400W HPS in 600W digital balllast?

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.

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?

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?

Blowed up yet?

LOL I guess I'm not the only one with a reckless and wild side. Seems like everyone wants to see this damn thing blow!!! I haven't tested yet. I'll keep everyone posted.

20min and it didn't blow or burnout. I'm kinda happy and disappointed now So now I have to wounder, since Curious Soul information might be incorrect...is....will it hurt my ballast?

Actually, I have a customer that was using about a 20% under rated bulb in a MH ballast. They were replacing all the lighting (for floros) and was thinking of snatching a light or two but they were 277V with no extra taps. Think it was 320W in a 400W ballast. Forgot the numbers, but something like that

But with an electronic ballast, I don't see why the MFG's can't add this to the mix. Its got a brain to regulate (and the sales pitch of keeping lumens constant over the life of the bulb) and can handle HPS & MH. so why not handle under rated bulbs?

It isn't supposed to hurt the ballast, but it isn't supposed to work.

Supposed to be able to put a bigger bulb and run with a smaller ballast, that is supposed to work.

Putting a smaller bulb with a bigger ballast is supposed to push more current thru the bulb and cause it to be destroyed.

All I can find is what I've read, no one wants to try anythign.

A guy on here last week even got a box full of free lighting and wouldn't give it a go to get the answer. I'd love to do it just to find out the answer.

I'll give you plus rep just for having the balls to try it instead of being afraid, and you even paid for your stuff.

Here is my research on the subject, when you get done testing let us know and I'll add it to my article so far.

Bigger Light Smaller ballast


Here is the deal, the answer is based only on research and has not been proven, the information was researched enough that I would consider it reliable but until someone wishes to prove it the answer will remain unknown.

First off, You should be able to burn a higher wattage H.I.D. bulb in a smaller ballast, 1000 watt bulb in a 600 watt ballast. The reason is that the 600 watt ballast will only allow 600 watts to go thru the ballast and it won’t let the 1000 watt bulb pull more than 600 watts. The 1000 watt bulb will burn like a 600 watt bulb. Since it is meant to burn 1000 watts, it is over rated for 600 watts and is supposed to last longer and retain it’s color temperature a lot longer than a normal 600 watt bulb. There are reports of street depts. doing this to allow extended intervals between bulb changes or burned out bulbs.

On the other hand using a bigger ballast to run a smaller bulb will cause almost immediate failure because the ballast will force the amount it is rated for thru the bulb. If you have a 1000 watt ballast and connect a 600 watt bulb to it, the ballast will push 1000 watts thru the 600 watt bulb causing failure or explosion of the bulb. You don’t want to do this.

You may want to think this is all backwards and it seems to be from normal theory, but bulbs act different in a circuit than most other devices and this is why.

Also you can write any company and try to get an answer, they will always tell you to use the correct bulb with the correct ballast, the reason is because they don’t wish to be sued when you do something stupid and try to blame it on their advice.

Yeah it was kinda stupid to try and would advise against it. But like I said I'm reckless and wild. Plus, we can't just live our lives on what people say. Granted I did solicit the advice then went against it, which kinda makes me an asshole. But I did seriously take into consideration Curious Souls advice and only did the experiment to prove his information right, so no one else would hurt themselves. It's going on a full hour and I haven't noticed any changes. But it was only a quick peak. I don't want glass shot into my eyes or face.

I'll clean my hand prints off the bulb when its done with its 12hr light cycle. I didn't bother with that initially cuz I thought it was gonna blow.

For anyone who wants to know I'm running a standard 400 Watt HPS Sylvania bulb that you can pick up at your local HW store, with a 600w digital electronic HPS ballast.

Interesting. But ain't a bulb a resistive load? Its going to draw what it needs, nothing more. A ballast isn't a constant current source.

la9 said:

Here is my research on the subject, when you get done testing let us know and I'll add it to my article so far.

Bigger Light Smaller ballast


Here is the deal, the answer is based only on research and has not been proven, the information was researched enough that I would consider it reliable but until someone wishes to prove it the answer will remain unknown.

First off, You should be able to burn a higher wattage H.I.D. bulb in a smaller ballast, 1000 watt bulb in a 600 watt ballast. The reason is that the 600 watt ballast will only allow 600 watts to go thru the ballast and it won’t let the 1000 watt bulb pull more than 600 watts. The 1000 watt bulb will burn like a 600 watt bulb. Since it is meant to burn 1000 watts, it is over rated for 600 watts and is supposed to last longer and retain it’s color temperature a lot longer than a normal 600 watt bulb. There are reports of street depts. doing this to allow extended intervals between bulb changes or burned out bulbs.

On the other hand using a bigger ballast to run a smaller bulb will cause almost immediate failure because the ballast will force the amount it is rated for thru the bulb. If you have a 1000 watt ballast and connect a 600 watt bulb to it, the ballast will push 1000 watts thru the 600 watt bulb causing failure or explosion of the bulb. You don’t want to do this.

You may want to think this is all backwards and it seems to be from normal theory, but bulbs act different in a circuit than most other devices and this is why.

Also you can write any company and try to get an answer, they will always tell you to use the correct bulb with the correct ballast, the reason is because they don’t wish to be sued when you do something stupid and try to blame it on their advice.

Click to expand...

BigBudBalls said:

Interesting. But ain't a bulb a resistive load? Its going to draw what it needs, nothing more. A ballast isn't a constant current source.

Click to expand...

Generally this is true as everything I've studied in electronics basically pulls the current it needs which makes it all backwards, a 600 watt bulb should be pulling too much current thru a 400 watt ballast causing ballast failure, but what I read about that is that HID bulbs draw electric different than everything else for some reason. That's just part of the mystery of this whole dang question.

la9 said:

Generally this is true as everything I've studied in electronics basically pulls the current it needs which makes it all backwards, a 600 watt bulb should be pulling too much current thru a 400 watt ballast causing ballast failure, but what I read about that is that HID bulbs draw electric different than everything else for some reason. That's just part of the mystery of this whole dang question.

Click to expand...

If the ballast was a constant current source then that resource would make sense to me. You can make a power supply that forces the current at a steady rate. But a simple inductive ballast isn't that.

But if you re-read the resource you quoted, he stated that he did NOT try it.

I can't see a HID puling current differently form everything else. I work with DC excited plasma discharge, and its still the same. We adjust the amount of available current (through vacuum tubes) and use the gas mix to adjust the differential of the voltage drop. (which stabilizes the power dissipation of the tubes)

Before it's over with you and I will probably chip in together just to find out the answer because I'm getting tired of wondering about it.