Date:         Thu, 25 Jul 2002 20:44:16 -0400
Reply-To:     David Beierl <dbeierl@ATTGLOBAL.NET>
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         David Beierl <dbeierl@ATTGLOBAL.NET>
Subject:      Re: Alt idiot light on
Comments: To: jrasite@eoni.com
In-Reply-To:  <3D4079BD.2050703@eoni.com>
Content-Type: text/plain; charset="us-ascii"; format=flowed

At 06:20 PM 7/25/2002, Jim Arnott wrote:
>I guess that I'm a bit fuzzy on this...
>
>Does not:
>
>The 12v through the idiot LED energize the field of the alt?
>Wiring is stone simple... two large terminals direct to battery +, one
>small terminal to LED.  If the current from the LED has to go through an
>open relay to get to the alt, how would the field ever get power?
>
>Jim

Circuit goes from +12 at instr panel, through an LED/resistor combination
*in parallel with another resistor* to supply more current than can safely
flow through the LED.  From there it goes to Alternator D+ terminal, in
parallel with fridge relay coil, battery relay coil, whatever else people
have hung on there to be driven by the Alt D+ signal.  Any such relay coils
are current sinks and will cause the light to light (at least dimly) even
though the wire is disconnected from its main load, the D+
terminal.  However the current through the circuit will not be enough to
activate the relay(s).

In normal operation, once the alternator starts charging the D+ terminal
becomes an output instead of an input, and supplies +12 at a reasonable
current capacity (??an amp or two??) to the circuit.  Since the LED is now
seeing +12v on both ends, it stops lighting up; but since the relays now
have enough current available to drive them they activate and connect the
fridge, aux battery, whatever.

Make sense?

d


>David Beierl wrote:
>>At 10:56 PM 7/24/2002, Dennis Haynes wrote:
>>
>>>If you have a camper, the refrigerator relay will also turn the light on
>>>with the alternator disconnected. The alternator has to actually be
>>>charging for the relay to energize the refrigerator.
>>>
>>>Dennis
>

--
David Beierl - Providence, RI
  http://pws.prserv.net/synergy/Vanagon/
'84 Westy "Dutiful Passage"
'85 GL "Poor Relation"