http://calsolarsolutions.com/rvandcabin.html

To summarise, you should know the following :

• Voltage is variable, it is like water pressure, devices can handle changes in voltage as long as it isn’t too much or to little.
• Amps are also variable, it is like the speed of the water flowing through a pipe.
• AmpHours is a rating of how long you can maintain that speed, it’s the bucket of water that will eventually get empty.
• Watts is the overall ‘usage’, Watts = Volts x Amps

Batteries

• Batteries are a 12V DC system, but they are really closer to 13V
• You need more than 17v or more to get a good charge into a battery
• Batteries do not like to be discharged below 12V, or 50% of their capacity
• A 50AH battery can give 1A for 50 hours, or 2A for 25 hours

Panels

• Panels are rated for their perfect conditions (midday, full sun, 25 deg C)
• Heat (aka the playa) reduces a panels’ output
• The angle to the sun reduces a panel’s output
• An 18V,75W panel really only puts out 15V,60A on average

Charge controllers

• 3-stage or PWM controllers are better
• controllers stop overcharging the battery
• controllers have a load (Amps) rating, if you panel has too many Amps, it will blow out the controller

So you have paid big bucks for your 30 batteries to run your house for a week, but after a month, they have all died. What went wrong?

Of course YOU DON’T WANT A CAR BATTERY!

A car battery is designed for short bursts of high output, for starting a car mostly.

You want a deep-cycle battery. They’re still 12V, but different sizes have different capacities. The Capacities are in Amp-Hours or AH. The higher the AH, the bigger the capacity (and the more expensive). If you go the roll-your-own route, take the advice here and buy a cheap costco deep-cycle, as you’ll probably kill it pretty quick.

Typically, for people who have large requirements, they get multiple batteries and wire them together.

Math Fun: Watts = Volts x Amps the “typical” 12V battery is rated at about 100 amps. You can safely use half of it, without damaging the battery. So a typical costco deep cycle battery holds 12v x 50a= 600 usable watts

How to wire for balanced voltage distribution (2 examples):

Why to “Diagonal Wire”: http://www.smartgauge.co.uk/batt_con.html

Several Different types

* Flooded (original style, open caps, add water)

* Gel

* AGM

* Spiral

* Starting

* Deep Cycle (Difference between Starting & Deep Cycle batteries)

All need to be recharged soon after being depleted, and none like more than a 60% discharge, the deeper the discharge, the more internal damage, and shorter the overall lifetime. Sitting discharged, sulfur crystals start to form, and they obscure the lead plates, reduceing capacity. (sulfation)

Hobbyist site (Bill Dardens Battery FAQ) http://www.uuhome.de/william.darden/

Commercial site explanation, but they are not the only answer http://www.battery-care.com/

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