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Old 24-10-2012, 02:19   #16
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Re: Very Overwhelmed

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Originally Posted by Dockhead View Post
....If you never use the start batt for anything but starting, and it has its own alternator, you don't really need to connect it to your solar and wind, so you don't need an echo charger.
All loads, windlass etc., should go to the Service bank so you only need a small starter battery. We don't use split charging but have a 5 watt solar panel just for the starter and an old VSR that can parallel the two if the starter volts get too low. That hardly ever happens here in the Med.
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Old 24-10-2012, 05:05   #17
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Re: Very Overwhelmed

This doesnt need to be an either/or question. My boat came with a battery combiner. I have since installed an echo charger. The combiner remains for emergencies but I have never used it that way. The echo charger allows you to never have to deal with which bank you are switched to. You are always drawing from the house bank and charging the house bank. The starter battery starts the motor and recharges from the house bank. Never have to touch a switch at all. I like easy. I like less things on my list of stuff to remember.
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Old 24-10-2012, 06:15   #18
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Re: Very Overwhelmed

Thank you for replies, My boat is 16tons. Can handle the weight no prob. She's not a speed demon and never built for that. We are adding to our systems in the future. Elect windlass,freezer etc. that's for all the batts and solar. Plus I got killer deal on new 8ds. Still slightly overwhelmed but I m thinking now to take one 8d out of second bank and adding it to the first for 3. 8d in house and just have one as start. As for echo charge or combiner still not sure.
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Old 24-10-2012, 06:22   #19
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Re: Very Overwhelmed

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Thank you for replies, My boat is 16tons. Can handle the weight no prob. She's not a speed demon and never built for that. We are adding to our systems in the future. Elect windlass,freezer etc. that's for all the batts and solar. Plus I got killer deal on new 8ds. Still slightly overwhelmed but I m thinking now to take one 8d out of second bank and adding it to the first for 3. 8d in house and just have one as start. As for echo charge or combiner still not sure.
More battery capacity is better -- of course! So if you really don't mind the mass of four 8D's on board, then -- combine all four into one fantastic house bank! And just buy a truck battery to start the main engine. Or if there's no place to put a fifth, even small battery, then you can do what you suggest -- won't hurt anything, but you will not be getting anything out of the capacity of the fourth 8D, and this deep cycle battery won't start your engine as well as a real starting battery, which is designed with thin plates to maximize CCA's.

As to echo charge vs. combiner -- I would go with echo charge (or better, DC to DC three stage charger). Combiner creates risk that you leave it set in the wrong position and kill all your batteries. You never want to use your start battery for domestic needs, and you will never need your house bank for starting except in some unlikely emergency, and jumper cables are good enough for that.
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Old 24-10-2012, 06:23   #20
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Re: very overwhelmed

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Same thing applies to the voltage combiner, there is a 0.5V drop across each diode. If your solar charge controller is putting out 14.4 volts your batteries only see 13.9. Thats ok for a start battery but not so nice for a second house bank your trying to get back to full charge.
There is no voltage drop in a combiner. The diodes inside are just small signal diodes used to collect the highest voltage to determine when to combine the batteries. A relay is used for the combining, and when combined, the batteries are essentially wired together with no electronics between them. There is a small amount of current used for the relay, but no voltage drop across its contacts.

Where you thinking of a battery isolator instead?

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Old 24-10-2012, 06:26   #21
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Re: very overwhelmed

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Yes, you are "over kill." Four 8Ds on a 37' sailboat with minimal consumption is excessive, especially on a boat with 375 watts of solar. You say you are living aboard? How low below the boat's original waterline does she sit now? Can she sail at all?

My guess is that your real problem isn't power; it's weight. Trade two of those 8Ds in on a group 27 starting battery. Switch the 1/2/both switch out for a proper combiner. Trade all those movies you've already watched for a Kindle or Nook, and teach yourself the lost art of reading.

Freedom, my friend, is realizing you don't need 720 AH of battery capacity on a 37' boat.
What a view you must have from that high horse

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Old 24-10-2012, 07:09   #22
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Re: very overwhelmed

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My logic with the two 8ds in each bank was that I could get tons of starting power but also alternate them weekly to get longer life?
In fact, by alternating them you are probably shortening their life.

In general, batteries will last longer the less deeply they are discharged. If you had all of these batteries in one bank you would discharge that bank half as deeply as you discharge the split banks. Hence, the batteries would almost certainly last longer.

With only one bank, though, you would not have a backup for starting the engine in case you inadvertently run the house batteries too low. So split off one battery for starting and combine the others, or get a smaller starting battery and keep it separate.

Just to reiterate my main point, though, for best battery life you want a large bank that is subject to shallow discharges.
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Old 24-10-2012, 07:25   #23
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Two 8D batteries are enough to start roughly 5000 hp worth of engine. What the hell do you need that much starting current for on a 38' sailboat?
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Old 24-10-2012, 07:34   #24
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Re: very overwhelmed

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In fact, by alternating them you are probably shortening their life.

In general, batteries will last longer the less deeply they are discharged. If you had all of these batteries in one bank you would discharge that bank half as deeply as you discharge the split banks. Hence, the batteries would almost certainly last longer.

With only one bank, though, you would not have a backup for starting the engine in case you inadvertently run the house batteries too low. So split off one battery for starting and combine the others, or get a smaller starting battery and keep it separate.

Just to reiterate my main point, though, for best battery life you want a large bank that is subject to shallow discharges.
+1

Exactly right. On top of the shallow vs. deep discharge issue, you have Peukert's equation -- you will actually use more power out of a smaller bank if you run anything with a high load (like an inverter). So one big bank is much better than two banks of half the size. Will last longer and will be easier to use.

Yet another argument for this is charging -- by about 80% charge, your batteries will be accepting only a fraction of the charge from your alternator which they were accepting at 60%. So with regular lead-acid batts, you are mostly only using that range between 50% and 80% charge anyway. Your bigger bank with four 8d's will accept twice as much energy from the alternator between 50% and 80% than a bank of two. So you will capture more energy when it's abundant.
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Old 24-10-2012, 09:49   #25
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Re: very overwhelmed

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Originally Posted by sailorchic34 View Post
So you have 2 8D's per side??? Seems like more then enough. I just have two Group 27's per bank (I can just lift a G27) and don't have a separate start battery.

I have the solar connected to my DC panel Buss which connects to the battery switch with a short bit of #2 I believe. I just use the battery switch to charge which every battery i'm using. Plus may switch over to the opposite bank half way thru the day if needed. Simple is good... Been working for me for years...
I'm of the same thinking. Guess I'm old fashion that way. I have 3 G31's to run the boat and a G24 to start the engine. I have 250 watts of solar through a MPPT to the DC buss to the 1/2/both switch. It's not perfect but it has always worked.
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Old 24-10-2012, 10:37   #26
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Re: Very Overwhelmed

As mentioned several times, the idea of alternating your house batteries has gone out the window. The batteries will last longer, charge faster, start your engine easier, and smell better if you use them as one giant bank.

You also should have plenty of charging sources to keep your batteries topped up for your minimal use (unless your fridge is 110v). What you will need to do is actively manage the wind generator, because you may overcharge the batteries if you don't.

You didn't mention what kind of 8D's you have. If they are regular truck starting batteries, you didn't get a great deal--they will not last many discharge cycles, and are more tolerant of overcharging, but not tolerant of undercharging. If they are gel, they are very tolerant of under charging, but overcharging will kill them in a matter of hours. If they are AGM, its kind of the worst of both worlds. Each type of battery takes a different management regime, and a battery monitor will help.

In any case, I am going to recommend that if you are living aboard you just use the both switch to tie them into one bank and forget about a separate starting battery, combiners, echo chargers, and the like. You have enough capacity and charging sources that it will take a number of cloudy windless days to drain your batteries down to 11.5v, and even then they will have plenty enough left to start the engine. The other thing you have to worry about is a shorted cell, but this is a very unlikely event and you have a big enough wind generator and solar array to get the engine going in less than a hour or two once you get the bad battery isolated.

Combining all the batteries into one bank worked well for me for 15 years of living aboard and one shorted cell at 0300 hours (why is it always 0300??).
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Old 24-10-2012, 10:45   #27
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Re: very overwhelmed

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There is no voltage drop in a combiner. The diodes inside are just small signal diodes used to collect the highest voltage to determine when to combine the batteries. A relay is used for the combining, and when combined, the batteries are essentially wired together with no electronics between them. There is a small amount of current used for the relay, but no voltage drop across its contacts.

Where you thinking of a battery isolator instead?

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Old 25-10-2012, 07:33   #28
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Re: Very Overwhelmed

"What's all this talk about making Puerto Rico a steak? Maybe they would prefer chicken. Some of them might even be vegetarians..."

And then one of my favorites...

"Why is everyone talking about presidential erections? That's no body's business but their own!"

We definitely lost a good one, way too early, when Gilda Radner died.
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Old 25-10-2012, 08:55   #29
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Re: Very Overwhelmed

"What's all this fuss I'm hearing about conserving our natural racehorses?"

Or the ones about "endangered feces" and "violins on television"...

Definitely one of the best.

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Old 25-10-2012, 13:13   #30
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Re: Very Overwhelmed

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Combining all the batteries into one bank worked well for me for 15 years of living aboard and one shorted cell at 0300 hours (why is it always 0300??).
I agree on both counts. A big, single bank can work well, especially if you are onboard most of the time and monitoring things, and 0300 is exactly when things go wrong, but most often when it is blowing like stink, you're on short scope, and there is very little room to drag.
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