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Need help with diode across battery and starter relays

 
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psm(at)att.net
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PostPosted: Tue Jan 01, 2013 9:19 pm    Post subject: Need help with diode across battery and starter relays Reply with quote

John,

I can't help you with your exact components, but I can probably firm up
your theory understanding enough that you can figure out how to connect
your diodes.

These are called clamping diodes. They prevent a huge voltage spike
when you open the circuit on a charged up inductor. The inductor in
question is the one that makes the electromagnet that moves the big
contacts in your solenoids (really relays). That means you want to
apply these diodes from the plus voltage of the primary circuit (the one
with the small wires rather than the monster wires going to the battery
and starter motor) to ground. It may be that the small control wires
actually connect to posts that have big wires on them too, but that is OK.

The cathode end of the diode goes to the plus 12 volt circuit and the
anode goes to ground. The cathode is usually marked with a stripe all
the way around the diode. If you install the diode backward you need to
throw it out and get a new one in there. It will melt down if high
current goes through it.

I hope that helps.

Paul
Camas, WA
On 1/1/2013 6:29 PM, w8n2bup wrote:
Quote:


After a lot of Googling, I thoroughly understand the reason for the diode but I am hoping that someone can give me the exact placement of a diode for both the battery and the starter contactors (relays) in my Jabiru 3300. First the battery contactor. I have a large post going to the battery, a small post going to the master switch, and a second large post going to the starter relay and elsewhere. When I put my voltmeter on the battery post, I have my 12 volts. When I put it on the small post, I was surprised to find voltage there, too, with the master off. When I flip the master switch on.,, it mostly goes away on the small post. In any case, the best I can figure is to put the cathode (stripe end) on the large post going to the battery and the anode on the small post. I was thrown a bit by some net comments saying it goes "across" the relay. Other comments showed it going to ground. On top of it all, my firewall kit came with a diode made with the cathode (band end!
) going to a small ring connector and the anode going to a large ring. Seems backward. Maybe someone accidentally reversed it? Now the starter relay. It has a few extra large spade connectors and posts. When I put my meter on diode setting, there appears to be a diode built into the relay. With no markings on the relay, I can't look it up to know for sure. I guess it wouldn't hurt to add a diode anyway with the cathode pointing to the battery relay and the anode going to the small starter switch wire post? Just hoping someone knows exactly what I have and how to connect the diode or diodes. If easier, please call me evenings at (913) 915-1989. Still W8N2BUP, John


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vk3eka(at)bigpond.net.au
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PostPosted: Tue Jan 01, 2013 11:16 pm    Post subject: Need help with diode across battery and starter relays Reply with quote

John,

Attached is a pdf of the wiring around the solenoid's on my O-200 powered
601XLB.

It may help with the orientation of the diodes.

Cheers

Peter
Wonthaggi Australia
http://zodiac.cpc-world.com


On 1/1/2013 6:29 PM, w8n2bup wrote:
Quote:

--> <johnrich987(at)hotmail.com>

After a lot of Googling, I thoroughly understand the reason for the diode
but I am hoping that someone can give me the exact placement of a diode for

both the battery and the starter contactors (relays) in my Jabiru 3300.
First the battery contactor. I have a large post going to the battery, a
small post going to the master switch, and a second large post going to the
starter relay and elsewhere. When I put my voltmeter on the battery post, I
have my 12 volts. When I put it on the small post, I was surprised to find
voltage there, too, with the master off. When I flip the master switch
on.,, it mostly goes away on the small post. In any case, the best I can
figure is to put the cathode (stripe end) on the large post going to the
battery and the anode on the small post. I was thrown a bit by some net
comments saying it goes "across" the relay. Other comments showed it going
to ground. On top of it all, my firewall kit came with a diode made with
the cathode (band e!
nd!
Quote:
) going to a small ring connector and the anode going to a large
ring. Seems backward. Maybe someone accidentally reversed it? Now
the starter relay. It has a few extra large spade connectors and
posts. When I put my meter on diode setting, there appears to be a
diode built into the relay. With no markings on the relay, I can't
look it up to know for sure. I guess it wouldn't hurt to add a diode
anyway with the cathode pointing to the battery relay and the anode
going to the small starter switch wire post? Just hoping someone
knows exactly what I have and how to connect the diode or diodes. If
easier, please call me evenings at (913) 915-1989. Still W8N2BUP,
John


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http://forums.matronics.com/viewtopic.php?p=391362#391362



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w8n2bup



Joined: 09 Apr 2008
Posts: 20
Location: Kansas City Area

PostPosted: Wed Jan 16, 2013 1:29 pm    Post subject: Re: Need help with diode across battery and starter relays Reply with quote

thanks to all. A combination of all of your responses gave me the information I needed

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