

| Subject: | Re: Why do JC Whitney Battery isolators have this VW caveat? |
| From: | Jeff Strickrott |
| Date: | Tue, 3 Feb 2004 16:34:30 -0500 |
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: > >> �--� 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 Jeep® and IHC vehicles). >> �--� 70 to 165 amps. >> �--� 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" > >------------------------------------------------------------------------ > > >--- >Outgoing mail is certified Virus Free. >Checked by AVG anti-virus system (http://www.grisoft.com). >Version: 6.0.576 / Virus Database: 365 - Release Date: 1/30/2004 > >
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