ship's batteries

[rplmilw]

We are wiring three (3) banks of four (4) 6v batteries in parallel to obtain the needed 24vdc and Amp-hrs for ship's power. The batteries are new, same mfg/type/Ahr, and presumeably "the same". Would like to hear opinions/concerns regarding charging, effects of lead lengths, ventilation (heat and H2), and replacement of individual batteries as they wear out.

 

[crutschow]

If all batteries are the same type and age, their charging should be reasonably balanced. All the batteries should be adjacent to each other so they are essentially at the same temperature, since temperature differences can unbalance the charging.

You need some ventilation to avoid heat build-up and, especially if the batteries not the sealed maintenance free type, to vent the combustible mixture of H2 and O2 that is generated during charging.

Lead lengths are not a particular problem, as long as the wire is large enough to readily handle the load current.

Unless the batteries are fairly new when one fails, I would replace them all, so that they remain reasonably matched for proper charging. If one fails after several years of operation, then it is likely that the others will also fail soon after that, so it makes sense to replace them all.

 

[Hero999]

Lead lengths are not a particular problem, as long as the wire is large enough to readily handle the load current.

That's true at low currents, at higher currents you need to consider the voltage drop and increase the wire gauge if needs be.

The wire must also be thick enough to handle the current anyway, regardless of the voltage drop.

 

[MRCecil]

The advice given by crutschow and Hero is on the money, but for added consideration I will add the following.

First, contact the battery manufacturer of the batteries you will be purchasing to find out the exact type of battery, antimony-acid or lead-acid or whatever, to determine the correct float voltage and charge rate for the battery in the configuration in which you have described. There is a difference in these parameters for the different types, which could result in an over or under charge of the batts, resulting in a shortening of their life, including excessive H2 emissions.

Second, I would strongly recommend bringing aboard a certified marine electrician, to, at the least, review the installation for ventilation, wire ampacity, charge and float rate/voltage, accessibility, installation practice (numerous factors), etc. Fire at sea can be very deadly. Better yet, get someone certified from the start to advise from the start.

Third, insure your charging/float system is stable and monitored periodically.

Forth, establish a regular PM schedule to check batt electrolyte level and specific gravity.

This may seem like overkill, but if you can't get in touch with the Coast Guard because of a fire in the battery compartment and you're dead in the water, you may wish those bases had been covered.

 

[Pommie]

In applications like this, how does one ensure the batteries are in the same state of charge prior to paralleling them up?

Mike.

 

[crutschow]

In applications like this, how does one ensure the batteries are in the same state of charge prior to paralleling them up?

Mike.

I would suggest charging them all individually before connecting them together.

 

[bychon]

I would suggest letting them sit for a few hours so their temperatures are all the same, put a car tail light across a volt meter, and measure their voltage under the light load that the bulb provives.

 

[MRCecil]

Mike,

Given they are new, as the initiator of the thread has stated, AND are provided the correct charge rate and float voltage the batteries will equalize. Routine PM's will show up any defective battery in the bank.

 

[Hero999]

Routine PM's will show up any defective battery in the bank.

What are PMs in this context?

EDIT:
Do you mean Post Mortems?

 

[Mikebits]

What are PMs in this context?

EDIT:
Do you mean Post Mortems?

Preventative maintenance is my guess. On ships the term PM is very common as all gear has a regular PM schedule that must be completed. PM reports are given to the Captain as he must ensure all equipment is being maintained. At sea, a crew member spends much of their time doing PM work from things like air ducts, toilets to radar. Just FYI

 

[MRCecil]

Hero,

As Mike has said PM is the short term for preventative or planned maintenance performed on a scheduled basis.

 

[Externet]

Beyond your questions, some advise from experience dealing with ships and batteries for a looong time :
Label/mark indelebly on each battery the date put into operation,
Spray paint red the positive terminals sorroundings and the positive load cables if they are not.
Use the anticorrosion felts
Use stainless steel nuts and bolts on terminals.
The best friend for a battery is a wire brush, keep one residing nearby.