On 5 Nov 2004 09:50:06 -0800, (Nick Wise)
wrote:

Chris wrote in message ...
I think you can use it. The 250watt is a maximum value that the ballast
should be used up to not the value it works at. The output is always
determined by the load on it. A 150watt load means the ballast works at
150watt. You can't give out 250watts. 250 watts is the voltage
multiplied by the current. The current being determined by the load, the
lamp.
Hope that helps,
Chris.

Nick Wise wrote:

Can a 175 watt bulb be used in a 250 watt ballast?

I have searched through the archives and the web and still have not
found a definitive answer to this. Can it be done? Will the initial
spark to ignite the 175 watt bulb be too much?

The reason I am asking is simple. I have 2x40 watt flourescents and
2x250 watt MH in my canopy, this makes for a lot of heat. I am
cooling it with CPU case fans, but since 175 watts produce less heat
and still an adequate amount of light (for my purposes), I was hoping
to switch to reduce heat.

If I can't do it, it's no big deal, I am just going to have to upgrade
my fans.



Nick, the 250W core has almost the same voltage output as the 175W.
The capacitor for both is different. One I believe is 10 mf and the
other is 15mf.
I would opt for increasing the cooling capacity in your situation. If
you haven't done so allready I would set them up for supply and
exhaust.
As a side note, I have changed all my planted tank lights over to PC
type. Longer life of bulb, less spectral shift, 85%+ lumen output at
end of bulb life and a lot less heat. I use a multiple of 40W and 55W
lamps in various Kelvin ratings from 4100 to 6400. I'm getting good
algaeg and plant growth with this setup.