Date:         Mon, 21 Jul 2003 16:24:26 -0400
Reply-To:     Tim Demarest <tim.demarest@POBOX.COM>
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         Tim Demarest <tim.demarest@POBOX.COM>
Subject:      Re: Vanagon alternator too weak for Optimas.
In-Reply-To:  <20030721194257.40226.qmail@web12202.mail.yahoo.com>
Content-type: text/plain; charset=us-ascii; format=flowed

OK Phil... Electronics I know a little about...

As long as the charging voltage is greater than the battery voltage (the
battery is *always* putting out 12 volts), then some current will flow into
the battery, and the battery will charge.

- Too high a voltage will send too much current into the battery, with
damaging results.
- Too low a voltage will send too little current into the battery, making
charging times longer.
- The voltage output from the alternator is limited by the voltage
regulator, a voltage regulator clamps it's output voltage to a set maximum.
Auto design engineers choose a regulator that will place the voltage high
enough above 12 volts to give quick battery charging, without being high
enough to damage the battery... 14.0 to 14.5 volts seems to be the common
working range (based on my experience putting voltmeters on various
alternator output studs over the years). I've only measured a value greater
than 15 volts once... on a vehicle that had already had the battery
replaced twice. Replacing the bad regulator saved the third battery.
- The VW regulators are designed to clamp at 14.0 volts, so you won't get
more than that out, no matter how new/upgraded your alternator is.
- The alternator output can be *less than* 14 volts for a number of reasons:
         1. The vehicle is drawing more current than the alternator can supply.
         2. The voltage regulator has gone bad.
         3. The alternator brushes are worn.
         4. The alternator is worn out.

- Installing an alternator that provides more *current* will not harm
anything in your system.
- Installing an alternator (or regulator) that provides a higher *voltage*
can damage your battery, or *any other electrical system in the van*... you
would be cranking up the voltage on every circuit in the van, not just the
battery charging voltage!

Hope this info helps some!

Tim




At 12:42 PM 7/21/2003 -0700, Phil S. wrote:
>i read in the archives that Optima does NOT recommend
>anything less than a 15 volt alternator output, if
>this is true, then we are all undercharging our
>optimas becouse the vanagon's Alt charges around
>13-14V. Even MORE confusing is that the battery guy
>told me any charge over 14.5 volts will destroy 12v
>batterys. Wha?
>Optimas FAQ:http://www.optimabatteries.com/faq.asp#q7
>  Would a LARGER alt help, or does the alt's voltage
>regulator get in the way? Please correct my figures
>as i am also repeating what the battery guy told me.
>
>Also My alternator is charging around 12.7v under
>load...the battree guy tells me i should be around
>13-13.5(tested with stereo/headlights on at 2000RPM's)
>He says my Alt is too weak, especially when i have the
>stereo on, fan, headlights and auxillary battery
>connected via a big relay switch. Apparently all this
>stuff is hogging precious juice from my batterys. He
>told me a bigger alternator would fix my problem. So
>anyone know where i can buy a larger amp alternator
>that might fit the Tiico bracket/pulleys? i found this
>alternator described as being higher output, at lower
>RPM's it at:
>http://www.amplepower.com/products/alt/index.html
>its chromed and looks ex$pen$ive.
>
>
>Thanks
>Phil 84' Westy w/ Tiico
>
>
>
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