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post #79 of Old 01-09-2019
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Re: Electric Conversion log for Kahleesea

Originally Posted by Captain Canuck View Post
Here's a great article that explains not only how, but why you wire parallel batteries a certain way.

SmartGauge Electronics - Interconnecting multiple batteries to form one larger bank
FYI, no doubt the wiring recommendations in this article are best practice.

It is relatively rare to see the common power post method (illustration # 3).

I don't recommend illustration # 4, as it needlessly places more terminals per post (risk of poor connection), and in practice is likely to result in a spaghetti breakfast of wiring.

Interestingly, some marine batteries are supplied with very short battery terminals, that in practice, will not support illustration # 4.

While the article touches on it, the consequences of wiring illustration # 1, are not as dire as indicated.

Illustration # 2 is definitely better practice, but if wired as indicated in illustration # 1, in time the internal resistance of each battery will increase, proportionally with it's proximity to the load connection, so that eventually the load per battery pretty much equalizes.

So in other words, the capacity of the nearest battery is relatively reduced, while the capacity of the furthest battery is relatively saved.

As a system, the resultant change in life expectancy will likely only be marginal if measurable at all.

This doesn't change that illustration # 2 is better practice and should be done this way if practicable.

When I encounter wiring per illustration # 1, I advise the owner that the wiring is suboptimal, but rarely will they pay to have it re-wired (if cables will not support illustration # 2 as is), unless planning a complete rewire for other reasons.

The worst I have had is a power boat I was called to because the electrical system was amuck. The series/parallel batteries were wired by the PO in a bowl of spaghetti fashion, which resulted in the new owner reconnecting batteries incorrectly in the spring, which had trashed the reverse connected battery before I arrived on scene.

After I diagnosed and corrected the specific wiring error (I had to draw myself a diagram to review the "as found" wiring and confirm the "as left" wiring), I quoted a reasonable fee (by local industry standards) to replace the batteries, correct the battery sequence and wiring routing, label it, and provide a proper wiring diagram for future reference and to help avoid recurrence.

Owner declined.

I had to leave knowing the boat, the owner, and his family were at risk of having a dead bank shortly after disconnecting charging sources, but there was absolutely nothing I could do about it.

(Addendum - I did offer the option of isolating the series pair that included the reverse polarity damaged battery, basically no charge, but that was declined also.)

Last edited by boatsurgeon; 01-09-2019 at 04:42 PM.
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