# Theoretical question about HID ballast contol

Discussion in 'General Electronics Chat' started by walk on, Sep 14, 2012.

1. ### walk on Thread Starter New Member

Jul 12, 2012
11
0
While doing some reading on HID bulbs and ballasts then somehow ending up on youtube (it always happens), I came across an interesting article about different methods of regulating the output power aka intensity. There are several methods practiced by manufacturers of dimmable ballasts, but to me the simplest (but not most efficient) way seems to be simply slightly adjusting the input. Attached is a Pout vs Pin graph from one of the articles. I'm not familiar with the rules regarding outside links, but if it's allowed I will gladly post it.

Assuming efficiency wasn't of great importance and the input voltage was always kept above the minimum required for proper operation, wouldn't a voltage divider before the ballast's input theoretically do the trick? Part of me says it makes sense, part of me says its too simple to work. Perhaps it's so simple because it isn't efficient? (Possibly why this simple dimmer knob isn't offered as a low cost attachment)
I don't have the parts (or courage) to see if it would work, but I was just curious and decided to ask if anybody could share their input.

File size:
28.4 KB
Views:
23
2. ### #12 Expert

Nov 30, 2010
16,031
6,542
I have too high voltage from the power company so the bulbs burn out too quickly. I use a transformer with its output wired to buck the power line voltage. This avoids using resistors rated at 35 watts and higher. Big resistors are expensive. I get old transformers out of dead air conditioners with input of 115, 208, 230 volts and 24 volt rated output. Put 125 volts on the 208 volt input and get 14.4 volts to lower the 125 volt source to 110.6 VAC. Happy light bulbs

walk on likes this.
3. ### walk on Thread Starter New Member

Jul 12, 2012
11
0
Ah, but I believe most of these bulbs are being used as headlights. As it turns out, those super bright lights that end up blinding people on the streets aren't properly marketed. They advertise them as a simple replacement bulb which just end up producing a ridiculous amount of light scattered in all directions. The proper ones are real HID lights, use a ballast, focus the light as not to be too bright for other drivers, and cannot be dual filament (since there is no filament). The attraction to the falsely advertised "HIDs" I guess is that the driver has dual filaments.

With a 12v source, a driver would be able to control the brightness with a simple switch to either engage or bypass a voltage divider that would serve as an intensity control (high beam - low beam). That's what brought me to do some light reading on the matter. The appeal of having the control to have 2 levels of brightness is what makes those super bright falsely advertised "HID's" so appealing. Since efficiency isn't much of a concern (battery being recharged while driving), I guess i'm wondering what makes this such a no-no. For a low cost product i think it would make drivers want to be safer about their choice of headlight. Maybe there's a fundamental concept I am missing. Or maybe my eyes are just getting old before i hit 30.

4. ### #12 Expert

Nov 30, 2010
16,031
6,542
The problem you are missing here is that this site does not discuss automotive modifications, like regulating headlights. You belong on http://www.electro-tech-online.com/

Good-bye.

walk on likes this.
5. ### walk on Thread Starter New Member

Jul 12, 2012
11
0
I understand, sorry if i broke any rules. I wasn't trying to talk about modifying headlight but, .... hm ok I guess that was what I was ranting about actually. I see your point haha. I do appreciate the reply and link. Thank you again.