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Battery

 
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Kadir



Joined: 16 Oct 2007
Posts: 6

PostPosted: Fri Dec 07, 2007 9:21 pm    Post subject: Battery Reply with quote

Could anybody please explain how deep cycle batteries operate!!

like when the battery states 12v 80ah or 24v 60ah!

i understand that for example the output is 80 amps over any hour, or have i totally wrong???!!!! Embarassed
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RenewableCandy



Joined: 12 Sep 2007
Posts: 12605
Location: York

PostPosted: Fri Dec 07, 2007 11:02 pm    Post subject: Reply with quote

For some reason people don't express the energy content of batteries in kWh. Instead, after the voltage they'll say, the the number of Amps times hours for which that current can run before the battery becomes totally flat.

So a 12V 60 AH battery stores a total of 12 times 60 Watt-hours, or 720 watt-hours (.72 kWh). Then you have to remember that even a deep-discharge battery doesn't want to be completely flattened: you should draw really only about 50% of that energy before you re-charge. The shallower the discharge, the more 'cycles' a battery can go through before it expires.

Car-batteries are really only any good if you don't plan on using more than about 10% of the stored energy before topping up the charge. However if you can get a bunch of them on the cheap they can still do what you need, but you just need more of them.

Depending on the type of battery, there may or may not be ways of rejuvenating it after its allotted number of charge-and-discharge cycles. Some of these ways are even legal and safe(!)
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adam2
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Joined: 02 Jul 2007
Posts: 6817
Location: North Somerset

PostPosted: Sun Dec 09, 2007 12:43 pm    Post subject: Reply with quote

The capacity of batteries is generally measured in ampere hours, this is an indication of how many amps can be supplied for how long. This is measured under ideal conditions, and with the battery being discharged very slowly, often over 20 or 100 hours.
For example a 60 A/H battery should be able to supply 3 amps for about 20 hours, or 1 amp for about 60 hours. If discharged at a greater current, the capacity would be less, for example at 20 amps, the battery might only last an hour.
As pointed out above, if the battery is to have a reasonable life, then it should not be discharged too deeply. (A full, 100% discharge would be acceptable say for emergency lighting in a theatre since this should be only a few times a year)
The capacity of most types of batteries improves during the first few charge/discharge cycles and then starts to decline. after repeated cycling the capacity drops to the point were the battery is no longer useful and must be replaced.
The number of full cycles varies from as little as 10 for car batteries, to several thousand for top qaulity deep discharge batteries.
Specifying a larger than required battery will generaly greatly extend the life for two reasons. Firstly the larger battery will be discharged to a lesser extent thus lasting longer, and secondly due to the greater initial capacity, the age-related drop in capacity can be greater before replacement is required.

The voltage of a battery is determined by the number of cells it contains, each cell is about 2 volts (presuming lead acid, which is the most common type) thus a 12 volt battery contains six cells.
12 volt batteries seldom exceed about 200 amp hours since they would otherwise be too heavy to readily move.
6 volt batteries are available up to about 400 A/H.
(4 volt, 8 volt and 10 volt batteries exist but are less common)

Larger capacities generally use single 2 volt cells, these are available up to many thousand A/H, though anything over about 1000 A/H may require lifting equipment.
2 volt cells are also used if a non standard voltage such as 14 volts, 26 volts, 32 volts, or 52 volts is required; such installations are now rare.

When connecting cells or batteries in series the voltages are added, but the A/H capacity remains the same.
For example, two batteries each of 12 volt, 60 A/H if wired in series will be
24 volt 60 A/H (batteries wired in series must be of the same capacity, and should preferably be the same make and age)

If however the same two batteries are wired in paralell, then the result will be 12 volt 120 A/H. (batteries in parralell must be the same voltage, and should preferably be the same capacity, age and brand)

The use of batteries is not entirley risk free and I recomend this thread

http://www.powerswitch.org.uk/forum/viewtopic.php?t=5455[url]
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Norm



Joined: 08 Feb 2007
Posts: 288
Location: Europe

PostPosted: Sun Dec 09, 2007 2:54 pm    Post subject: Reply with quote

adam2 wrote:
.......................
Larger capacities generally use single 2 volt cells, these are available up to many thousand A/H, though anything over about 1000 A/H may require lifting equipment......................


Not really, I am a not very fit 58 year old and I managed to install all 24 of my 1250 A/H two volt cells. An average guy would have no trouble lifting them. I suspect the limit would be about 1500 A/H but if two guys were handling them, perhaps a little more. I hope this doesn't sound like nitpicking but it is important if this limits somone's choice of installation.

Here's mine.


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kenneal - lagger
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Joined: 20 Sep 2006
Posts: 10581
Location: Newbury, Berkshire

PostPosted: Mon Dec 10, 2007 2:51 am    Post subject: Reply with quote

ex MOD submarine batteries must be much better quality then. My 960Ahr 2V ex MOD cells are about all I can carry before the acid is put in. They must weigh about a cwt.(just over 50kgs)(58 yr old cob building, rugby playing small holder)
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