Date: Sun, 29 Apr 2007 02:51:23 -0500
Reply-To: Matt Roberds <mattroberds@COX.NET>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: Matt Roberds <mattroberds@COX.NET>
Subject: Re: Battery dead AGAIN!!!!
In-Reply-To: <20070429040437.NDBN22717.fed1rmmtai102.cox.net@fed1rmimpi03.cox.net>
Content-Type: TEXT/PLAIN; charset=US-ASCII; format=flowed
> From: PB <pbrattan@GMAIL.COM>
> Date: Sat, 28 Apr 2007 16:07:07 -0700
>
> (I'm [charging the battery on] 2 amps because somehow I think that
> 6 amps would be harmful. Is that right, or can I use 6 amps?)
1.21 gigawatts.... Great Scott!
98% of the time, for a car starting battery, the 6 A setting won't hurt
anything. The 2% covers the cases where the battery is damaged or
something weird is going on.
The main thing with most simple battery chargers is not to hook the
charger up and then fly off to your villa in Spain for a week. As the
battery charges up, the charge rate will drop off, but will never
completely go to zero. For a few hours this doesn't matter much at
all. Over a longer period of time, the overcharge will tend to make
the electrolyte (acid) level in the battery go down, and if it gets
down too far, the battery can be damaged.
The 2 A range is most useful for charging "small" batteries, like a
garden tractor or motorcycle battery. Or, if you know your car
starting battery is pretty discharged but you don't want to babysit
the charger, you could use the 2 A range to do most of the charging
overnight, and then work on the car some more in the morning.
The 2 A range can also be used to play certain tricks on a "regular"
car starting battery that is getting old and doesn't want to play
nice anymore. By the time you are playing those kinds of tricks, you
should already be thinking about a new battery, but judicious use of
the charger will usually let you drive to town for a new battery
instead of walking, or keep the battery going until payday.
If your charger has an ammeter on the front of it, pay attention to it.
On the 6 A range, it will probably indicate something close to 6 A when
you first hook it up to the battery, then gradually drop off. It will
probably never go to zero... it may get to 1 or 2 A and stay there for
a long time. If the meter reading hasn't changed in a couple of hours,
the battery is _probably_ as charged up as the charger can get it.
As a rough guide, a Vanagon starting battery is going to be something
like 40 amp-hours. What this theoretically means is that when you are
running things from the battery, you could get 10 amps from it for
4 hours, or 20 amps for 2 hours, or 40 amps for an hour, etc. (In real
life you don't get that much.) But this also gives you an estimate of
how long it takes to charge it. If it's a 40 amp-hour battery, and
it's totally dead, a 2 A charger will take at least 20 hours to charge
it back up all the way. A 6 A charger will take at least 6 hours and
40 minutes to charge it back up. In real life it will take longer than
this, mostly because the charger doesn't give a full 2 A or 6 A charge
all the time, but it gives you a minimum amount of time.
[From a later message:]
> There's a 1.3 A draw on the battery.
Yup, that's enough to kill a battery pretty good overnight. Over 12
hours, that would take 15.6 amp-hours out of the battery, which is
somewhere around a third of its capacity.
> The stereo has a 6 cd changer, and a giant amp and woofer that take up
> the whole underseat compartment in the back.
It sort of sounds like this is an aftermarket system - not originally
installed by VW. If so, any wiring associated with it is almost
immediately suspect. With a system like this, the stock Vanagon "radio"
fuse is probably only powering the head unit in the dash, and the amp
under the seat has its own power connection. The head unit tells the
amp when to turn on and off. You should probably still try the test of
pulling the fuses to see if one of them makes the 1.3 A draw go away -
the "radio" fuse might make it stop, or the fuse for the power windows
or the wipers or the heated massage chairs might make it stop - but you
can also try to disconnect the amp as follows.
Inspect around the amp for a couple of thick-ish power cables going into
it. They might be hidden under a plastic cover that's attached to the
amp but they should be there. One of them is the ground and will probably
go to the van body a short distance away from the amp, but the other one
is the power wire. Take a look at this wire and note the thickness and
insulation color. Then either follow the wire to its other end, or prowl
around the van looking for the other end of the wire. Some "usual
suspects" would be the positive post of either the main or aux batteries,
the fat battery cable connections at the starter motor (under the van),
the fat wire connection at the alternator (on the engine), or possibly
the main fuse box. Once you find the other end of the amp power wire,
first disconnect the negative cable at both the main and the aux
batteries, then unhook the amp power cable. Try the test with the meter
again and if the draw is gone, there is a problem in the stereo/amp
wiring or maybe in the amp itself.
Matt Roberds
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