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Old 11-23-2007, 10:02 PM   #1
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I have question about the use of 6volt and 12volt batteries for use as deep cycle house batteries. I have looked through the database and could not find anything that looks or discusses this topic.

Our boat, Fortuna, came with 6 x 6volt 100ah batteries wired in series/parallel to provide 12 volts. We were told that the battery capacity is 600amp/hrs which I now know is wrong and is actually 300amp/hrs, which leads me to think that either the broker or owner had no idea about batteries.

So to my question, is there any benefit to utilising 6 volt batteries over 12 volt batteries in the house bank?

I know that the 6 volts are smaller and easier to handle those massive 300amp/hr 12 volt batteries. But you will need twice as many

connected in series to get the required 12volts.

On a side issue, I know battery capacity requirements will differ from boat to boat, but on average what is a reasonable amount of amp/hr capacity to have. When I replace the batteries I have (Trojan 105's) I was thinking about upping the capacity to 600+ amp/hrs

Again, as usual, any help or advice would be very welcome!
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Old 11-24-2007, 03:08 AM   #2
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Hi Footprints,

Golf cart batteries are "true deep cycle" batteries with thick lead plates that are more tolerant of deep discharge and they provide up to 500 recharge cycles. So that may be the reason for the 6 volt batteries being on your boat ( that is if they are the Trojan batteries that I think they may be).

From a cruising point of view - especially in the tropics - when a 6 volt battery fails - getting a replacement will not be easy. Therefore 12 volt is better for cruising. Therefore it might be a good idea to obtain a couple of deep cycle 12 volt batteries - in dry/no electrolyte condition and store these for the time that you have to convert.

You don't say what charging/distribution/utilization voltage is presently on the boat - if 12 volts - Try finding a copy of The new "12 Volt Doctor's Practical Handbook" has an expanded troubleshooting section. ISBN 1 878797 13 1

These outfits may have a copy - here are their tel. numbers near you :-

Crystal (0) 7 - 4031 1481

Garrick (0) 7 - 4031 8461

A & R (0) 7 - 4041 0591

Collins (0) 7 - 4038 1786

Gemini (0) 7 - 4053 2654

Good to hear that you have a good friend on the cat - I also have great memories of "Mix" cross between White English Bull terrier and a Brindle Staffordshire Terrier.

Cheers

Richard
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Old 11-24-2007, 03:38 AM   #3
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Richard,

Thanks for your reply!

We currently have 6 x 6 volt Trojan 105's running the 12volt system. We have 2 x 120amp alternators, 2 x 120watt solar panels and an AirX wind gen. The solar panels are wired to the batteries through their own regulator, while the wind gen and alternators run through the switchboard. (previous owner placed a plethora of battery "kill" switches around the boat as he was paranoid that someone would steal it! Hence the solar panels running direct to the battery to keep them topped up.)

I have included a pic of our current set up as it may do more justice in explaining than what I can.

I have vague recolection of reading something or someone telling me that running 6 volt batteries in series/parallel has benefits over straight 12volt batteries. But for the life of me I cannot remember what it was, hence this post.

Both Mel and I have some reservations about whether or not Toby, our dog, (aka "shark bait") will adjust to the boat life, especially when we move aboard it May next year and set sail!

Damien
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Old 11-24-2007, 09:28 AM   #4
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Quote:
Originally Posted by Footprints View Post
I have vague recollection of reading something or someone telling me that running 6 volt batteries in series/parallel has benefits over straight 12volt batteries. But for the life of me I cannot remember what it was, hence this post.

Damien
Hi Damien,

Maybe someone will provide answer to the question . One advantage might be that if one 6volt battery dies, you still have the other half of a 12 volt setup. In general I see that having to connect 6volts by cabling to get 12volts there is bound to be some loss - and the more connections one has there more opportunity for corrosion and or bad connections.

By the way , your picture shows a battery "box" that when you come to convert the 1st stage could be a combination of 3 Trojan SCS 225's + 4 Golf 105's, as opposed to the 6 Golf 105's - whatever, the 105's have a good reputation.

You could speak to Mike Brauer at 7 4124 8673, he is with Alco Bats - who I found in my data base as being helpful.

Richard
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Old 11-24-2007, 02:06 PM   #5
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Getting in, and out of the boat is a huge plus. The weight factor is why I will probably go to the golf cart batteries. Trying to stick something large, and cumbersome in a tight hole can be tough.
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Old 11-24-2007, 09:27 PM   #6
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Getting in, and out of the boat is a huge plus. The weight factor is why I will probably go to the golf cart batteries. Trying to stick something large, and cumbersome in a tight hole can be tough.
True, except that in the case of Trojan batteries, whose Golf cart batteries are "true deep cycle" batteries with thick lead plates. The weight difference is very small between the 105's and the 12 volt SCS 225.

The other negative factor was the issue of replacement of the Golf cart battery in far off cruising places.

Here is a comparison table of Trojan's 6v versus 12v :-

Trojan_DCyc_Bats.jpg
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Old 11-24-2007, 10:42 PM   #7
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Quote:
Originally Posted by Footprints View Post
We currently have 6 x 6 volt Trojan 105's running the 12volt system. We have 2 x 120amp alternators, 2 x 120watt solar panels and an AirX wind gen. The solar panels are wired to the batteries through their own regulator, while the wind gen and alternators run through the switchboard. (previous owner placed a plethora of battery "kill" switches around the boat as he was paranoid that someone would steal it! Hence the solar panels running direct to the battery to keep them topped up.)
This is the exact arrangement that I have for my house batteries. I also have two 12 Tojans for starter batteries. The system works wonderfully for many years. If I were you, I'd leave it just as it is.
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Old 12-04-2007, 01:55 AM   #8
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Hi Guys,

I emailed a friend of mine, who is currently stationed in the Marshal Islands, the same question about 12 volt versus 6 volts. It explained to me the benefits of having my current ( pardon the pun) set up.

Hope it helps!

This is his answer, including my question:

I have six, 6 volt 225amp/hr batteries wired in series parallel to achieve a 12v, 675amp/hr house battery.

Now my question is:

What is the benefit of having 6 volt batteries as opposed to 12 volt batteries. Apart from physical size (which isn't much) is there any "electrical" benefit in having 6 volts batts vice 12 volt.


Short A' - Massive electrical benefit!

Ok, long A' - 1 "battery" = 1 bucket of water, so, if you have 2 buckets of water to make "1 battery" the battery has more Capacity as it is physically larger but is still 1 battery! Imagine how much Capacity you would have if you use 6x2Volt cells just like submarines do! They do this for a whole bunch of justified reasons mate. The measured values remain the same but the longjevity of battery materials is increased due to much less stress.

Ok, longer A' - Using 6V high capacity batteries in series allows a lot more storage room due to the the "cross section plate area". They are keept at the same distance to maintain capacitance, stability and internal resistance (IR). IR determines charge rate! A larger capacitor (battery) has greater Capacity, storage and longer life as the overall plate area is not expossed to as much cycling service depth of discharge as a sigle 12Volt battery. Hence, it is harder to get down to the duty cycle of the battery because you have more amps stored (capacity). This also improves safety and reduces heating - thus water loss from electrolite.

Batteries in Parrallel oppose each other as their internal resistance is different, as Voltage is constant in parralles - it is current determined by resistance that changes, so, Batteries in Series don't oppose each other because the resistance remains the same and hence does current so voltage is what changes. Batteries are all about internal resistance and capacitance.

By the way, the best filter on the boat for supression of back EMF (voltage spikes) is your battery due to its capacitance, so the more capacitance you have (in series) the better as well.

Note - Make sure that your Pos and Neg for load come off opposite ends to each other of your battery bank! And, your supply (charge) go onto the other opposite ends. This will reduce inner plate lag, sulfation and negate negative terminal sloughing to a degree. You use more of your plate area with this configuration and hence your battery will last so much longer and supply better.


Clear as mud!!!!

Damien
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Old 12-08-2007, 02:00 PM   #9
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Design engineer husband Michael read this over my shoulder and said, "Excellent discussion--very well spoken." He applauds the battery explanation and agrees completely. I'm afraid I'm with Damien in my struggle to understand!

Normandie
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