On 28/04/2011 15:16, Justin Richards wrote:
> Sealed Lead Acid was a choice of battery but have nothing to base this
> on.  Various solar suppliers appear to supply gel and lead acid.

The semi Sealed "Calcium Technology" low maintenance lead acid used on=20
Cars and Lorries seems to last best. The voltage seems to rise sharply=20
from 13.6V to 14.2V at fully charged allowing cut off of charging. Gel=20
cells seem poor for repeated deep discharge and have sightly lower=20
terminal volts.

Important is a good "smart Charger" that can deliver current equal only=20
to load current when battery is charged. For long life of battery, it's=20
likely you only normally want less than 50% discharge. So maybe a 80 Ah.=20
56Ah is common car battery size.

I'd choose the Solar panel to be able to charge battery at discharge=20
rate x 2 at least on an overcast day and supply the equipment current at=20
your location, assuming there is no automatic panel cleaning and long=20
term use. Here the winters are much shorter days (about 8hrs so much=20
less light, maybe need twice as much panel here)

The Electronics payload should work over 10V to 16V range and the load=20
should be disconnected to protect battery if the battery is below 10.7V=20
approx (or according to datasheet).

It's important if Performance quoted for Battery or Solar panel is=20
average or minimums. i.e. 10,000 average life is useless on a 4,000 hr=20
requirement if significant % of units only last 1000 hrs.




--=20
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