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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!!!!
Comments: cc: PB <pbrattan@GMAIL.COM>
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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