Shoptalkforums.com

For Your Air Cooled Pleasure!
It is currently Sun Nov 23, 2014 6:44 am

All times are UTC - 6 hours [ DST ]




Post new topic Reply to topic  [ 43 posts ]  Go to page 1, 2, 3  Next
Author Message
 Post subject: LED alternator warning light
PostPosted: Mon May 25, 2009 10:18 am 
Offline

Joined: Thu Apr 27, 2006 4:11 pm
Posts: 19
I've read some articles - I think on other websites - about some difficulty with using a LED to replace the stock warning light in the speedo. I don't have a stock speedo, and I have LEDs for all my warning lights. Will I not get a charge from my alternator because of the minimal load from the LED? Also, how would I wire it up correctly, I'm a little confused with the diagram for the stock light, it's almost as though it's backwards... can someone educate me on how exactly that circuit works?


Top
 Profile  
 
 Post subject:
PostPosted: Mon May 25, 2009 3:28 pm 
Offline
User avatar

Joined: Sat Feb 15, 2003 3:01 am
Posts: 2290
You are 100% correct; the LED light will probably not allow the alternator to begin charging.

My sketch below shows how to overcome this.
The 100 Ohm resistor will pass enough current to start the alternator.
The additional diode protects the LED against reverse voltage and also prevents engine run-on which can occur, especially with any kind of electronic ignition. An ordinary 1 Amp diode (200V rating) will suffice here.

I'll assume that the LED lights you have are rated for 12V operation and have some kind of limiting resistor built-in. If not, the light will need an additional resistor in series.

Speedy Jim
http://www.nls.net/mp/volks/



Image


Top
 Profile  
 
 Post subject:
PostPosted: Tue May 26, 2009 10:32 am 
Offline

Joined: Thu Apr 27, 2006 4:11 pm
Posts: 19
This is beautiful. Thank you. Just so I can wrap my mind around it, I tried to isolate the oil light circuit, do I have this correct?
My LED is from Watsons (if I recall correctly) and was for 12V. There's a white lead and a black lead. Does it matter which direction the current flows?
Image
[/img]


Top
 Profile  
 
 Post subject:
PostPosted: Tue May 26, 2009 12:11 pm 
Offline
User avatar

Joined: Sat Feb 15, 2003 3:01 am
Posts: 2290
Yes, your (nice) diagram is correct.

The LED won't work if connected backward. But I don't know what polarity Blk and Wh is on their LED's. Try it and see which works.

Jim


Top
 Profile  
 
 Post subject:
PostPosted: Tue May 26, 2009 12:19 pm 
Offline

Joined: Thu Apr 27, 2006 4:11 pm
Posts: 19
Thank you. I'll let you know how it turns out.


Top
 Profile  
 
 Post subject:
PostPosted: Wed May 27, 2009 10:44 pm 
Offline

Joined: Thu Apr 27, 2006 4:11 pm
Posts: 19
So far, so good. Well, sorta. Rewired, turned the key, and on popped the light. Fired up the car, struggled to get her to run (that's another story entirely) and the light won't go off. I think it's because I've been cranking and cranking, and not able to keep the car running long enough to recharge the battery. She's on the charger now, so we'll try her again tomorrow.

Fixed my oil light circuit too, thanks to Speedy Jim's oh-so-easy diagram. Thank you!

Now if only I can get her to run right...


Top
 Profile  
 
 Post subject:
PostPosted: Thu May 28, 2009 10:49 pm 
Offline

Joined: Thu Apr 27, 2006 4:11 pm
Posts: 19
Circuit works like a charm, and the alternator is charging. Thanks for the help!


Top
 Profile  
 
 Post subject:
PostPosted: Wed Jun 24, 2009 2:40 pm 
Offline

Joined: Tue May 17, 2005 9:36 am
Posts: 206
Bit of a bump from me: I'm running the stock light on a 75W internal alt. My gen light won't go off until my RPMs hit about 2600, right about the time my main jets kick in from the idles on the Webers. Once the revs get high enough, the light goes off, my volt meter begins to read ~13V. however, from this point forward, the Alt continues charging regardless of RPMs.
Any thoughts?


Top
 Profile  
 
 Post subject:
PostPosted: Wed Jun 24, 2009 4:19 pm 
Offline
User avatar

Joined: Sat Feb 15, 2003 3:01 am
Posts: 2290
That happens with some alternators.

The fix is to add a small resistor across (in parallel with) the dash warning light.

Try the 100 Ohm 2 watt resistor (or anything close to that). 100 Ohms will add 120 ma of excitation current initially which should be enough to get the alternator going even at low RPM's.

If you get run-on after adding the resistor, stick the diode shown above in the circuit.

Speedy Jim
http://www.nls.net/mp/volks/


Top
 Profile  
 
 Post subject:
PostPosted: Sat Jul 04, 2009 3:49 pm 
Offline

Joined: Tue May 17, 2005 9:36 am
Posts: 206
Thanks much, Jim. I'll let you know if it works next time I have a spare minute to try it


Top
 Profile  
 
 Post subject:
PostPosted: Mon Jul 06, 2009 8:13 am 
Offline
User avatar

Joined: Mon Sep 08, 2003 8:12 am
Posts: 9570
ZAZ..

Thanks for the post.

timmy


Top
 Profile  
 
 Post subject:
PostPosted: Mon Aug 10, 2009 12:18 pm 
Offline

Joined: Tue May 17, 2005 9:36 am
Posts: 206
uh..no problem

Haven't been able to try the fix yet; I'm sure if you do a search, you can find out that I've been trying to get my newly busted transmission sorted out. Priorities.


Top
 Profile  
 
 Post subject: LED warning lite for Alternator
PostPosted: Fri Aug 28, 2009 1:33 am 
Offline

Joined: Fri Aug 28, 2009 1:24 am
Posts: 3
I followed Speedy Jim's instructions and diagram to put an LED as warning lite. It worked well first try....but I see it charging my battery at almost 17 volts ! !
Any ideas of what I should do ?


Top
 Profile  
 
 Post subject: Re: LED warning lite for Alternator
PostPosted: Fri Aug 28, 2009 6:32 am 
Offline
Moderator
User avatar

Joined: Sun Oct 23, 2005 8:14 pm
Posts: 14033
Location: Georgia near Savannah
chayes wrote:
I followed Speedy Jim's instructions and diagram to put an LED as warning lite. It worked well first try....but I see it charging my battery at almost 17 volts ! !
Any ideas of what I should do ?

Welcome to the STF chayes. Can you post a pic of you Alf or Gen?
The regulator controls the amount of charge.

_________________
Hot, humid air is less dense than cooler, drier air. This can allow a golf ball to fly through the air with greater ease, as there won't be as much resistance on the ball.


Top
 Profile  
 
 Post subject:
PostPosted: Fri Aug 28, 2009 7:32 am 
Offline
User avatar

Joined: Sat Feb 15, 2003 3:01 am
Posts: 2290
Quote:
Can you post a pic of you Alf or Gen?



Alf:

Image



Gen:


Image


:lol:


Top
 Profile  
 
Display posts from previous:  Sort by  
Post new topic Reply to topic  [ 43 posts ]  Go to page 1, 2, 3  Next

All times are UTC - 6 hours [ DST ]


Who is online

Users browsing this forum: No registered users and 1 guest


You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot post attachments in this forum

Jump to:  
Powered by phpBB © 2000, 2002, 2005, 2007 phpBB Group