Batteries Good or Bad?

[markpj23]

I have 4 house battery banks on the boat.
Previous owner says the batteries are about 18 months old.

-#1: single Group27
-#2: single Group27
-#3: two 6-volt Trojan T-105s
-#4: two 6-volt Trojan T-105s

I can never get the voltage on any bank to go above 12.4 volts, no matter how long I run the chargers. Useful charge duration seems to be way too short, banks 1 & 2 will barely last overnight with very little load (occasional head & FW pump use, one courtesy light bank). Banks 3 & 4 are better, as I'd expect, but still do not seem to last as long as they should.

I saw a previous survey report where at least one battery bank was found dry. I suspect I need to replace all batteries but don't want to waste money.

I have 2 chargers connected to the 4 house banks PLUS the engine starting battery. Engine cranking seems fine. Curiously enough, the genset battery has no charger connections at all other than the genset alternator.

The chargers are a mismatched pair, one is a smallish Pro-Mariner solid state unit and the other is a much larger unit whose manufacturer I cannot remember. When starting both chargers I get an initial charging amperage of 90A. I've not yet verified how they are connected but they logically must be in parallel. I get charging current to all 4 banks using one charger or the other, which seems to confirm that.

How do I tell for certain the true battery condition? Is a hydrometer the only way or is there another discharge test I can run? Or do I just bite the bullet and start over - I also have doubts about the chargers installed and will likely replace them.

[Jon D]

It sounds like batteries might be sulfated. I would get a hydrometer and check [it's the only way to know for sure]. Then run an equalization charge while watching the water levels and adding as necessary. That should help.

[Rick]

You need 3-step battery chargers as well as an alternator regulated by a 3-step charger else you will never be able to properly recover a deeply dishcarged battery.

Early Pro-Mariner chargers are all taper chargers not sufficient for deep-discharge battery recovery or maintanence.

Temperature compensation is a must, whether it by by manual setting of the acceptance voltage or automatic, especially with extremes of either warm or cold for the capacity recovery and/or longevity of deep-discharge batteries.

[Alan Wheeler]

To add to Rick. I take it you have the following. Each group 27 is 12V and connected in parrellel. The T-105's are connected in a group of two in series and then the groups of two are connected in Parrellel to the with the other T-105's and the Group 27's??? Am I followign correctly?? OK,if the above is true, you have to many mismatched loads. The charger, no matter what it is, will not charge ALL batteries correctly. In fact, you run the risk of boiling some if not all. When in parrellel connect, you need batteries of the same in both size and age or the loads of each will be different enough to upset the charge. One battery wil start drawing a different amount than another.
As Rick said, you need 3 stage charging. I use 3 stage on shore power only and a non 3stage alternator. Only because I am not off shore power long enough to have a compleate charge,or lack of it, be an issue. But as we extend our time out, that will soon become an issue we will have to address.

[ssullivan]

Not that I'm an expert... far from it. But since I've been wrestling with many of the same issues you are, I would follow the advice Rick just gave. He's right... (I dare say always right about electrical systems!)

Make sure you have the right charging capability there, or no matter what batteries you buy, or when you bought them.... they'll die an early death.

You might want to check out the chargers I just bought. Iota chargers. They are smart chargers and try to make some approximation to the amp hour law of charging. They are quite inexpensive for the type of system you end up with.

Once you have the right foundation, a set of 4 Trojan T-105s can be had for around $360

[markpj23]

Wheels - as I think of it I'm not certain of the wiring configuration. I have a 4-position house battery selector, and can thereby select either of the 2 single group 27s or either of the two twin T-105 banks.
I can only use (draw from) one bank at a time.

The two chargers simultaneously charge all 4 house banks AND the engine start battery. Schematically I guess there must be a common bus / battery combiner between the chargers and the banks. There's only one cable on each battery terminal so I know there's some other connections being made behind the distribution panel.

So I have 5 banks consisting of 2 pairs of T-105s, 2-Group 27s and a single Group 24 battery all connected to two mismatched chargers. Sounds like I'll NEVER get an even charge if the info in this thread is true....

[Alan Wheeler]

Sounds complex. I would look at simplifying your system. Wait till the batteries are no longer workable, but when you need to replace, I would look at having one house bank and one start bank. Having two or three house banks means each bank would be drained more easily and thus be detrimental to there longevity. Having one large bank means you will have large AH capactiy and probably not be using all the capacity. Not allowing you ra banks to drain to far means they will last longer.
The Battery change over swithch should be there to give you the ability to switch the house bank into engine start, should you ever have an engine bank failure. I did away with that switch. It is too easy for someone to switch in the engine start to the house bank for more capacity. No switch, no temptaion. There are other ways of doing the job for me if it ever occurs. And in 35years of being on boats, it never has been an issue.

[Jon D]

What Alan said..

KISS the system especially the house bank. Larger bank will give much better performance in the end especially if you size your alternator/charger correctly. FWIW the electrical expert I work with never likes to see more than 3 batteries in parallel making up a bank unless there is no other option. Reason is it tends to cycle the battery at the end that you connect to more than the rest of the bank.

[Rick]

Jon D,
The proper manner to interconnect ANY number of batteries including ALL combinations of series and/or parallel is so that one (and only one) negative as well as one positive distribution point leads away from the entire bank.

WITHIN the bank wire the interconnects so that each single discrete battery "sees" exactly the same total length of wire (assuming that all interconnect wires are the same size) in ultimately reaching the positive and negative distribution points. That way your entire bank will "source share" regardless of differences in discrete battery sizes (which can be mixed).

It is sophomoric to limit a battery bank design to only 3 batteries when considering this necessary planning for wiring.

Let me know if I did not explain this sufficiently well to visualize.

[markpj23]

Rick - if I understand you correctly, then I can mix/match battery sizes as long as the total wire length 'seen' by each battery is the same?

So if my furthest battery is say 36 inches from the main connection, then I use 36 inch leads to all batteries - even the ones right next to the main connection.

I'd not have thought that a few feet of copper would make such a difference to batteries.. Thanks for the info!

[Rick]

To be technically accurate for a mix of different sized batteries the ratio of parasitic wire and connection resistance to the ratio of the battery's internal resistance must be equal for all in combination in order to source share.

Normally if you have all of the batteries within a rectangle you can usually map out graphically the most efficient manner of making up equal lengths of cable (for equal "sized" batteries) which often yields a layout that has one cable near one apex of the rectangle and the other diagonally opposite, the pair representing a positive and negative for the entire bank.

Working out the math of using "real" numbers of parasitic resistances and internal resistances will show that in the case of high charge currents (like 100A or so for a 400A-h battery bank) and high discharge currents (like using 200A to an inverter driving a microwave oven) it becomes obvious that several hundred milli-Volts difference between terminal voltages can occur with incorrect battery wiring layout. This can cause one or more batteries to fail to receive sufficient charge acceptance voltage (and, therefore current). For loads it can cause the overall battery bank voltage to "crash" prematurely causing a low voltage battery cutout of an inverter.

Once I was flown across the country to solve an OEM problem with a trucking firm using Trace inverters to drive a microwave oven in the sleeper. The inverter was cutting out very quickly due to low voltage of the battery bank.

All that I had to do was re-route the existing batterey interconnect cables and the problem was solved. Other than having to pay for the labor of doing the re-wiring of existing trucks there was no further change required. Obviously the existing various cable lengths allowed me to do this else new cables would have to have been made up.

[colemj]

Rick,

A lot is made about taking the positive and negative leads off of opposite ends of a paralleled bank. What is the drawback of connecting each positive terminal of a 12V battery to a common post (and same for the negative terminals) and connecting the house DC and charging system to the junction posts?

For example: 3 batteries with 6 short cables - one from each of 3 positive terminal to a common junction and one from each of 3 negative terminals to a common junction. The two junction terminals then become the "battery" hookup point for the DC systems.

You could put switches on the 3 positive connecting cables, which would allow you to isolate any of the 3 batteries if one went bad without bringing down the DC system.

Mark

[Rick]

That forms a discrete positive and negative distribution post for each polarity. If single distribution posts are used they form "star" connections which are as close to ideal as is reasonably easy to get in big wiring situations.

There is a "stacking protocol" to use with distribution posts. The idea is to place the highest current load and source leads at the center of the stack (so that the terminals are intimate with each other) and place the lower current handling terminals on both sides (top and bottom, if you will) so that the smallest current handling wires are on the very top and bottom of the stacking protocol.

Doing this stacking protocol minimizes ground and power loops that minimizes voltage differences between all of the terminals.