docking lights.

Thanks in advance. Have been trying to figure out the best way to run a portable halogen spot light. 85 watt h3 fog light pair. I plan to be able to run them series/off/parallel. I have looked over the relay diagrams and have a grasp, somewhat.

Where I am having trouble is the switching, I would like to use 2 switches, on/off/on for the fogs, and a push button that would break the circuit to the fogs and redirect it to the red green bow lights. When you turn the bow lights off the fogs would kick back on. What switch/relay?, how and would this work with the fog lights in the off or parallel position. Have been trying to figure this out on my own, but don't think I am wired that way.

This is a on smallll aluminum boat on a private waterway. Foglights for safety, running light to combat the bugs.

An SPDT (changeover; 5 pin) relay.

Fused +12V to 30 (common).
Normally Open NO contact 87 to the +12V input power for the H3 series/off/parallel switch.
Normally Closed NC contact 87a to the +12V bow lights.

Fused +12V to switch, and out to relay coil+ 86.
Relay coil- 85 to GND (battery-).

Note that when the switch is ON, the H3s are selected.
When off, the relay is off and the bow lights are selected...
Hence giving minimum power consumption with the bow lights (ie, less the 60mA to 250mA coil current.
That could be swapped but IMO it's the best solution. IE - if forgotten and the battery flattens, you don't want the relay dropping out and connecting the H3s.)


PS - the above can be done with an SPDT push button switch instead of a relay. (Though a relay is nice if you want to add a battery protector circuit later - ie, a low voltage cut-out LVCO. Then again, if not a dual-(threshold)-sensing LVCO, maybe the LVCO should cut the lights entirely?)

oldspark, thank you.

No need for an LVCO...maximum run time even at a reduced voltage is more important than longevity....in this case.

Yeah, I figured so.
Hence why I like the relay ON for the H3s.
If flat, the relay will drop out. The battery then recovers a bit with the lower bow light load.
Of course that could mean the relay turns on again, but the relay's pull-in current is higher than its drop-out voltage (obviously). Hence a "natural" hysteresis. (A resistor could be added to increase the relay's drop out voltage...)

Of course the battery may well be stuffed by then (especially if an AGM as it should be for salty marine), but if max lighting for safety is the important issue...

And that's all "what if" anyhow.
Somehow I suspect you won't forget the foglights are on. (Just stay awake LOL!)   


Good luck!
And yeah, enjoy your boating.