Saturday, Apr 04, 2009 at 03:42
Hi Phil and Helen,
I also considered this option some time back and decided, because of physical size issues and looking at advantages vs disadvantages not to go ahead with it.
A couple of facts.... generally if a 6volt battery was the same physical size as a 12 volt battery, all things being equal it would have twice the ampere hour capacity and half the voltage. As the BT is 12volt system you would need 2 x 6volt batteries connected in series, you would have 2 x the Ampere Hour capacity, 2 times the weight and use 2 times the accommodation space.
You could install 2 x12 volt batteries connected in parallel which would take up the same amount of space, weigh about the same and give twice the Ampere Hour capacity of one 12 volt battery. So.... we are back to square one!
At the time I was looking at Trojan batteries. here is a comparo...
A SCS225 12volt battery is rated at 130ampere hrs at the 20hr rate, is 337mm long, 173mm wide, 248mm high and weighs 30kgs.
A T145 6volt battery is rated at 244ampere hrs at 20 rate, is 264mm long, 181mm wide, 292mm high and weighs 33kgs.
You will need 2 of each. The 6volt batteries are taller and wider (they would not fit in my BT even if I made a new battery box), for me end of story.
If you currently have 4 x 12volt batteries you would need 4 x 6volt (connected 6+6 in series, times 2, connected in parallel) to achieve the same capacity, if you have 3 x 12volt you would have to go with the 4 x 6volt (more space reqd) option or reduced capacity with the 2 x 6volt option.
The 12v arrangement gives you 260ampere hrs, weighs 60 kgs, is longer, narrower and lower.
The 6v arrangement gives you 244ampere hrs, weighs 66kg, is shorter, wider and taller.
Very similar outcome.
Benefits of the 6 volt arrangement... the batteries are in series, there is no discharge one battery to another as with parallel connections.
Benefits of the 12 volt arrangement... the batteries are more generally used and therefore available and also dispensible. Should one battery fail it can be disconnected and you still have 12volts (not the capacity you once had, but useable). If you have one of the 6volts fail you are up the creek! The availability of 6volt batteries at Woop Woop is probably limited.
6 volt batteries are more suited to stationary solar system where space and weight are not as much an issue.
As far a lasting longer.... not sure, battery life is directly proportional to cost, use and care no matter what the voltage.
I am now using Lifeline (AGM) 12volt batteries (not cheap but very good) and have installed an isolation switch for when I'm not using the BT. I also keep them charged.
Hope I have not confused you!
Regards
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