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Old 09-23-2011, 03:44 PM   #1
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Series/Parallel or Parallel/Series

Most coaches that I know of (Monaco) which use four (identical) six volt batteries for the house 12volt power have their batteries wired in a series/parallel arrangement. The pictorial diagram below shows this. Each pair of 6 volt batteries is made into a 12 volt "battery bank" with the same AH capacity. Then these "12volt battery banks" are connected in parallel resulting in 12volts at double the AH capacity.


However there's another possible way that 12 volts could be achieved from the four six volt batteries, that is, to connect each pair of 6 volt batteries in parallel, creating a 6 volt "battery bank" with double the AH. Then the two 6 volt "battery banks" are connected in series resulting in 12volts at double the AH capacity.


The end result is the same, but wiring a bit different. There may be advantages and disadvantages of each. Essentially the second setup differs from the first in that the "midpoints" of the two + to - connections are in common. Knowing that in any parallel battery circuit, the slightly stronger battery will be "drawn down" from by the weaker, does this variation provide advantage or disadvantage? ... Reasons?
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Old 09-23-2011, 04:04 PM   #2
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This is good. I don't know why but I have never thought of this. The only time where I would see the use of parallel/series would be in cold weather when you need the extra cranking amps. Great Post!!
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Old 09-23-2011, 04:55 PM   #3
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re: "in any parallel battery circuit, the slightly stronger battery will be "drawn down" from by the weaker,"

this is one of those myths some seem attached to.

for a battery to draw down another, it would have to be at a lower voltage. Parallel connections, by definition, have the same voltage at the connection point.

you might get some traction out of this myth by positing the normal internal discharge rate. That is a bit higher in an older, 'weak', battery, but that amount is very small and the only scenario where it would be an issue would be in storage where the batteries were not properly maintained.

A good resource on this topic (optimum battery bank wiring) is smartgauge.com.
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Old 09-23-2011, 05:17 PM   #4
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re: "in any parallel battery circuit, the slightly stronger battery will be "drawn down" from by the weaker,"

this is one of those myths some seem attached to.

for a battery to draw down another, it would have to be at a lower voltage. Parallel connections, by definition, have the same voltage at the connection point.

you might get some traction out of this myth by positing the normal internal discharge rate. That is a bit higher in an older, 'weak', battery, but that amount is very small and the only scenario where it would be an issue would be in storage where the batteries were not properly maintained.

A good resource on this topic (optimum battery bank wiring) is smartgauge.com.
Maybe "drawn down" is the wrong terminology. Let's see, two batteries "A" 12.2v and "B" 12.1v. Connect in parallel (no load); before connection, "A" is 0.1 v higher in potential. Won't there be current flow between battery "A" to battery "B" until the voltage at the terminals is the same?

PS: the link"smartgauge.com" goes to a website about aptitude tests.
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Old 09-23-2011, 05:19 PM   #5
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This is good. I don't know why but I have never thought of this. The only time where I would see the use of parallel/series would be in cold weather when you need the extra cranking amps. Great Post!!
These are house batteries so cranking amps was not an issue. The resultant AH at 12vDC should be the same.
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Old 09-23-2011, 06:34 PM   #6
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Quote:
Originally Posted by rpasetto
There may be advantages and disadvantages of each. Essentially the second setup differs from the first in that the "midpoints" of the two + to - connections are in common. Knowing that in any parallel battery circuit, the slightly stronger battery will be "drawn down" from by the weaker, does this variation provide advantage or disadvantage? ... Reasons?
Here's a link to a website that may lead you to an answer. Check the other info on this website for more than you ever wanted to know about batteries.

If you don't find the answer to your question, use their 'contact' feature for a specific answer to a specific question. I've asked them battery questions before and found them to be responsive.

Take care,
Stu
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Old 09-23-2011, 06:39 PM   #7
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These are house batteries so cranking amps was not an issue. The resultant AH at 12vDC should be the same.
Your right.
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Old 09-23-2011, 06:40 PM   #8
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Here's a link to a website that may lead you to an answer.
Stu

What website we talkin' about here Stu????
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Old 09-23-2011, 06:51 PM   #9
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Sorry, maybe I'm missing something. I'm failing to see the advantage of the extra complexity/connections/wiring in the second example? KISS logic will normally rule?
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Old 09-23-2011, 06:52 PM   #10
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Originally Posted by KIX

What website we talkin' about here Stu????
Doh!!!

Oh, dopey me.

http://batteryuniversity.com/learn/a...configurations

That'll help.

Take care,
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Old 09-24-2011, 06:37 AM   #11
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There is no difference in performance with either. The first diagram and the one most often used may result in fewer connections and less cable used.

Bob
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Old 09-24-2011, 06:50 AM   #12
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Sorry, maybe I'm missing something. I'm failing to see the advantage of the extra complexity/connections/wiring in the second example? KISS logic will normally rule?
There's a slight extra complexity; probably one additional cable depending on how the setup is actually wired, however, perhaps shorter cables. That may explain why manufacturers wire the four 6v battery setup the way they do... that is to save a few bucks. On the other hand there may be advantages to doing something a bit different, perhaps more costly, than the manufacturer did.
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Old 09-24-2011, 05:30 PM   #13
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There's a slight extra complexity; probably one additional cable depending on how the setup is actually wired, however, perhaps shorter cables. That may explain why manufacturers wire the four 6v battery setup the way they do... that is to save a few bucks. On the other hand there may be advantages to doing something a bit different, perhaps more costly, than the manufacturer did.

On the bold, that's my question. What might that advantage be?
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Old 09-25-2011, 05:05 AM   #14
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On the bold, that's my question. What might that advantage be?
??? To whom are you addressing your question? ???

The question which I raised in my initial post, repeated here is: "... does this variation provide advantage or disadvantage? ... Reasons? "
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