alternator warning light

Printed From: the12volt.com
Forum Name: Relays
Forum Discription: Relay Diagrams, SPDT Relays, SPST Relays, DPDT Relays, Latching Relays, etc.
URL: https://www.the12volt.com/installbay/forum_posts.asp?tid=121158
Printed Date: May 15, 2025 at 5:30 AM

Topic: alternator warning light

Posted By: LqDFx
Subject: alternator warning light
Date Posted: April 04, 2010 at 8:03 PM

I want to know if this relay diagram will work for lighting up a dash light if my alternator circuit breaker trips?

The Pos (+) from fuse box will be a live with ignition on only.

Any help would be great!

posted_image

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Sony XAV-A1 HU, RF P4004 AMP, RF P3001 AMP, 2 RF 10" P1S410 Subs, LA S2.35.2 Dash Speakers, LA S2.525.2 Door Speakers, RF FRC3268 Rear Speakers

Replies:

Posted By: gabedemelo
Date Posted: April 05, 2010 at 3:26 AM

looks right just make sure you get side of breaker that goes cold when tripped,... obviously

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GreenGables

Posted By: LqDFx
Date Posted: April 05, 2010 at 12:21 PM

I just figured out that it will not work! The battery will push back down the line and provide power to the relay. I need a way to isolate the circuit breaker from the battery.

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Sony XAV-A1 HU, RF P4004 AMP, RF P3001 AMP, 2 RF 10" P1S410 Subs, LA S2.35.2 Dash Speakers, LA S2.525.2 Door Speakers, RF FRC3268 Rear Speakers

Posted By: awdeclipse
Date Posted: April 05, 2010 at 3:10 PM

https://www.bcae1.com/circuits.htm

Little more then halfway down. "Blown Fuse Indicator"

Posted By: LqDFx
Date Posted: April 06, 2010 at 2:16 AM

awdeclipse, I have been looking at that page off and on all day and I can honestly say I am baffeled by it! I am not really great with the elctronic circuits as of yet and I am stumped as to really even start building that circuit!

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Sony XAV-A1 HU, RF P4004 AMP, RF P3001 AMP, 2 RF 10" P1S410 Subs, LA S2.35.2 Dash Speakers, LA S2.525.2 Door Speakers, RF FRC3268 Rear Speakers

Posted By: awdeclipse
Date Posted: April 06, 2010 at 7:07 AM

Well I always go about things one of two ways. Trying to understand it before building it, or just following the circuit and figuring it out later if it doesn't work. posted_image

Here is another site I find useful to help break down the basics of transistors. If anything the site usually serves as a quick reference for myself as I work with transistors few and far between these days.

BJT Switches Overview

Posted By: oldspark
Date Posted: April 07, 2010 at 7:21 AM

If the load-end of the breaker has loads of a few amps or more, a 2W-3W bulbs across the breaker should suffice.
Otherwise a 12V LED (LED with resistor) for smaller loads, or maybe add a resistor from the CB downstream (load) end to ground.

I am curious - this is not a battery-alternator CB? What does it power?

PS - re-reading it sounds like the battery to alternator...
The problem is you will normally be sensing a mere change of 1-2 Volts if the fuse/CB opens. (13V is the alternator fails - but its charge lamp should come on for that....)

I recommend a voltmeter, then you can see how good your system is under different circumstances (overnight voltage, cranking, overcharge (>14.4V long term) & undercharge (under 13.8V at reasonable revs).