How to match a ballast to the light (or other power consumer)?

Gary

Newbie

Posts: 10

How to match a ballast to the light (or other power consumer)?

« on: April 19, 2011, 05:36:06 AM »

I'm trying to understand the relationship between the ballast and (for example) the lamp--fluorescent, Mh, HPS, HID, etc. I have read the wiki articles on Ballast and Gas-discharge lamp, so I have a superficial understanding of why they're needed.

But suppose I'm building a system which needs Mh or HPS lamps, such as a hydroponic plant growing system. Once I design the desired physical layout and figure out how many lights I need, how do I figure out my ballast requirements?

What electrical parameters do I have to match (e.g., watts, volts, amps, ohms, etc.)?

If I use multiple ballasts, how are those "ganged" together?

Can I use an over-designed ballast (e.g., 1000W ballast for 600W total of lights, 220V ballast for 110V lights)?

Can I ever use an under-designed ballast?

I hope you get the idea of what I'd like to know!
Thanks to you both T & B for providing such clear explanations! I appreciate the time you took to do that. OK, here's what I understand:

1. In general, a ballast must be "matched" to its lamp, both in watts and in volts.

2. In general, one ballast per lamp is required (except for ballasts for multi-lamp fluorescent fixtures).

3. A ballast performs two functions--it "jump-starts" the gas-discharge lamp; and it stabilizes the current once the lamp is started.

Are these fair summaries of what you said?


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Brian_T

Newbie

Posts: 5

Re: How to match a ballast to the light (or other power consumer)?

« Reply #1 on: April 19, 2011, 05:44:04 AM »

Ballasts serve two functions: the first is to start the light and the second is to adjust the power factor or in some way current limit the power to the lamp. The old way in the fluorescents was to power the heaters briefly to generate enough mercury vapor for a discharge to begin at 110 volts. As soon as the bulb starts to fully conduct, the internal resistance drops to ~ 10 ohms or so depending on the bulb. At this point, the ballast does it's thing and current limits. Newer ballasts are 'trigger'start and furnish a high voltage to get the discharge going before, they again. current limit.
The electronic ballasts do the same trigger thing but current limit by varying the waveform of the power. If every fluorescent was exactly identical, I believe you could use just one ballast that was rated for the current. Consider even if this happened, one bulb in a colder corner would need a longer time to light and would not get the trigger spike long enough to fully conduct.
You MIGHT get away with using 220 volt ballasts on 110 input but I don't think the ballast would run correctly. If you have lots of ballasts and a spare fixture, try it. A ballast for a 40 W bulb would blow a 20 W bulb.An under designed ballast would not allow the discharge to be powered enough for full light out or possibily to keep it lit. The cheapest fluorescent system is the one I use. I got surpluss old fixtures that ran on 277volts. They were cheap because they were old (some of the ballasts hum a bit) and unless you have a 440 volt 3 phase lighting circuit, they are useless. Astep up transformer would be too expensive and changing out the ballasts to 110 volts is more expensive than new fixtures. What I did was to find a 110/110 to 220/220 transformer. Using simple wiring I connected the 220 side to 110 and got 55 volts which I joined in phase to a 220 volt line. 220+ 55 =275 volts! The lights cost 1$ each and the transformer colt 5$ A 1 kw transformer will furnish 55 volts for 18 4 bulb fixtures.
HPS fixtures require a very special ballast and playing with the wrong one will blow the expensive bulbs out.
The next thing you should consider is the power company reporting your 24 hour round the clock operation to the narcs. If you are just growing veggies, no problem. If other things are being considered, you also have to block any of the grow light from getting out where it can be seen by the narc's recon from the air using special filters on their cameras.


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trent0123

Newbie

Posts: 7

Re: How to match a ballast to the light (or other power consumer)?

« Reply #2 on: April 19, 2011, 06:38:56 AM »

Ordinary fluorescent lamps are the only ones that can have several lamps run by one ballast, but even then, the ballast is specifically made to run several lamps.
Each type of lamp you've mentioned requires its own type of ballast. Furthermore, each wattage of lamp requires its own ballast. So if you are using two 1,000 watt MH lamps, you just buy 2 ballasts made for 1,000 watt MH lamps (and 2 fixtures and everything else.)
Ballasts cannot be ganged together.
A 1000 watt ballast will not run two 500 watt specialty lamps of the types you mention.
If you use a ballast of higher wattage than the lamp, the lamp will run hot and burn out, possibly explode.
If you use a ballast of lower wattage than the lamp, the lamp will still burn out prematurely.
If you try using the wrong ballast, you may see that the lamp appears to work, but don't be fooled. The lamps are expensive and have a limited lifetime to begin with. The wrong ballast will just cost you more money.


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