How to use 12VDC headlights on your 24VDC system .

[Blood_of_Tyrants]

Being an electrical engineer, I thought there must be an easy way to use cheap 12vdc headlights on a 24vdc system and then it hit me: just wire the headlights in series and use a cheap relay to switch them.

The first drawing is a standard 24vdc high-low headlight wiring.

The second is slightly modified with 12vdc headlights replacing the 24vdc ones and a relay to switch the ground and operate the lights properly. This works because each headlamp will drop 12 volts and the relay switches on when the lights are on high.

All you need is some 14 gauge wire and a 24 vdc coil ice cube relay and relay socket. Together, the relay and socket will cost less than $20 and they are available at any large electrical supply house. The only drawback is that if one bulb burns out, they both go out.

http://img.photobucket.com/albums/v260/BloodofTyrants/c565c606.jpg

http://img.photobucket.com/albums/v260/BloodofTyrants/4b9c3abe.jpg

 

[dc3coyote]

Do you have any pics?
This looks simple I just getting lost in the step down?
I like the idea should save money in installing multiple lights for a lightbar on a Pinz maybe.

 

[cranetruck]

....... The only drawback is that if one bulb burns out, they both go out.....

That is why it shouldn't be done this way, driving without headlights is not particularily safe, just get out on the road at night and turn them off for a while and you'll know what I mean.

Not sure why a relay is needed at all and if you use one, check the spec for "lamp loads", over 100 amp inrush current in this case.

 

[Towerguy1]

RE: Re: How to use 12VDC headlights on your 24VDC system .

I agree about Cranetrucks "safety" issue. If one light goes out the other is exposed to 24V and pops, abruptly leaving you in the dark! You could use this idea for aux. lighting, fog lights, driveing lights, but not for anything "mission critical".

 

[jeli]

RE: Re: How to use 12VDC headlights on your 24VDC system .

If one burns out the path is broken. Yes the other will go out but it won't burn out. Cool idea to use the second ground wire to back feed. All you need is the leads off a couple burned out bulbs to use for the wiring harness.

 

[Towerguy1]

RE: Re: How to use 12VDC headlights on your 24VDC system .

I stand corrected.....Oops

 

[Blood_of_Tyrants]

RE: Re: How to use 12VDC headlights on your 24VDC system .

No, the second bulb won't burn out because once the first bulb burns out, there is no path to ground for the second. On the plus side, if one high beam goes, just tap the dimmer switch and you are now on low beams, or vice versa. The relay is to provide for a separate path for high and low.

It works like this, if the lights are on low, the power goes through the low beam wire, the relay is de-energized and power travels through both low beam elements and eventually to ground. When you tap the dimmer switch, the high beam wire gets voltage, which energizes the relay causing it to switch from the normally closed (NC) to the normally open (NO) contact, which provides a path to ground for the high beam elements.

As for inrush, don't worry, the inrush is for a fraction of a second, anyway.