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Old 16 November 2005, 12:07   #21
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Hi Richard,
Not sure exactly where the losses are, but from memory it is a culmination of several factors. I think it had something to do with resistance in the extra cable, different internal impedances, different manufacture tollerances and the fact they are charged in parrallel. Probably quite a few other reasons as well.

I doubt you would see much loss at all in two brand new identical batch batteries, charged seperately. But after a few charge / disscharge cycles they would decay at different rates, the Sods Law bit, and that I think was why it was reccomended to derate them.

Anyone able to expand on that?

Tim'mers.
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Old 16 November 2005, 12:14   #22
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well for me it starts and goes + i have the back up of a second battery, after the original first start of the day, as these opti's do take some spinning over,and it never sounds like its spinning that fast. modern engines i guess + she is tight as not even got 10 hrs on it as of yet,
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Old 16 November 2005, 12:31   #23
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Quote:
Originally Posted by Swifty
Very true, but the first warning I would have had of a problem would have been too late. 2 flat batteries!
Yes, but you would have been 'home' by then
Quote:
Two 80 Ahr batteries in parrallel does not make a 160Ahr battery. There are losses involved (Sods Law?) and it should be de-rated to about 85% making about a 140Ahr.
What losses ?, certainly when I used banks of lead acid cells in emergency lighting systems we never derated them (at least not because we paralleled them up)

Quote:
and back to the point, if you are going for belt and braces, where would you put the blocking diode? It needs a volume of air to dissipate the heat,
If you used the one I mentioned, even at a cranking current of (say) 500 amps the 80 mV drop would only be 40 watts for a few seconds, that I would have thought would be OK within the battery box. There are no losses in a relay based system.
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Old 16 November 2005, 12:49   #24
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Quote:
Originally Posted by Swifty
Brian,
Quite agree, but a yacht engine is not an outboard.

And back to the point, if you are going for belt and braces, where would you put the blocking diode? It needs a volume of air to dissipate the heat, so would probably have to go inside the console. Then it would need long cables that are very thick (battery cables) and so on. Like MadMat says K I S S...

Tim'mers.
Arn't they!! Hmmm

Exactly where our's is along with the batteries, very little voltage drop and on one boat we spin an opti.

Brian
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Old 16 November 2005, 14:17   #25
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Nick,
Been trying to find the book with the parralleling battery advice. Sure it said derating is advised for traction batteries because they deteriate over time. The losses affect their cranking ability. -or something like that.

Quite agree though about use in emergency lighting etc. much lower current involved.

Brian,
I have just re-read the specs for the X split. Quite impressive. Must be lots of voodoo art and not just a diode on a heatsink. Still quite expensive though.
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Old 16 November 2005, 14:24   #26
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Quote:
Originally Posted by Swifty
Brian,
I have just re-read the specs for the X split. Quite impressive. Must be lots of voodoo art and not just a diode on a heatsink. Still quite expensive though.
Timmers
Yep a lot of Voodoo bangs gone the 0.6v silcon junction vd!! Expensive yer NOT WRONG!! good kit though unsure about reliability so far so good but then it's 9 Months old.

Regards

Brian
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Old 17 November 2005, 20:27   #27
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I think you originally asked hwere you can get the batteries from and what type to get.


http://www.aquafax.co.uk/html/produc...n.asp?ID=16963

http://www.aquafax.co.uk/html/subcategories.asp?ID=26 highly reccomend Blue sea switches

Make sure you use Marine grade cable also available from this fine emporium. if you are interested you can use our account and get yourself a bit of dicount!
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