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Old 09-07-2012, 11:24 AM   #21
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OK Flywright here we go.

The reference above cites 35MM as the standard wire size for a bank of batteries. Since I'm in the USA I tried to cross reference 35mm wire to AWG to see what size wire we're talking about.

Here's a link to the cross reference I found

American wire gauge - Wikipedia, the free encyclopedia

It appears that the 35MM wire cited in your post is somewhere between 1 and 2 AWG.

I believe that many of our house banks are similar to mine. I have four L16HC 6 volt batteries totaling 840 amp hours. They are interconnected with 4/0 AWG wire which is a heck of allot larger and much less resistance.

Normal charge rate for bulk charging is around 120 amps, then decreasing from there as the regulator switches modes.

Discharge rate for my bank averages about 25 amps.

While the article is interesting, and I enjoyed reading it on a professional level, it may not be as applicable to the actual use in our boats as it might at first glance seem.

One of the the specific reasons it may not be as applicable as it seems is that it uses 100 amps as a test amperage. That amperage is not valid for a long term discharge amperage, although is is partially valid for recharging.

Another reason is that as indicated above the wire sizes do not match the reality of medium to large battery bank installations normally found on at least larger boats. That wire size is not applicable for any sized boat with a 2KW inverter, as you need the larger wire to supply the full rated capacity of the inverter (even if you never plan on using that much inverter power).

These two issues, larger wire sizes, and smaller currents, significantly change the calculations the writer of that article made, and significantly reduce the real world issues associated with parallel battery installations.
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Old 09-07-2012, 12:11 PM   #22
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I am in the camp that believes that given proper cable gauge and minimal lengths, the difference is not enough to have a significant effect, especially with less than a very high current draw. Charging, there would be no effect whatsoever. I have a background and education in electronics and electrical circuits that supports this view.

Just to make things interesting, my boat was factory wired with the positive connections as in "method 1" and the negative side as in "method 3".

If you combine batteries that are not in close proximity to each other, the cable resistance would indeed have an effect.
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Old 09-07-2012, 12:15 PM   #23
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ksanders, You may be right on the cable size issue. Mine are also oversized, but that does not change the voltage and load balancing advantage one gets from properly connecting the bank in series/parallel.

Within limits, I agree that when it comes to cable size, bigger is better.
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Old 09-07-2012, 12:37 PM   #24
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Over-sized wire? Been there, done that!

(4x6V wet cells with 000 wire with plans to add 2 more soon... 1xSeries32(?) starter... separate banks... 2xOn/Off switches w/single combine)
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Old 09-07-2012, 01:30 PM   #25
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Quote:
Originally Posted by ksanders View Post
OK Flywright here we go.

The reference above cites 35MM as the standard wire size for a bank of batteries. Since I'm in the USA I tried to cross reference 35mm wire to AWG to see what size wire we're talking about.

Here's a link to the cross reference I found

American wire gauge - Wikipedia, the free encyclopedia

It appears that the 35MM wire cited in your post is somewhere between 1 and 2 AWG.

I believe that many of our house banks are similar to mine. I have four L16HC 6 volt batteries totaling 840 amp hours. They are interconnected with 4/0 AWG wire which is a heck of allot larger and much less resistance.


Normal charge rate for bulk charging is around 120 amps, then decreasing from there as the regulator switches modes.

Discharge rate for my bank averages about 25 amps.

While the article is interesting, and I enjoyed reading it on a professional level, it may not be as applicable to the actual use in our boats as it might at first glance seem.

One of the the specific reasons it may not be as applicable as it seems is that it uses 100 amps as a test amperage. That amperage is not valid for a long term discharge amperage, although is is partially valid for recharging.

Another reason is that as indicated above the wire sizes do not match the reality of medium to large battery bank installations normally found on at least larger boats. That wire size is not applicable for any sized boat with a 2KW inverter, as you need the larger wire to supply the full rated capacity of the inverter (even if you never plan on using that much inverter power).

These two issues, larger wire sizes, and smaller currents, significantly change the calculations the writer of that article made, and significantly reduce the real world issues associated with parallel battery installations.
While I'm no expert...the battery wire/cable guide I've been using for quite awhile which gets used often and used by West Marine shows that a 4 gauge wire between batteries would handle a 90-130 amp draw with less than a 3 percent loss.

I would probably never use anything less than #2 batt cable but that's overkill right there. Not sure why yacht manufacturers use heavier stuff all the time if it costs so much more..maybe it/s a time/materials thing.

Obviously the wires running to the loads may have to be much larger.
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Old 09-07-2012, 02:10 PM   #26
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Quote:
Originally Posted by FlyWright
ksanders, You may be right on the cable size issue. Mine are also oversized, but that does not change the voltage and load balancing advantage one gets from properly connecting the bank in series/parallel.

Within limits, I agree that when it comes to cable size, bigger is better.
Actually the cable size has everything to do with the voltage and load balancing. Larger cable equates to less resistance and less voltage drop.

Wire size and the corresponding resistance values are the core of the calculations that were used in the article you cited
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Old 09-07-2012, 03:13 PM   #27
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All cable or wire sizing requires the length (combined out and back) to be useful.
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Old 09-07-2012, 03:56 PM   #28
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Here's a good calculator to take into effect all the variables in cable sizing.

Blue Sea Systems
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Old 09-07-2012, 04:25 PM   #29
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In addition, follow your manufacturers cable size recommendations. Our inverter/charge manufacturer says 4/0 from their unit to the batteries and less than a 4 foot run.
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Old 09-07-2012, 05:35 PM   #30
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Quote:
Originally Posted by ksanders View Post
Actually the cable size has everything to do with the voltage and load balancing. Larger cable equates to less resistance and less voltage drop.

Wire size and the corresponding resistance values are the core of the calculations that were used in the article you cited
Yes but in FlyWright's defense?...there is such a thing as too big as in WAYYYY overkill...5 amps in 4/0 or #4 just doesn't matter unless you are running sensitive electronic test equipment (even then) ...like I pointed out 4/0 is appropriate for the runs to the loads if they are big enough (inverter)...but just connecting multiple batteries in one bank doesn't need anything near approaching that from what I have read.
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Old 09-07-2012, 11:13 PM   #31
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You guys are giving me a brain ache!!
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