Battery explosion [RE-wrenches]

[Joel Davidson]

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The design of PV systems without controllers has changed over the years.

Direct electrical connection of the array to the battery system without
regulation is advisable only when the peak output current of the array is
less than 5% of the charge capacity of the batteries (amp-hour rating) in
the system (charge equals current x time). - Solar Photovoltaic Applications
Seminar: Design, Installation and Operation of Small, Stand-Alone
Photovoltaic Power Systems, DOE/CS/32522-T1, July 1980

To obtain the benefit of self-regulation, you must have the proper size
battery. Figure at least 3.5 ampere hours of battery for each watt of module
power rating. For example, a 42 watt, 30-cell module should be connected to
at least 130 ampere hours of battery storage. In addition, the modules and
the batteries should be within 20 degrees F of each other. - The New Solar
Electric Home, 1987

In the past, designers have made self-regulating PV systems with peak PV
current output of 5% or less than the battery ampere hour capacity and
charge voltage below the battery float voltage. The NEC requires a
controller on PV Systems with charging currents greater than 3% of battery
amp-hour capacity. - The New Solar Electric Home, 2005 (draft)

----- Original Message ----- 
From: "Allan Sindelar" <allan at positiveenergysolar.com>
To: <RE-wrenches at topica.com>
Sent: Thursday, December 02, 2004 1:41 PM
Subject: Re: Battery explosion [RE-wrenches]




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Fair question, for which I don't know the answer. Wrenches, what are safe
guidelines for when a charge controller is unnecessary? Below what C/ rate?
And is it different for an automotive starting battery that will never have
water added than for a deep cycle flooded battery?
Allan

----- Original Message ----- 
From: "John Veix" <john at gosolar.co.nz>
Why bother with a Sungard if the size of the panel is less than 1/3 of the
battery a/h rating ?

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