I have four L16H 6V batteries for my 840AH 12V house bank. Due to space
and balance limitations two are on the port side of the companionway and two
on the starboard. The fuse, battery switch and power connections are on the
starboard side. I am running 5' of 4/0 cable between them. It has been
recommended to me by several people that I parallel each pair and then
series across the companionway. That does not seem right to me as it would
put the full amp load at 6V on the longest cables.. I am thinking it would
be better to series wire each side so the longer cables are carrying 12V and
half the amps

Am I missing something?

--
Glenn Ashmore

I'm building a 45' cutter in strip/composite. Watch my progress (or lack
there of) at: http://www.rutuonline.com
Shameless Commercial Division: http://www.spade-anchor-us.com

You are correct. With two pairs of series-connected 6v batteries, the
current across the companionway will be half of that with two pairs of
parallel-connected batteries.

There will be losses in the 4/0 cable when you load the bank, of course.
At normal charging currents, the voltage drop in the 4/0 cable will be
insignificant.

A further advantage of 12 volt banks P&S is that each can be used
independently in the event of a problem. Not so easy with two 6 volt banks.

The advantages of two 6 volt banks are not immediately obvious to me.

Chuck



Glenn Ashmore wrote:
I have four L16H 6V batteries for my 840AH 12V house bank. Due to space
and balance limitations two are on the port side of the companionway and two
on the starboard. The fuse, battery switch and power connections are on the
starboard side. I am running 5' of 4/0 cable between them. It has been
recommended to me by several people that I parallel each pair and then
series across the companionway. That does not seem right to me as it would
put the full amp load at 6V on the longest cables.. I am thinking it would
be better to series wire each side so the longer cables are carrying 12V and
half the amps

Am I missing something?

On Wed, 8 Mar 2006 11:19:08 -0500, "Glenn Ashmore"
wrote:

I have four L16H 6V batteries for my 840AH 12V house bank. Due to space
and balance limitations two are on the port side of the companionway and two
on the starboard. The fuse, battery switch and power connections are on the
starboard side. I am running 5' of 4/0 cable between them. It has been
recommended to me by several people that I parallel each pair and then
series across the companionway. That does not seem right to me as it would
put the full amp load at 6V on the longest cables.. I am thinking it would
be better to series wire each side so the longer cables are carrying 12V and
half the amps

Am I missing something?

I agree with you. For adequate parallel installation, make sure the
cables from each pair to the strips are identical, also re total
length (total length of both + and - cable should be identical). That
way you prevent different charging and draining of each 12-v set
Len.

"Len" wrote
I agree with you. For adequate parallel installation, make sure the
cables from each pair to the strips are identical, also re total
length (total length of both + and - cable should be identical). That
way you prevent different charging and draining of each 12-v set

Which brings up another quandary. The voltage drop across 5' of 4/0 will be
small but my house alternator is capable of delivering over 200 amps and the
inverter can draw pretty close to the same thing. Electrically the ideal
place to tap in the alternator and house loads is under the sole in the
middle of the companionway but I am a wee bit worried about having those
high power connections down in the bilge.



--
Glenn Ashmore

I'm building a 45' cutter in strip/composite. Watch my progress (or lack
there of) at: http://www.rutuonline.com
Shameless Commercial Division: http://www.spade-anchor-us.com

On Wed, 8 Mar 2006 11:19:08 -0500, "Glenn Ashmore"
wrote:

I am thinking it would
be better to series wire each side so the longer cables are carrying 12V and
half the amps

Am I missing something?

Possibly.

You would then be paralleling two 12 volt batteries with unequal
lengths of connecting cable. That could result in uneven rates of
charge and discharge between the port side and stbd side due to IR
losses in the longer cables.

There may be a way to avoid that but I'm struggling with trying to
describe it without resorting to ASCII art. Basically you run two
jumpers from port to stbd to make the parallel battery, and then you
pick up the positive feed from one side and the negative feed from the
other. This requires a bit more wire but it tends to even out the IR
losses between the two banks.

There are also some safety considerations to think about when
paralleling large batteries. If one battery develops a short in a
cell, it is potentially dangerous to have its parallel twin
discharging into it at high amps. One way to minimize the risk is to
insert a large fuse or breaker into one of the parallel links.

Your alternator will not be delivering 200 amps for very long, if ever.
When charging current is "high" the closer bank will accept charge
faster than the farther bank. Eventually, as the charging current
diminishes, the voltage drop across the 4/0 cable will fall further into
insignificance.

Apply Ohm's law and work out the numbers.

Chuck

Glenn Ashmore wrote:
"Len" wrote

I agree with you. For adequate parallel installation, make sure the
cables from each pair to the strips are identical, also re total
length (total length of both + and - cable should be identical). That
way you prevent different charging and draining of each 12-v set


Which brings up another quandary. The voltage drop across 5' of 4/0 will be
small but my house alternator is capable of delivering over 200 amps and the
inverter can draw pretty close to the same thing. Electrically the ideal
place to tap in the alternator and house loads is under the sole in the
middle of the companionway but I am a wee bit worried about having those
high power connections down in the bilge.

Did that. At maximum output I am loosing about 0.05 volt across the cables
if the pairs are series and the sides are parallel. When it drops to
absorption stage it gets pretty insignificant. But you always strive for
perfection don't you? ;-)

--
Glenn Ashmore

I'm building a 45' cutter in strip/composite. Watch my progress (or lack
there of) at: http://www.rutuonline.com
Shameless Commercial Division: http://www.spade-anchor-us.com

"chuck" wrote in message
nk.net...
Your alternator will not be delivering 200 amps for very long, if ever.
When charging current is "high" the closer bank will accept charge faster
than the farther bank. Eventually, as the charging current diminishes, the
voltage drop across the 4/0 cable will fall further into insignificance.

Apply Ohm's law and work out the numbers.