ballast electrical question

[hillegom]

I have a 400 watt MH ballast that I would like to use for a 250 watt bulb.
I was told by an electrician that that is possible to do. As long as I do not use a bulb larger than 400 watts everything will work properly.
So he is saying I could run a 175 watt as well.
What do you guys think?
Would this change the kelvin of the bulb, not running the specified bulb wattage?
Would this waste electricity?

Thanks

[mike31154]

I think you're going to cook a lower wattage lamp with that 400 in short order. From everything I've read so far, MH ballasts are matched to the lamp they are intended to fire with respect to wattage. You're asking for a possible fire.

Here's an excerpt from a 'DIY guide to MH Lighting Systems':

"Ballast

The ballast provides the proper starting voltage, operating voltage and current to the lamp to initiate and sustain the arc. HID lamps have a negative resistance characteristic, which causes them to draw an increasing amount of current, hence need a current limiting device. The ballast provides these functions.

Once the lamp is selected the next step it to select the ballast that will be used to drive the lamp. When putting together a DIY MH lighting system it is very important that the ballasts be matched to the lamp in use. An easy way to match the ballast to the lamp is through the use of the ANSI designation. For example, when using a lamp designated M-57, look for the ballast with the same designation. For lamps without ANSI designation, it is best to call the lamp manufacturer and get a recommendation on the ballast to be used.

Most ballasts (except the electronic ballasts) used for Metal Halide lighting are of the CWA (constant wattage autotransformer) type. This is lead circuit ballast, and consists of a high reactance autotransformer (core-coil) with a capacitor in series with the lamp.

Any ballast rated for the lamp will function properly, but may come in different configurations, each with its pros and cons, differences in prices and amount of DIY work required. There are several manufactures of ballasts that will operate the same lamps, and often the exact brand is not important. The ballasts can be cross-referenced with another company's ballasts if a specific brand is desired."

Proceed at your own risk, but I'd have some reservations as to the qualifications of the electrician that provided the advice in your post. I might seek a second opinion. Which you are sort of doing by posting here...

[banditpowdercoat]

Definately NOT a good idea!

[mike31154]

Here are a couple of links to some tech info on magnetic HID ballasts and their application.

http://www.atlaslightingsupply.com/h...ting-guide.pdf

http://www.atlaslightingsupply.com/Ball_Tech_Info.pdf

I don't have anything on electronic HID ballasts. I do know some newer electronic ballasts are able to fire different types of MH lamps, that is pulse start, probe start, ignitor start etc. but they still need to be voltage matched to the lamps they are going to operate.

[donlite]

My company makes light fixtures I have never tried it with core and coil or electronic ballasts but I do not recommend it. If the bulb is open make sure you are using a double envelope lamp. Good Luck, Don

[Delphinus]

If it were me I'd just sell the ballast and buy a 250'er, or see if someone wanted to trade.

[hillegom]

Thanks everyone for all the help.
And thanks to mike 31154 for the links, which convinced me not to use the 400 watt ballast.
The link said that if you used a bulb that was not rated for the ballast, whether bigger or smaller in watts, then you would decrease the end of life of the ballast.
So I will be wanting to trade this 400W ballast with capacitor for a 250W ballast. Will post tomorrow.

[BCOrchidGuy]

If you're using a magnetic set up the hydroponics shops will have good deals, sometimes Home Depot has outdoor MH security lights for a reasonable price. Electronic ballasts though are much nicer to use, virtually no heat and much more efficient.

Doug