Date: Tue, 20 Apr 2010 15:24:22 -0700
Reply-To: "Mike \"Rocket J Squirrel\"" <camping.elliott@GMAIL.COM>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: "Mike \"Rocket J Squirrel\"" <camping.elliott@GMAIL.COM>
Subject: Re: charging aux battery: too much of a good thing?
In-Reply-To: <4BCE26A7.8010605@cox.net>
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mark drillock wrote:
> Today I was able to fire up my 3 battery system for the first time. A
> dedicated 125 amp hour deep cycle was added for the Vitrifrigo fridge
> only. With the Zetec it fits easily in the engine compartment and is a
> foot from the alternator. I used short #6 wires with a Surepower 1314
> between the alternator and the battery, and ran #6 between the neg post
> and the engine block.
>
> As part of this setup I added an amp meter for the fridge battery so I
> could see how fast it was charging and then know how long I needed to
> run the engine to get another night of camping. I was surprised to see
> the meter reading over 60 amps going into the battery when I first
> started the engine even though the battery was fairly full. This quickly
> tapered down over a few minutes to a steady 25 amps. I wonder if maybe I
> have too much charging?
>
> I have not been able to pin down the capacity of this Ford alternator. I
> have seen it listed as 105 amp, 115 amp, and 130 amp. I don't care much
> either way as 105 would be plenty but it would be good to know. I am
> measuring 14.5+ volts at the alternator which I believe is pretty common
> with modern vehicles but I wonder how good it will be for the battery
> long term. I could slow down the charging rate by switching to longer
> and thinner battery cables but this would not drop the voltage much
> after the battery was full. That seems too high for a "float charge" but
> I don't know how it will be in practice. Anybody know? Suggestions?
>
Well, I'm no battery expert, but I do watch charging currents, etc., on
my rig and I think that what you're seeing is quite normal. The battery
will cheerfully suck in a lot of current initially and a good alternator
will deliver, assuming fat wires. But as you saw, that initial high
inrush current quickly tapers. IOW, the alternator and battery were
designed to be connected, and it seems a stretch that the design
engineers would have assumed .1 ohm of resistance or anything. Higher
resistance in the wire would reduce the initial inrush current, but I
don't think you need to do that.
--
Mike "Rocket J Squirrel" Elliott
84 Westfalia: Mellow Yellow ("The Electrical Banana")
74 Westrailia: (Ladybug Trailer company, San Juan Capistrano, Calif.)
Bend, OR
KG6RCR
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