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Date:         Thu, 12 Jun 2008 21:54:33 -0700
Reply-To:     Stuart MacMillan <macgroup@COMCAST.NET>
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         Stuart MacMillan <macgroup@COMCAST.NET>
Subject:      Re: Why AGM batts don't last as long as they should
Comments: To: Philip Zimmerman <philzimm1@OBERON.ARK.COM>
In-Reply-To:  <fe31bd517b47398374c32d7cc3634678@oberon.ark.com>
Content-Type: text/plain; charset="us-ascii"

Yes, it's a problem due to higher internal resistance of the AGM and Gel design. Marine alternators are set to the proper 14.4 volts needed for AGM charging, and are much more robust compared to car alternators. I'll have to do more research on car alternators to see if there is any way to get the 14.4 needed. But maybe just another specific charger is the simplest way to deal with this.

Stuart

-----Original Message----- From: Vanagon Mailing List [mailto:vanagon@gerry.vanagon.com] On Behalf Of Philip Zimmerman Sent: Thursday, June 12, 2008 9:15 PM To: vanagon@GERRY.VANAGON.COM Subject: Re: Why AGM batts don't last as long as they should

Good to hear your report of this confirmation Stuart! Anytime I hear of a Vanagon with a dead AGM or two, I'm curious to know what is the charging voltage at the battery terminals? If anything less than the "magic" number of 14.2 or so, an AGM is going to perform poorly or less than optimal.

I further concur with your suggestion for utilizing a Charger specifically designed for AGM's on a routine basis. Any battery (let alone an AGM) will perform better following a good full three-stage charge from a 110VAC Charger. Gotta keep those electrons stirred-up....

Phil Z. Campbell River, BC -----------------------

Date: Thu, 12 Jun 2008 11:37:31 -0700 From: Stuart MacMillan <macgroup@COMCAST.NET>

After talking to a few marine electrical experts, it seems the problem with AGM's in cars is the alternator voltage is too low. You need 14.2 volts to fully charge a discharged AGM, and most alternators put out about 13 to 13.7 volts, depending on load, which is fine for flooded standard and deep cycle batteries, but never fully charges an AGM. So, either find someone who can tweak the alternator output, or buy a charger specifically designed for AGM & Gel and use it at least once a week.


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