Electrical Engineer question... (1 Viewer)

[Stecz]

I have an auxiliary fuse/relay tray I've made for my '97 LX. I added it to have a clean place to do any extra wiring. That way, I have easily accessible fuses for add-on circuits for things like, underhood lights, backup lights, fogs, and I also have cornering lights.

The way the cornering/ditch lights work is that I have the right and lift lights connected to separate time delay relays and when I turn on the right turn signal, the right relay is tripped and it stays on for 2 seconds after the last turn signal flash. This work great, however, I've decided that it would be really cool to have the ditch lights turn on with my forward facing driving lights with the high beams. I can't just use the same relay as my driving lights because I would then be connect the cornering lights together and would always go on.

So, can I put some sort of diode or something in the line from a third relay (power for main aux lights) so I don't connect the two ditch lights together?

that way the ditch lights will turn on if either, turn signal relay is tripped, or the aux light relay is tripped.

 

[george_tlc]

You can use a pair of diodes to "or" the two signal sources together *IF* the signal sources are same active polarity. i.e. when turn is on the enable signal is low and when driving lights are on the enable signal is low. Or vice versa.

cheers,
george.

 

[Stecz]

You can use a pair of diodes to "or" the two signal sources together *IF* the signal sources are same active polarity. i.e. when turn is on the enable signal is low and when driving lights are on the enable signal is low. Or vice versa.

cheers,
george.

I was going to do it this way:
I was going to add a third relay triggered by the high beams and have a big diode on the connection to the lights. If I trigger the time delay relays, when I turn the high beams off, the ditch lights would stay on for 1-2 seconds after I turn off the high beams.

The question is, can I get a diode that can handle 5 amps or so.

The other alternative is to have a second set of relays (one for each ditch light) that is triggered by the high beams. I could probably get by with one extra. One relay triggers the lift ditch light and the other relay triggers the right ditch light and the rest of the forward aux lights that I install. That might be the easiest.

 

[george_tlc]

Clearly job #1 is to decide exactly what it is you want to achieve

Yeah, 5A diodes are not an issue to source. But if the diode is just being used to energize your relays, even 1A is plenty. A typical 40A automotive relay only needs maybe 0.1A to fully energize its coil.

cheers,
george.

 

[Stecz]

I don't want to energize the time delay relays... those work exactly like I want. In addition to the lights being powered on with the time delay relays. I want the lights to power on with the highbeams. I could energize the relays with the highbeams also, but since they are time delays, they would remain turned on 2 seconds after I turned off the high beams. I want to power the lights with another relay that is triggered by the highbeams and turn off instantly when the high beams turn off.

So I need a larger diodes so that I can isolate the two ditch lights from each other when powered by the relay triggered by the relay? I probably need to draw another diagram of what I'm thinking.

 

[Stecz]

This is what I'm thinking

Yes, there are more wires than that on the relays, but the triggers would come from hi-beams or turn signals and then the power to the lights are the wired coming out of the tops of the relays.

 

[george_tlc]

Are the ditch lights LED? If not, I'd suggest trying to use LEDs, they will draw a lot less current if you use the diodes.

Consider that a decent diode (schottky etc) will be around 0.5V drop at 5A, that means you have 0.5 x 5 = 2.5W of heat that the diode needs to dissipate, that's quite a lot, especially in an automotive environment where temps can easily get to >40C.

cheers,
george.

 

[Stecz]

The ditch lights are LED and I was going to use LED spots as well. If the diode's will generate a lot of heat, maybe it is worth it to use relays. It would just mean that I have a total of 4 relays powering the ditch lights. I'll have to redesign my fuse/relay board to handle more relays, but that's not a huge deal.

 

[george_tlc]

Comes down to how much current each side of your LED ditch lights draws. Assume about 0.5V voltage drop across the diode and multiple by the current. That will give you watts. With regular diodes that don't have a heatsink tab or stud you want to consider about 1W as maximum dissipation, especially in a vehicle that can see some hot conditions.

cheers,
george.