge your house bank.

Then switch back to your house bank and charge your reserve/charge bank.
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Old 29-09-2010, 06:54   #30
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Joe,

It's a good question.

When you put a load on the batteries, the load will tend to reduce the voltage as measured at the battery terminals. How much reduction will depend on the size of the load.

Most battery chargers derive their "smart" charging profiles by measuring battery voltage. A lower voltage will tend to make the battery charger continue to supply current to charge the battery and, at the same time, supply current to the load. In other words, providing the battery charger capacity is larger than the load...almost always the case...battery charging will continue even while there is a load attached.

That said, flooded batteries will only accept so much current...usually in the 20-25% of capacity range. So, a 100AH battery is only going to accept 20-25 amps charging, so long as the voltage is held within the normal charging parameters (i.e., less than about 14.5 volts). Doesn't really matter how large the capacity of the charger is, the battery is only going to accept so much. After it reaches about 80% of capacity, it's only going to accept much less current...again, despite the size of the charger.

AGMs are different...they'll accept a LOT of charging current, usually much more than the charger capacity.

Your question seemed to imply that it might be better to split the housebank into two banks to ensure better charging. Don't do this. You're much better off with a single bank and a charger of adequate capacity (i.e., at least 20% of the total bank capacity and, preferably, at least 20% more than any anticipated load on the battery bank while charging).

Bill
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