Build your own HID-Ballast

[part2wanksta]

is there any way to make a core and coil ballast power the hqi bulbs. even if the quality is lestened

[Megaman]

Will the ballast design work with a hqi-t bulb? I'v just bought two bulbs and were thinking about building this, but now I'm not sure if it will work. Anyone knows?

[Megaman]

I guess that no one knows if it works with hqi-t. I will just have to test it then. Hopefully it won't explode on me.

[karma]

Hopefully

[Megaman]

I'v now got my ballast to work with my hqi-t bulbs, although it does not work good. I had to modify the starter quite a bit to make the bulb ignite at all.
I also need to have two of the coils disconnected while the bulb ignites to get a voltage peak that is large enough, and I disconnect the igniter after startup otherwise the bulb starts to twinkle and the starter breaks.

When the bulb is started up and have got warm it settles around 120V, 1.6 A. That is not correct as it should be 96V and 1.8A. I'm not sure how bad that is though.

[mathias]

It was a long time ago I did something with this ballast design.

Yes it should work with hqi-t bulbs. The important thing with this
ballast is that the: Current * Voltage = Wattage of your bulb. Normally the bulb itself will decide how much voltage it will run on, the ballast will then reduce the current so you always will get the wattage of your bulb.

An example, if your have a 150W bulb and the voltage stop at 120V after warmup the current should be 1.25-1.3A.

Megaman, do you use the ballast with 2* 30W ballasts and 2 * 36W ballasts ? If you get 120V and 1.6A that´s abolutely to much = 192W the lamp will get overheated and maybe turn it self off. Do you use the electronic igniter or the normal glow-tube starter ?

[Megaman]

Nice to see that you are here again Mathias!

Originally posted by mathias
The important thing with this
ballast is that the: Current * Voltage = Wattage of your bulb.

An example, if your have a 150W bulb and the voltage stop at 120V after warmup the current should be 1.25-1.3A.

But that assumes that the bulb is a reasistor and a real bulb is not that. The bulb is spec. for 96V, 1.8A and that is 173VA. It will still get 150W because with AC, watt is not voltage times current, it also depends on the phase between them. (But I think you know all this already)

Originally posted by mathias
Megaman, do you use the ballast with 2* 30W ballasts and 2 * 36W ballasts ? If you get 120V and 1.6A that´s abolutely to much = 192W the lamp will get overheated and maybe turn it self off. Do you use the electronic igniter or the normal glow-tube starter ?

Right now I'm actually using 3*40W and one 36W. That seems to me not to be enough though as the voltage is still too high (not enough current to decrease the voltage over the bulb, the bulb has negative resistance. I can see the current decreas and voltage go up when it is started.)

I'm using the electric starter, although I'v tried to modify it in order to get it start the bulb. I don't really know how to modify it so I'v just tried to increase/decrease all possible resistors and capacitors with half descent results. I think I need a larger voltage spike for it to ignite properly.

[mathias]

As far as I know, is the bulb a resistance and it does not change characteristic depending on frequency.

The ballast work as a 6dB lowpass filter for speakers with a coil. A 30W ballast has more H (Henry) than a 40W ballast. The lower H (Henry) you got in the ballast the more power will the bulb get, at a given frequency 50Hz or 60Hz.

You are feeding the bulb with too much power, if you increase the current the voltage will also increase, the negative resistance is only when the bulb warmup. Try to remove one ballast, it should decrease the voltage to a more normal level.

The electic starter does not give a large voltage spike if you reduce the H too much (High wattages ballasts or too many), and it will therefor only work with 150W bulbs.

[Megaman]

Originally posted by mathias
As far as I know, is the bulb a resistance and it does not change characteristic depending on frequency.

Hmm, I wonder where I got that from, I don't remember.

Originally posted by mathias
The electic starter does not give a large voltage spike if you reduce the H too much (High wattages ballasts or too many), and it will therefor only work with 150W bulbs.

I'm running the bulb on 3x40W ballasts now, During startup though, I can't use more than 1 of them in order to get enough inductance (Henry) to start it. I'v also modified the starter a bit but it is still not good. I have to modify it almost every time after I have run the bulb to make it ignite again. My modifications are lot of trial and error because I'm not sure how it works.

The bulb gets around 115V and 1.2A when running. That would be around 140W which I think is good enough. I'm not sure wether it is good for the bulb though as it is spec. for 1.8A. It maby shortens the bulb life and changes its spectral output or something.

[Guy Grotke]

I suggest you look at the waveform with an oscilloscope, to see what a standard MH magnetic core ballast does to the voltage over time. I know that standard fluorescent magnetic ballasts generate a high voltage spike in every half cycle. I think this is essential to get the ionized gas conducting. Then most of the current conduction takes place after the spike, until the dropout voltage is reached near the end of the half cycle.

If ionization is incomplete, I would expect that the lamp arc would have a higher than normal resistance. That would give you a higher voltage and lower current than normal: Pretty much what you are seeing.