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Mains battery charger...

 
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contadino



Joined: 05 Apr 2007
Posts: 1268
Location: Puglia, Italia

PostPosted: Sun Jul 20, 2008 7:02 pm    Post subject: Mains battery charger... Reply with quote

Could someone point me to a decent charger that I could use to charge (and maintain a charge on) a bank of leisure batteries from the mains? I'm thinking somewhere in the 160-200ah range. I haven't decided on the nature of the batteries, but I suspect they'll be lead acid on availability grounds.

Ta.
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Vortex



Joined: 16 May 2006
Posts: 6097

PostPosted: Sun Jul 20, 2008 9:42 pm    Post subject: Reply with quote

I use the big F**** Off rapid/trickle charger from Halfords.
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contadino



Joined: 05 Apr 2007
Posts: 1268
Location: Puglia, Italia

PostPosted: Mon Jul 21, 2008 6:53 am    Post subject: Reply with quote

Is that this one?

http://www.halfords.com/webapp/wcs/stores/servlet/product_storeId_10001_catalogId_10151_productId_210939_langId_-1_CarSelectorCatalogId__CarSelectorGroupId__varient__categoryId_31335_crumb_33958-123101_parentcategoryrn_31335

It says the max battery capacity is 110ah. I wasn't aware that these types of chargers had maximum capacities until yesterday.

I found this one after a bit more googling, which goes all the way up to 500ah. A bit more expensive than I was hoping, though.

http://www.theultimatefinish.co.uk/Store/Product/ProductDetails.aspx?ProductId=145
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Vortex



Joined: 16 May 2006
Posts: 6097

PostPosted: Mon Jul 21, 2008 8:52 am    Post subject: Reply with quote

No, mine is a big orange box. Rather chunky.

It's labelled "RAC" ... maybe it's their product?

Maybe no longer stocked?
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adam2
Site Admin


Joined: 02 Jul 2007
Posts: 6555
Location: North Somerset

PostPosted: Mon Jul 21, 2008 9:34 am    Post subject: Reply with quote

There are three basic types of battery charger for lead acid batteries,

The first and simplest is a basic transformer and rectifier circuit with no control or regulation. This sort of charger reduces the charge rate as the battery voltage increases, but DOES NOT stop charging when the battery is full.
If not turned off by the user there is a clear risk of overcharging, especialy with sealed batteries.
Except for short term, temporary or emergency use I would advise against use of this sort of charger.
The sole advantage is cheapness and simplicity.

The second type of charger uses an electronic regulating circuit to maintain a constant output voltage regardless of changes in supply voltage. These are generally known as float chargers. For a 12 volt battery the correct voltage is about 13.75/13.8 volts.
Idealy this voltage should be slighty increased in cold conditions and reduced in hot conditions, the larger and more expensive chargers have a temperature sensor for this purpose.
This type of battery charger can be left connected permanently and will never overcharge the battery.
Also this charger will charge a battery of virtualy any size, for example a 1 amp charger, will eventualy charge a 1000 A/H battery, though it might take months.
If the makers recomend a maximum battery size, this is to ensure charging in a reasonable time such as 24 hours, a much larger battery will eventualy charge.
Constant voltage chargers are most suitable for standby batteries that are not discharged often.
The drawback is that they are very slow to fully recharge a discharged battery, the float voltage of about 13.8 volts is too low to achieve this in a reasonable time.

The third and most sophisticated type of charger is known as a three stage charger and contains some quite sophisticated electronics.
This provides a three stage charging process and should fully recharge a discharged battery, but can be left connected indefinatly without risk of overcharging.
The first stage uses a constant current, equall to the rating of the charger, say three amps, the charger continually monitors the battery voltage, and when this reaches say 14.4 volts, the charger automaticly selects stage two. This is a constant voltage of 14.4 volts for a timed period of some hours. When the correct time has elapsed, stage three commences which a constant voltage of 13.8 volts.
Such chargers are the best choice for batteries regularly discharged such as for golf carts, electric wheelchairs etc.
A 3 stage charger MUST BE at least roughly the right size for the battery. If the battery is too small, then the constant current charge will be too high and may damage the battery.
If the battery is too big, then in constant current mode, the voltage may not quite reach 14.4 volts which triggers the next stage. The charger may therefore stay in constant current mode longer than desired, or even indefinatly, and thus overcharge the battery.
If the power fails during charging, then the whole process starts again, the odd power cut does not matter much, but regular interuptions (such when switching between mains and generator) must be avoided as they will lead to needless repeating of the timed 14.4 volt charge and risk overcharging.
Also no load should be connected to the battery being charged with a three stage charger, as so doing will "confuse" the charger.

If you wish to maintain in good condition a seldom used battery, then I suggest a constant voltage float charger.

If you wish to use grid or generator power to top up batteries normally charged from PV or solar, then I would consider a basic non regulated charger, of moderate size. Simply keep an eye on the battery voltage and turn the charger off when done.
If this results in only say 80% charging, it does not matter that much since the regulated wind or solar input should do the rest.
If slight overcharging results that does not matter much either if it IS slight and not often repeated.
(these crude unregulated chargers are not really suited for regular use, but should be fine for limited topping up of batteries normally charged otherwise)

Except in special cases I would avoid three stage chargers for RE systems since they are very expensive in sizes to suit the large batteries often used, and they are easily "confused" by connected loads or power interuptions.
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