Electrical Question: Diode...
Thread Starter
Pro
Joined: Oct 2003
Posts: 641
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From: Storm lake Iowa
Electrical Question: Diode...
I've wanted on several occasions to draw power directly from the alternator terminal (for such things as electric fuel pumps, headlight relays and cooling fans) but there's a problem: A charging wire to the battery comes directly off the alternator, which makes the terminal "hot" all the time, even when the car is not running. I've worked around this by drawing power from other ignition switched points and by using relays, but I'd like to eleiminate this "backwash" current from the battery by incorporating a "one-way valve" (read: diode) into the battery-charge wire. Can anyone suggest to me the specs of the diode I'll need to look for? I need something that will impose minimal resistance on the circuit, and not object to the voltage/amperage involved.
Thanks!
-Roy
Thanks!
-Roy
Team Owner
Joined: Jul 1999
Posts: 65,492
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From: Orange Park Florida
Allthough you can try it, I would not recommend it, reason is the .5-.7 volts forward (conducting) voltage drop across the diode with most likely screw up the voltage sensing of the regulator and make for weak battery charging, you can try it, but thati's my expected result....
you will need a larger heat sink from Radio Shack I think or an old color TV set, and a stud mounted diode of about 50 amps forward capacity, and a Peak Inverse of only 100 volts would do fine, so that's not a large issue....mount it in a cooler spot, NOT ABOVE THE HEADERS.....
GENE
you will need a larger heat sink from Radio Shack I think or an old color TV set, and a stud mounted diode of about 50 amps forward capacity, and a Peak Inverse of only 100 volts would do fine, so that's not a large issue....mount it in a cooler spot, NOT ABOVE THE HEADERS.....
GENE
Melting Slicks
Joined: Nov 2001
Posts: 2,668
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From: Eastern US XX
Originally Posted by Grinchia
I've wanted on several occasions to draw power directly from the alternator terminal (for such things as electric fuel pumps, headlight relays and cooling fans) but there's a problem: A charging wire to the battery comes directly off the alternator, which makes the terminal "hot" all the time, even when the car is not running. I've worked around this by drawing power from other ignition switched points and by using relays, but I'd like to eleiminate this "backwash" current from the battery by incorporating a "one-way valve" (read: diode) into the battery-charge wire. Can anyone suggest to me the specs of the diode I'll need to look for? I need something that will impose minimal resistance on the circuit, and not object to the voltage/amperage involved.
Thanks!
-Roy
Thanks!
-Roy
Relays are your best solution - why don't you like them? Simple, elegant, and distinct (on is on, off is off), and essentially no circuit load. You can get the Bosch type in various amp ratings and they are very easy to find and connect.
Thread Starter
Pro
Joined: Oct 2003
Posts: 641
Likes: 2
From: Storm lake Iowa
I don't have anything against relays, they work very well and have been my solution to this issue in every case thus far. The wiring is just a little more cumbersome (although the advantages are significant). It would just be nice to have a full-voltage power point (~14.4 volts) live only when the car is running that doesn't require relay switching. Obviously I can (and have) get along without this luxury thus far. I just wondered if there was a downside to the diode idea...I hadn't thought about the voltage regulating aspect.
