Adding a battery bank

[btrayfors]

Originally Posted by W3GAC

..... Maybe our long life two bank experience was due to having plenty/ over capacity on either bank so that our typical use never taxed either bank that may be been working alone. .......

You think?

Your two bank system obviously works well for you, with a capacity of 400+ AH in each bank. Clearly, as a knowledgeable boat owner who pays attention to such things your system works fine for you.

I happen to have a two-bank system, too, but I ALWAYS keep them combined into one large 700AH bank. Why? Because:

1. I get more actual AH from the system, since I'm drawing only half as much average amperage (about 6A or 150AH in 24hrs) from the single bank as I would from each bank alone;

2. It's cheaper to recharge them via mechanical means....I can put twice as many AH back in the same amount of run time for my generator or main engine;

3. I don't have to worry about which bank I'm on today; no need to switch....ever;

4. If any battery in the system goes bad, it's a piece of cake to remove a battery cable or two and isolate or remove the offending battery; and

5. If a shorted battery should pull down the bunch...and I don't notice (which is unlikely, since I have a large digital battery voltmeter which is visible from anywhere in the cabin)....then I always can run the engine/alternator or the generator to recharge after removing the shorted battery, since these share a common independent start battery.

How has this worked for me? Well, I'm kind of a battery nut, having done quite a bit of research in my shop and on my boat and in collaboration with other marine electricians and battery companies and installers. I can only say that it's worked very well: I, too, get 7-8 years from my golf-cart flooded batteries, before they drop below 80% of measured capacity and I replace them.

Whether or not a two-bank system (operated as such) or a single bank system is more advantageous depends on a host of factors, including:

1. size of the bank vs. daily AH budget;
2. onboard charging capability and means;
3. chemistry of batteries (flooded, gel, AGM, TPPL, etc.);
4. type of cruising service; and
5. interest, knowledge and practices of owners.

For most small boat owners who want a reliable and trouble-free electrical setup, I believe that the recommended single bank house battery system with a separate start battery automatically charged via a voltage follower device (EchoCharge or DuoCharge) or battery combiner is the way to go. Hands down.

Bill

[noelex 77]

I think there is some confusion about the different battery options. There are four popular systems:

1. A single bank.
This is used for house and starting

2. Two equal banks.
Usually one is functions as the house bank and the other is is kept in reserve for starting. When the banks have been recharged they alternate functions with the start bank becoming the house bank.

3. One large bank and a much smaller starting bank
The starting bank is usually just a single small starting (as opposed to deep cycle) battery. The starting battery is only used for starting. It is recharged quickly and remains close to 100% SOC. The better systems have a means of starting the engine from the house bank if the start battery fails.

4. As above in 3, but the house bank is split into two.
Even though the house bank is spit, it is where possible, run as single bank. It is only split to facilitate testing, equalisation, occasionally fully charging the batteries, if a fault develops in the system ,or when running disparate battery chemistries.

All the options work, but my view is that they become better as you go down the list. 3 is the most popular for modern production boats. 4 only has a very slight extra cost over 3, but has greater versatility and redundancy.

There are some variations on the above. Some yachts use the start bank for some other duties such as the anchor winch. A separated dedicated battery in the bow is also sometimes used for the anchor winch/ bow thruster. 24 v systems may be more complicated with separate 12 and 24v banks.

A further option worth considering is a small emergency battery mounted high above the waterline to power the VHF and possibly GPS in the event of flooding. This is compulsory for certain yachts in some countries.

[mitiempo]

Originally Posted by noelex 77

I think there is some confusion about the different battery options. There are four popular systems:

1. A single bank.
This is used for house and starting

2. Two equal banks.
Usually one is functions as the house bank and the other is is kept in reserve for starting. When the banks have been recharged they alternate functions with the start bank becoming the house bank.

3. One large bank and a much smaller starting bank
The starting bank is usually just a single small starting (as opposed to deep cycle) battery. The starting battery is only used for starting. It is recharged quickly and remains close to 100% SOC. The better systems have a means of starting the engine from the house bank if the start battery fails.

4. As above in 3, but the house bank is split into two.
Even though the house bank is spit, it is where possible, run as single bank. It is only split to facilitate testing, equalization, occasionally fully charging the batteries, if a fault develops in the system ,or when running disparate battery chemistries.

My view is that they become better as you go down the list. 4 only has a very slight extra cost over 3, but has greater versatility and redundancy.

I fail to see any benefit to #4 over #3.

My preference:
Large single house bank - with all charging sources direct to it. Separate start battery charged with ACR, Echo Charge or similar. Windlass (if there is one) powered from house bank.

I cannot see what advantage can be gained over this arrangement.

The only improvement I would make to my preferred arrangement would be to enlarge the house bank even further. By doing so the batteries would cycle less deeply, extending their life beyond the dollars required to do so.

[noelex 77]

Originally Posted by mitiempo

I fail to see any benefit to #4 over #3.

There are a number of advantages. None of these are essential, but the extra cost of implementing 4 is minimal. Some include:

1. You can mix batteries of different chemistries and ages in your house system with much fewer compromises.

2. Redundancy /fault finding.
A fault in a single battery, a bad connection, or defective battery switch will only effect one bank.

3. Easy equalisation.
Equalisation voltages are not ideal for some electronics. One bank can be equalised while the systems are kept powered by other, avoiding exposing the electronics to the higher voltage.

4. It is easier to periodically fully charge the batteries with wind/solar
AGM batteries in particuar benefit from a periodic 100% (or as close as possible) charge. This is easier to do if the bank can be split.

[conachair]

Originally Posted by mitiempo

I fail to see any benefit to #4 over #3.

As Noelex pointed out - makes it possible to do an equalising cycle on one bank without shutting everything down, also you can capacity test a bank on it's own and get a bank on it's own back up to 100% charge every few days when away from shore power.
None of which are of much interest to the average weekend sailor but living on the hook well worth a little extra wiring IMHO.

[Zach]

I found this discussion interesting, about splitting the house banks on a switch to be able to equalize and desulfate.

Equalizing and supplying enough amperage had me looking at high amp alternators as I'm not planning on installing a shore power connection with the associated charger on my boat to be able to equalize them.