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Old 07-03-2013, 21:03   #31
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Re: wiring solar output

While I could run my two banks as one with the switch in "BOTH", the two sets are not the same age and I have had issues in the past with an older battery pulling down the good ones.

Plus the closer set of batteries would draw down a tiny bit faster due to lower ohms in the closer set wiring. So not quite equal wear on the batteries when they are not located in the same area. Least I think that should happen.
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Old 07-03-2013, 21:12   #32
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Re: wiring solar output

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Originally Posted by FlyingCloud1937 View Post
Or maybe if you were running one super bank then you wouldn't have a cell level failure.

If you did, then either by wire or by switch you could have taken the cell level bat that failed off line.

Power Design is about equal amounts of charge/Discharge, or/in other words charge cycle management.

It really isn't difficult.

Lloyd
Hum, The problem is once a battery cell shorts out, it will pull the rest of the batteries in that bank down. That can cause damage to other batteries in the group as well. More then likely before you notice the problem. Cell failure happens regardless of if its a single battery or a group of 10 or more. Just ask Boeing about that....
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Old 07-03-2013, 21:17   #33
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Re: wiring solar output

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Originally Posted by sailorchic34 View Post
It also gets me in the habit of checking voltages a few times a day.
sailorchic34 -

i don't have one of those fancy amp counters; i use a digital voltmeter to check for battery level, for which i've been crucified on this forum. i'm also not an electric whiz. so tell me why and how you use a voltmeter when all those with great minds (and deep pockets) insist i need an amp counter.
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Old 07-03-2013, 21:19   #34
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Re: wiring solar output

Great advice guys - thanks
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Old 07-03-2013, 21:40   #35
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Re: wiring solar output

OneStep -

Every installation I do for someone else includes some form of amp/energy counter for battery monitoring. It's expected, and if your head isn't involved it may even be needed.

My own boat has a voltmeter and an ammeter, nothing else. Don't even have a regulator on the alternator, just a rheostat. Only thing that has a controller is the solar panels. The controller for everything else is me being involved in the process. Also not a popular approach here or anywhere else.
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Old 07-03-2013, 22:14   #36
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Re: wiring solar output

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ok, so I could install the Duo charge device between the 2 house batteries with the same result?
Morningstar duo charge solar controller. I fitted one, it works a treat and NO hassle or fiddling with anything. Keeps both banks separate. Couldn't be happier.
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Old 07-03-2013, 22:34   #37
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Re: wiring solar output

Flying Cloud, yes if it was switched that way. Unfortunately it wasn't but I hear you - it shouldn't be difficult
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Old 08-03-2013, 09:50   #38
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Re: wiring solar output

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sailorchic34 -

i don't have one of those fancy amp counters; i use a digital voltmeter to check for battery level, for which i've been crucified on this forum. i'm also not an electric whiz. so tell me why and how you use a voltmeter when all those with great minds (and deep pockets) insist i need an amp counter.
Well I too only have a digital Volt meter. But then my electrical load are simple and don't really change day to day. Oh I have a clamp on amp meter but don't normally use it day to day.

Now a volt meter is only good for checking SOC on the resting battery set. Its not perfect but then again nether is the battery monitors. I also after a few years can look at the voltage of the active set and can pretty much figure out the SOC in the active bank. well after the suns down anyway.

The thing to remember is the voltage of the active bank under load will be lower then SOC. If you have only one house bank, it may be hard or impossible to figure it out. I use two separate house banks (no start battery) so can compare active and inactive readings.

Now if you have lots O toys on the boat or a single house bank, then a battery monitor might be a good idea. But for fridge, lights and computer, I find that the volt meter is fine. But then I do a lot of things that many folks here say will not work... To date that includes the DC volt meter, using 120V refrigeration, two house banks, back stay mounted anchor light, just to name a few.
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Old 08-03-2013, 10:30   #39
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the use of a 1-2-all switch is still used because thats the way it has always been done and its in most boats.
But it is old and outdated. I removed mine years ago and went with a larger bank.I just tell the grand kids to flip the house or engine switch and all is well. I find that I use the same power but discharge the entire bank less. Discharge use of 25% insted of discharging to 50% I feel it gives the bank a longer life by not over discharging. I can combine if needed but why would you combine a low bank with a charged one. I do have a seprate start batt.
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Old 08-03-2013, 10:47   #40
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Re: wiring solar output

Guess I'm just an old fashion girl and a new fangle world. I mean I still think a Bruce type anchor is pretty good. It does not budge in 50 knot winds. A bugger to get back up too after that, let me tell you...

It should be noted that most of the time, my batteries are only 25% down after a night of work. But then My boat is almost Amish, just plain and simple..

I'm still surprise my netbook does not have tubes in it...
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Old 08-03-2013, 11:12   #41
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Sailorchic, your just a analog girl in a digital world!
PS my favorite kind
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Old 08-03-2013, 11:37   #42
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Re: wiring solar output

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Originally Posted by sailorchic34 View Post
Hum, The problem is once a battery cell shorts out, it will pull the rest of the batteries in that bank down. That can cause damage to other batteries in the group as well. More then likely before you notice the problem. Cell failure happens regardless of if its a single battery or a group of 10 or more. Just ask Boeing about that....
It's pretty rare that this happens but if it does the bad battery can always be manually isolated.

Nigel Calder makes a very succinct argument against multiple house banks.

"(By Nigel Calder)

IS IT BETTER TO HAVE ONE OR TWO BATTERY BANKS FOR HOUSE USE?

The popular arrangement of having two house banks alternated in use needs scrutiny before I go any further.

LIFE CYCLES: As we have seen, the life expectancy of a battery in cycling service is directly related to the depth to which it is discharged at each cycle - the greater the depth of discharge, the shorter the battery’s life.

This relationship between depth of discharge and battery life is NOT linear. As the depth of discharge increases, a battery’s life expectancy is disproportionately shortened. A given battery may cycle through 10% of its capacity 2,000 times, 50% of its capacity 300 times and 100% of its capacity around 100 times.

Let’s say, for arguments sake, that a boat has two 200-ah battery banks, alternated from day to day, with a daily load of 80 Ah. Each bank will be discharged by 40% (80 Ah of one of the two 200 Ah banks) of its capacity before being recharged. The batteries will fail after 380 cycles, which is 760 days (since each is used every other day). If the two banks had been wired in parallel, to make a single 400 Ah battery bank, this bank would have been discharged by 20% of capacity every day, with a life expectancy of 800 days, a 50% increase in life expectancy using exactly the same batteries.

But now let’s double the capacity of the batteries, so that the boat has either two 400 Ah banks, or a single 800 Ah bank, but with the same 80 Ah daily load. The two separate banks will be cycling through 20% of capacity every other day, resulting in a total life expectancy of 1,600 days. Doubling the size of the battery banks in relation to the load has produced a 210% increase in life expectancy. The single 800 Ah bank will be cycling through 10% of capacity every day, resulting in a life expectancy of 2,000 days - a 25% increase in life expectancy over the two (400 Ah) banks, and a 250% increase in life expectancy over the single 400 Ah battery bank!

There are two immediate conclusions to be drawn from these figures:

1. For a given total battery capacity, wiring the (house) batteries into a single high capacity bank, rather than having them divided into two alternating banks, will result in a longer overall life expectancy for the batteries."

End quote:


I set up cruising banks quite regularly and the benefits of a single large bank are:

#1 Less cycling depth, which equals longer life.

#2 Any benefit of the Peukert effect which gets cut when you cut the banks in two.

I tend to suggest one large bank for reasons beyond even what Nigel Calder touches on.

It is more efficient to charge one bank than two, unless using 100% free energy. Even then, with solar or wind, the time allotted to "finishing" two banks is less efficient due to the longevity of the time the bank spends acceptance limiting and the time the "finishing" charge takes.

The single larger bank will also not be as dramatically affected by Peukert effect and you'll actually wind up with more usable amp hours out of a single larger bank, with the same daily load, than you do with two smaller banks using the same average daily load. By cutting the bank in half you lose both the positives of size on DOD and the Peukert effect.

For example a bank with a Peukert of 1.25 and a average load of 8A it looks like this:

100Ah bank, Peukert 1.25, load 8A = 88Ah's
200Ah bank, Peukert 1.25, load 8A = 211Ah's
300Ah bank, Peukert 1.25, load 8A = 351 Ah's
400Ah bank, Peukert 1.25, load 8A = 502 Ah's
600Ah bank, Peukert 1.25, load 8A = 834Ah's
800Ah bank, Peukert 1.25, load 8A = 1200 Ah's

By using a single larger bank, and considering the Peukert effect, it means that your bank will have shallower discharges, not just because it is one large bank, but if the average load stays the same, and you increase bank size, you will actually get more out of the larger bank due to Peukert.

Something to consider anyway. You can always run them as one bank and keep a hidden isolation switch too.
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Old 08-03-2013, 12:18   #43
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Re: wiring solar output

Ah, Nigel and I don't always see eye to eye. Think he said 120V refrigeration does not work either. Yet I use my magic chef unit at anchor and find it pulls no more amps in 24 hours then a typical 12V unit. BTW I did that as an experiment, as everyone (quoting Nigel) said it would not work. While the amps running is higher, the run times are quite short, even in 90 ish cabin temps.

I have combined the two banks into one from time to time and tried just leaving the battery switch in both. I found that I got to 80% SOC faster keeping the batteries separate. That's using solar. If running the engine, many times I'll run the switch in both.

While I agree that Nigels statements are quite correct as far as they go. Having two separate battery banks with different cabling lengths changes the ohms /charging rate to each set. That is the battery banks are not balanced so one tends to take more charge then the other. Its not much, but with low amp solar charging, I thing there can be some downside to using two separate sets as a common house bank.

Hum the Peukert effect is related to effective amp/hr where a higher amp load reduces the effective amp capacity of the batteries. So the typical 12V LA battery is about a n=1.2 ish for the peukert equation. That's slightly different then overall SOC. Agreed that a bigger house bank, properly wired is better.

If I had the space I would place all four batteries adjacent to each other with a reverse return (pos fed from one end, neg from the other) to balance the charge rates across the batteries. As I don't, I find from trial and error that for me charging the banks separately from solar works (for me) better. YMMV...

With a boat at anchor its probably better to get the batteries up to 80-90 ish percent then trying to get the last 3-4 percent. Not sure that happens.Not for me anyway..
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Old 08-03-2013, 12:44   #44
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Re: wiring solar output

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By using a single larger bank, and considering the Peukert effect, it means that your bank will have shallower discharges, not just because it is one large bank, but if the average load stays the same, and you increase bank size, you will actually get more out of the larger bank due to Peukert.
AH No... the Peukert effect is a subtractive effect. You can't get more then 400 amps out of a 400 amp rated hour bank. The Peukert effect reduces the effective amp capacity due to higher amp discharge rates. But it does not work in reverse.

At rest you have a 400 amp hour bank. As amp draw rises the effective capacity of the bank is reduced. The more amps drawn the more its reduced. So a high amp load might reduce the effect amp capacity by 50% or more. Depending on battery type.

AGM has the lowest factor, gel the highest and LA in the middle. The overall effect is the same ratio weather its a 200 AH bank or a 1200 ah bank.

But you never get more amps out of a rated bank then what its listed for. Not in this universe anyway...
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Old 08-03-2013, 12:45   #45
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Re: wiring solar output

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While I agree that Nigels statements are quite correct as far as they go. Having two separate battery banks with different cabling lengths changes the ohms /charging rate to each set. That is the battery banks are not balanced so one tends to take more charge then the other. Its not much, but with low amp solar charging, I thing there can be some downside to using two separate sets as a common house bank.
Yes if they are not wire appropriately this can happen. I have a number of customers with half the bank on one side of the boat and the other half on the opposite side. Not ideal and I'm not a fan of it but it can be done. Neg goes up port and positive goes up starboard or vice versa. The parallel wiring is then carefully matched lengths of appropriately sized wire. I've not measured any intrabank imbalances on these set ups when done this way. When set up with pos & neg feeds on just one side of the boat I can and do measure intrabank imbalances.
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