I have a 600w ballast and no backup bulb. Can I use my 400w bulb til I get my replacement 600w bulb? I tried it out for a bit and it lit. Just made a lil hum noise. My ballast features a soft-start.

Whats the worst that can happened? I don't care about damaging the bulb. But I don't want to hurt my ballast.

I had this same question before and I spoke to my light supply guys about this, and they said it will only hurt the bulb. As in, it will burn out much faster than usual. They said it would not hurt the ballast.

I do not have a definite answer but I would recommend not to.

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I'm thinking of a Master Plan.......

Ballasts are used where a load does not regulate its own current consumption well enough. These are most often used when an electrical circuit or device presents a negative (differential) resistance to the supply. If such a device were connected to a constant-voltage power supply, it would draw an increasing amount of current until it was destroyed or caused the power supply to fail. To prevent this, a ballast provides a positive resistance or reactance that limits the ultimate current to an appropriate level. In this way, the ballast provides for the proper operation of the negative-resistance device by appearing to be a legitimate, stable resistance in the circuit.

A HPS bulb cannot regulate it's own current consumption so the 400 watt bulb will draw more and more (upto 600W provided by the ballast). It'll blow at best and shatter the glass all over your grow room at worst. I don't think it'll effect the ballast but why blow the bulb for the sake of a few minutes light, or however long it takes for the slow start to work up to 450 odd watts?

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I'm thinking the last guy nailed it. If you've already ordered the replacement why not just scrounge up some fluorescents to keep your plants alive until you receive the new bulb.

Thanks everyone. Did not expect so much help so fast. Curious Soul seemed like he pretty knew what he was talking about. So lets fine out!!! I'm a lil on the reckless wild side. I'll let it run and wait for the explosion. I have a shop vac

Curious Soul...I'll give you total props if the darn thing explodes.

Okay, well if you're going to do it anyway could you put a video camera on it. It would be cool to see the explosion

I don't have a cam but I wish I did. It would help a lot to get Curious Souls point across.

How long did it last? Was it spectacular?

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Blowed up yet?

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My Grow: http://www.rollitup.org/grow-journals/77350-stealth-wardrobe-grow.html