Batteries: Individual or Banks?

[cburger]

Well I am fianally getting ready to move on board full time in a couple of weeks and need to start thinking about 12volt systems to run the boats refrigeration. The boat is currently set up with the capacity for 3 batteries, one starting and two house all wired individually to two seperate switches allowing the ability to isolate the start from the house batteries, also the house batteries go to two seperate DC panels. All of the switches can be selected to combine all the batteries for charging, etc.

It has been indicated to me that this layout is not such a bad thing for a couple of reasons, i.e more closely being able to care for the batteries as individuals and maybe save some money in the process.

The question is will converting the system to be able to combine two 6volt golf cart batteries really net that much reward over leaving the existing setup in place? My refrigeration is an older Nova Cool that is 12volt only and will be wired direct to a battery or batteries drawing maybe 4.5 amps on high setting.

[Vasco]

The latest thinking is that all the house batteries should be in one big bank.

[bloodhunter]

Assume your existing setup is two 12v batteries for the house and one for the starter. I found that I could get move amp hours for the buck from golfcart batteries. Also the golf cart batteries seem to have smaller footprint than the 12v batteries but are taller. that was good for me as I was able to get four of them into the space I had available. giving me about 500ah. Could nothave gotten anywhere near that from the three 12volt batterie4s I could fit into the space.
Also it's probably not a good idea to wire anything except bilgepumps directly to the batteries.

[cburger]

Thanks fellas.

[Sumner]

I agree with the other posts above. One house bank will make the batteries last longer and they will charge better. How are you charging them? Also as mentioned you will get more bang for the buck with the 6 volt batteries.
When the 2 12 volt batteries go bad on out Mac we will replace them with 2 6 volt batteries. The Endeavour has 4 6 volt that will be wired as one house bank and 1 12 volt start battery.

After drawing up a lot of wiring diagrams and looking at a lot I like Maine Sail's diagram...




... and his reasoning for it...

1/BOTH/2/OFF Switches Thoughts & Musings - SailboatOwners.com

... We also bought a Blue Sea Automatic Charging Relay (ARC/combiner) #7610 that will be connected between the #1 and #2 posts above to assure that both batteries will be charged. In addition to the charging from the alternator our solar panel output will also go to the house bank where the alternator wire is shown above. Take the time to read his thoughts on the link above--good info.

Wired like that with the appropriate fuses by the batteries you will be able to turn the power off at any time, decide if the starter will receive current from the starter battery or house bank and all of the batteries will stay charged without you needing to remember switch positions. Also having the alternator always wired to the house bank you forgo damage to it.

Good luck,

Sum

[Sumner]

I forgot to add...about the fridge you mention 4 1/2 amps. That might be in the ball park and is important, but the really important part is how much of the day will it be running. If it is an upright like what we took out of our boat it probably doesn't have much insulation and will loose a lot of cold air every time you open the door. If you are running on shore power this is not a big deal, but it you are having to replace all of that power into your batteries with running the motor or solar/wind then it is.

For that reason we took the time and spent the money to replace the upright with a chest type...

Endeavour 37 Interion Mods Index

...and now we use very few amp/hours of elect. every day for a fridge,

Sum

[cburger]

In the back of my mind I kind of figured that going with the the golf carts was the best solution, its just that I have spent so much money on the old girl lately that I am really feeling the pinch. I was thinking about just installing one house battery to run the fridge for the winter and then regrouping in the spring.

To answer some of the previous questions, charging is a 10SI GM alternator producing approximately 80 amps, Charles 40 amp charger, refer box of very high quality and insulation, top loading, Nova Kool instructs to wire compressor direct to the battery with inline fuse. Regarding the amperage draw of the my particular fridge setup, batteries will be recharged shore power and the AC charger.

[ranger58sb]

Without regard to wiring schema and switches, if you have space available you could also maybe consider simply replacing each single 12v house battery with two 6v golf cart batteries, choosing replacement sizes that would increase available amp-hours.

I would ignore NovaKool instructions to wire direct to battery. (Dunnoe where those are built, but as is often the case, with manuals created by one tech in his native language and then translated to English by another tech who may or may not know English... they may have meant to "12v power source" instead of literally, "battery.")

-Chris

[Maine Sail]

Originally Posted by cburger

In the back of my mind I kind of figured that going with the the golf carts was the best solution, its just that I have spent so much money on the old girl lately that I am really feeling the pinch. I was thinking about just installing one house battery to run the fridge for the winter and then regrouping in the spring.

To answer some of the previous questions, charging is a 10SI GM alternator producing approximately 80 amps, Charles 40 amp charger, refer box of very high quality and insulation, top loading, Nova Kool instructs to wire compressor direct to the battery with inline fuse. Regarding the amperage draw of the my particular fridge setup, batteries will be recharged shore power and the AC charger.

6V batteries are fairly inexpensive, comparatively speaking. Many Sam's Club locations sell the Deka/East Penn 6V's which are the same brand and battery that West Marine sells for more than double the price..

The Duracell EGC2 (Sam's brand name for the East Penn product) is a 230Ah battery so four of them would give you a bank of 460Ah's. They run about $84.00 - $89.00 each depending upon the club. 460 Ah's for $356.00 is about 77¢ per Ah......

A single larger bank will almost always last longer than running two separate banks due to having a shallower cycle depth and Peukert's law. A bigger bank will yield more Ah capacity, at the same average current draw, than two smaller banks will at the same average load.. You ideally should have two banks on the boat for redundancy, a start and house or a reserve/start and house but it is generally better to not "split" or "alternate" the house bank.

For example lets take a stab and say you will use 80Ah's over a 24 hour period. (this is pretty average for my customers with refrigeration) This equates to an average load of about 3.3A. While it won't always be 3.3A it likely won't be much higher or much lower for very long.

Two 200Ah banks looks like this:

Bank #1 200Ah - 80Ah = 60% State of Charge

When you alternate banks you draw that one to 60% SOC every cycle as well.


One 400Ah bank looks like this:

Bank 400Ah - 80Ah = 80% State of Charge

By cycling the bank shallower you gain more cycles and yield longer life.



But, there's always a but....



If we figure the bank has a Peukert of 1.27

The 200Ah Bank @ 3.3A average draw yields an Ah capacity of about 270Ah's, at that average load. This gives you roughly 135% of your banks 20 hour rated load..


However...


The 400 Ah Bank @ 3.3A average draw yields an Ah capacity of about 650Ah's, at that average load. This gives you an extra 162% of your banks 20 hour rate.

The larger the bank becomes, at the same average load, the larger the effective Ah capacity becomes and the shallower the cycles...

Hope that made sense and my early morning, pre-coffee, math is correct..

[Maine Sail]

Originally Posted by ranger42c

Without regard to wiring schema and switches, if you have space available you could also maybe consider simply replacing each single 12v house battery with two 6v golf cart batteries, choosing replacement sizes that would increase available amp-hours.

I would ignore NovaKool instructions to wire direct to battery. (Dunnoe where those are built, but as is often the case, with manuals created by one tech in his native language and then translated to English by another tech who may or may not know English... they may have meant to "12v power source" instead of literally, "battery.")

-Chris

Most refrigeration makers suggest this because the wiring to and from a the DC panel, especially on older boats, can be suspect and they wind up with voltage drop issues.

If the DC + & - main + & - feeds are sufficiently sized to run all the way to the DC panel and then from the DC breaker to the compressor without significant voltage drop to cause issues then there is no problem pulling DC from the DC panel. I have worked on a number of boats where the entire DC panel is fed from the battery bank by 10GA wire. When you stack all the other loads on top of the start up load on the fridge compressor they can often drop out on low voltage during start up... These are normally "recommendations" not necessarily absolutes.

[Mark Johnson]

I suggest using one house bank of TWO 6V Trojan L-16s, connected in series for 12V., and a small separate engine battery.

This house bank would be around 360 Ah, and if you use a smart 3 stage charger, WITH an occasional equalize, AND bring it back up daily... (easily done with solar panels, for the last 50% or more), then you can easily get over 10 years of reliable service from them. If you use Hydro Caps, you only need water a few times a year!

I would have ALL charging sources go to the house bank ONLY, and let the engine battery get its very small charge by way of a Blue Sea battery combiner.

This very simple system has kept us happy and "fully charged", in a reliable and economical way, for 15 years and counting... (Much of this anchored out and/or cruising). We bring our house bank up to 100% daily, and are 100% solar self sufficient, 95% of the year. This daily top off, re-zeros our Link 10 charge monitor, and keeps it dead on accurate!

Trojan's TALL L-16s have many times the "cycles" of many other brands, and TWICE that of even "their" 12V counterparts. Longevity was designed in, for the harshest imaginable service environment.

M.

[Captain Bill]

I agree that the house batteries should be in a single bank, though I believe that it is prudent to have a switch in place that you can use to isolate the individual batteries in the bank. I recently had a short in one of my house batteries which caused a severe overheating problem. The shorted battery was hot because of the short and the other battery got very hot from feeding so much power through the short in the other battery. I just by chance touched the battery compartment and noticed it was hot. When I got it open and measured the temperature it was 174F. I disconnected all charging and an hour later the temp had risen to 187F. At that point I disconnected all of the wires and yanked the batteries out of the box and on to the deck where they started to cool off. If they hadn't they were going overboard. In any case I had to run all my electronics off of the start bank until I got the batteries replaced. If I would have had an isolation switch I probably could have easily determined which battery was the problem battery and run on it.

[David M]

Originally Posted by Captain Bill

At that point I disconnected all of the wires and yanked the batteries out of the box and on to the deck where they started to cool off. If they hadn't they were going overboard.

I hope you don't mean that you literally would have thrown the batteries in the water. Just in case anyone does not know, they should be recycled instead.

[Maine Sail]

Originally Posted by Captain Bill

I agree that the house batteries should be in a single bank, though I believe that it is prudent to have a switch in place that you can use to isolate the individual batteries in the bank. I recently had a short in one of my house batteries which caused a severe overheating problem. The shorted battery was hot because of the short and the other battery got very hot from feeding so much power through the short in the other battery. I just by chance touched the battery compartment and noticed it was hot. When I got it open and measured the temperature it was 174F. I disconnected all charging and an hour later the temp had risen to 187F. At that point I disconnected all of the wires and yanked the batteries out of the box and on to the deck where they started to cool off. If they hadn't they were going overboard. In any case I had to run all my electronics off of the start bank until I got the batteries replaced. If I would have had an isolation switch I probably could have easily determined which battery was the problem battery and run on it.

Isolation switches can be a good idea but I generally prefer to treat them as "service" type switch hidden from crew and only there for emergencies that way you are not routinely separating the house bank and it stays better balanced.

[Captain Bill]

Originally Posted by David M

I hope you don't mean that you literally would have thrown the batteries in the water. Just in case anyone does not know, they should be recycled instead.

If the batteries had not started to cool down it would have meant that the batteries were in a state called thermal runaway. The ultimate result of in the worst case of thermal runaway is that the electrolyte reaches it's boiling point and the battery explodes. This is a rare condition, but not unknown. I was 120 miles at sea and if the batteries had not started to cool down I would have thrown them in the ocean. You would have to be a total moron to keep them on the boat and let them explode. I personally know one person who was injured by an exploding car battery and it did some pretty good damage to the car as well and I certainly would never allow that to happen on my boat if I could prevent it.

Maine Sail: I agree that the isolation switches would be only for use in a maintenance or emergency situation, not everyday use. Under normal circumstances the batteries would be treated as a single bank. Sorry if I didn't make that clear.