John, You are absolutely right if discussing a generator. The field is composed of 2 or 4 electro-magnets mounted to the outside shell and the magnets will hold enough magnetism once magnetized that you don't need an external battery for the generator to re-start. But a alternator rotor retains so little magnetism that it usually takes a small amount of current to start one up. That initial current is supplied through your GEN dash light. Then, once the alternator starts up a smaller of two diode bridges inside the alternator provides current to the regulator. The larger diode bridge provides current to the car's electrical system. BTW, this is why your GEN light stays on when your alternator or regulator fails. The alternator rotor is no longer receiving excite current from the regulator and it continues to draw the small amount of current through your GEN light. But the current is not enough to drive the alternator to put out any real power. Tom www.towercooler.com
-----Original Message----- From: Vanagon Mailing List [mailto:vanagon@GERRY.VANAGON.COM] On Behalf Of John Rodgers Sent: Saturday, April 24, 2010 12:39 PM To: vanagon@GERRY.VANAGON.COM Subject: Re: alternator installation It's been a long time since I have thought on this - but I seem to recall that a strong charge from the battery(or jumper battery) is required to activate the field of the Alternator or the thing won't charge, even if it is turning. If your battery is strong enough to turn your starter motor - which takes a whopping amount of amps to turn against the load of the engine - it should be charged sufficiently to activate the field. John Rodgers Clayartist and Moldmaker 88'GL VW Bus Driver Chelsea, AL Http://www.moldhaus.com
On 4/24/2010 11:41 AM, Bill MacLachlan wrote: > Hi all > List wisdom& experience needed: > I'm installing a new alternator. > Label on the new alternator says have the battery fully charged before > hooking up the alternator. > My battery is low. > How critical is the warning? > Do I have to dig out the trickle charger and recharge the battery first? > > thanks > > Bill M > 82 GL I4 > > > |
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