Normal battery isolators are a poor choice in a VW due to the forward voltage drop. All power diodes drop over 1.0 volt when cool. As they heat up, the drop increases. The vw senses and control the alternator output internally so this drop is not compensated. Only 11.5 to 12 volts actually charges the battery. Many American cars sense and control the charging voltage remotely so the alternator output will increase to overcome the resistance. The alternator can be modified to overcome this. I feel it is not worth the effort. Virtually every RV manufacturer uses relays to isolate-charge the "house" battery(ies). It is simple, reliable, and low cost. It is also more efficient as you do not have the heating effect with a relay. Dennis
-----Original Message----- From: Vanagon Mailing List [mailto:vanagon@gerry.vanagon.com] On Behalf Of Julian Burden Sent: Tuesday, December 11, 2001 2:11 PM To: vanagon@GERRY.VANAGON.COM Subject: Battery isolator I was told that a regular battery isolator will not work in a Vanagon by someone who was told by someone who . . . I did not believe this as my understanding is that a battery isolator is just a pair of diodes on a big heatsink. But, then I looked at the JC Whitney website catalog - they list several isolators, many of which are described as not suitable for all VW vans! Why is this so, and what do I need? |
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