Relay help.

[Snowboy]

I want to be able to control the relay trigger wire for my lights so I can either shut the lights off with the trigger wire or turn them on if it’s dark enough or flip the headlight switch to trigger the relay.

Do I use a single pole singe throw switch or Double pole double throw?
Do I run the trigger wire to the switch and from the switch to the relay?
Should I add a 1N4005 diode going to terminal 86 which I assume is the trigger? Do I need one going to the switch as well coming off the headlamp connector?

Reason for diode.
Activating relays is done by connecting voltage to a coil, which in turn creates a magnetic field that pulls over the switch. When voltage is removed from the relay, the energy that is stored in the coil will send current the other way by increasing voltage to several hundred volts, and a small arc will be visible between the contact elements of the headlight switch. Over time, the switch will only work intermittent, and will eventually totally fail.
That’s why a serial diode is essential to protect the headlight switch.


Dave.

[Alan]

This should do what you want except you will be interrupting the trigger lead to the existing relay instead of adding a new one. http://www.snowplowing-contractors.com/alan_reverse_lights.html

I don't think there is enough reverse spike from a ice cube realy to need the diode. Those relays are available with a diode built into them, IF they are the regular SPST kind, I'm not sure the SPDT relays are available with diode protection already in place.

The only way I've run diodes was so that they would take the reverse surge to ground. I can never remember which way to orient them so I usually test them by temporairly tieing in the power to the trigger terminal through them. If the relay triggers the diode is backwards for your application. Reverse the diode and tie it to ground, then hook up the trigger lead and you should be good to go. If the circuit takes out a fuse when triggered it's a pretty good sign that the diode is in backwards.

[Snowboy]

Thanks Alan.

This is for my HID setup. Initial draw is 23'000 volts so I don’t want to take chances. Want to do it correct the 1st time around. I was on the Osram Sylvania site and they say not to use solid state relays with HID lights. I priced a Hella solid state relay anyways and its $50.

The hot lead wire going to the switch can that be a small wire 16ga? does it have to come from the relay or can I use a fused power source IE my power tap block which has a 30amp main fuse and I could add a inline fuse but don’t think its needed.

Dave

[Alan]

Initial draw of the lights may be 23KV but that's on the output side of the transformer. Voltage on the input side will never be more than battery voltage, 13.8 or thereabouts. Amperage through the relay is also irrelevent. All we're dealing with here is coil draw of the relay. I can't believe that the relay handles more than 40 amps, or that it will be more than an ice cube relay, those come in a 70 amp version which commonly has 3/8" blade terminals. Even at that it's still a small coil. The trigger wire can be most anything, all it has to deal with is the coil current. I would not run it on a 30 amp circuit, I'd fuse it seperately with maybe a 2 amp fuse.