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Author Topic: Noob question: 12V single units or 6x2V banks?  (Read 2272 times)
spinach
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« on: January 27, 2009, 09:27:32 PM »

Am trying to learn all I can about small scale renewable generation systems as am contemplating combined hydro/solar in an off grid situation. That's a steep enough learning curve as it is but now I've got around to batteries it feels like I've just walked round a corner and slap into a vertical cliff face.

Aside from the whole question about batteries being less than ideal in the first place, my mind now feels completely boggled by the vast number of potential configurations and types out there. Am I right in thinking the general consensus is that lead acid is still the best bang for buck available? And that 12V is the optimum? If so, can someone please tell me what the essential differences are between single 12V units and the 6x2V banks that seem to be recommended for solar/wind/hydro applications. What are the pros and cons to each configuration and why are they designed that way?

Very appreciative of all the expertise on these forums. Great place to hang out and learn.


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billi
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« Reply #1 on: January 27, 2009, 10:28:50 PM »

Quote
nd that 12V is the optimum? If so, can someone please tell me what the essential differences are between single 12V units and the 6x2V
If their wouldnot be the problem of cable size and other issues  , i would expect one huge single cell 2 volt would be clever  Roll Eyes

But in general i wouldnot say 12 volt is optimum , perhaps we are limited cause so much gear is available in 12 volt , but personally i think 24 volt or 48 volt systems make more sense then 12 volt ideas

for example my solar chargecontroller  costed 500 pounds  and can take 60 Amp  photovoltaic   = about 800 watt PV at 12 volt = 1600 watt at 24 volt = 3200 watt at 48 volt     of a panel i could attach to the one chargecontroller

I prefer 2 volt cells  to 12 volt batteries (made from 2 volt cells)

billi

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1.6 kw and 2.4 kw   PV array  , Outback MX 60 and FM80 charge controller  ,24 volt 1600 AH Battery ,6 Kw Victron inverter charger, 1.1 kw high head hydro turbine as a back up generator , 5 kw woodburner, 36 solar tubes with 360 l water tank, 1.6 kw  windturbine
Justme
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« Reply #2 on: January 27, 2009, 10:29:07 PM »

To keep a very long story short. You need the 2v cells. They will cost more but will last longer & perform better. Higher volts than 12v can be better as cabling can be thinner for the same load especialy if you are going to wire the house all in 240v ac & not use any 12v kit.

Justme
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Navitron solar thermal system
30 x 58mm panel 259L TS
1200watts solar 120vdc
FX80 Solar controller
Victron 12v 3000w 120a
6kva genny
6 x 2v cells 1550amp/h 5C
24 x 2v cells 700amp/h 5C
Total bank 4350 amp/h 5C
johnrae
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« Reply #3 on: January 27, 2009, 10:44:51 PM »

In simple terms,

a) once you get above about 200AH battery capacity, 12 volt batteries are too heavy to man-handle easily
b) go for as high a voltage as possibly as Billi says
c) if a cell goes dud on a 12v battery the whole battery is dud whereas if a single 2v cell fails it's much cheaper to replace
d) if you want high capacity (AH) then they are generally only readily available as single cells

jack

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martin
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« Reply #4 on: January 27, 2009, 10:59:40 PM »

I'm with Billi on the voltage thing - for a big capacity battery bank, you're better off with 24 or 48 volts for the simple reason that current (amps) is a great consideration at low voltages. Low voltages mean lots of amps - look under your car bonnet - 12v, lead to starter, thick as your finger.......... if that were 48volts it need only be a quarter as thick....... Smiley
For most installations the "conventional" way to run a home off batteries is to use an inverter (a gadgety wotsit that turns battery power into AC "mains" type power). This means that your domestic cabling can be "normal domestic grade" - it's relatively cheap and plentiful to obtain and install. So that means that you'd need a 48volt inverter to give your "mains" voltage from a 48v battery bank.
The other advice I'd suggest is to "start backwards" - minimise your projected electrical use as much as you can,
 never use it to do any heating if possible, and even look at things like gas fridges - then you design the system to capture and store your projected needs.....
Hope that helps! Grin
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Justme
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« Reply #5 on: January 28, 2009, 09:32:17 AM »

Low voltages mean lots of amps - look under your car bonnet - 12v, lead to starter, thick as your finger.......... if that were 48volts it need only be a quarter as thick....... Smiley

1/8th or less

Justme
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Navitron solar thermal system
30 x 58mm panel 259L TS
1200watts solar 120vdc
FX80 Solar controller
Victron 12v 3000w 120a
6kva genny
6 x 2v cells 1550amp/h 5C
24 x 2v cells 700amp/h 5C
Total bank 4350 amp/h 5C
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« Reply #6 on: January 28, 2009, 09:43:43 AM »

I wasn't talking about cross-sectional area, but good old-fashioned "thickness" Wink
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stephend
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« Reply #7 on: January 28, 2009, 01:50:02 PM »

One other thing to look out for lead acid batteries is that some manufacturers now offer re-combiner caps that can be attached to the cells so that the hydrogen released is transformed back into water and drips back into the cell - meaning that you don't have to top up as often.  Both Rolls and Hopekke (sp?) offer this feature in some of their bats.  (I don't have any experience with using these, just saw them advertised)
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Justme
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« Reply #8 on: January 28, 2009, 03:55:18 PM »

I think you can get those caps as an add on for others too.

Justme
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Navitron solar thermal system
30 x 58mm panel 259L TS
1200watts solar 120vdc
FX80 Solar controller
Victron 12v 3000w 120a
6kva genny
6 x 2v cells 1550amp/h 5C
24 x 2v cells 700amp/h 5C
Total bank 4350 amp/h 5C
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