# DIY ballast, can it be done?



## WildRice (Dec 20, 2005)

Hi all, I useually hang out with the LED crowd, but last week I got a free used microsun 65W HID bulb. It was in a lamp that had a ballast assembly. can a simple driver be built to power this 'tube'? I am not really looking to power it at FULL power, just really want to see what it can do. I have loads of parts around and I have built several HeNe power supplies. Can anyone help point me in the right direction...

Jeff


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## mattheww50 (Dec 20, 2005)

You don't have a lot of choice about powering the beast. It isn't like an Incandescent where lowering the voltage just lowers the colour temperature and output. In an Arc, if you don't maintain the temperature of the arc with sufficient energy, it simply goes out! If you don't maintain enough voltage across the electrodes, it goes out. That's why you don't find HID's on dimmers, and Fluoros that can be dimmed require special ballasts.


While you can overdrive HID's, generally if you try to significantly underdrive them, they don't work very well, if they work at ALL! The Arc in the lamp is based upon a given set of operating conditions, and substantial energy is needed to maintain the conditions that are required for the arc to 'live'. So the answer is you probably cannot even get a 65 watt HID to light driving it with less than about 50 watts.


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## WildRice (Dec 20, 2005)

OK, got it. as far as driving it at spec, 65W, can a simple ...inverter... be made. I mean, what is the running voltage after startup. 

Jeff


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## 3rd_shift (Dec 21, 2005)

It looks like what is needed, is an electrical schematic of an HID ballast assembly.
Now I'm kinda curious too. 

I would love to know how to make a ballast assembly with the hopes of squeezing in a bigger ballast and bulb into a larger THOR.
I have already seen the awesome power of what I had originally thought was a 250 watt HID. :huh2: 
Only to learn later on that it was only a weeny little 100 watt metal halide HID bulb just CRANKIN' out a truckload of very white light in the parking lot. :wow: 

Since then, I have wanted to squeeze one of those badboys into a cordless light of some kind at work.
The Costco 35 watt HID was quite impressive, but the 100 watt, 120 volt parking lot light was a solid 3 times brighter.  :rock:


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## Mike Painter (Dec 21, 2005)

This might give you some info look under  Electrical Requirements  part way down the page.


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## 3rd_shift (Dec 21, 2005)

The info in that link is a bit aged, but still spells out the basic issues involved with hid lighting quite nicely.


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## winny (Dec 21, 2005)

Although HID lamps are far more complicated to drive then incandescents, it's not rocket science.

The basics of a HID ballast is something like this:
Start with making an arc by applying enough voltage, probably a couple of kV would do.
When you can sense some current going through the lamp, start limiting the current according to specifications and switch to using about 130 Hz or so square-wave, both positive and negative.

My next goal in life is to get my Master of Engineering with building the most bad-*** electronic HID ballast as my degree project. So if you can wait a year or two, I can tell you exactly how it's done.


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## Flummo (Jul 19, 2006)

The thread might be a bit old, but I think it is time to see if we can't make it wake up. 

I found this when I searched for DIY ballasts får car HID. Maybe it can be useful for someone? Using MCU and such is a bit out of my league, but if someone can figure out how to build a ballast w/o that I think I will give it a try... http://pearlx.snu.ac.kr/Publication/01243694.pdf


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