Date:         Tue, 19 Jun 2007 12:00:48 -0400
Reply-To:     Dennis Haynes <d23haynes57@HOTMAIL.COM>
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         Dennis Haynes <d23haynes57@HOTMAIL.COM>
Subject:      Re: Low-voltage alarm
Comments: To: camping.elliott@GMAIL.COM
Content-Type: text/plain; format=flowed

Keep in mind these voltage guidelines assume the battery is at rest. Under
load the voltage will be lower and being charged obviously higher. This is
also why battery capacity should be matched to the load, 6-8 hour rate.
Discharging or charging too fast will also damage batteries.

Dennis


>From: Michael Elliott <camping.elliott@GMAIL.COM>
>Reply-To: Michael Elliott <camping.elliott@GMAIL.COM>
>To: vanagon@GERRY.VANAGON.COM
>Subject: Re: Low-voltage alarm
>Date: Mon, 18 Jun 2007 21:33:32 -0700
>
>It's true: 11.7V pretty much means that the battery is at 25% state of
>charge. It's a good place to stay above: "Occasional dips into [this
>range] are not harmful, but continual discharges to those levels will
>shorten battery life considerably." ["State of Charge,"
>http://www.windsun.com/Batteries/Battery_FAQ.htm#Battery%20Voltages]
>
>10.5V at 77 degrees F is considered fully-discharged.
>
>Determining a battery's state of charge by reading its voltage is not
>real accurate; measuring each cell's specific gravity with a hygrometer
>is the most accurate method, but it's messier business than I care to
>deal with inside our Westy. Given the inaccuracy of the voltage method,
>maybe 11.7 volts as a trigger point ain't bad. But one wonders how
>accurate that cut-off gizmo's voltage measurement circuit is.
>
>It comes down to how deeply you are willing to discharge the battery. I
>try to keep our house battery at no less than 80% state of charge (per
>the XBM battery monitor, no less than 12.4V on the volt-o-meter).
>
>--
>Mike "Rocket J Squirrel" Elliott
>71 Type 2: the Wonderbus
>84 Westfalia: Mellow Yellow ("The Electrical Banana")
>74 Utility Trailer. Ladybug Trailer, Inc., San Juan Capistrano
>KG6RCR
>
>
>
>TC typed:
>>>Yes, but it cuts out at 11.7 volts.... too high to be of any use for
>>>RV's.
>>>                                         David (dsl82westy)
>>please explain  I thought that was about when a 12v battery has 25% charge
>>left
>>12.8-13.2v is ~ full charge, & fully discharged is about 11v
>>so 11.7v is really low discharge pt even on deep cycle batteries if you
>>want
>>optimal life of the battery
>>
>>
>>~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>>~~~~~
>>>>Would this sort of low voltage cut-off gizmo do the trick ??
>>>>
>>>>Tom
>>>>
>>>http://canadiantire.ca/browse/product_detail.jsp?PRODUCT%3C%3Eprd_id=845524
>>443294641&FOLDER%3C%3Efolder_id=1408474396672454&bmUID=1182208017428
>>