

| Subject: | Re: Charge warning light LED question - David B. |
| From: | David Bjorkman |
| Date: | Thu, 10 May 2012 07:51:27 -0500 |
<div style="FONT-FAMILY: Arial; COLOR: #000000; FONT-SIZE: 24px"><DIV><FONT size=2 face=Tahoma>Boy, I love that kind of talk. It's a good thing this list exists. Sometimes the book is just not enough.</FONT></DIV><DIV><FONT size=2 face=Tahoma></FONT> </DIV><DIV><FONT size=2 face=Tahoma>Dave B. (the other one)</FONT></DIV><DIV> </DIV><DIV style="MARGIN: 5px 0px; BORDER-TOP: #bcbcbc 1px solid"></DIV><SPAN style="FONT-FAMILY: arial; COLOR: #000000; FONT-SIZE: 12px">On 05/09/12, <SPAN>David Beierl<dbeierl@ATTGLOBAL.NET></SPAN> wrote:</SPAN><DIV> </DIV><DIV style="FONT-FAMILY: arial; COLOR: #000000; FONT-SIZE: 12px">At 04:59 PM 5/9/2012, Scott Daniel - Turbovans wrote:<BR>>it works fine.<BR>>I know an LED would be brighter.<BR>>LED's have polarity ..<BR>>so wondering if an LED will work there for a warning light.<BR><BR>You could use an LED the way the Vanagon does, but in addition to the<BR>series resistor for the LED you'd have to add another resistor in<BR>parallel to the <FONT size=2 face=Tahoma>pair</FONT>, to get enough current to excite the<BR>alternator. Take a look at 90.8 fig 4. R3, 150 ohms one watt or<BR>better (notice the space around it) is wired from panel hot to<BR>D+. K2, the indicator LED in series with 470 ohm R4 is also wired<BR>from panel hot to D+. You can see this on 97.91 track 50-51. As of<BR>'87 they apparently changed to two shunt resistors instead of one,<BR>presumably 300 ohms each (97.108 track 50-51). I suspect they did<BR>that because they were getting overheating problems on the flexible<BR>circuit, so they put in two half-watters in parallel to spread out<BR>the heat load a little.<BR><BR>In this setup the 150 ohm resistor is supplying the "tickle" current<BR>to get the alternator going; the contribution from the LED and its<BR>resistor is pretty minor.<BR><BR>Yrs,<BR>d<BR></DIV></div>
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