Focus Fanatics Forum banner

1 - 4 of 4 Posts

61 Posts
Discussion Starter #1
What I would like to find:
When you pull the stock on the steering column toward you, the high beams are energized before power is cut to the low beams. I need a single pole switch or relay the behaves in the same way, closing the second circuit before the first is opened and vice versa, but I don't know if it has a specific name.

What I'm doing:
I have CCFL halo rings that are not presently hooked up. I plan to use them as DRLs. I have acquired this gizmo (schematic) to control power to them. But I would also like to install a DPDT 3 position (on-off-on) switch to provide an override. Bottom position would energize the green wire on the controller to turn the halos off. Middle position would leave everything to the controller. My initial plan was to use the top position to splice in power from the battery saver relay circuit (not simply switch to the BS circuit but connect the BS circuit to the already hot wire coming out of the control module) directly to the CCFL halos. That way I could turn the halos on even with the car off but mitigate the possibility of draining the battery if I space out. I NOW SEE THE PROBLEM WITH THIS. If I left the switch in the top position, then things not on the battery saver circuit could draw power from it when the car was off.

You're probably asking 'why not just switch to the battery saver circuit instead of splicing it in'. The answer is two part. 1) Correct me if I'm wrong but flashing CCFLs decreases both the ballast and bulb life so maintaining constant current once they're on would be preferable and 2) I like to make things unnecessarily difficult/perfect; it's a great way to learn new stuff.

Other thoughts:
Alternatively, and perhaps a safer option , would be to have an inline capacitor that can supply power for the few milliseconds it takes for a switch or relay to flip. I know essentially nothing about how that would be done though. It would need to supply 12 volts at 2 amps for a second or less.

As a third option, I can give up on my dream of having full control over my new CCFL halo DRLs and leave it to the device I purchased to take care of that.

Thanks for reading!

11,867 Posts

184 Posts
Useing a capacitor to keep ccfl on during switching would work just fine. Use a polarized cap in parallel. Below is formula to calculate needed capacitance and an example

Capacitance in Farads*F = Current I x time t / voltage dV

If the load current is limited by resistors and not a constant current load, the current will drop as voltage reduces, so the above calculation needs to be changed to a*I x dT / dV*calculus form where dT tends to zero. This becomes a bit more messy. So, let's keep things simple:

For the output case with a 3 Volt drop over 10 seconds, assuming*constant current*load, capacitance works out to:

F = 0.03 x 10 / 3 = 0.1 F = 100,000 microFarads

61 Posts
Discussion Starter #4
Eureka! (ish)

In the past two days I have gone deeper down the rabbit hole of electronics than I ever imagined I would. And for what? So I could turn my halo lights on with the car off (why even bother?!) and have them automatically turn off if I forget. Oh no! I didn't stop there. I realized that if I just tap into the battery saver circuit, then any time the GEM reset the battery saver relay (like if I tap the lock on the remote or open a door to get something out of my car), the halo's would come on for another 20 minutes or whatever. I wanted them to stay on after the car turned off, but stay off once they turned off, until I stuck the key in the ignition.

I bailed on the idea of a capacitor even before I realized the lights would keep getting turn on by the GEM any time I touched my car. I didn't like the idea of having to burn off so much power through a resistor so I came up with a way to allow the cap to charge off current through a resistor but discharge directly to the load in the event of a power drop and still allow a clear path for normal power to bypass the resistor. I think it would allow the cap to charge slowly without blowing a fuse but discharge all energy to the intended device. Probably pretty basic, and I don't actually know if it will work as I expect:

How the DRL control module works:
Purple cable with the fuse (left) provides the source of power for the lights.
Purple cable without fuse (bottom) sends power to the lights, controlled by module.
The module sends power to the lights 30 seconds after current is applied to the red wire.
The module cuts power to the lights when no current is applied to the red wire.
When current is applied to the green wire, the module cuts power to the lights.
When the grey wire is grounded, the module cuts power to the lights.
Circuits made with either the green and grey wires will supersede the circuits made with the red wire.

How I've expanded that functionality (I think):

Based on what I've learned in my electronics odyssey, I believe I have engineered a mechanism that will not bypass the DRL control module as the source of power for the halos, that will (with the dash switch in the top position) keep power to the halos until the battery saver circuit first shuts off, then it will stay off until they key is inserted and turned to the run or start positions!

When the dash switch is placed in the top position, it energizes the upper relay. The now energized relay closes a circuit that brings the battery saver circuit into engaging the same relay. This means the relay should stay closed once the key is turned off. Two diodes prevent back-flow (one circuit powering devices on another circuit when it shouldn't). At the same time, the upper relay engages power the the lower relay. The lower relay disengages the parking break sensor and attaches the red power sensor to the battery saver circuit without breaking its always-there connection to the run/start power. In this way, the control module thinks the key is in the on position (because it's getting power from the battery saver circuit) and doesn't see if the parking break is engaged. Both relays should stay engaged until the battery saver relay cuts power the first time, then both relays will disengage restoring the DRL control module's sensor wires to their intended connections. The relays can't re-engage until the start/run power comes on with the key and engages the first relay again.
Lights turn off automatically but don't turn on again until the key is turned!

The only imperfection I can see is that once the dash switch is in the top position, even for a second, the DRLs will stay on until the next time the battery saver cuts power. The DRLs can still be turned off in this state, but only if the dash switch is moved to the lower position, applying current to the green wire and overriding the red wire's signal to turn on the lights. I'm dead certain there is a way overcome this little flaw so I'll keep [?|] until I figure it out.

Some of the resources I've used to learn:
(in order of perceived usefulness)

General / Multiple: (page on relays: capacitors:

free schematic creation tool:

Relays: - this whole site appears pretty good but I haven't read beyond the relay page.

Capacitors: + (A farad is 1 amp second of electrical energy a.k.a. one coulomb stored at 1 volt!)

Resistors: +'s_law

1 - 4 of 4 Posts