Battery isolator causing charging problem?

[Oil Phil-M]

Have a dual battery setup with an isolator in my 72 Westy. This problem started a few months ago.

Alternator light doesn't come one when I turn the key to on. Start the van, the volt and both amp meters indicate that no charging is happening. Rev the engine up to around 2500 and then snap, things are charging again and remain charging regardless of engine speed until the engine is turned off.

It feels like somehting in the system doesn't recognize that charging is needed until an amount of electricity is created by the alternator (tied to the engine speed) is created. Changed the indicator bulb, alternator (used), regulator (new) and the problem still persists. Only thing I haven't touched is the isolator.

Anybody experience anything similar before?

[WestyPop]

Nope. Had the same SurePower http://www.surepower.com/isolator.html isolator wired into the '68 Westy since 1984; no problems yet, knock on wood(Baltic Birch, of course).

A suggestion would be to bypass the isolator & auxiliary battery, just for test purposes. Then you can get a better idea of whether it's the alternator or the isolator causing problems.

IMO it's not uncommon for VW alternators, even in a bone stock system, to leave the red "ALT" light glowing at idle, just after start-up, until the throttle is 'blipped' to 1000-1200RPM. It doesn't usually require 2500RPM, however. That sounds a little too questionable to deal with for very long.

Some have said that it may have something to do with Bosch not providing for a large enough 'kick' in the alternator's self-exciter circuit.(?) Even a "Rebuilt by Bosch" 90A alternator on one of my W/C VWs does it, but the light goes out @ 1200RPM. Voltage pops right up to 14+ at the same time.

J.R.
68 Westy
(+ others)