Date:         Tue, 3 Feb 2004 16:34:30 -0500
Reply-To:     Jeff Strickrott <jstric01@CS.FIU.EDU>
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         Jeff Strickrott <jstric01@CS.FIU.EDU>
Subject:      Re: Why do JC Whitney Battery isolators have this VW caveat?
Comments: To: laurasdog@WEIRDSTUFFWEMAKE.COM
In-Reply-To:  <5.2.1.1.0.20040203071549.025bdeb0@mail.gct21.net>
Content-Type: text/plain; charset=ISO-8859-1; format=flowed

Can you post the link to the volvo site?

TIA
Regards,
--Jeff Strickrott
82 Westy, South Florida

Steve Delanty wrote:

> At 06:04 PM 2/2/2004, Jim wrote:
>
>> ā--¦       For all vehicles (exc. '86-01 Chevy, GMC, Toyota and all
>> Volkswagen vans with alternators and vehicles with Motorola 35-, 37-,
>> 55- and 62-amp alternators that do not have red terminal plate--used
>> on '73-80 AMC JeepĀ® and IHC vehicles).
>>        ā--¦       70 to 165 amps.
>>        ā--¦       Run accessories in vehicle without draining battery
>>
>> Why can't I run an isolator in a vanagon?
>>
>> Jim
>
>
>
> Jim,
> The problem is that it would cause the battery charging voltage to
> become excessively low...
>
> Battery isolators typically contain 2 large diodes to isolate the
> batteries. These diodes have a voltage drop across them of roughly
> 0.6 volts, so the batteries charge at a voltage 0.6 volts lower
> than the alternator output.
> "Real" charging systems have a separate wire from the voltage regulator
> to the battery so that it can sense the actual battery voltage and
> adjust the charging output accordingly. This serves to compensate
> for any voltage drop in the wire from the alternator to the battery
> and will also compensate for the voltage drop across a battery isolator.
> This setup makes for a nice stable charging voltage that isn't greatly
> affected by changes in load current.
>
> However, there are some cheesy charging systems that do NOT
> measure the voltage at the battery, but instead measure it right
> at the output of the alternator. The GM "1-wire" alternators and
> the Bosch alternator use in the Vanagon are notable examples.
> It's a truly pathetic way to charge a battery and the only reason
> it is done is to save a buck. It generally leads to very poor battery
> voltage regulation, especially if the wire from the alternator to the
> battery is long and thin. (Vanagon!)
>
> The good news is that it isn't too difficult to add an external Ford
> style regulator to the stock Vanagon alternator, although it does
> require removing and partially disassembling the alt.
> I did it on mine and it made a big difference in charging performance.
> There's a Volvo related website that explains how to do it if you
> are interested.
>
> If you try and use a diode type battery isolator with the stock
> Vanagon system you will likely end up with an extremely low
> charging voltage at the battery
>
> Steve
> EJ22 -> '86 Westy "Escape Pod"
>
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